# Race car suspension Class

by Ranger Mike
Tags: class, race, suspension
 Sci Advisor PF Gold P: 1,473 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) Attached Thumbnails
 P: 41 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
 P: 41 To specify: Using front tie down shocks and a lr with stiff bump and light rebound.
 Sci Advisor PF Gold P: 1,473 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!
 P: 41 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.
 P: 41 Btw this spring setup has been very close with equal dampening all 4 corners
 Sci Advisor PF Gold P: 1,473 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 lets 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.
 P: 41 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/chassiste...g_your_shocks/
P: 41
 Quote by 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 lets 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
 Sci Advisor PF Gold P: 1,473 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!
 Sci Advisor PF Gold P: 1,473 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 cant 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..
 P: 7 I'll be at IMIS- and the ARS chassis seminar
 P: 7 I haven't been to it yet either, but iv heard there's lots of good info. I'm looking forward to it
 P: 14 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.
 Sci Advisor PF Gold P: 1,473 I use perfomance 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!
 Sci Advisor PF Gold P: 1,473 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
 Sci Advisor PF Gold P: 1,473 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..
 Sci Advisor PF Gold P: 1,473 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 ....???

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