Automotive Race car suspension Class

[Cape15]

this confirms the heavier rt rear spring on the old setup. Was to compensate for the lft rear getting more load due to 3rd link offset.
the hollow sway bars are very sensitive to wall thickness. what is the wall thickness of the arb and what is the arm length and overall bar length?

The bar is a one piece 45 1/2 inches wide center to center 14" arms and 3/4in inside diameter 1 1/8 in outside diameter so the thickness would be 3/8in.

 

[Ranger Mike]

bar is 145# at maximum 14" arm length
170# at 13" arm length
202# at 12" arm length
222# at ideal length of 11 1/2"

at 11 Inch arm length bar has spring rate of 243# , write all these setting down so you can tune at the track.

https://www.gtsparkplugs.com/Sway-Bar-Calculator.html

once the Roll center located and ARB and spring package it close to ideal we tune with the front ARB and rear panhard bar to fine tune. The car (on paper) is set up optimally. Now the real world influences like track banking, track conditions can be adjusted for. The other racers will have to fight flakey 3rd link problems ( too much left rear load has to be compensated with stiffer right rear springs and does not really fix the problem), lack of right front down force because they got no ideal body roll to add downforce. You have taken the time to fix camber build, bump steer, rear roll steer, maximum left side weight. car is as good as anyone can make it. Now you are fighting the weather and the track.

 

[Ranger Mike]

Rear axle camber bending on stock rear ends.
You can bolt on camber snouts to the quick change rear ends and get up to 2 1/2 ° camber. Now here is a trick to bend the stock Ford rear end and gain 1/2 ° camber. This is about all the stock splines and gears will take but adds significant performance when running hard spec tires. Note the tire contact patch on the diagram.


'Chassis Engineering' by Herb Adams came to mind where he describes camber and toe adjustments on a Ford 9 inch by means of heat shrinking. So to gain negative camber one would heat the top of the tube which will initially expand and then contract on cooling more than it expanded on heating causing permanent deformation. There is even a number (just found the book). Mr. Adams says that if you heat a 6 inch section of the tube until it is red hot, it will shrink for about a 1/2 degree bend.
On Ford 9 inch rear ends consider the adding of supports to keep the tubes from flexing.

You can run up to about 1/2 degree of negative camber in a Ford 8.8, Ford 9 inch non floater, and a Chevy 12 bolt by bending up the rear axle tubes with a little heat from a torch. A sharp axle guy can take the end off the tube and reweld it at a very slight different place higher on the tube than before and with a little angle to it. I have seen a Ford 9 in a Camaro Stock class that ran for 8 years with a little more than 1/2 degree of negative camber and the axles looked like new. The inner splines can take that much mis-alignment and there can be that much just in production tolerances. SCCA allow that much negative in American Sedan and American Iron and most guys put that much into the rear ends without wearing them out at all. To get more than that in a floater or non-floater you need to have the axle splines machined in a slight barrel shape which allows them to flex inside the splines at a larger angle. It doesn't take much.

 

[Savem c10]

RM!! I gotta tell ya we went to practice this afternoon and made few small adjustments to the roll center moving it more to right and wow what a difference 5 to 6 degrees can make on handling. I have studied a lot and want to thank you for teaching me and others on this forum . Wish you could have seen where we started with this car and where we were today . I will post Rms recommend set up if anyone is interested this would be for a 104.5 inch wheel base perimeter chassis at 57 LS and 2800 total weight. Rm thanks again hopefully tomorrow we carry the checkers .

 

[Ranger Mike]

Thank you Savem,

Glad you changed the front roll center from the left side to the right side offset and right height!

Kind words always appreciated. All I do is post what is in the books I reference and add a little clarity. You racers do all the work. the garage set up is half the battle. track tuning and driving is the other. Thanks again.
rm

ps don't forget to bring a cardboard ( for the trophy)

 

[Savem c10]

Hahaha you got it RM . We’re heading to the track early. I enjoy the education and have a never give up attitude. We will be successful …. I’ll report back with cardboard or without LOL. Have good day.

 

[hallpa00]

Great forum - thanks to very one who has shared…
Here’s my situation
Running in a pro truck series on 1/2 mile high bank asphalt.
2850 lb min weight on metric base chassis
57 % left
What is unusual is the chassis and body lead to very low rear weight - 44.3% in my case
We run around 57% cross. I have modified the front roll center and I think it is ok.
Springs are LF 550, RF 650, LR 200, RR 180, front antiroll bar is estimated at 632.
Our track experience is tight in, loose off. My sense is this:
Rear metric roll center is high and we can’t do much to change it. Also - rear weight is low so effective overturning moment is low. Shocks show little travel at rear (1”) compared to front (2-3”). My thought is to stiffen the rear to take more load and offset what the RF is seeing.
My question is this: do I only need to increase the RR and how far should I expect to take it? Is there a rule of thumb for rear roll stiffness versus front roll stiffness and how would that vary with a low rear weight car?
Many thanks for any insights.

 

[Ranger Mike]

Hall
welcome. my first question is what is the rear suspension? 3 Link? what is panhard bar setup? What rear roll steer do you have? what is rear track width? what is 3rd link location relative to the right rear tire centerline?
Strictly by the number you need to get at least 48" rear weight. 2850 lbs. total weight time 48% = 1368 #


you now have 44.3% rear weight or 1262 # so 106 # difference.


You could take 106# off the front and put it in the rear. But, Duke Southard wrote his book, Short Track Chassis set-up and had this nugget of information.


You do not need to go crazy on frame modification to get 48% rear weight. Note where the battery, fuel cell and ballast weight is now and do some calculations.

 

[hallpa00]

RM
Thanks for the info.
Class rules dictate the use of the stock metric 4 link rear suspension, although we do use a Ford 9 inch differential. The battery is located between the driver and the differential and we have a large fuel cell behind the differential as well as 60 lb of lead ballast. I’m slowly replacing heavier body panels with lighter plastic on the front to allow more rear weight percentage. I’ll do more calculations to consider other moves (alternator, battery further aft, etc.)
Rear springs are located on top of the axle tubes about 20” outboard of the center section. Rear track width is 63”. We target the lower rear links to be flat on the right and slightly angled down to the front on the left (about 1/2” lower front to back) on the left to give us a slight roll steer on the rear (all stock links on the rear). There is not much I an do to affect rear roll center except to change ride height which also affects the roll steer of course. In general, does it make sense to stiffen the rear? I’ll get another shot at the track in 2 weeks so trying to plan our changes.

 

[Ranger Mike]

i need tire temps on all 4 tires on a good run. outside middle and inside on each tire. do you know the location of the front roll center?

 

[drobbie]

Reading through the last series of exchanges, you have given a very simplistic look at the car setup (not that the remaining details don't also matter). But I have a quick question; it appears many of the recommendations you give are for roll centers, and spring rates are for cars that have travel 3-4 inches of suspension travel. My question is, what compensations or changes when you have a car that only travels 1-1/2 inches because of a 2-1/2-inch ride height and uses wider tires? Weight is roughly the same.

