Automotive Race car suspension Class

[Ranger Mike]

Anti Dive

I was in a manufacturing facility last week and saw the 2013 Dodge Viper chassis. That car had huge Anti Dive. On the front the upper A-Arm mounts were more or less parallel with the ground but the lower mounts were significantly angled. Rear was like this as well but not as dramatic. If you think about it Detroit thinking is to have the car go straight when you mash the brake pedal so anti dive throws a lot of caster into the front geometry when in dive. The motion of the lower A-Arm moves the bottom of the spindle forward with upward movement and this adds caster which makes the car go straight under braking. Since the arc of travel is “ straight” up as a true race cars front end would be, this adds to spring rate somewhat. Anyway, that’s the rationale as far as I can figure it...

 

[THORPE]

Thorpe ...great...now your getting it. When you dropped the ft RC you lengthened the lever between the CG and RC so stiffer springs were required to counter the body roll. You got more turn in becuase you used the weight transfer to plant the right front tire better and this gave you more cornering ability.. Excellent. The Lft rear was lifting at turn in BEFORE YOU CHANGED SPRINGS as expected because the right front was loading more and thus unloading the left rear. Also you reduced the " jacking effect" caused by the tire contact patch and RC that tries to lift the left front; hence left rear as well. Montitor the tire temps,,,LR spring change may be in order too? Your camber build should be reduced as a result as well which is a good thing so tire temps should tell you this too. Glad to hear about the change in handling..keep it going!

Thanks for the info. I've learned a lot from this thread. Mostly you.

Just to make sure I have my head right, when u say possible lr spring change you mean stiffer correct?

We don't really have a way to measure tire temps on these small scale cars. I may can use an infrared temp gauge that we check engine temps with but I haven't tried that before.


I'm going back to review your spring info. This weekend I ran a split in the front springs. Stiffer lf. Equal in rear both stiffer than front.

The rear Rc is a bit higher than front. I have fully independent and adjustable a arms in rear to play with.

 

[Ranger Mike]

correct on left rear needing stiffer spring to keep the tire in contact with the track. Typically you will have non equal springs on rear too if you are set up to turn left. You could do it with wedge but a tad stiffer spring will do it too.

 

[John LNZ]

Hi Mike. I am a new member to this forum. I am a racecar fabricator in New Zealand. Have found your posts on this site really interesting as I am very much into the physics and the effects it has on racecar set up and construction. I build various types of cars for dirt oval racing exclusively on 1/4 mile tracks. These are spaceframe cars which are classed as "Super Saloons" in NZ and are unique to NZ but similar to a late model with late model front suspension with a sprint car type rear end and tyres. My initial question to you is could you please explain the physics behind moving the LR wheel further out on a slick track as we are struggling for forward bite. I notice a lot of guys are doing this and would like to understand the physics behind it. Many thanks

 

[Ranger Mike]

Thanks John..means a lot when we get reports from the other side of the world...and I was the guy who thought the internet was a FAD...
we went thru this on page 26 of this forum with a fellow running a drawf car...wider is better in that you have more cornering ability in that for a given set up you will transfer less weight and the tires can better accommodate the weight that is transferred. Also the Left rear to right front leverage is improved slightly...and thus side bite off the turn with a tad more wedge..read the whole page as we had a good debate on this...
General Rule of thumb - 1 inch lower COG transfers 3 to 4 % less weight. 1 inch wider car transfers 1 to 1 1/2 % less weight.
Assume we have a race car with 66 inch wide rear track and we add 100 weight to the ballast and we locate this weight 20 inch from the center line of the left rear tire. 20" divided by 66" = 37% of the added weight will go to the right and 63 % will go to the left side of the car ( diagonal weight is not in this calculation). Now if we increase the track width on t he left side by one inch we have 21" divided by 67" = 31% right side weight and 68 % left side weight. (from Short track chassis set up by Duke Southard)

 

[THORPE]

Ranger mike:

What do you feel is more important On dirt oval?

Getting shocks to work perfectly with spring rate for each corner of the car

or

Using dampening to control weight transfer.

This is to settle argument.
I feel like proper spring selection should be used to control weight transfer and dampening should be used to control that particular spring

 

[THORPE]

To specify:

Using front tie down shocks and a lr with stiff bump and light rebound.

