# Race car suspension Class

by Ranger Mike
Tags: class, race, suspension
 Sci Advisor PF Gold P: 1,422 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 transfered 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 alot of heat when you dampen the suspension and this is the main culprit.
 Sci Advisor PF Gold P: 1,422 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-St...ing,31463.html  P: 2 Notice my postscar were gone? I gotwas deleted forand being a spammer somehow? Anyway now that im 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_fi...455image_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?  Sci Advisor PF Gold P: 1,422 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?  P: 2 You know I bet that ol wagon did "wink" :) thanks RM  P: 2 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  Sci Advisor PF Gold P: 1,422 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.  P: 1 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  Sci Advisor PF Gold P: 1,422 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
 P: 3 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?
 Sci Advisor PF Gold P: 1,422 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?
 P: 3 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
 P: 3 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
 Sci Advisor PF Gold P: 1,422 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.
 P: 7 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