 

[Ranger Mike]

I owned a Formula Continental car raced in SCCA. Was like an Indy car. The car had rocker arm suspension so we had wheel travel of 2 inches and shock travel of 1 inch. Ride height was 1 3/4 inch to 2 inches, road course dependent. The trend back then was to use Bump Stops and even droop limiters. The idea being to have minimal camber build. Nonsense. All they did was turn a very expensive race car into a giant GO Kart. We took these bump stops off and threw away the droop limiter. We were Division Champions for 3 or four years because we let the SUSEND-SION do its thing. Suspends the Mass centroid via 4 springs that counter momentum of this mass trying to Roll over when cornering.
These cars were built in England and got shipped to the USA with tall hard skinny tires. We Yanks immediately bolted on spongy fat smaller diameter tires and went fast...to a point. The Roll centers were still for the taller tires. Only a few racers figured this out and milled down the uprights (spindles) to have correct geometry that would make the cars take off! And they did.
Drobbie, even the BBSS cars have some degree of body roll , slight as it may be but Roll Center placement is critical to have. Do not confuse shock travel with wheel travel as they are not the same. On paved track cars ideal shock travel is 1 1/2 to 2 inch right front and 2 to 2 1/4" on right rear. The ideal Wheel travel is 3 inch right front and 2 inch right rear.

 

[drobbie]

Thanks, Ranger Mike. You have confirmed a theory I have based on the studying I have done over the years. This gives me the direction I needed to make the car handle correctly. BTW, I have been working on Roll Center all winter and made the necessary changes to get it as optimum as possible. Thanks for all your great guidance.

 

[hallpa00]

Regarding the Pro Truck discussion...
My front roll center is 2.0 inches above ground and about 1 inch to the right of center. I use the Performance Trends software to tune. Most of the movement of the roll center is down as the front end droops in entry to the corner. My estimate of the CG height is 18 inches.
Here are some recent tire temperatures:

LF RF
Out Mid In In Mid Out
162 155 152 177 171 170
Average = 156.3 Average = 172.7

LR RR
Out Mid In In Mid Out
160 156 152 181 175 162
Average = 156 Average = 172.7

What I deduced from the temperatures is that I need some small camber adjustments but the average temperatures at each wheel suggest that the balance is close.

The track geometry indicates we need 2 inches of stagger and I run pretty close to that as much as possible.

One other area of concern I have is that the RF tire compresses about 3 inches whereas the LF only travels about 2 inches (based on math using the shock travel indicators). The rear only shows about 1.5" of travel (of course this is only measuring compression so I don't know about extension). I was considering crafting some shock travel indicators to measure both directions.

I mentioned the tight in/loose off behavior based on driver feedback (and from helmet video it seems to be accurate). We run nitrogen in the tires and as the race goes on the car gets looser and looser probably due to heat in the RR tire.

My last thought is that I can't be sure that one of the rear shocks is hitting an extension limit during cornering - I should be able to check this with the indicators mentioned above. Could that cause our behavior?

We run middle of the pack now - if I can find .1-.2 seconds per lap we would be top 5 in a field of 20+.

 

[Ranger Mike]

Hallpro welcome
absolutely cobble up trave indicators on all four corners. These are a must. Yes do check for chassis bind and make sure you do not have any.
Initial look at tire temps say the ft and rear left side need more positive camber. add 1/2 degree +
Rt ft to rt rear temp Ave is too close, car on verge of oversteer
rt rear should be 10° cooler than rt ft. so you need more cross weight as the lft rear to rt ft difference too big at 16°
try to get to 6° to 10° spread
do not change more than one thing at a time or things get real muddy. check chassis, put travel indicators on and change the camber on left side as you really need to put these tire to work.

Then run it , take tire temps, add cross weight a little at a time. make small change one at a time and you will gain every time. may be real small but 0.1 sec adds up!!

 

[hallpa00]

RM - many thanks for the advice. I will do as you suggest and report back in 12 days!

 

[Cape15]

bar is 145# at maximum 14" arm length
170# at 13" arm length
202# at 12" arm length
222# at ideal length of 11 1/2"

at 11 Inch arm length bar has spring rate of 243# , write all these setting down so you can tune at the track.

https://www.gtsparkplugs.com/Sway-Bar-Calculator.html

once the Roll center located and ARB and spring package it close to ideal we tune with the front ARB and rear panhard bar to fine tune. The car (on paper) is set up optimally. Now the real world influences like track banking, track conditions can be adjusted for. The other racers will have to fight flakey 3rd link problems ( too much left rear load has to be compensated with stiffer right rear springs and does not really fix the problem), lack of right front down force because they got no ideal body roll to add downforce. You have taken the time to fix camber build, bump steer, rear roll steer, maximum left side weight. car is as good as anyone can make it. Now you are fighting the weather and the track.

RM- thank you for last few responses for me. I finally made it out to practice and my car actually rotates in the middle of the corner which is amazing since i have always been fighting with tight tight tight in the center of the corner. however i am slightly tight entering the corner and my RF tire is average 23 deg. more than the RR. I was thinking from all ive read through these posts that i might take out the RF spring of 325 that you recommended in my prior post and go to a 300 on the RF and go from there. Is that a good idea and would that ruin my center of corner? Also just curious as to your adjustments processes at the track or if there is a post you can direct me too that I might have missed on this thread. Thanks again!

 

[Ranger Mike]

Yes a rt ft spring rate decrease is called for. Or add spring rate to right rear. Looks like we need to kill off some rt rear traction and cut down the PUSH.
You are very close.
you can soften the front ARB (sway bar) by lengthen the arm.
you can raise the rear roll center with panhard bar.
many options before swapping springs.


Try adding spring rubbers to right rear spring. quicker than swapping springs and better fine tuning.
these fine tune to 10#, 20# 25# a must to fine tune before spring swap

https://carolinaracingsupply.com/pr...oNfJg-sM18NQFdRVgY2GprXaapXvvnu4aAniYEALw_wcB

the rubbers below are over kill in my opinion but some racers use them.

1” spring rubber will approximately 100 lbs. ¾” is approximately 75 lbs.

https://www.speedwaymotors.com/Spee...9rFQjegyPdLVh4aa7clemUlwpqBvoKLcaAultEALw_wcB

post 1638 on track tuning. I have written about this but cant find it!

 

[Ranger Mike]

Track Tuning Tips
See post 1419 on page 41 for driver tips
Track tuning

Two things any crew chief better have in the tool box , next to the Rolaids, are Stagger tape and a Tire Pyrometer. Preferably one with a memory that will permit you to take readings and will display three readings per tire.

Tire temperatures are the only real way to tell what is going on and it is empirical. Learn how to use the tire pyrometer and make a habit of doing it correctly. I have a nice techy one that tell you to stab the right front tire inside, middle and outside then move to the right rear tire. The cursor ques you where to take the readings. Insert the sensor needle 1/8 inch into the tire at a 45 degree angle and be consistent. You will be stabbing three places on the tire face. Inside edge ( not on the edge but an inch from the inside edge) the middle and the outside ( not the very outside..,an inch from the outside edge). When taking readings try to do it as soon as the driver comes off the track as these tires cool very quickly. Tune and test day is ideal as you can do it on the track if you are solo ones in that session. Then jack up the car and take tire stagger readings right front first. Record the tire growth and this will tell you about stagger.