 

[Ranger Mike]

The purpose of a shock is to dampen the kinetic energy stored in the spring during weight transfer. Specifically the shock converts this vertical energy to heat energy by creating resistance to movement within the shock. Shocks control the RATE of weight transferred during cornering. Shocks have nothing to do with the amount of weight transferred during cornering. They can affect how quickly the weight is transferred. So using shocks dampening to control weight transfer is not exactly correct. Using the dampening to control the RATE of weight transfer is correct.
The amount of weight transferred is dependent on the center of gravity, roll axis and roll rates. Where the weight is transferred is dependent on the spring rates. How quickly this weight is transferred is controlled by the shocks. So Thorpe, you are a little closer to the true purpose of the shock than the other fellow..my opinion. And you are right on with the tie down scenario in that you are tuning the chassis regarding rate of transfer after you get the spring rate real close to perfect!

 

[THORPE]

Thanks for the info. We just agreed to disagree lol.

What I'm looking for this weekend is s small bit of tire loading control by change in transfer rate.

On a med bank track with decent grip.
I plan to run:

Rf lf Soft.
Lr 2 rates higher than front.
Rr one rate up from front.

Then stiffer bump and rebound in both lf and lr.

From what I understand stiffer lf bump and lr rebound unloads lr tire load sooner on entry and takes cross weight out.
Then stiffer lf and lr bump adds cross weight on exit.

My hope is to be slightly loose entry and slightly tight off witch fits my driving style.

 

[THORPE]

Btw this spring setup has been very close with equal dampening all 4 corners

 

[Ranger Mike]

All things are relative so i would make small changes like when you are on on a wet tacky or very tight track you want to loosen the chassis up on corner entry. Use a tie down shock on the Left front. This let's the left ft. drop down easily at corner entry and takes weight off the RR tire. This makes the car pivot around the Left Ft which makes it easier to steer in the the corner. The tie down shock delays weight transfers off the lefty front. In the middle of the corner when the chassis is transferring weight to the RR., it keeps the LF tied down to prevent a quick weight transfer to t he right rear. A stiffer LR shock with stiffer rebound holds the weight on the LR longer at corner entry not allowing as quick a transfer to the RT FT tire.

 

[THORPE]

Ok I see where you are going with this and it makes sense. Thank you for your time.

I got off track a little after reading this article about initial weight transitions.

http://www.circletrack.com/chassistech/ctrp_1210_adjusting_for_transitions_fine_tuning_your_shocks/

 

[THORPE]

All things are relative so i would make small changes like when you are on on a wet tacky or very tight track you want to loosen the chassis up on corner entry. Use a tie down shock on the Left front. This let's the left ft. drop down easily at corner entry and takes weight off the RR tire. This makes the car pivot around the Left Ft which makes it easier to steer in the the corner. The tie down shock delays weight transfers off the lefty front. In the middle of the corner when the chassis is transferring weight to the RR., it keeps the LF tied down to prevent a quick weight transfer to t he right rear. A stiffer LR shock with stiffer rebound holds the weight on the LR longer at corner entry not allowing as quick a transfer to the RT FT tire.

I did exactly this ^^^^ yesterday for practice and absolutely love it.

Also found a problem I've been fighting for while now. My upper links.
When I drew out the geometry I must have misinterpreted something and had the inner links higher. Thought I was lowering my rc but instead had raised it.

Made the swap real quick to lower them and WOW. All I can say. It was that great. Finally made everything I've been working towards come together for a great setup.

Thank you for your knowledge you are willing to share on here I know it has helped me tremendously

 

[Ranger Mike]

Thanks for the kind words..Ifin we were racing each other on the same track I doubt I would be as Christian...seriously I appreciate it.
I hope everyone realizes I have sourced some pretty good books and if everyone bought these, they would we able to figure things out..all I do is save a little time in the process and hopefully do not impart BAD advice that screws up some ones good set up...Like Jimmy Johnson just demonstrated, you have to FINISH to win. So this winter is the time to check and inspect every nut and bolt on the car. When in doubt ,,replace it!

