I plotted my rear suspension, now what...

[mean78malibu]

I took some time to measure out as much as I could and came up with the following. Looks to me like the upper arms are angled down too far. I want to get better 60' times, and I'm hoping this is where it is being lost.

108" is the wheelbase and 22" is the CG (center of the cam from the ground), tires are 28" diameter. It would help to know my real weight distribution I assume, but I guessed about 58/42 for this drawing based off of a drawing from baselinesuspensions.

 

[Norm Peterson]

I doubt that you want to make the uppers closer to horizontal. Those numbers suggest that you have about 87% anti-squat, so your rear end shouldn't be dropping a whole lot on launch.

9.88 x 108.1 ÷ 55.71 puts the force line at 19.15" above the ground at the front axle line. That's 87% of your CG height.

"Flattening out" the uppers will reduce the anti-squat, so the car will squat more (not less).


Norm

 

[Doober]

Where is a good source for a lot of this math?

 

[Norm Peterson]

There might be a list of chassis books floating around here somewhere. I've get a fairly good list, just not on this computer.

the Millikens' "Race Car Vehicle Dynamics" is one comprehensive (if somewhat pricey) source.
Herb Adams' book has the "anti-squat" sketch but you might have to develop the equation from it yourself.


Norm

 

[mean78malibu]

Thanks Norm. What you are saying is correct, the car does not squat at all. I just took the 130# springs off and put on some 110#'s since I figured the 130's were too stiff. I will have to look into some more equations like the one you used. It's getting cold out, time to sit around and contemplate.

 

[KEVINS]

Actually it looks pretty good and the UCA's could be angled down a little more to move the IC back more. I'd leave it alone and work on the rest of the suspension to get it to hook if you can.

ks

 

[mean78malibu]

Actually it looks pretty good and the UCA's could be angled down a little more to move the IC back more. I'd leave it alone and work on the rest of the suspension to get it to hook if you can.

ks

Thanks for your website and information, I am learning a lot. Hopefully I can get a good starting point for next season. COAN is getting this converter back again because it should hit a lot harder than it does.

 

[James Bond]

i'm actually surprised IC length is so short. whats the upper control arm frame mounting location hieght? also your rear upper and lower spread seams .5" greater than what i've measured. also on baselines page kevin GN has a .5" smaller spread. you may want to recheck this dimension as its the key value. i would expect your AS value to be lower than you think and the IC length to be longer.

 

[mean78malibu]

i'm actually surprised IC length is so short. whats the upper control arm frame mounting location hieght? also your rear upper and lower spread seams .5" greater than what i've measured. also on baselines page kevin GN has a .5" smaller spread. you may want to recheck this dimension as its the key value. I would expect your AS value to be lower than you think and the IC length to be longer.

The front hole of the upper arms is 17.25". I missed that linear measurement in the drawing. I measured from the floor to the center of the bolts, and took my time. I'm assuming the difference is from the tire height and angle the car sits at. I'm trying to borrow a set of scales in the next couple weeks so I can get a better drawing on here. My weight distribution should be different than a GN since I ditched the factory steering, front control arms, and have aluminum heads.

 

[1BAD442]

ic point is 2 far out and 2 high up in the car ideally u would like 2 see 48 in out and 8 up