BC RACING/KIDO/FORTUNE/ETC. How do these companies come up with their spring rates?

[MJ DOOM]

Have a 2000 750il.

Weight distribution is 50/50. Stock spring rates are 151 lbs/in in the front. 166 lbs/in the rear.

But every coilover application I see for the e38s have higher spring rates in the front.

BC Racing - 9k front 6k rear
Fortune - 10k front 8k rear
KW Comfort 343 lbs/in front 314 lbs/im

Even lowering springs have higher rates in the front.

Why is this? Does it help oversteer/understeer? Is it to make the ride more comfortable?

Any ideas guys?

Thanks,
Mike

[GGray]

Have a 2000 750il.

Weight distribution is 50/50. Stock spring rates are 151 lbs/in in the front. 166 lbs/in the rear.

But every coilover application I see for the e38s have higher spring rates in the front.

BC Racing - 9k front 6k rear
Fortune - 10k front 8k rear
KW Comfort 343 lbs/in front 314 lbs/im

Even lowering springs have higher rates in the front.

Why is this? Does it help oversteer/understeer? Is it to make the ride more comfortable?

Any ideas guys?

Thanks,
Mike

on a 50/50 car it makes the car under steer slightly less...

[MatthewH]

Aftermarket kits invariably increase understeer probably to avoid liability.

[GGray]

Aftermarket kits invariably increase understeer probably to avoid liability.

That is 100% incorrect...

[JimmieG]

This is the same thing I have going on but with a e34 touring with s52. I went with BC Racing coils and went up 1K on the springs with swift springs. The back seem spot on ride good and damping and rebound seem perfect but the front are not seems no matter how stiff I go the rebound is not enough. So I was thinking about just changing the fronts from 8k to the same as the rear 7k.

Jimmie

[GGray]

This is the same thing I have going on but with a e34 touring with s52. I went with BC Racing coils and went up 1K on the springs with swift springs. The back seem spot on ride good and damping and rebound seem perfect but the front are not seems no matter how stiff I go the rebound is not enough. So I was thinking about just changing the fronts from 8k to the same as the rear 7k.

Jimmie

Try this... Its something I figured out on the ISC suspension which is close in design and function.

I ended up having to preload the springs in front almost 18mm before it stopped banging the bump stops. Made a huge improvement pre loading the front start out adding 1/2inch or 13mm of pre load front and back since the rear is the same design.

May or may not help, it helped on my touring.