Race car suspension Class

[Ranger Mike]

maybe...after i get done wit h Tech inspection..after my bday...

 

[Ranger Mike]

i got to a get off line ..bday party going..just want to say thanks..racers...we risk life and limb for astupid trophy..work on a freezing concrete floor in winter..repair a p.o.s crtaftsman lawnmower to save tire money..show up at the kids school play smelling like 90 weight...church lady thinks you are th devil..

yeas i am a little ..happy.. tonite..remeber this

three people you never piss off...
Army Cook
You fav bartender

most important...

never ..ever ..piss off the Flag Man!

did we break 350,00 0 yet??

 

[Philthy]

Going back to my question on page 38 and replies on page 39 I have remedied the problem.
In the end I purchased Susprog3D software and drew up the front and rear. With the front I found that shortening the instant centre by lowering the top control arm did a few positive things. The dynamic roll centre (in tilt and bump) remained closed to the static R/C and the camber gain in bump + camber loss in droop improved. I reduced camber down from 4 degree neg to 3.2 degrees neg and then went racing. The instant centre ended up right in the centre of the opposing tyre with a 80 inch track width. The angle in the top arm meant I had to modify the arm so the rod end would not bind.
The on track performance was great, car was a dream to drive straight out of the truck and the tyre wear looked very very good. Podium result so I would say worth the effort. Thanks for the input, some of it headed me down the right course.

 

[Philthy]

Next question. The coilover spring angle on a live rear end? Is there an advantage to angle the spring so as to minimise the spring rate gap between the rate in bump and the rate in roll?
For instance my car has 550 lb spring that give a 550lbs rate in bump however the rate in roll is only 245 lbs.
If I angle the spring somewhat the bump rate reduces to 422lbs and the roll resistance rate increases up to 299lbs.
The new spring angle runs close to 90 degree from middle of coilover to roll centre (low rear roll centre on my car with watts link horizontal under the diff).
Makes sense to me, just wondering if it is worth the re-fabrication and whether it will reduce lap times as the car handles pretty good now...but maybe could be even better?

 

[Ranger Mike]

Philthy at this point i would say you are the best expert to decide on your car. You are there. You have reached that point where you can pretty well figure things out and set them up to win. If you know that much on spring rate, stay with your set up. I like the fact you run Watts linkage. Always liked those setups. A real bear to get right but once you did, it ran away from the panhard bar set ups. You spring setup sounds good. Glad i could be of slight assistance.

 

[Ranger Mike]

I am off to the Caribean ...

on vacation..thanks to all you racers and enthusiasts on making this thread a popular one.

 

[Ranger Mike]

jared 0020 i apologize...
i missed that question...please let me address this in a week...again, i missed it being in hurry with the cruise and my Bday and all..not like me to ignore people so i will get on it upon my return..

 

[Jared0020]

No problem just when you get a chance

 

[Ranger Mike]

Jared 0020 asks- Can you explain Jacking Force and how to achieve the best way of doing it.
Jacking force – This is the reaction of the tire contact patch to momentum in the cornering process.
Newton's laws of motion
The three laws proposed by Sir Isaac Newton concerning relations between force, motion, acceleration, mass, and inertia. These laws form the basis of classical mechanics and were elemental in solidifying the concepts of force, mass, and inertia. ◇ Newton's first law states that a body at rest will remain at rest, and a body in motion will remain in motion with a constant velocity, unless acted upon by a force. This law is also called the law of inertia. ◇ Newton's second law states that a force acting on a body is equal to the acceleration of that body times its mass. Expressed mathematically, F = ma, where F is the force in Newton's, m is the mass of the body in kilograms, and a is the acceleration in meters per second per second. ◇ Newton's third law states that for every action there is an equal and opposite reaction. Thus, if one body exerts a force F on a second body, the first body also undergoes a force of the same strength but in the opposite direction. This law lies behind the design of rocket propulsion, in which matter forced out of a burner at high speeds creates an equal force driving the rocket forward.
The American Heritage® Science Dictionary