 

[Ranger Mike]

Real good questions hear. Stagger – on open diff car , it is a waste of effort. The differential is doing its job and tire size will not impact the drive motion at all with this setup. Are you running stock diff or Ford 9 inch model?
But...you can use stagger on right front to add or take out wedge or cross weight. So when you are tire matching keep this in mind and 1/2 inch will do some good for you. Now back to the spring thing...wedge bolts or jack bolts are for at the track FINE TUNING ...period. If you go to the track without knowing where your Roll Center is and what's base line spring rate be you have no business cranking on a stupid jack bolt!..
You have restrictive rules on weight jack bolts..ok..use the stagger to tune it. You can buy spring rubbers to add more rate.
Sway bars ( anti roll bars) ..get as many different ones as will fit and know their spring rates and swap these out at the track until you figure out proper spring package. Shocks...you should have a good base line on these but I assume nothing and we can revisit later. Not knowing all the rules you face all I can do is suggest.

I recommend you spend the $ 100 for Roll Center software. Measure the car, find out where the Roll center is.. Next , before you do anything, look at the rules to see if you can change the roll center height, legally. As a minimum, change the Front RC location to offset it to the right to plant some down force on the right front tire. Then see if you can drop the front RC and still keep it 3 to 3.5 inch to the right. When we drop the RC we kill off camber build and the jacking effect on the right front. Rear RC should come down as well and again depends on rules and you can get different spring heights and spring rates as the software tells you.

Next work on eliminating bump steer and know your camber build curve over +/- 3 inch travel.
More tips are to concentrate your efforts on going after big chunks of things like horsepower. Do look at a trick 2 barrel carb ( why put on a 4 bbl. carb when the tires can't possibly hook up.)
Hedders are good, after market ignition is good if..if... you have battery big enough to run the car all night without the alternator. I like a point eliminator type distributor kit like a photo cell and straight coil..no CD ignition. Simple and easy to trouble shoot at the track. In fact , forget roller rocker arms, big intake valves, trick engine stuff.. just the basics..keep cost down for more tire money. Spend it on brake caliper upgrades and better lighter rotors. Add brake bias pedal so you can dial in front to rear brake bias. Eliminate all the rubber suspension bushings and replace with brass or aluminum. But I am sure you fellows are already on top of this..my point is to show the newbies some areas to improve..economically..

 

[mustngthundr]

I'll be at IMIS- and the ARS chassis seminar

 

[mustngthundr]

I haven't been to it yet either, but iv heard there's lots of good info. I'm looking forward to it

 

[missile07]

Which roll center software package do you prefer? I have been looking at the Performance trends & Auto-Ware. Both look similar but Auto-ware looks more up to date and more user friendly.

 

[Ranger Mike]

suspension software

I use performance trends and recommend you call Kevin Gertgen, who I have worked with since 1999.

BTW..i am honored to be nominated for an award on Engineering Forum poll

Threads in Forum : 2012 PF Member Awards

...thanks guys, I appreciate the votes!

 

[Ranger Mike]

Auto Ware software is a good product from what I can see..

I think Kevin and the Performsnce Trends software is a little more advanced in that it has the higher end capabities of watching dive and roll dynamically and can use data loggers to collect the data input..plus i have many legacy programs already form over the years...

any serious racer needs at least one of these to find Roll Center and adjust accordingly

my opinion

 

[Ranger Mike]

Street stock rear ARB

A lot of you sent private messages to me about running in very restrictive stock classes and what “ advantages” you can make over competition.
One area often overlooked is the Rear ARB or Sway Bar. We have discussed the Soft Spring Big Bar set up in pretty great detail in previous posts here.
The whole idea of using a BIG Bar on the rear is to permit spring squat and thus more traction coming off the corners. Since you are forced to run hard spec tires, any advantage to putting more traction down will be a great advantage 9 all other things considered.)

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 So 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. If you take a turn fast enough, the tires on the inside of the turn actually rise off the road and the car flips over.

Too much Roll is bad. It tends to put more weight on the outside tires and less weigh on the inside tires, reducing traction. 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.

Back to the “ street Stock “ set up. If we replace the spindly stock “ sway bar’ with a much beefier one, and we switched to much softer rear springs, we still control the body roll and at mid turn after the weight transfer has zeroed out, we can point the car and jump on the throttle much quicker since we wil be loading the rear tires to more of a degree than with our previous set up. Just something to think of when its snowing out side..