The optimal tire temperatures should be in a range of 190 to 240 degrees. On a short track it is normal for the outside edge of the RF tire & the inside edge of the LF to be 5 to 10 degrees cooler. This is because of the way the tires travel down the straightaway. On a larger track with longer straights, this spread will be even further. On an oval, the RF tire will have more negative camber, thus resulting in the inside edge of the tire contacting the track more than the outside edge giving you the higher temperature. On the LF you will run with more positive camber, so just the opposite holds true. While cornering these temperatures should even out if you have the correct amounts of camber & or weight transfer. The more camber you run, the higher these spreads will be. On a small track were you spend a lot of time cornering, you'll find the spread not as high. This is because your spending more time cornering than on the straights, thus distributing the temperatures across the face of the tire more evenly. If you try to achieve even temps across the tire you may develop a push. This is telling you that you have too much positive camber. Although the tire may be flat on the track, on a straightaway, the tire will not be flat on the track while cornering.
The best way to read tire temperatures is to run 10 laps on a particular setup. Read the temps and don't expect to learn everything reading the temps only once. It will take a number of these sessions to sort everything out that is going on with the tires. Make sure you are not locking up the brakes or making any sudden changes in your steering outputs. These will all create erroneous tire temperatures readings.

A tire with too much NEGATIVE camber will show an excessively higher temperature at the INSIDE edges. Lean the top of the tire out to the outside.

A tire with too much POSITIVE camber will show an excessively higher temperature at the OUTSIDE edges so lean the top of the tire in.

A tire that is OVER inflated will have a higher middle temperature than the inside & outside edges.

A tire that is UNDER inflated will have a lower middle temperature than the inside & outside edges.

A car with too much toe OUT will show higher temperatures on both INSIDE edges of the front tires.

A car with too much toe IN will show higher temperatures on both OUTSIDE edges of the front tires.

A RF tire that is HOTTER by more than 10 degrees over the RR indicates a tight PUSH (understeer) condition.

A RF tire that is COLDER by more than 10 degrees over the RR indicates a loose ( oversteer) condition.

A tire with the HIGHEST average temperature is the corner of the car that you should work on first.

A tire with the LOWEST average temperature is the corner of the car that you should work on second.

A RF & LR diagonal average that is the same or higher than the front & right side average indicates too much wedge.

A RF & LR diagonal average that is more than 10 degrees lower than the front average and right side average indicates not enough wedge.

Let’s look at a few examples.

RF
I----M----O
208--202--194
Indicates too much negative camber.

RF
I----M----O
194--202--208
Indicates too much positive camber.

RF
I----M----O
204--188--197
Indicates an under inflated tire.

RF
I----M----O
204--210--197
Indicates an over inflated tire.

RF
I----M----O
204--198--194
Indicates correct camber. Overall average temp is 198.6.

RR
I----M----O
227--225--223
Overall average temp. is 225.

If the RR & RF temp above came off the same car we have a very loose racecar. The RR is 26 degrees hotter than the RF. If this RR is also the hottest tire on the car, it indicates the RR is spinning and or sliding in the corners. We need to go to a weaker RR spring to keep more weight on this tire and prevent the wheel spin. This should cool this tire & tighten up the chassis.

Caution -Temperature Averaging works when you have a fast car and need to fine tune it. If your car is a log wagon and wallowing around like a whale cure the handling first.





Panhard bar
Do not forget- The mid point between the right and left side anchor points on both panhard bar and J bar is the Roll Center. This Rear RC can be offset many inches from the vehicle centerline.

When Panhard bar has chassis mount on frame right side the Rear roll center will DROP under body roll. Opposite if chassis mount on left side.

If you raise both mount points on the Panhard bar, you are raising the Rear RC. The rear roll center will still move downward in body roll as above stated.







Tuning with sway bar (ARB)

A quick review of the ARB - sometimes also called anti-sway bars or anti-roll bars. Their purpose in life is to try to keep the car's body from "rolling" in a left turn.
When you are inside the car, you know that your body gets pulled toward the outside of the turn. The right part of the car on the outside of the turn gets pushed down toward the road and the left side part of the car on the inside of the turn rises up. In other words, the body of the car "rolls" 10 or 20 or 30 degrees toward the outside of the turn.

Too much Roll is bad. It tends to put more weight on the outside tires and less weight on the inside tires, reducing traction. The proper amount of body roll will load the right front tire and assist in improving traction through the turn. Ideally, we would like the body of the car to remain flat through a turn so that the weight stays distributed evenly on all four tires.

ARB tries to keep the car's body flat by moving force from one side of the body to another. When you go into a turn, the front suspension member of the outside of the turn gets pushed upward. The arm of the ARB gets pushed upward, and this applies torsion to the middle section. The torsion moves the arm at the other end of the rod, and this causes the suspension on the other side of the car to compress. The car's body tends to stay flat in the turn.

If you have too much ARB, you tend to lose independence between the suspension members on both sides of the car. When one wheel hits a bump, the ARB transmits the bump to the other side of the car as well, which is not what you want. The ideal is to find a setting that reduces body roll but does not hurt the independence of the front or rear springs.

Tune by adjusting the ARB Arm length. Longer arm is softer spring rate while shorter Arm increases the spring rate in front.

 

[Ranger Mike]

Mid turn Handling and corner exit cures

Much has been written in this class about Roll center location and offset and the need for proper location. I have been sent many messages from racers thanking me for this information and now the car is pivoting, rotating and corner entry is much better. This post will deal with Mid corner and corner exit problems.

Mid Turn handling problems usually come down to Stagger and Cross weight.

We must use Stagger so the tires will not shed going through the turn. Put a Styrofoam coffee cup on its side and roll it. The top or bog end rolls different than the small diameter bottom. On circle racetracks in USA we turn left so the left rear tire is smaller diameter then the right rear tire so assist the turning process. There is no way around this and all racers in your race must use stagger. You can, however, use a few tricks to assist you. We took an old refrigerator apart and used the vacuum pump to pump out the compressed air in our tires. We filled the tire with Nitrogen. Compressed air has moisture, and this turns to steam and expands the tire when heated and your right front tire will heat up. Nitrogen expands at a much lower rate and holds stagger longer. One side benefit is the nitrogen molecules and fatter and do not bleed through the tire side wall like air does. When the tire does expand it throws weight to the left rear tire. It adds Wedge or cross weight.

minimum stagger you need is:
D + .5 (TW) x CL \ D - .5 (TW)
where D is the track diameter in feet
TW = rear track width of the car in feet ( divide inch measurement by 12)
CL = the left rear tire circumference

example- race track has 200 ft. diameter
car has 64 inch track (64 / 12 = 5.33 inch)
left rear is 86 inch circumference.
run the numbers and you get 88.33 inch right rear circumference or MINIMUM 2.33 inch stagger. If you run a locked differential or spool we add 10 percent to minimum stagger. If the track banking is 0 to 10 degrees, add another ten percent. If banking is 15 degrees up, take off ten percent from min. stagger.