Think of the Go Kart we all drove as a kid. Tube frame with and engine, seat and brakes..maybe. Going back the Newton’s Law. – The Go Kart bombing down the front straight will continue in a straight line until some other force is placed upon the kart. In this case the tires turn inward to corner and change the vehicles speed and direction. Momentum meets the tire contact patch and we have a reaction. The tires will hold and we turn in successfully or they shear and we continue on to the tire wall. Imagine a pole vaulter running toward the cross bar and planting the pole in the cup. The pole stops and the vaulter continues on but his direction and velocity has changed as he moved upwards and over the cross bar. Same thing here. We do have Jacking Force here but it is small.

In your mind , draw a line from the contact patch of the right front tire to the Center of Gravity ( drivers belly button). Its 24 inch for this kart. Next draw a line from the CoG to the pavement ( usually a few inches). 6 Inch on this driver. From this pavement point to the tire contact patch makes the third leg of our triangle. The hypotenuse angle is very small ( see attached pic of hypotenuse angle B). About 15 degrees. So we have a 15 degree jacking force and the tire contact patch countering all the forward momentum of the Go Kart.

Go pick up that old bristle shop broom. You have the best sweep job when you sweep at a 45 degree angle to the pile of dirt on the shop floor. Now lower the broom handle until its just 15 degrees from the floor and push it. Not much work is applied..right?

Things get a little more complicated when you add suspension to the works. Now you have a CoG at the camshaft height, and you have a Roll Center that the CoG will move through. You also have added springs and shocks (dampers) to assist the tire contact patch and jacking force.
Look at page 24 post # 470 and page 34 post # 691 for more in detail explanation. Bottom line is on typical stock car set up with Roll Center at 3 inch height and centered, we have 15 degree jacking angle. When we move the front RC 3 inch to the right it becomes 22 degree jacking angle and we need this to impart down force onto the right front tire to make it stick in the turn.
See post #62 page 4 on fat kid sitting on tire to aid down force...

 

[vinny1A]

Can you help to find a base setup for a Wissota Superstock Dirt car?

Our car is a Camaro stubbed, tubular chassis with a 3 link rear end. Stock lower a frames, tubular uppers, 26" panhard bar.

We run a 3/8 well banked clay track.

The fast guys are running a very heavy bite, we just purchased a car and this is how it looks:

Wheel Weights
RF 618
LF 706
RR 946
LR 584

Springs
RF 950
LF 850
RR 350
LR 450

Rear springs are mounted on trailing arms, rules say they must.

RR trailing arm 26" at 3*
LR trailing arm 20.5" at 14.35*

Rules dictate that we run a solid 3rd link.

Panhard bar is chassis mounted on left side, mounted to the rearend 16" right of center of gears, 1.5" below axle tube, 10.5*. (Ford 9" floater rearend, 62")

Is this setup usable, or should we make changes?

Front roll center was calculated to be 3" up and 5" left of center.

Any help would be much appreciated.

 

[Ranger Mike]

