Rear coilovers did I choose rates correctly

[72dan]

I just got some AST 5300 coilovers, they look really nice.
I plan to track and want to put on a rear wing so high rates were suggested.

I went with 700 lbs front and 1,000 lbs rear.

But then I was reading in some threads that the rear rate should be lower since I am going to a true coilover and the spring is moved outward towards the tires.

What rates have you used? What about tower reinforcement front and rear?

[warp10]

Originally Posted by 72dan

I just got some AST 5300 coilovers, they look really nice.
I plan to track and want to put on a rear wing so high rates were suggested.

I went with 700 lbs front and 1,000 lbs rear.

But then I was reading in some threads that the rear rate should be lower since I am going to a true coilover and the spring is moved outward towards the tires.

What rates have you used? What about tower reinforcement front and rear?

Yes a true rear coil will need less spring than the OEM separated spring would need. Don't know the exact math but you should consult your shock manufacturer.

[steven_s]

I'm assuming AST gave you the converted spec similar to 700/1000 true to divorced set up.

1000 on divorced would be crazy on our car, can't remember but think it was somewhere between 350-500 rear?

[Richbot]

The motion ratio is better for the shock than the spring. Need a lower rate for a true coilover iirc (it’s inclined slightly but the ratio difference is big like 0.8:1 for the shock vs 0.5:1 or so for the spring)

Stock rear rate is 600lb/in

Seems like going to a 650-700 on a true coilover would be plenty but I don’t have any experience to back that up

[Melchior]

The math is pretty easy if you’re just trying to match the 1000 lb-in rates you already have for the rear.

I’ve seen posted motion ratios of:

Rear Spring: .563
Rear Damper: .813

Wheel Rate = Spring Rate * MR^2
WR = 1000 * .563^2 = 316.9 lb-in

Using this wheel rate, find the equivalent spring rate at the shock motion ratio.

316.9 / .813^2 = equivalent spring rate = 479.4 lb-in

If you were to take your 1000 lb springs and run them, using the damper motion ratio you get 660 lb-in rear wheel rate.

I don’t know enough about your car or setup to tell you if 645/660 (700/1000) wheel rates are correct. My setup is 475/313 wheel rates (514/1000 on divorced setup) and its pretty balanced on a square tire setup. Yours would be a lot more rear bias, but depending on tires, wheels,swaybar, aero, ect, it might be close. My guess is you’d need to swap closer to 650-700 lbs (430-462 wheel rates) to get close on balance.

[135]

I posted a response a couple weeks ago in the 1-series Track forum for someone who converted from divorced to coilover
https://www.1addicts.com/forums/show...0#post22916410

It discusses some of the theory but you really need to determine what your target undamped ride natural frequencies are and perform the calculations to arrive at the required spring rate.

[72dan]

Originally Posted by Melchior

The math is pretty easy if you’re just trying to match the 1000 lb-in rates you already have for the rear.

I’ve seen posted motion ratios of:

Rear Spring: .563
Rear Damper: .813

Wheel Rate = Spring Rate * MR^2
WR = 1000 * .563^2 = 316.9 lb-in

Using this wheel rate, find the equivalent spring rate at the shock motion ratio.

316.9 / .813^2 = equivalent spring rate = 479.4 lb-in

If you were to take your 1000 lb springs and run them, using the damper motion ratio you get 660 lb-in rear wheel rate.

I don’t know enough about your car or setup to tell you if 645/660 (700/1000) wheel rates are correct. My setup is 475/313 wheel rates (514/1000 on divorced setup) and its pretty balanced on a square tire setup. Yours would be a lot more rear bias, but depending on tires, wheels,swaybar, aero, ect, it might be close. My guess is you’d need to swap closer to 650-700 lbs (430-462 wheel rates) to get close on balance.

I think your answer makes sense i’ll give it a try.

[Samo6556]

I haven't been able to test mine much yet but for the little bit I've driven mine on the street,the car feels good. I have a moton clubsport set up with true coilover and went with 800/400.

[///M3 Gusta]

Off topic but who did you get your ASTs from?

[aus]

Are you guys reinforcing the rear strut tower?
AST has a couple E92's they show at events and both don't have reinforced rear towers and they say it's been fine.
.

[Greg S]

700/1000 is way off for a coilover rear, send me a PM if you want my $.02. I ran a while without reinforcements, I later tied the roll bar into them. IMO, it's not an issue running a true rear coilover on an E9X.

[72dan]

Originally Posted by ///M3 Gusta

Off topic but who did you get your ASTs from?

I purchased from Turner Motorsport. Took a while they are custom made in Holland. Turner has been a really great resource.

Had the car out at Auto Club speedway two weekends ago, car definitely handles better. Now even in M dynamic mode the stability control is too conservative.
All mono ball suspension it will get high peak g forces and the computer backs out the power.

[italyix]

I'm running 550lb rear rates on true coilover

700 fronts

[MSY]

Way way too high. You want 400 to 600 tips for rear coilover