Wedge or cross weight

Checking for Wedge – Crazy! I spent an hour googling and no photos of this. Word picture time. When the race car enters the turn the left rear spring goes into droop because the spring is extending to its max travel and the right rear spring is compressed. The left side droop means the left rear tire has minimum traction. We use wedge (cross weight) to increase tire load on the left rear tire. This increases tire bite off the corner. We attained this with the jack screws we have on the car. We add cross weight or Wedge to force the left rear spring into the track when cornering.

We measure Wedge with a ½” socket placed on the floor jack and center it under the rear end housing to lift both rear tires. The right rear should lift up an inch, 2 inch or 3 inch as the track demands, just as the left rear tire shows daylight under the contact patch.

In the turn, the body will roll over and the wedge drives the left rear to wedge the tires to keep in contact. The % cross weight on street stock is usually 1 to 2 % total weight, Late models with slicks run 2% typically.

Rule of thumb - every inch of wedge is 1% Cross weight. When the wedge goes past the normal amount (and inch more than what the normal amount is) then make a left rear spring change. Then reduce the wedge to under the normal amount and adjust at the track as required. Cross weight is adjustable because the local track will change due to temperature, amount of rain washing off the oil and rubber, etc. You need to have a way to dial the chassis in for new conditions and not use it up for basic chassis setup.

 

[Ranger Mike]

You really have two Race cars - Corner Exit Fix

Think about this, racers. Where are races won on the round track?
On the straights!
In road courses we win by out braking the other racers. We have 9 left hand and 8 right hand turns and only two to three straight we can out gun the other guys but rules are so tight the HP is very close. So many races we won by sucking in the younger drivers to go way deep into the turn that they overload and go super squirrelly and have to back off because they drove over their head!

In round track we gun the other cars on corner exit. (Australian and euro racers, this means out accelerating the other car on corner exit. I have many Aussies and Euro readers and THANK YOU much for reading!) But we are so concerned with pushing going in and loose off, we never concentrate on how to win. If we can gain advantage by hooking up BETTER than the other racer on corner exit, we can gain an advantage and accelerate past him to get a half nose or whole car advantage going into the next turn. But we spend NO TIME working on this. Crazy!
History - Remember back in the muscle car day. The 426-cube engine would torque up the left front. Many motor mount broke as the rubber mount would separate. We had to put a chain on the left side of the motor and chain it to the chassis. Engine torque would twist the car lifting the left side up and add load to the right rear tire. The car would swerve left when you dropped the clutch at 5000 to 7000 rpm. Look on a country road Saturday morning for the rubber tire tracks showing this after the hot rodders had fun the night before. Tire marks going to the left!

Why? Because the Right rear tire was loaded, the rear left side tire was unloaded, car shot to the unloaded side, instant push under acceleration. Factory engineers realized this and the big cubic inch cars had 7 leaf right rear springs and 6 leaf left rear springs to counter this. Otherwise, you had a built-in push under acceleration to the left.

Here are typical recommended cures for phase three corner exit problems –

Loose on exit – decrease tire stagger

Increase cross weight

Soften right rear spring

Check for right rear tire over inflation.

Check brake bias

Change rear roll center

The problem with these solutions is you will impact the corner entry handling. It took a huge amount of time to get the right front tire to perform and a major chassis change like a spring change or Roll Center change just screws up the entry!

No one has addressed the elephant in the room.

You really have two race cars! You have a round track car great for phase one and two. You have a drag car at corner exit! I say again, you have a 600 HP, 3000 lbs. drag car with a locked rear end and two different size tires with a huge difference in rear tire weight, side to side trying to race down the straights. We need to hook up these rear tires WITHOUT CHANGING THE CORNER ENTRY SET UP.

Discussion - Factory late model chassis builders are great craftsman and build quality late model race cars. A great value but all in all generic as they did not know what track, or the track rules or conditions the car would race. It saved a huge amount of time for the small race teams. They had one great platform so you could customize for your track and rules! Here is the problem.

Usually, the car was sold with 4 race wheels to accommodate the track rules regarding tire size. You had to race 10-inch tires max, so you got 4 ten-inch-wide tires and appropriate wheel. Makes sense No one is a mind reader. Again, the rules for cars would vary all over the places. Different tracks had different rules on engine offset, % left side weight. maximum track width etc. goes on and on. You got a generic, well built, safe race car that out of the box was pretty darn good.

The car probably had 1 inch engine offset to the left as this was universal. The factory car was set up with at most 52% left side weight. This is still the norm, I think. The majority of racers today are running these older chassis unless you have cubic money and buy the latest, greatest, new chassis. The big problem is your race team decides on where to put the weight and what wheels to use.

Wheels - factory chassis guys ship the car with standard wheels on all four corners. Normally the wheel has 4 inch offset measuring from the back of the wheel to the wheel backing plate. Saves money and is a good baseline. If you take the 4-inch offset wheel off the car and put 3 inch offset on the right side of the car and 5 inch offset on the left side of the car you gain left side weight. You can gain 2% more left side weight doing this. Now you are at 54% left side weight. Now you add a 1-inch spacer between the hub and the backing plate so you can get up to 56% left side weight. Some even go radical using 6 inch offset wheels. Next you find out the track has a 58% maximum left side weight rule, so you move weight around to do this. Now you are at the legal 58% left side weight.

The problem
The location of the top link on any factory chassis is about a 52% left side weight set up on the standard 4 inch offset wheels and the tire track width. A very logical and safe starting point. Unless you ordered it with a specific requirement to change these settings.

The problem is the 3rd link is mounted at the original 52% weight location and should now be at the 58% location and it is not.
Why is top link mount so critical? The top link is the rear end link that pulls the race car. This top link directs all rear end force to the chassis. The rear tires grip the track and try to pull the rear end to the rear. On the bottom, the trailing arms push the car to the front and try to climb up under the car.

We are discussing left turn race car where you want a left side weight bias. When in a turn you want the left side weight rolling over to the right side to assist the car with better traction (tire grip). Correct location of the 3rd link mounting is a real help so the tires are pulling on the third link equally otherwise when you step on the gas, one tire will bite more than the other and shoot you toward the outside of the track or the inside.

If the 3rd link is offset to the left more than the right side, the left will have more load and the right rear tire will have less load. Exactly opposite of the muscle car scenario above. What really happens is more force is added to the side of the car the link is biased to. In this case we have more force added to the left rear tire, so we create an on gas, corner exit LOOSE condition.

The 3rd Link Location (Static)

Mark each rear tire centerline. Measure the distance between them. This is the track width. Let's say 66 inches so the mid-point is located at 33 inches. Now measure the right-side tire centerline to the middle of the top link. Let's say it is 34 ¼ inches. 34 / 66 = 52% left side weight. If you are scaling at 58% left side weight we multiply the total track width time the % so 66" x .58 = 38 ¼ inches. The top link mount should be at 38 ¼ " so, move it left 4" then the push goes away.

See attached photo a forum member, RaceMan12 posted on page 46 post 1602 this post. You can make this happen.

Look at photo below. Notice the original top link mount was offset about 1 ½ inch to the left of the quick-change housing centerline. The racer relocated it about 4 inches more to the left. See post # 1576 page 46.

This is a huge step to solving the traction problem and it will only get you close.
The 3rd Link Location (Dynamic)
The problem is that this is a static fix. Look at the cross-weight illustration below. We have left rear tire weight of 1027 # and right rear tire weight of 560# when we scale the car. We use the Static measurement of % left side weight to locate and center the 3rd link to provide 50-50% traction.

