Coilovers for BMW E30

[eraserr]

I am planing to build coilovers for BMW E30. I could buy a kit, but I would rather do it myself with combination of remade housing, hardened bilsteins and coilover springs.

I am wondering which spring rate to choose for front and back. I saw somewhere that drifters have from 8 to 20 kg/mm springs (450-1125 lb/inch).

Is it better to have stiffer springs and what would be best? The car will be for track purposes only, so there won't be any confort issues.

Is there a downside having very stiff springs?

What do you think would be best?

Thank you!

 

[Tom]

Drifters run anything from 8/6 front/rear up to 12/10 (i think phil ran these for a while)

Harder springs obviously help to stabilise the car mid drift to give more control. As far as i know the harder springs are ideal for smooth circuits however for bumpier airfield circuits too hard a spring rate will cause the car to hop around when going over the bumps which will cause problems.

 

[Bon Bon]

Well "anything up to 12/10" is for nissan S14s....

E30 rear springs are quite far in towards the center of the car on the trailing arm I think, and judging by moffats M coupe you want to run really hard rear springs to compensate for the leverage that the trailing arm has on the spring. Unless you run coilover springs on the rear, then the arm doesn't have that much leverage on the spring.

I'd try and find out what kind of springrates are used on the usual race spec coilovers, and work from that.

 

[eraserr]

I'd try and find out what kind of springrates are used on the usual race spec coilovers, and work from that.

That would probably be a good idea, but I don't think this data will be easy to find.

As I understood you, because of the position of springs towards the center, it is good to use very hard springs in the back, harder than in front or at least as hard as at front.

You mentioned M Coupe, yes, E30 and M Coupe have very similar suspension, so if I find some data for M Coupe, it could be usefull for E30 as well. There is some difference in weight, but the design is the same.

@TomP:
To stiff springs and bumpy track results in hopping. Is it possible to estimate which springrate is optimal and which is too stiff?
As I looked over the japanese drift cars, most of them use around 12/10. In heavier cars they use even stiffer, and in some very light AE86 8/6.

Thank you all for help.

 

[Sideways M3]

I am planing to build coilovers for BMW E30. I could buy a kit, but I would rather do it myself with combination of remade housing, hardened bilsteins and coilover springs.

I am wondering which spring rate to choose for front and back. I saw somewhere that drifters have from 8 to 20 kg/mm springs (450-1125 lb/inch).

Is it better to have stiffer springs and what would be best? The car will be for track purposes only, so there won't be any confort issues.

Is there a downside having very stiff springs?

What do you think would be best?

Thank you!

Have a look on www.s14.net and http://www.e30m3performance.com, should find some usefull info on there. If you are going to fit true coilovers to the rear you must reinforce the strut towers preferably linking them to a roll cage. The rear struts aren't designed to take spring loads. A value i recall seeing alot is 400lbs front and 600lbs rear, this is with the standard spring location. As you can see there is a significant difference in spring rates to get a similar wheel rate front and rear, in that position. Hope this helps.