 

[Ranger Mike]

Excellent points..pls look at page 2 on how we figured weight that was transferred and look at page 20 for rear motion rates.. We really got to be on top of the front ‘ spring rates’ ( and ARB) to control roll and proper rt ft wheel loading.. the rear...well... we are not talking about a heck of a lot of transfer...i.e. we got a 3100 pound street stocker...going into a medium to high bank turn..
on stock hard tires...for the sake of this discussion we assume we corner at 1.3 G...way high but the figure is common in prior posts so here is the math..
3100 pound car times .35 means 1085 weight transfer up front and left to right. We figured that 75% is going up front so 75% of 1085 is 814 pounds...so both springs and the ARB have to handle 272 pounds with motion rate is figured in...mean while we have 25 % of 1085 pounds or 271 pounds going from left to right in the rear. This is not a lot of weight for the springs to handle. In fact , if we add in the rear ARB we have 271 / 3 = 90 pounds for each spring and the ARB to deal with.
Typical ( per post 308 page 20) Ford 9 inch rear end has a .688 Motion Rate (MR)... so we have the formula WR = (MR x MR) x SR (spring rate).. just FYI...a .688 MR squared is .473
so if we want to handle 90 pounds of weight with each spring ( ARB calculated separately but to have same effectiveness) the math is
90= .473 x SR so...SR= 90 / .473 or 190 lbs. spring...typical stocker run 250# or so Rear springs WITH OUT the ARB.

So you see , the opportunity of using the rear ARB to counter left to right roll and potential for rear squat to really hook up the tires is pretty good.One rumor from the NASCAR side of the house was the rear ARB was mounted in such a way as to close the skirt gap of the skirting on both sides of the new Car of Tommorow..AT SPEED...which is very difficult to detect when going thru tech inspection. Somebody talked and now the ARB links have to be perdendicular to the ground as viewed from all sides. Seems some enterprising team chief figured out if you can seal up the skirting better than the other guy, you got more grip going into the corner and could run deeper..so...if you use some really compliant mounting bushings and angled them ...?

 

[Ranger Mike]

Metric chassis rear steer tips

Again many of you have messaged me on advice on gaining an advantage “ legally”.
I looked up my notes from flogging the old GM metric chassis during my door flapper days. I was into chassis measurements big time and wanted to MAP the rear end movement relative to ride height and was trying to understand what was happening when the car was in the turn.
I found that by setting the chassis on stands and mapping the rear end movement using 3 inches of right rear down and 1 inch left rear up, the metric chassis pulled the right rear tire forward almost 3/8 inch more than the left. This was AFTER I loosened the bolts holding the trail arms ..etc... as the stock serrated teeth bound up the components when “ properly tightened”. Anyway, this movement when rolling into a turn, would have the effect of tightening the car on corner exit or anytime the power was applied. I learned three things here. 1. Stock rubber bushings flex and can be to your advantage. 2. I had to free up the components to swing free when race ready and replacing the inner metal spacer that had teeth with a smaller diameter non toothed spacer was a must. Also I replaced the stock bushing bolt nuts with lock nuts at could be run down tight and then backed off a turn to prevent bind. 3. As the venerable Stroker Mcgurk once said..” If some is good and more is better then too much is just enough “ so I went on to see how much flex I could get out of the rubber bushing. More on this later.

You have to measure your car to find out where you are relative to where you want to go. If the rear axle pivots so the right-rear pulls forward, this will tighten the car. If the left rear pulls forward, the car will be looser.

Roll steer can be affected by using very soft rubber bushings. I tried the old tire softener trick but it seriously and quickly deteriorated the bushing and was a mess. With softer bushings on the right rear lower trailing arm, you have roll steer loosening the car on entry. This would reverse with the power on and tightens up the car on corner exit. The soft bushing allows the right rear wheel to pull rearward under braking. With acceleration, the right rear will push forward and this tightens the car on corner exit.

You can soften these bushings by drilling holes in them parallel to the bolt. This permits more compressibility..
Before you loosen up all your bushings, you better think about it.