This remount does not take into account the dynamics of corner exit. Look at # 43 car lifting the front end under acceleration. It is also twisting and throwing left side weight over to the right side. We have to dial this additional left and rear weight into the equation.

Let us say we have 100 lbs. weight coming of the left front tire and dumping on the right rear tire under acceleration. The car is twisting and unloading 25 lbs. from the left rear tire and it goes to the right rear tire

Now we have a dynamic left side % weight of

Lft ft rt ft

677 747

Lft rear rt rear

1002 685

We now have 54% left side weight under acceleration.

How to properly measure the dynamic weight transfer?
Take the car in full race trim to a straight section of road parking lot, airfield.
Set the damper (shock absorber stops) and make a full power acceleration for 50 feet. Do not brake, coast to a stop, let the chassis settle. Read the shock travels on all four corners.
Next step is to scale the car and floor jack the chassis in front and on left side to duplicate the shock travel you recorded.
You can read the weight scale on each wheel to find a truer dynamic left side weight % and then calculate 3rd link position for a much better 50-50% rear traction.

We have now calculated the Static 3rd link location and the Dynamic 3rd link location. Somewhere on this range will be your maximum traction location. When relocating the 3rd link mounts both at chassis and on the rear end, make it adjustable so the link can be shifted from left to right. I recommend a few 1/4 “thick spacers and many Spacers. ½ “spacers. This way you can dial in the location for maximum traction.

Testing best location of 3rd link Spend a Saturday at the parking lot doing nothing but launching the car. I would recommend using some orange traffic cones to mark out the radius of your turn number one of your local track, on your parking lot. We are seeking best corner exit 3rd link location under power during this outing. We have a pretty good idea of static and dynamic location but to optimize it we need to drive around the radius at speed to throw some rear and left side weight and nail the throttle. This will truly give the best 3rd link location.

Get car in race trim with an old set of tires. Make sure the stagger is right. Work on hook up of both rear tires so you have straight Gas on acceleration when you mash the go pedal. Adjust until you go straight and leave equal tire marks on the pavement. (You do not need to leave tire tracks though it would help). The point is to launch the car and adjust so it goes straight when you gas it on corner exit. When you can take your hands off the wheel when you gas it and it shoots straight, you got it.

If it wants to drift to the left, move the 3rd link a little to the right until it runs straight. Use the tire pyrometer so both tires are getting the same heat (load) on launch. This is very hard to do because you need to compensate for the smaller diameter left rear tire.

Always overlooked. Take time to tune the CARB. Accelerator pump shot, jetting, read the spark plugs. Launch the car, kill it and coast to a stop. You want to read the spark plugs. Tune for best throttle response. You are tuning for the straights that are the majority of the race track. You do not want a bog off the corner. You are throttle off with carb butterfly's (throttle plates) closed.
So you are in fact, in a drag race when you exit.

Now ask yourself this question? Has the local hot dog racer done this? Or is he buying the latest expensive whizzy bit or speed trick for more horsepower he cannot use really use because he is fighting a corner exit loose condition? He just figures this is how it is and has to live with it. His answer, more power. Is he going to spend a day working on this aspect of winning? I remind you Racers, Caroll Shelby quote number one - https://www.shelbystore.com/carroll-shelby-quotes-s/2499.htm

There's never enough horsepower... just not enough traction."​

Do you really think your brother drag racers spend hours getting the car to go straight when the green light pops?
Drag races are won and lost at the starting line. Ok top end matters but lets be real.

When you are down to launching the car, you are very close to best your car can be.
What will this cost you? a few gallons of fuel, old tires, and time! And a Parking lot????

One final thought - do drag car tune with rear roll center? NO! This is for working out phase one and two cornering problems. Do not forget you have two cars, not one.
Yes, this takes time but if you can tune the rear traction without screwing up the corner entry, it got my vote!

 

[Low Budget Racer]

Many thanks to RM for this forum, I started racing less then a year ago & was always at the back, found this forum after last race of last year & moved third link & used the track tuning tips above with the tire pyrometer. My first race this year I didn't get a chance to take tire temp readings after the feature but that's a good problem to have. I also forgot a big enough box. My car has never been so consistent. The next race will be more challenging for me as I will have to start from the back. I owe my first win to this forum & a little luck!!! Thanks again to everybody keeping this forum alive!!!

 

[Ranger Mike]

Thank you for the kind words. An inspiration to all of you racers. It is not me who does the hard work, long winter nights under the car in a cold garage! But you all know the feeling once you start getting real close!
Good Job Low Bud!

 

[Ranger Mike]

We use the torque link to help hook up t he hard spec tires we have to race! This lets us dial in amount of rear traction and it is one of the best ways to aid corner exit with the tires we have to run.
Thanks again to Paved Track Stock Car Technology by Steve Smith! A lot of tuning advice on this in this book.

Torque link or 3rd link with spring / shock top link or the toque link should be mounted 12 to 13 " at 3rd link location desctibed in previuods posts. Once you figure this, mount it on top of the axle housing, and 1 to 3 inch behind vertical center line of axle housing.

Angle the top link downhill about 20 degrees. And usual adjustment is between 15 to 25 degrees. On asphalt we run 3 to 7 degrees.

Adding more downhill angle will tighten up the car under power off the corners, but the hook up does not last as long and by using a lesser angle the car will hook up more smoothly but not as quickly.

you may want to add a shock damper to the 3rd link mount. this will control rear end looseness and wheel hop under braking. The axle damper should mounted 5 degrees up hill. Never mount it level or downhill. If the rear end loosens persist at corner entry use more axle damper uphill angle adding no more than 2 degrees at a time. max 7 degrees uphill angle on dirt.
If rear is too tight at corner entry decrease downhill angle.

Lower trailing arms usually mount 3 to 5 inches below axle center line. The most common center to center length for lower trailing arms is 20 inches.

Lower trailing arms normally mount 5 degrees uphill. Uphill angle gives better forward bite. Both links with same angle create slight roll over steer. You can change wheelbase to control rear steer by shortening or lengthening one of the lower trailing arms. Many dirt cars run 20.25 inch right side
lower trailing arm 1/4 inch longer than left side, to increase roll over steer.

 

[Ranger Mike]

One of my most admired drivers Parnelli Jones
https://www.msn.com/en-us/sports/ot...1&cvid=12a37389c60b4fceb327cc0b63a46392&ei=31

 

[Ranger Mike]

Part 1 - These race tips only works for the very restricted classes of racing.
If you are limited to a 2 barrel carbs, hard spec tires, no major engine modifications, and if you are racing a 4 cylinder class, see PART 2
This is how we out qualified the other formula car racers in SCCA. We had 2000 cc 4 cylinder engine and maybe 145 HP on the dyno. A 12 HP gain is an 8% HP advantage over a competitor racing on a hot humid day.

The temperature of gasoline has an impact on how much power an engine will produce. When your fuel is at a lower temperature it will have a higher density level, this allows more to enter the combustion chamber. This increased amount of fuel inside the cylinder will allow for more combustion in the chamber, thus creating more horsepower. Having fuel stay at a lower temperature also will prevent it from moving to a vapor state inside the fuel lines before it enters the engine.

