Suspension Plotting

[orange395w]

For some of you this won't make much sense if you haven't read into suspension plotting at all. Baseline suspensions.com has great info on suspension tuning, which is where I've learned the little that I do know. Kevin at baseline provides suspension plotting when you buy his suspension components, but I got tired of measuring everything and then waiting half the day or the whole day to get a plot back showing me where I was at, so I bought my own software.

My last run at Barona I cut a 1.44 60ft which was my best ever. Then after things were working good like an idiot I changed my rear springs thinking that it would get better and even added the transbrake at the same time. Well that turned out to be a huge mistake!

After having a rough time of it at Irwindale I found out that my "Instant Center length was 29" and my Anti Squat was 154%. The short IC length and the high anti-squat were causing the car to slam the rear end and then lift the rear wich would unload the tires.

An ideal IC length should be between 30-40". Kevin at baseline told me to start at 33-35" and the software tells me to start at 41". Well I swapped my old springs back in today and set the suspension up with the little capability of adjustment that I do have. I wanted to get in between what Kevin @ baseline suspensions and the software recommended. I feel confident that the car will run alot better than it did the last time out. This is what I came up with

The Green box is the software's recommended IC length. The dotted line that extends from the rear tire to the front is known as the nuetral line. Where the blue dotted lines coming from the upper and lower control arms intersect is known as the "Instant Center". If anyone with an SN95 or Fox wants to plot their suspension I can let you know all of the things that need to be measured and when you are done I will punch it in the software and let you know where you are at.

Reference: www.baselinesuspensions.com

 

[Gibs]

Do they have anything for the classic stangs?

 

[orange395w]

Here is what you need to do in order to plot your suspension.

1. Make sure the car is at full race weight. That includes fuel, N20, YOU or weight to represent YOU in the driver's seat, and the suspension should be settled.

2. If you don't fit under the car you must make or barrow (hint, hint) blocks that allow you to get under the car while it is level and loaded in order to get accurate measurements.

3. Your pinion angle must be set before taking any measurements unless you do not have the ability to adjust pinion angle.

THINGS TO MEASURE: (All measurments are taken from the center of the respective bolt holes.)

1. upper control arm length
2. Lower control arm length
3. Lower rear control arm height
4. Lower front control arm height
5. Upper rear control arm height
6. Upper front control arm height
7. Center of Gravity height = Ground to center of Crank bolt + 5"
8. Wheelbase

 

[orange395w]

Do they have anything for the classic stangs?

This software is only for 4 link suspensions.

 

[Gibs]

I realized that after I posted.....I was gonna say, I dont have control arms......LOL Thanks though...



GIb

 

[DrunkFatguy]

Good Info Orange, another tool to determine if you need to check your setup is simply watching vids of your car's reaction during launch.

 

[02gt]

I think i have to check the suspension again, i think the rear sits too low because ever since i cut the springs i have a hard time hookin, tires seem to hit way too hard and then they break loose, which springs did you use bobby? non gt coupe spings????

 

[orange395w]

I think i have to check the suspension again, i think the rear sits too low because ever since i cut the springs i have a hard time hookin, tires seem to hit way too hard and then they break loose, which springs did you use bobby? non gt coupe spings????

I put the old SN95 GT springs back in. The suspension sits much better with them in. For some reason with the softer Fox V6 springs I couldn't get the Instant Center where I wanted it.

 

[Gibs]

I have stock S197 GT springs......

 

[orange395w]

I have stock S197 GT springs......

They won't work for him.

 

[Gibs]

nevermind then, I thought they may have fit.

 

[spdpilot]

Good post! This has been around for a while and should be 101 for anyone wanting to get into drag racing, but people have become too focused on Power.

I have been saying for a while that it is cheaper for people to make more power these days, especially on factory supercharged cars, then for people to actually spend the time working with suspension formulas.

Back in the day, HP was limited to about 400-450 flywheel unless you spent big bucks. So people were forced to learn this if they wanted to go fast. And there were no "off the shelf" parts back then. You made your own. And if you made your own suspension parts, you better know these formulas. It is a lost art that even the newest mechanics knew back then, but these days, just toss a blower or nitrous kit and call it done. Back then, there were a few paxtons on carb'd cars, otherwise it was 4-71 and that was huge money. Now people laugh at 400hp cars. But some of the old school racers can beat 700hp cars in a properly set up 400hp car even today.

Yes, I know, the 70's was a long time ago, I am old, what can I say.

Good stuff Orange!