Spring Rates & Motion Ratios

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Bry5on

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This may be a long shot but I'm looking for data regarding what the spring rates are of the various stock and aftermarket suspension setups. I'm an engineer and vehicle dynamics nut and want to build the suspension of my soon to run e9 to be bounce/pitch and roll balanced but also slightly firmer than stock all-around. I fear that the aftermarket setups have succumbed to the typical solution of a saggy rear spring that is compensated with a larger rear sway bar instead of doing their ride dynamics homework to create a balanced spring pair that is merely tuned with sway bars. Spring rate data would prove or disprove this notion!

I'm also hoping that someone has already measured or calculated the motion ratio of the rear suspension so that the proper spring rate can be married with the front, please chime in if you've got this!

I'm looking more for hard data than subjective opinion, although any relevant info that you've got would be welcome - as a relative newbie I wasn't able to find what I wanted through the forum search feature

Thanks guys
 
I have a box of new ST/La Jolla springs, not yet installed. If you guide me through the measurements, I'd be glad to post.

I also have a full "as is" front & rear alignment data (toe/caster/camber) - and discovered my Coupe is not symmetric.

Also, given how flexible the chassis design is, I'm not getting overly enthusiastic (read parts) about trying to tweak or customize the suspension setup. Just a nice/fun street car.
 
Vbigdog said:
I have a box of new ST/La Jolla springs, not yet installed. If you guide me through the measurements, I'd be glad to post.

I also have a full "as is" front & rear alignment data (toe/caster/camber) - and discovered my Coupe is not symmetric.

Also, given how flexible the chassis design is, I'm not getting overly enthusiastic (read parts) about trying to tweak or customize the suspension setup. Just a nice/fun street car.
Click to expand...

Unfortunately it'll probably be tough to find a shop that can measure spring rate for you although if you're a seasoned DIYer with a welder and some lifting weights you could fashion something up yourself! You might have luck contacting a local shop that builds race cars or trucks.. Thanks for the offer!
 
decoupe said:
ST springs which La Jolla Independent said are the same spec as his lowering spring sets are 250lb front and 225lb rear and same wire diameter.

Some recent discussions related to this and please share your conclusions.

http://www.e9coupe.com/forum/showthread.php?t=17502
http://www.e9coupe.com/forum/showthread.php?t=15532
Click to expand...

Thanks for the info, I do have some experience with custom coilover setups and even made my own custom sorings for my old 850i! Unfortunately it appears to be as I feared that the spring pairing (even if motion ratio was 1:1) will not lead to a pitch/bounce balanced ride for street comfort/control.

Does anyone happen to have a good overhead shot of the rear subframe with trailing arms? The motion ratio and thus spring rate matching could be approximated from a good photo
 
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