If you want more roll steer to tighten up the car on corner exit you would soften the bushings on the right lower trailing arm. This compresses the wheel base on that side during acceleration by pulling the right rear forward. It would then steer to the inside. Softening the left side lower trailing arm bushings would offset much of the right side compression. This would loosen the car. Softening both might be an aid to forward traction because the rear end bottom mounting points ( trailing arms) shorten up and thus move forward in the chassis adding weight to the rear tires and more traction.
Beware- If you are using roll steer to tighten the car on corner exit, it may loosen the car on corner entry.

So why do all this...so you have an advantage over the other racer who looks at other areas for an advantage, The rules say stock trail arms and mounting locations and in some cases, no eccentric bolts...so...think about it...you could get up to 1/2 inch movement that could make all the difference.

 

[Ranger Mike]

Happy New Year and you got the best present possible...yeah I agree. Shock location half way between the mount point and Ball Joint will be pretty in effective. The closer to the BJ the better and if rules say you got to run stock location on the shocks...run a racing shock. And you MUST run a shock ( damper) to complete the proper susension. In some cases we need to run a tie down shock to keep transferred weight where we want. Stock location is not excatly racing ideal but as a minimum you need a shock and automotive engineers spent millions on designing the set up and it is a compromise for ride comfort, performance and economy of manufacture.

Stock shocks will not stand up to the abuse of racing. We run Penske 3 way shcoks and have to rebuild every year. The shock oil deteriorates and the thin metal shims wear out. You get a lot of heat when you dampen the suspension and this is the main culprit.

 

[Ranger Mike]

street stock racing shock

Speedway Motors has a bunch of racing shocks specifically for your class..I like this one myself..affordable and who is going to claim your " used shocks" for $ 50.00..never seems to happen..make sure you paint them same as your original shocks and smear a lot of grease and dirt on them...

http://www.speedwaymotors.com/QA1-S...-size-Camaro-Extra-Heavy-8-Valving,31463.html

 

[Maliwagon99]

Notice my postscar were gone? I gotwas deleted forand being a spammer somehow? Anyway now that I am back up and running I can ask more questions. On the rear ARB will a aftermarket stock mounting one suffice? I have seen some that mount to the rear end with similar bushings as the front mounted on the housing then the ends hooked to the LCA ahead in the front with some adjustable links ie http://www.hotchkis.net/_uploaded_files/78-88_gm_g-body_extreme_sport_rear_sway_barproducts455image_2.jpg . Since it doesn't say anything in the rules about it id like to try but I have a good feeling if I start winning that will be the first "gray" area fixed and that bar mounting system isn't cheap. Your thoughts?

 

[Ranger Mike]

I would mount a stock appearing ARB on the rear as close to " stock " location as possible and I do not think they will say anything because the car came with one from the factory..right?

 

[Maliwagon99]

You know I bet that ol wagon did "wink" :) thanks RM

 

[John LNZ]

Hi Mike. A question for you please... We have a car that is still struggling for side-bite on a flat slick trac. I am considering reducing my front roll couple by either reducing my right front spring or lowering the rate of my swaybar. I figure that this should transfer more weight onto the right rear through the first part of the turn. Am also considering reducing the rebound on the left rear shock and increasing the gas pressure hopefully speeding up the weight transfer left to right. What would be your opinion on this?
Thanks

 

[Ranger Mike]

Welcome and thanks for reading the notes.
I assume you want to hook up faster and better to drive out of the turn..right?
Flat track needs a lot of stagger and this is what drives you off the turn.
Don’t forget when you increase stagger you have to add cross weight to keep the same down force in the car.
Spring change- As stiffer left rear spring will tighten the car from middle of the turn to exit by keeping the cross weight in the chassis. Side bite and traction usually are a factor of the rear lower trailing arms and we need to look at these. Are you running 3 link or 4 link? Torque link? Do you have spring loaded radius rod on the rt rear?
Raising and lowering the front of the rear trailing arms impacts the amount of load placed on the rear tires under acceleration. The trailing arm up hill angle adds more load because the rear end wants to move under the chassis as it hooks up against these links. The uphill angle of the arm reacts against the twisting motion of the rear end and ultimately loads the tire. Classic axel thrust. If you want more right rear side bite move front of the rt rear trail arm up hill a few degrees. But if you wil be taking load off the left rear when you do this. Typical setting are 3 degrees on the left rear and 2.5 degrees on the rt rear. Watch out for roll steer and know what the change does when you change this. See post 116 on page 8 of this forum.