Welcome Vinny
Thanks for the great question.
Looking at the set up numbers FOUR things stick out immediately.
1. The front Roll Center is too far to the left of the center line. This car will be pushing going in and loose off the turn. The right front tire does not have adequate down force to stick the tire going into the turn. That’s why it will push. The rt ft tire will slide going in.
2. The rear springs are way too stiff. going to #220 spring instead of 350 and 450 make sense. Running the #450 spring on the Left rear tells me it was an attempt to load the right front tire. This may have been successful but is not the hot set up.
3. The rear trail arm link angles of 3° and 14.35° tell me there is a lot of rear steer going on and add to this the different length links ...some one has induced roll steer to make the car hook up at corner exit.
4. Your 2854# car should have 53% left side weight for dirt – you have 45%. The rear weight should be 53% and it is...this is good- the cross weight on dirt should be 49 to 50% but yours is 42%. Again this leads me to believe the car pushes bad going in so the former owner backed way off the wedge (cross weight) to take out the push.So was this designed this way or is it a result of some ones tinkering over a few seasons to make the car work?
I suspect some one swapped out a front spindle and went to AFCO ball joints which moved the Roll Center from the stock .5” height ( centered) to the left at 3” height. This is usually done to improve bump steer and camber build curve by some one who knows what the yare doing. Too many times it is done because of results from the pit bull session. The Track hot dog was running a Chevelle front spindle so I need to get one. The unintended consequence is that there is not enough body roll going thru the Roll Center to plant the right front tire. So it pushes. This is detailed in Steve Smiths book “Street Stock Chassis Technology” which is a must if your going to win. Apparently you have software to find the roll center and this is great. Move it 4 inch to the right of center and keep it at 3 inch height.
Vinny all of this is strictly conjecture on my part ..from an arm chair and not eye ball to eye ball..so take it for what its worth...On the rear, measure the roll steer. I can not guess what’s going on when two different link trail arms and move in roll and bump but I will bet the wheel base is changing big time.
Measure it. Panhard bar should be ok. You did not saw if you run ARB or sway bar..should be 1.25” diameter if allowed. What is the front Bump Steer? What is camber gain per inch? What's is the Ackermann?
I can tell you one thing..you got a lot of work to do and most of it is not going to cost money just time. You got to find these answers before going to step two.
But this is where you re-build your car to WIN. savor the moment!

 

[vinny1A]

Mike, thanks for the reply. I noticed I reversed the LR/RR weights. Weights should read:

FL-706
FR-618
LR-946
RR-584

This doesn't fix the front end, but makes the percentages better.

We cannot run sway bar.

Car does push on entry.

 

[vinny1A]

OK, I believe I have fixed the RC in front, as I have it moved to 4" Right of center and 5" off the ground.

I also scaled the car and here are the new numbers:
LF-747
RF-598
LR-900
RR-679

51.2% Cross
56.3% Left
54% Rear

Question is this- With my RR trailing arm of 26", and my spring mounted at the 19" mark, doesn't this give me a .730 ratio which would mean the spring rate is actually 255# on the axle? (350# spring x .730= 255#)

With my LR trailing arm of 20", and my spring mounted at the 12.5" mark, doesn't this give me a .625 ration which would mean the spring rate is actually 281# on the axle? (450# spring x .625= 281#)

So if I put the 350# spring on the LR at a .625 ratio, that would equal 218.75# correct?
and if I put a 300# spring on RR trailing arm at a .730 ration that would equal 219# correct? (This would get me closer to the 220# which you recommended.

I'm learning, so please be patient! Thank you so much for your help!

 

[Ranger Mike]

Vinny i think a roll center 5" above ground is going to be too tall. 3 inch if you can do it...3.75 max.
i am not following you on the rear end layout...can you post photos? Are you mounting standard spring coils on the lower trailing arms? are they coil over?
you may be right on with your motion rate and true spring rate calculations..im just not visualizing it.

 

[vinny1A]

Standard 13" coils mounted to trailing arms. Swivel base mount on arm, adjustable screw bucket on top. (Don't know how to upload pics)

 

[Ranger Mike]

you are correct. you know how to figure motion rate so go for the lower rate springs around 225#
the Camaro originally had a leaf spring rear end and some one fabricated the current trail arm set up. as long as you know the wheel rate you can get her to the winners circle Vinny!

 

[vinny1A]

Mike,

Thanks again for all your help, and sharing your wisdom. We ran the car on Sat night, and boy what a difference! We went from a back marker to competing with the top 5! Car is getting into the corners as it should, but I was lacking forward bite off. I'm thinking the reason is because of the stiff rear springs.

I do not have a tool to check tire temps (yet), but by "feel", both right sides were about the same temp (hot), and I had no heat in either of the left side tires. If I raise my panhard, and soften my rear springs, will I gain forward traction without sacrificing entry/middle handling, as well as make the LR work a little harder?

