Race car suspension Class

[Ranger Mike]

All race cars have spring compression, even Indy cars. If they did not they would be big go karts. You need at least an Inch even on the hairiest BBSS set ups. Two to three inch is ideal, over 3 inch is for dirt set ups. If the roll center stays close to the origin by 2 to 3 inch over first 2 inch of compression, you are taking advantage of 90% of the tire down loading.

When the frame starts hitting the track, increase ride height 1/4" until it stops.

 

[Ranger Mike]

C10 ,where is the 3rd link or top link located (attachment point to the chassis, not the rear end.) on the rear end? Mark the center lines of both rear tires. Now tell me distance the 3rd link is from each center line.

 

[Savem c10]

C10 ,where is the 3rd link or top link located (attachment point to the chassis, not the rear end.) on the rear end? Mark the center lines of both rear tires. Now tell me distance the 3rd link is from each center line.

Morning RM yes I’ve read your literature on this and our track width is 64 inches and our left side weight is 57% so we do 64×.57 which equals 35.91. I had to do some specific modifications to the third link area on the CHASSIS which I’ve done and it’s exactly right where the third link needs to be and we’ve actually run the car one time with this way and I will tell you, it makes a significant difference on handling. I’ve got it I’ve gotta get back to work. We’ll chat later. Thank you RM.

 

[Ranger Mike]

Morning RM yes I’ve read your literature on this and our track width is 64 inches and our left side weight is 57% so we do 64×.57 which equals 35.91. I had to do some specific modifications to the third link area on the CHASSIS which I’ve done and it’s exactly right where the third link needs to be and we’ve actually run the car one time with this way and I will tell you, it makes a significant difference on handling. I’ve got it I’ve gotta get back to work. We’ll chat later. Thank you RM.

Excellent work! good job!!

 

[Cape15]

Hello Everyone, I am so glad to have found this forum in my search to making my asphalt super late model faster! I have recently come across information that some of my competitors are putting lead on their lower LF control arm and wrapping lead around the rear end housing to help with weight staying on those tires throughout the corner. Has anyone tried this? and is this a viable theory? More curious than anything. We have a no bump stop rule and no ride height rule 2700 lbs. tight 1/4 mile flat track with 10" American Racers and 66" track width. Haven't played with roll centers in the past but thanks to this forum will definitely fool around with it this year.

 

[Ranger Mike]

Welcome Cape
read post 562 on page 17 about Polar Moment. In my opinion, making a race car back into a go kart is stupid.
This is what not properly using the Suspension makes the car as well as Bump Stops...why have springs??
Many post here on this as well. That has to be one tight paperclip track you race on or else it is the Mount Lawn baseball Diamond! Anyway, figure out your roll center and set up car from there. let the monkey see monkey do crowd waste their time on trends and gimmicks, you study the basics and then get the checker.
Look at the current trend of having the front roll center to the left of center line.
It is acting thru a lever that is 11 degrees to the right front tire patch. Think it won't jack up the car??
darn sure will. The proper location is on the right of center line acting at 5 degree angle. Will still scrub off some cornering momentum but not lift the left side of the car. Adding lead to the left side a-arm is a bandaid not a cure.

 

[Cape15]

Thank you for the timely response. I've never heard of Mt Lawn until today but it does seem eerily similar to my track of Seekonk! I will most certainly will be implementing this new understanding to my car as well as other knowledge I have gotten from reading through prior posts. Thank you.

 

[Cape15]

I have been reading a lot from Bob Bolles publications and he mentions a lot about matching front and rear roll angles, not the roll centers themselves front and rear but the actual chassis roll together so the chassis wants to roll the same going through the corners. I may have missed this, but I have looked some thoroughly through this thread and haven't found this concept discussed much on here and was curious if that theory holds true. And if so, how can I find out how much the front and rear is rolling on my chassis as I know shock travel indicators aren't the most accurate and I def. don't have the money for a data acquisition system, if I have missed it, my mistake I honestly tried looking!

Also, in a prior post it was mentioned that for an asphalt car it is best to start at 52% Rear percentage. The car I have now came with a 17 gal. fuel tank. We run 40 lap - 50 lap races, so I was thinking if it was better to maybe put an 8 gal. fuel cell in that I have already have and take that 55lbs difference and put it lower onto the frame rail just behind the rear axle so I can maintain the higher rear percentage but have it lower in the car. Would this sound like a good idea if I can keep 52% rear? Or should I measure out the polar moment that RM mentioned and place the extra weight there, but lose the 52% Rear? Any suggestions would be appreciated. Thank you.

 

[Ranger Mike]

good suspension software will show roll. Shock indicators are good devices to feed back at the track.
do not change the weight % until you know what it is now. Do you have scales?

 

[Cape15]

Yes I do. We ran last year around 50.5% Rear with a no ride height jacking force based setup that we were told most everyone else ran . 600 LF 250 RF 600 RR and 150 LR with a 1 5/8in. Diameter sway bar. Around 56% cross. and 56.8% left. Never paid attention to roll centers. Was competitive one night with good pace but turns out we were way light when we were on track scales and once I added the extra weight we slowed right down the last races of the year. So I am hoping to change everything this year and start fresh

 

[Ranger Mike]

Go to the smaller fuel cell. You are very close on left side 58%. I would try to mount weight close to polar moment but shift back to try to get 51.5 rear weight. Perfect for 1/4 mile track. Cross wt between 54-57.5%
do not get hung up on target numbers. everything in racing is a compromise. You get it to within 0.5% of target, close enuff. Example - 58% left side weight is 1566 on 2700 lbs. car, 57.5% is 1552 or 14 lbs.


read post 1660 on page 48 on 3rd link location. Let me know your 3rd link location.
You do not need a data acquisition system. fabricate shock travel indicators for each shock that measure bump and droop.
if you want to win, buy the software and find the roll center location.

 

[Cape15]

So my rear tread width is 65 1/2 (max allowed is 66") and my left weight percentage is 56.8% as mentioned above (max allowed under rules is 57%). Multiplying them comes out to 37 1/4" I measured that over from RR tire centerline and my current third link (solid bar) is an extra 3/4" farther to the LR tire, so I can remount it closer to the 37 1/4" mark. As described in your previous post. I will change to smaller tank also and move around the lead. Also looking into changing the lower links to level, parallel to centerline and making them longer.

 

[Ranger Mike]

65.5" times 58% = 38"
i would wait until you can actually get the 58% left side before final 3rd link change. Yes even 3/4 inch on those hard spec tires will make a big difference when you step on the gas.

goood job!

 

[Cape15]

On a prior post it was briefly discussed but what would be the ideal engine mounting location on an unequal lowers chassis in conjunction with Roll Center location if I have longer RF lower control arm than LF, should I place the engine in the center of chassis and then have the 3" RC to the right or should i move the engine as far over to the Left as rules allow and keep the RC location at 3" right or change that so the engine's weight doesn't have as big effect as the chassis goes through the corners?

 

[Ranger Mike]

Ideally we want the maximum left side weight we can get. Do this first then worry about Rc location. We need accurate left side weight % , this is critical. We can check the rear 3rd link location and correct.

Next, we want to use an offset roll center to put more downforce on the right front tire to add traction. On asphalt we want 3" offset to right , on dirt 4" offset.