 

[hariss]

Formula Suspension Design

Hallo Mr. Mike, I read your post and that was really helping. I just read about how to design good RC location for double wishbone suspension and I've been tried to design suspension for formula SAE. I assume that good RC location is 1 inch above ground (minimize jacking effect and non rolling overtunning moment) is that correct? That I don't understand is how to get optimize length for upper control arm (find inner pivot location on upper ball joint / find final IC location) so that my design with RC 1 inch above ground and initial fsva length approx 78 inch has optimize length for upper control arm.

Thank's

 

[Ranger Mike]

Hariss welcome and thank you..many people and racers have posted here...I think 1 inch abov pavement is a good start...I recommend the chassis software as a very good tool to get the proper height and location as well as seeing the RC migrate thru bump...it is worth the $ 100 or so...well worth the effort to get the checker flag!
if not possible send me provate message
rm

 

[tscott8]

Ranger Mike, what do you know about the new "Weight Jacking" setup taking the asphalt late model series by storm. I notice the guys running it use short upper arms for fast camber change and a ton of lf upper angle. People running this have a ton of travel and I've seen upwards of 12 to 15 degrees of lf camber become 0 at mid corner. What is going on here that I can use to be successful?

 

[Ranger Mike]

TSCOTT, i am currently in Europe and do not have access to my notes. Will return in a week. I will be able to give better reply with notes but suspect the trend has some merit. How do you know the camber goes to zero at mid turn? any more insite on what and where the weight is jacking to?

 

[tscott8]

I just know from observation that the lf stands up for proper camber because I've measured old tires in the trash pile from the top team doing this. It is suppose to load the lf i assume, because that car can turn really good. Just from basic observation they use a short rf spindle where the rf lower is all the way down and the rf camber change is very minimal while the lf is really tall where static angle on the lf upper is probably 25 to 30 degrees. I've also heard that the pin angles on these trick spindles are less than 5 on the rf and 15 on the lf. This team runs hillbilly on the front with a 2" bar and hardly any spilt in the back springs, sometimes hillbilly back there. We race Nascar late model stocks around nc and va

 

[tscott8]

I think it is called "weight jacking" because when the side force is applied to the cg and the cars chassis wants to roll to the right but the tires pull to the left, the lf suspension jacks down on the spring because of the high angle in the upper

 

[Ranger Mike]

Long plane ride home...ok...when we swap in the taller left frt spindle we shift the front roll center to the left, which is what we want to plant the right front tire..a lot of previous posts on this a few pages back. Typical NASCAR spec late models run around 17 degrees upper A-arm angle while the outlaw series run 20 degrees rt top and up to 26 degrees lft ft top A-Arm. If you look at post 325 and 332 on page 21 at King pin inclination angle you can gain more insite. Bottom line is when going into a left hand turn you are pivoting on the scrub radius ( see post 325 i think). This makes wheel base longer on the right side. When in a left turn, Scrub lengthens the right side wheel base and tends to loosen the car. When you counter steer, it shortens the wheelbase and adds understeer. This is a driver friendly situation as it has a very stabilizing effect to the cars handling in driver feed back. The driver needs feedback in a turn because it tells him how heavy the tires are loading and when they are on the edge of traction. We need more scrub on the left side due to posative camber we run. In outlaw series we run all kinds of trick upper and lower A-Arm combinations but in restricted series you have to look at what is still " open" and go with radical king pin angles and scrub radius tricks to help the front pivot. If you look at the camber build on an outlaw super late model is really goes to zero at mid track on rt ft and darn near same on lft ft...remember..it is all about the tire contact patch.