 

[Ranger Mike]

Good job Vinny
You did the work..i am positive you could have figured it out..all i did was copy some notes from a few books...you are on your way to a checker soon!

watch the cross weight % with any spring rate change. Keep it in the guidelines. You are going the right way with lighter rear spring rates.
I would change out the both rear springs to begin with. I always change by 50 lbs. but you know best since you know your car!

Panhard bar is good adjustment but do only one change at a time. I like a level panhard bar and you have 10 degrees angle. I think this is loading the right rear tire too much and taking heat away from the left rear. Don’t change it until you see how the rear spring change works.
Basically you will be lowering the rear roll center when you lower the panhard bar.
Cars with crossweights of 52 to 55% performs better with rear RC at center or offset to the left rear tire. A left off set RC means you need slightly stiffer rt rear spring because you have more of a percentage of body weight to deal with. Vinny beware of lower rear rc because it means stiffer rear springs to offset body roll. Ball park rc height for Ford 9” is 10 to 11.5 inch.

Did you correct the ft roll center height or is it still 5 inch? My worry is the rear rc may be close to the same height.

Raising and lowering the trail arms has direct results on rear tire loading under acceleration. Up hill angle adds more tire loading because the rear end is trying to move underneath the chassis as it pushes the links forward. This is called Axel thrust. By raising the front of the trail arm you increase traction. But remember that it will free up the car under braking as well so go gradually. Typical setting are 3 degree uphill on left front trail arm and 2.5 degree on right frt trail arm. Beware of too much angle due to causing rear steer. These setting are for EQUAL LENGTH trail arms and you don’t have these. I would not monkey with the angles yet. Just keep this in mind once the springs are changed.

Change the springs and run it.

 

[vinny1A]

Front RC was corrected, and I ended up with 3-1/4" above ground, and 4.5" to the right. Camber curve is not perfect, but FR had even heat across the face, so I am going to leave front alone.

And just to clarify, when I change rear springs, I should go with the LR lighter than the RR? And this will help to keep more weight over the LR, therefore making the LR work harder?

Last thing- I have around 270# of ballast on the car. Currently it is all clamped on over and around the LR. Should I try to move it around, or leave it?

 

[Ranger Mike]

Good job on Roll center and front end..leave it alone
you are correct on lighter rear springs. The left rear can be slightly heavier 25 to 50 # than the rt rear.
If your rear weight, cross weight and left side weights are in guidelines then don’t bother with the weights until total rebuild this winter. Then put it at polar moment for best results
post # 562 page 29..good info on COG post 563 page 29

please look at post # 253 on page 13 for 3rd link mount also #707 page 36
check out post # 284 on page 15 about spindle heights..also 809 on page 41

tire temps see post 468 on page 24

 

[drobbie]

You reference the rear springs in the last post is confusing "The left rear can be slightly heavier 25 to 50 # lighter than the rt rear." It states both heavier and lighter for the left rear. Which one is to be lighter? RR or LR?
Also is it the same for dirt and asphalt?

 

[Ranger Mike]

good one...was not enuff coffee ..just about all 3 link dirt or paved use heavier lft rear spring or same spring rate as as rt rear...
this is a general statement and there are exceptions..for instance

four link street stock chevelle set up is opposite
like 175 lr and 250 rt rear...the screwed up front end these cars run mean a ft roll center to the left side...rules dictate these things and camber build over rules the rc relocation which is almost impossible unless you bend the rules big time..

 

[mikey531]

I am still chasing a possessed racecar. I have posted questions before and Ranger Mike was a lot of help! Over the winter we did the front end did the roll center and got the front end the way it is supposed to be. It was really messed up. We have a couple of decent runs but one thing that is driving us crazy is ride height. We have a raceworks asphalt modified chassis. We set the ride heights at home and the left front was set at 2 1/8. We practiced and put new tires on and we dropped almost 1/2 in ride height on left front. The tire circumference we took off was 80 inches and the new tire we put on was 80 7/8 inches. Went to tech and we were very low ! We put put rounds into the left front and got it to ride height and then changed the other 3 corners to got close to our setup. We have checked everything for binding checked the shocks and everything is free and working. We are lost.