What Does a Cool Can or Fuel Cooler Do?​

A cool can for fuel or fuel cooler is a device that helps regulate the temperature of the fuel in your vehicle's system. By reducing the heat of the fuel, it can improve overall engine performance and prevent fuel vaporization, especially in high-temperature environments. This can lead to a more consistent fuel delivery, increased power, and improved fuel efficiency. Cool cans and fuel coolers are particularly beneficial for vehicles that experience fuel heating issues, such as those with high-performance engines or operating under extreme conditions.

What Is the Difference Between Cool Cans and Fuel Coolers?​

Cool cans and fuel coolers serve a similar purpose of cooling the fuel, but they differ in their design and installation. Cool cans are compact, cylindrical containers that are typically installed between the fuel pump and carburetor. They utilize heat exchange technology to dissipate heat from the fuel. On the other hand, fuel coolers are inline devices that are installed in the fuel line itself. They incorporate various cooling mechanisms, such as heat exchanges or fans, to cool the fuel as it passes through the system. Both cool cans and fuel coolers can effectively reduce fuel temperature, but the specific choice depends on your vehicle's setup and application requirements.

What is desired is a way to improve the volumetric efficiency of the Internal Combustion engine. All an IC does is act as a heat pump. converting chemical energy, gas, into heat and usable power. Te more fuel you can pack into the combustion chamber, the faster you go. For years racers used a cool can to cool the. fuel. It is simply a can with a coil of aluminum fuel line mounted in it. the racer would put ice in the can before a race. Theoretically, the fuel is cooled more than ambient temperature and is a denser mixture of fuel / air thus more power. This is why older cars had chokes on the carburetors, to "choke off" the air supply in real cold weather. The choke had a thermal spring that would kick off once the IC reached operating temp. Cool can, I can testify, after much testing, is not a good solution. There not enough time or cold enough media to cool the fuel. Back when drag racing in the 1960s, we went so far as to run acetone and dry ice in the can. It froze the fuel line up to the fire wall..ran like a bat out of he--... but..our driver was overcome by fumes and started our Super Stock 63 Plymouth 426 Wedge in high gear at the starting line. These cars had the push button automatic transmission. Have you ever heard a 426 cubic inch motor lug down when the hammer is dropped at 7000 RPM?




Cool can with ice does add about 2 to 3 HP on carburetor engine s but not direct port injection setups. The carb setup means charge cooling from just under the carb to the intake valve. The colder gas mixture can cool the air and create a larger charge before entering the cylinder head. Direct port injection just squirts in cold gas with no charge cooling effect.




118° F fuel to a 10 HP gain with 58° F fuel super chilled


Anti freeze freezes at - 34° F

Acetone freezes at - 128° F


Dry ice cools to - 106° F



We did not have enough room on the formula car ( like Indy cars ) to mount the cool can and i think it would have been illegal anyway in SCCA. So I designed a fuel system to take the fuel out of t he fuel bladder , cool it down and return in to the fuel bladder. This is for the Qualifying event not the race. I used a Facet 12 volt electric fuel pump an d 120 vac to 12v adaptor. Had quick disconnect fittings and plumbed it into the fuel line and fuel tank vent line. I used a Blue moroso cool can in series with a medical freezer.

A regular freezer will cool to 20° F above zero. A medical freezer will chill to -20° F. Inside the freezer I installed a small oil cooler. It was in a plastic container that could hold a gallon of antifreeze.


Why the freezer? Many tracks are located out in the boon docks and i could not depend on getting dry ice readily. We always had a gas generator to power the air compressor, coffee maker, microwave. So on boon dock tracks the freezer would freeze to minus 20° F and we would cool t he fuel for qualifying. I would put ice in the moroso cool can so the fuel would bet chilled a little before going into the freezer.

When we had dry ice available we would put acetone in the cool can and plastic container ( had to replace it with an aluminum one reall soon after t he first freeze).

Yes it worked and no one caught on. I did not have a pyrometer that would read that low so can not tell the temperature the gas was cooled to before we qualified but i can tell you there was a lot of condesation dripping from the car. We made it a point to wash the car outside the garage in plain sight just before qualifying. I made it a point to have a can of PAM (spray on canola oil you use in the kitchen) stashed under the car while washing. If you looked you could easly identify it! ( Intresting note- soon after we did this and qualified number one at a few races, alot of other racers began washing their car and wanted to know what soap / washing mixture we were using) monkey see, monkey do!

 

[Ranger Mike]

PART 2 -
Regarding the 2 barrel carb limit - Many have messaged me about racing in the 500 cfm 2 barrel car classes and how to maximize the setup. If the rules state you must run this CFM carb, do it.

You will be surprised to learn your Holley 4412 500 cfm 2 barrel only flows 353 cfm! The new XP 4412 with stream lined air horn and all the new tricks flowed 392 cfm. Both a far cry from 500 cfm.



Can you still get an edge on the rest of the field? Absolutely. I do not condone some of the following but this carb restriction has been in effect since the early 1960s. The math I use here is extremely simplistic as real world results show my numbers go out the window when Rpm goes up and dynamic flow kicks in. I will not be addressing the rework of the carb as you can pick up 50 cfm by just polishing and porting , smoothing things internally. See video below at bottom, on reworking stock carb
Lets look at the numbers. A Holley 500 cfm 2 bbl carb has venturi diameter of 1.3/8". There are 2bbl carbs with 600 cfm and have 1.45 diameter venturi. First thing was to keep open one of the intake manifold holes used to draw vacuum. Tech would make sure these were all capped but is did work. You can run a vacuum gage into the cockpit and if it happens to slip off during the race you may get and increase. A 3/16" hose will yield 0.11 sq inch.

Back in 1950, one race team set up the car so the carb was mounted with springs on top of the carb mounting flange. When the driver mashed the throttle pedal the carb would be jerked rearward and air would enter the intake manifold. Of course they jetted for the fat side and won a lot until TECH caught on. Next the boys drilled the carb mounting threaded bolt holes thru the manifold. Now you can have air enter the intake. The trick here is to use a 4 barrel intake manifold and use a 2 bbl to 4 bbl adaptor plate. Now you have 8 bolts that can be drilled out , cross drilled. It simply looks like the bolts have been cross drilled for safety wire. These holes can access the plenum chamber in the manifold under the carb. Serrated washers look like they are threr to lock the bolts but really can pas a lot of air as they do not mate flush to the carb or adaptor plate. This was pretty obvious once TECH caught on to it. Next thing tried was milling or filing a taper on the carb manifold mounting surface on both front and back sides but leaving the left and right side stock so the carb would mount flat but had a taper air leak under the carb. This gave additional air area to the intake. Bottom line is if you choose to go this route be prepared to be caught!

https://www.holley.com/products/fue...MIpMeNxbnjgAMVeQitBh1OGAXqEAQYAiABEgJIiPD_BwE
Looking at the area the 1.378 bore has 5.9 sq. Inch area. The 1.45 dia. has 6.6 sq. inch. 5.9 - 6.6 = 0.70 sq. inch difference. I will leave it here as you have a major clue about what you can do. Now it is up to YOU!

see below - stock 256 cfm two barrel carb to 300 plus



https://www.vaautoracing.org/oval6.htm

How to hide two carbs under the intake manifold, 1950...

https://www.museumofamericanspeed.org/cheatermanifold.html

hiding carb under the intake manifold.