 

[mustngthundr]

tscott8: I've been digging into the setup you're shooting for myself. We don't have any locals at the tracks I run at using it, but at the invitationals the out-of-town cars run a setup like this and they are extremely fast. Considerably faster than our top regulars. I haven't found a whole lot of info on it either, mostly gathered info from eavesdropping and observing what they were doing from a distance, cause they certainly weren't going to show you, matter how nice you asked. I've heard terms used with it like "camber thrust", "jacking force, are the most common. I've been told a correct shock and bumpstop package is a must. I've experimented with copying this setup, but I can't say I fully understand it. I've recorded the fastest times our current chassis has ever turned, but I struggle with consistency, partly due to being a rookie in a SLM, but definitely because there's more to it than I understand. Anyone that could give more insight, either by posting on here or private email, I'm eager to learn and would be happy to share any info I have. Also thanks Ranger Mike for your help on this forum, it is a great source of information

 

[Ranger Mike]

Doc Hathaway wrote one great piece on this whole scenario.
It is a must read. It is a mandatory read before you do another thing today.http://ismasupers.com/downloads/Tech-02%20Suspension%20Geometry%20relations%204.pdf

Everybody else sets up the car with your typical camber setting, caster splits and recommended “ hot set up” Kingpins and spindles. Some may even know enough to add the proper offset on the front Roll Center. The car gets around the track pretty good if you hit on the close spring rates and shock package. And you wil be competitive with every body else because you have copied every body else “ hot set up”...maybe better because you have the proper RC height and offset...but..
all this stuff is static set up where as the suspension moves and we are trying to use a static setup in a kinematic ( moving ) world. The guy who understands what is happening in this kinematic world will be able to set up and run a lot better.

Basically the new " hot set up" is to run very soft springs that will hit the rubber bump stops ( post 220 on page 14 above) just when you make mid turn. You want the springs to take the max load before bottoming BEFORE the rear end comes around on you.

This setup uses the King pin Inclination Angle to crank in caster to " weight jack" from the inside rear tire to the outside front tire to build proper camber. But, KIA adds camber to the LF and takes away camber from the RT FT unless you have accounted for this by compensating for it during suspension movement. Hence. the different KIA. Min camebr loss on RF by low KIA, where you want the LF to ad more Pos camber so larger KIA on left spindle. You want the max tire contact patch on both front tires at mid turn. Scrub radius and caster do this weight jacking. If you set up your particular chassis correctly, with differing Kingpin Inclination Angles (KIA) and scrub radius ANNNDDDDD you run softest spring rate to rubber bump stops, you will be using the transferred weight to the max to plant both front tires to turn the car. Don't forget the Roll Center offset which comes from the different spindle heights. One more thing. Static caster and camber does not tell the whole story. Depending upon your set up, different outcomes happen when we have a tire contact patch acting thru the scrub radius as the suspension moves. You must know what is happening at the tire contact patch while this whole compression / weight transfer is happening.

Because there are so many variations of A-arm lengths, spindle / ball joint heights, spindle heights, etc..it is impossible to replicate the fast guys set up unless you have an identical chassis. You must understand the theory to make it work ON YOUR car!

It is like it has always been. Tires, Tires , TIRES..and the guy who makes the max tire contact patch on all four tires a higher percentage of the time will run faster and better and win.
hope I did not confuse you..clear as mud?
rm

http://ismasupers.com/downloads/Tech-02%20Suspension%20Geometry%20relations%204.pdf

 

[mustngthundr]

Thanks Ranger Mike, your response was definitely helpful, as was the article in the link. After reading I'm sure my caster setting was off on both sides, probably camber settings too. I've invested a lot of time and money into (attempting) to educate myself on the kinematic aspect of the sport, and admittedly have a long ways to go before I'm happy with my personal level of understanding of the chassis and dynamics involved to make a fast race car. Our fast and consistent regulars have new chassis set up by their respective manufacturers, and they don't change anything on the car without calling them. There are few respectable cars that are set up by years of trial and error but not much understanding of what is actually going on. I don't want to be one of those guys, and I've come a long ways in the last few years, but there's a lot of aspects that I definitely don't understand. We did try to more or less copy what the super fast cars that came up a couple times a year were doing, hoping to eventually figure out what they are doing that works so good, and use it to my advantage as a regular until everyone else figures it out as well but try to stay a step ahead. We were close a few times, super fast and just trying to fine tune, and somewhere in the fine tuning throw something way off and struggle to get back. We did go as far as checking what was going on static and in dive, use performance trends software to map the geometry and a chassis r&d program to balance the chassis and set wedge. We have an awsome shock package, and more power than we could ever use at the tracks we run at. The biggest problem we keep running into is a corner entry push, and as we know a poor entry results in a poor corner overall. I've been told I drive in too hard, and that may be a portion of the problem, but we did get it to work really well a few times so I think a setup error is definitely more of the problem. To try to reduce the chance of it being a brake system issue, even though everything was rebuilt before last season, everything is new for next season except the pedal, and a package recommended by an extremely seccusseful team that races all over the country. We run 10 inch Hoosier tires, spline 1 7/16 3 piece sway bar, 10 degree spindles, bump steer set to near zero through the full range. Tire temps were always pretty decent, showing good use of the contact patch, but I've since learned about measuring the tire wear as well so our camber on the right may initially be a little low. Roll center about 10 inches left and 2 inches above ground, about 2 inches of movement through travel.