 

[Ranger Mike]

when you are setting up the car at home base do you use the same 4 wheels and tires aired up to track PSI? at track and at home base do you have level concrete pad to measure ride height?
Did you measure all 4 tires for circumference before and after running hot laps? I assume you do not run nitrogen in tires only air. One thing that could cause drop in Lt Ft ride height is right rear tire growing after hot laps. Could gain stagger and throw wedge into left ft.
from Longacre web site...food for thought...Wedge will change due to a variety of things that are explained below. When you notice a wedge change, have a look at the total weight. If the total is the same then odds are your scales are operating fine and there is something in the car that needs correcting. If the total changes by more than a few pounds then you could suspect a scale problem and should call the manufacturer for more direction.

1. Stagger Effect
   Cars that run high amounts of stagger and a locked up rear end can experience changing wedge due to the tires getting ready to "skip" like when you are push through the pits around a tight turn. Weight will momentarily be miss-applied as the tires excerpt force through the rear end gears. The axles literally climb up the ring gear causing an occasional wedge variance. To avoid stagger effect problems simply remove an axle cap and pull an axle out past the spline on the rear hub. You can even see the stagger affect on cars with differentials however it is less common.
2. Chassis Binds
   1. A-Arms
      Sometimes A-arms can be in a bit of a bind to get the caster right. This usually happens when more shims are used on one A-arm bolt than the other. You can see wedge numbers change due to this added resistance. Try to avoid uneven shimming and be sure to keep your A-arms greased at all times.
   2. Ball Joints
      Ball joints have a fair amount of friction and need to be greased often. The friction can cause wedge variations if the car is not settled properly. Damaged ball joints should be replaced.
   3. Sway Bar
      When weighing your car or making spring changes you should always have the sway bar disconnected. Many of the wedge variances I hear about are due to sway bar binds. I connect the sway bar only after the weigh process is completed. On late models I like to load the bar with 1/2% of wedge. On Cup style cars I like the bar to be completely neutral. You can set the bar to your liking but try to do it the same way each time and note your weight readings with the sway bar load if it is not set to neutral.
   4. Camber Changes
      When you adjust camber you are changing the tilt of the tire. Adding camber changes the wedge in the car to a small degree. Keep this in mind when recording your weights. If camber is changed, wedge will change a bit as well.
   5. Shock Rebound
      Shocks with high amounts of rebound can artificially hold weight in a corner, especially when cold. Settling the car usually works the hydraulic fluid to get consistent readings. However, high amounts of rebound can make the weighing process harder. If possible, disconnect the shocks. On coil over type cars settle the car thoroughly.
   6. Tire Pressure Changes
      Air pressure changes moves cross weight and will change the numbers on all four corners of the car. Be sure to have the air pressure set before you begin the weigh job. I have seen slow leaking tires or bleeders that are still bleeding cause the weigh job to be a real hassle as the wedge keeps moving every time you check it. Be sure the tires hold air before you begin.
   7. Stagger Changes
      Make sure the stagger is set. More rear stagger takes bite out of the car. Less rear stagger puts bite in the car. More front stagger puts bite in the car. Less front stagger takes bite out of the car. Make sure you do your shop set up including ride heights with the proper amount of air pressure and tire stagger.

 

[mikey531]

We do use nitrogen, and we have a level pad checked with a laser we run a string cross corners under the tire to measure ride height and this after the car has sat between races. The stagger and circumference was the same as before so that ruled out tires and last time we raced we were fine. It happened once last year on a cool night (50 degrees) and again last night as it was 47 degrees. But how can a car drop a half inch on the left front? We have checked and rechecked for any binding and the car is set up in a warm shop. All we did was practice on our old tires put on the stickers went to the series scales our weights and corners were almost the same as what we had but the right height stick would not go under the left front. We went back and pumped in 17 pounds and it passed ( then I dropped it back to race pressure) but when we came back in from the heat race and checked ride height we were almost a 1/2 inch lower. and the tires had more pressure in them ! The tire circumference was within 1/2 inch on all four corners. The only thing is something causes it to drop in the cold? This is very frustrating. Thank You !