Regarding hard spec tires read post 572 and 573 on page 17.

 

[Ranger Mike]

Thanks for the support

 

[alpharomeofifetwo]

Hey ranger Mike! Looking for some help here.
Understand physics and math pretty well but I’m stumped on this:

Metric dirt street stock has 0 traction mid off on dry slick entry is great.
High bank, paperclip dirt oval 3/8 by my calculations but they claim it’s 4/10.
Turn diameter avg 345’ (330’ on one end, 360’ on opposite)

Springs/wheel offset (15x8 rims)/ tire circ (H500)
LF 750 2” 86” RF 700 2” 87.25”. 1.25” stag
LR 100 (20”) 2” 85.75” RR 225 4” 86.25” 1/2” stag

Front TW- 69”
Front RC 2” up, 3.75” passenger side (photo attached with info)
Rear TW 65”
Rear RC low
RR Upper 13.5°
RR lower 11°
LR upper 18°
LR lower 16.7°
Lowers can be raise but bower moved down. Must bolt within 2 3/4” of bottom of housing.

Scale:
53.2 left LF 711 RF 650
52.5 rear LR 812 RR 691
51.0 cross. LR 5” of compression at ride height
120lbs bite RR 0” of compression at ride height

Ride height front 8.25” ground to center of bolt on lower bushing both sides.
Rear deck height 40”

Dynamic shock compression in inches:
LF 4” RF 4.5”
LR 1.5” RR 4”

Hot Tire temps after 25 lap race
Outside/ middle inside <><> inside middle outside
114 110 122 | 141 145 158
129 135 139 | 215 161 179

Hot psi cold psi
14 20. 11 17
14 18 11 13
160lbs ballast located directly above rear end and forward maybe 6” right under decking (estimate 32-35” to center of lead.
One 45lbs bar location passenger side 12” in front of rr tire

Unknown variables:
Front and rear CGH
Rear RC exact height
Rear ride height to frame / bolt

Issues:
Loose mid of bad in slick

Possible solutions- increase lateral traction by means of:
Increase rear TW by moving to 3” or 2” RR offset
Lowering rear CGH
Softening 225 RR spring to 200 or 175 lbs

Sorry for the long read of details but let me know what you think or if you want to get together via pm for some data analysis!

 

[alpharomeofifetwo]

 

[Ranger Mike]

alph, welcome

Issues:
What size ARB (sway bar) in front??? solid sway bar i assume. what diameter, what length? any preload?
What are camber settings?
Have you checked to see if rear end is bent?


Loose mid of bad in slick ?????
Photo of Roll center lay out says it is located to the left of center. You said it was on passenger side???
Lowers can be raise but bower moved down. ?????? what the heck??

please review spelling of your post so we can discuss

 

[Ranger Mike]

alph
after looking at the set up a few things stick out.


Why is rt rear tire inside temp so high. Is axle tube bent? see post 1326 on page 38. read post 1703 on page 49.



The rt rear tire is under inflated. same with left ft tire. Center temp way low!


rt ft tire has too much positive camber.


diagonal tire temp average is 141


ft tire temp avg is 131


right side tire temp avg is 167


diagonal avg to rt side is 26° should be 16°less, within 10°


not enough cross weight , car is loose off, left rear tire not doing the work.





your spring package and since no ARB, can not really comment


your setup


lft ft 750


rt ft 700


lft rear 100


rt rear 225


the following is recommended setup for 2800 pound dirt car street stock


lft ft 1000


rt ft 1200


lft rear 175


rt rear 250 and with 1.025 diameter arb on ft.


not knowing if the ft rc is offset to the right side as recommended, i can only guess you have too soft a frt spring package making car nose heavy and not enough weight on rear to hook up tires on corner exit.

 

[alpharomeofifetwo]

alph, welcome

Issues:
What size ARB (sway bar) in front??? solid sway bar i assume. what diameter, what length? any preload?
What are camber settings?
Have you checked to see if rear end is bent?


Loose mid of bad in slick ?????
Photo of Roll center lay out says it is located to the left of center. You said it was on passenger side???
Lowers can be raise but bower moved down. ?????? what the heck??

please review spelling of your post so we can discuss

No sway bar
Static Camber settings are on the image
LF +6° RF -7°
Read end is not bent. Brand new car, brand new 60” quick change rear end, rear end is centered and not leading or trailing.

Front Roll center drawing is from a front view looking back, as if you were standing in front of the car looking at it, driver side on right, passenger side on left. Roll center is on passenger side.

The lower trailing arm bracket has multiple mounting holes underneath the housing but can only be a max of 2.5” from bottom of tube to the center of the bolt. I’ll attach an image below. I can not move the mount to a lower bracket hole but I could drill another hole above it.

Re: follow up reply-
The tire pressures were too low, it was rolling the tire over/under to the middle of the H in Hoosier on the side wall. That will definitely be adjusted.

 

[Ranger Mike]

can you put another spindle nose on the right rear quick change tube that has camber? A 36° difference from inside to outside temps on the rt rear is huge. Should be within 10°
the inside tread edge is burning off!

 

[alpharomeofifetwo]

can you put another spindle nose on the right rear quick change tube that has camber? A 36° difference from inside to outside temps on the rt rear is huge. Should be within 10°
the inside tread edge is burning off!

I believe I had a small frame rub on that RR. Forgot to include that in my response. That would cause the increase in temp

 

[Ranger Mike]

I would say you are in a very good position. Roll center is ok so corner entry should be good as you u stated. You know the problem on rt rear regarding tire temps. It still looks like a spring change though. cannot tell until the tires are at best camber, inflation so total spread from inside middle and outside is 10° on spec tires. Typically, the right rear temp average should be between 10 to 15° cooler than the right front average. Seriously consider the springs recommended.

 

[alpharomeofifetwo]

I would say you are in a very good position. Roll center is ok so corner entry should be good as you u stated. You know the problem on rt rear regarding tire temps. It still looks like a spring change though. cannot tell until the tires are at best camber, inflation so total spread from inside middle and outside is 10° on spec tires. Typically, the right rear temp average should be between 10 to 15° cooler than the right front average. Seriously consider the springs recommended.

Here’s where the fun part is in my general curiosity:
This exact set up feels pretty good on a tacky/wet track if not a touch tight mid off (needed to add cross)

We also have screw jacks/weight jacks on all four corners of the car so we can smash springs to change load/ride height. I’m not sure if that was factored into the calculation you had or selection process for recommend spring changes.

What I was considering doing was adding rounds in (compressing) both the RF/LR and taking round out (decompression) of the LF/RR.
I will take my load stick out later today and see what static and dynamic numbers I can come up with.

If you’d like, I can pm you some footage from in the car and the rear suspension. Rather not post links so I keep my competitive edge

Thank you so much for all the advice and quick replies! Math & physics are so fun.