Thanks again for all the info you put on here, it definitely helps. If there's anything else I should be looking into based on this info or if you need more info about the car is be happy to put it up.

 

[Ranger Mike]

Mustngthundr...thanks you..

question- is car pushing going in and loose coming off turns?

 

[mustngthundr]

Typically not loose on exit. From about mid- turn off its usually pretty decent unless I get held really tight to the inside, then it will get a little loose.

 

[Ranger Mike]

When we have Roll Center too far to the left of centerline, the car will not turn well. We have to load the right front tire with down force to assist the tire. See Post 251 on page 16 Body roll does not give enough leverage to stick the rt ft tire. It slides sideways thru mid corner. When we exit, there is not enough lift from the Lft Ft on to the RT Rear to add traction.
Your roll center is 10 inches to the left. You are right on with the suspension software as thsi is the tool to figure out the set up.
We must locate the RC to the right of centerline so at least half the left side mass sprung weight is rotating thru it to stick the Rt Ft. Unless you have Aero adding a lot of down force at the end of the chute, you need this to stick the rt. ft. So we run 3 to 4 inch offset to the right of centerline just for this purpose.
As a minimum relocate the RC to center...3 inch to the right is ideal. This means you will have a little more than 55% left side sprung weight wil rotate thru the RC ( on 66" track width car). This will make your set up consistant and you can fine tune from here.

 

[mustngthundr]

Ok that makes sense. I'll give it a shot. Thanks again!

 

[NaLLa8705]

Hey mike!

Finishing up my race car build, found a friend with chassis software, now wondering where to measure my upper control arm pivot points so i can determine roll center. The upper control arms on my car are angled so at what point do I pick to plug into my software? Dead center?

 

[Ranger Mike]

welcome and sounds like a good plan. On all the chassis software i use, i have to measure the height and location from center line of the top outer pivot point and top inner pivot point and the software calculates the angle. The better and more accurate you measure, the better. I had to make stop blocks to jam under the lower A-arm to maintain exact height and slipped off the front tires on occasion when running wide tires and big wheel offsets masking the outer pivot point. Eventaully I borrowed a portable cmm arm.

 

[NaLLa8705]

Perhaps my question wasn't clear enough, or maybe because I haven't I looked at the software I am confused, but what I am having trouble understanding is where on the pivot do I pick the point to put in. The arm is angled like I drew up in paint.

That is in a two dimensional plane...

 

[Ranger Mike]

on circle rack analyzer use attached..i use suspension analyzer which requires 3D input

 

[rohitsr987]

hi..i am building a groscope sysytem to balance two wheelrs..i need to know what is roll torque and how it can be countered?

 

[07superstreet]

Mike,
Hello, i am new to the discussion. I stumbled across this website and forum, luckily i might say, trying to find some information to help my race team. We have a stock snout, camaro frt. clip, tubular 2x3 tubing, chasis. It's been difficult getting the handling on this chasis. Before, we had a stock camaro chasis and we had figured out what it took to make that chasis work, but we were behind everyone else. They had swicthed to the chasis that we have now. With the old chasis, we would run 49-50% frt. and rear percentages. Only reason for that was that was all we could get. On this chasis, we run 55% rear percentage and 52-54% left side. The issue we are having is with ride height. We can not find anyone that can or will give us ride height numbers for this chasis. In reading all the information on this thread, i see that ride height and all related to that are very important. I know that if we can get the proper ride height, everything else will fall into place. Thank you so much for all the information you give. I have been glued to this thread since i found it.