 

[Ranger Mike]

see post # 572 page 29 for detailed discussion on heat cycle diameters
One weird thing I ran into that caused me to build a tire heat cycle machine was an incident regarding tire stagger. The drill on tune and test day was to air the tires with nitrogen ( more on this later) measure the stagger ( outside diameter of each tire with a small tape measure deigned for this. The tries were hot lapped and when the car came in we immediately jack up t he car and remeasured the stagger. In one case the stagger was SMALLER than when the tire went out? An we had HIGHER air pressure...How the heck did this happen..the darn thing shrank! It took a few days and many telephone calls but I found the answer. Seem that when the tire is manufactured, it is inflated after the last press mold operation. The post manufacturing inflator was operated by some college kid working over the summer and the tire was over inflated and permitted to cool and took a set that measured considerably higher diameter than normal so when he tire was heated up again, it snapped back to the proper nominal diameter. Well this got me to thinking of a better way to heat cycle the tires so I built a heat cycle machine. These were Hoosier Slicks on super late model car. It is worth looking into as the stickers are the only variable you mentioned.

 

[mikey531]

We bought tires with the same chalk mark and checked circumference with a tire tape when he came back from the heat race and each tire was less than an inch different from what we practiced with earlier. We check stagger after every run just like you do. The tires we run are Hoosiers. There has to be something holding up the car when we do the setup in the shop, but even when we come back the next day ride height is still ok. I even checked the springs again to make they were seated. We use the same driver and he didn't gain any weight. I will keep looking. Thanks again.

 

[Ranger Mike]

I would pull all the shocks and check them. You may have defective valve that could tie down the front or is stuck open on rear shock hiking up the rear end

 

[Ranger Mike]

This problem was rattling around my brain all day..how do you loose ride height. If the tires are not having post inflation problems as earlier described and the chassis is bind free and sway bar is not an issue ( it is unhooked when doing set up and set to neutral), and you do not have a weird rear end hike caused by ring and pinion interaction...all that is left is the shocks.
And this makes sense. You set the car up in a warm garage. The chassis drops after hot lap session. The conclusion is the shocks have been heated up and drop to a level lower than the colder set up height. A gas shock and all shocks these days are Gas shocks can reach 302 degrees F during hot laps. I would guess we have a defective shock on the left front. How long have these shocks been on the car? We run Penske 3 way gas shocks and they must be rebuilt every year ( our race schedule). The shock oil can wear out and the shims can wear and loose tension. Heat does this. If you have run the shocks more than one season...it is a safe bet they are shot and the only real way to check them is on a shock dyno.

Penske shock oil has many different weights like engine oil but the viscosity rating is at 100 degrees C or 212 degree F.
http://shop.penskeshocks.com/files/downloads/rsf%20data%20sheet.pdf

I have been told this works but try at your own risk..
Get out the old bathroom scale and measure how much force it takes to compress the shock in question. Next , give the old lady some spending money and send her to the mall. Take the shock and put it in the oven at 200 degrees, then take it out with that oven mit measure the force it takes to compress it. If it offers no resistance you found the problem.

Make sure you use plenty of air freshener to hide any signs of you trespassing in her kitchen.

 

[mikey531]

This is what I have suspected too, and I did not know how hot a shock would get and it happened both times when it was cold at the track. It was about 50 degrees on Friday. The other thing we have to do is double check ride height when we get to the track to make sure the shock didn't lock down. We are buying new front shocks before the next race. I really appreciate the help and knowledge as I am still learning all the adjustemnts available on a modified. My son and I raced a metric chassis and we were very successful, but I didn't have as many adjustments. Thank you again !

Mike