 

[Ranger Mike]

sounds like a good plan. yes put more cross weight in.
fix camber , adjust inflation, fix rear end rub so we can get good tire temps. If we subtract the inside temp on rt rear tire we are still hotter than the rt ft tire indicting loose condition. Try adding spring rubbers to the frt springs to drop the rt rear tire temp. Looking for 10 to 15° cooler than the rt ft tire temp average.

 

[Ranger Mike]

are you running coil overs on front?

 

[alpharomeofifetwo]

are you running coil overs on front?

No sir. Big spring car
5.5x9” springs on front
5x20” on LR, 5x13” on RR

I just got some more measurements for you though:
LF static compression 1” + 3.25” dynamic = 4.25x750= 3187lbs dynamic load

RF static compression 1.5”+ 4.25” dynamic = 5.25x700= 4025 dynamic load

RR static compression 1” + 3.75” dynamic = 225lbsx4.75”= 1069lbs dynamic load

LR static compression 5”+ 2” dynamic = 100x7= 700lbs load

Ballast: 160lbs lead direcetly above the center of the rear end 34” from the ground to the middle of the lead blocks

Screw jacks: on the front I maybe have 4 turns in the Left Front and 5-6 turns in the Right front. (Take those turns out and the screw Jack bolt will come out

 

[alpharomeofifetwo]

LF static compression 1” + 3.25” dynamic =

I think I’ve discovered a major issue. The LF has a 2.25” drop roll bar upper shock mount so it’s pushing the whole shock down and The shock is bottoming out. Here is what it has currently and I’m going to change it to a roll bar swivel style (yes, I know the phot is of a different roll bar diameter lol)

 

[Ranger Mike]

I looked up the set up for a street stock car on dirt for a 3200# car, 400 # more than your car
I had setup for dirt car 2800#
Lt Ft 1000 Rt ft 1050 Lft rear 250 rt rear 225
so i still think you are too soft on frt springs but we have to get the camber, frame rub and shock mount right before we can get good tire temps.
my opinion
rm

 

[alpharomeofifetwo]

so i still think you are too soft on frt springs but we have to get

Been doing my due diligence on this refrigerator with wheels the past two days, love some good math problems.

Here’s what I’m guesstimating:
Load transfers
Front loads (measured with a load stick: https://pitstopusa.com/products/weh...MIzOqMy_-AhwMVQVJ_AB1hzAXBEAQYAiABEgLZkPD_BwE) at dynamic travel are about 2000lbs on the RF, LF is about 1800lbs.
RR load is getting to 1075lbs
LR load is going to 700lbs

We run tubular after market and front uppers and lowers so I’m 110% not even coming close to frame clearance issues or bottoming out.
As far as spring package goes, my understanding is that all I’m doing is changing how fast I load and unload a corner.
Stiffer spring = Quicker loading, quicker unloading in relation to the tires
Shocks control how fast the springs load/unload in dynamic travel

What I’ve deduced is that my issue is one thing only(with the exception of the few known for certain issues aforementioned): load transfer
Issue #1 Load Transfer via ballast placement
With me having roughly 160lbs of ballast mounted high and centered over the rear end, I’m transferring too much load laterally to the RF and RR, effectively unloading the LR.
Possible solution- Move ballast lower and to the left. Reduce CGH and load transfer

Issue #2 Load Transfer via Shocks
This is a little tougher to track down for to an exact fix but we’re getting closer to fine tuning.
The LR could have have too stiff of a compression not letting the LR get the weight transfer under acceleration.

The RR could have too soft of a compression letting excess load transfer to there under acceleration.

Less likely but still possible variables in this:
The LF could have too stiff of a rebound, transferring load to the RR

The RF could have too soft of a rebound, not letting the LR load under acceleration

 

[Ranger Mike]

what is motion rate of the spring? Now this makes sense.
i assumed you were running stock A-arms. are you running slider attached at different angles and mount point from stock? look , if you want my help...tell me your setup!

 

[alpharomeofifetwo]

what is motion rate of the spring? huge!!
i assumed you were running stock A-arms. are you running slider attached at different angles and mount point from stock?

I’ll have to get you that information later tonight or next weekend. I’ll measure middle of inner pivot point -> center of spring then inner pivot to outer ball joint. MR= D1 / D2

I figured that’s what you were getting at because I realized where those spring rates you recommended were coming from. Keeping the car up off the frame.

 

[Ranger Mike]

If you have GM metric A-Arm and have 700# spring in stock location
not enuff, too nose heavy , loose off

 

[Savem c10]

Looking for decent base line set up for a straight rail asphalt late model racing on a 1/3 mile flat track 8/12 degrees of banking , 2800 lbs 57% left side 101.5 wheel base on 8 inch slicks with coilovers per rules . This car has jacking force front end geometry I would like try it this way . Also arb is 1.5 spline bar I don’t want to change that . So I’m looking for spring rates all corners wheel weights / rear trailing arm angles. Thanks .

 

[Ranger Mike]

Savem,
you have been on this forum too long , have learned much , and are a racer with advanced knowledge.
You know me and my fanatic requirement about roll centers!

1. where is the front roll center located, height and offset.
2. Where is the 3rd link located relative to the track width

8 inch slicks tell me you are in spec tire and car class, true or not?
1.5 spline bar ??? wtf????????
this don't mean sh** to a tree??? clarify! asking me for base line spring rates when i do not have any clue about ARB spring rate is .. well Savem, come on man?

did you read post 1721 above?

Savem, Yes, I am harsh but you have too much potential!

 

[alpharomeofifetwo]

If you have GM metric A-Arm and have 700# spring in stock location
not enuff, too nose heavy , loose off

I’m slowly coming to terms with this idea.

I did get to check the MR on every corner but the RF
LF 2.5” shock travel to 1.5” spring travel(5:3)
LR and RR and pretty close to a 1:1 ratio
RF Guesstimate based on load stick #’s would be a 2” spring travel to a 4” shock travel 1:2

No spring sliders. Springs sit on a cup mounted atop the center of the axle tubes, vertically 90°
The rear shock have a screw stud mount aft of the rear end tubes that comes down from above at pretty close to 90° and mount on the back side of the of the lower trailing arm bracket.

Keep in mind I had two issues in the suspension:
LF bottomed out shock
LR shock mount bolt broke

Shocks:
The set up I’m running right now is a tie down RF it goes down and stays down… unless you wait 3-5 business days for it to come back up.
The LR is very hard to compress and wants to stay up. Pinning the RF down
LF is an easy down, but has a good amount of Rebound
RR has a is a medium comp/Reb
I have the shock data if you have Roehrig software

We have a test n tune next Friday (12th) and race on Saturday. I’m going to bring all my springs and make changes to ballast, wheel offset etc to see what we can do

 

[Ranger Mike]

alpha
think about it. if you have the front roll center right, putting down force on the rt ft tire, going IN to the turn, why keep it mid turn and coming out? tie down shocks are a Band-Aid because the roll center is not correct.
you tie all the weight down to the right front tire until h222 freezes over thru mid turn and corner exit. Mean while the lft rear shock is saying, no no no, do not come back Mr. Weight. Tie down shock keeps weight on rt ft forever . You already are mid turn and need the weight to hook up on EXIT. Does this not sound like nose heavy? Now on corner exit you have no traction? wonder why?