Eric_Oz_S2

I'm in the process of ditching my t bars and therefore changing my coilover spring rates to suit. I'm going to go a fraction softer in the rear this time so I need to work out what I have now (t bar plus coil spring) and determine the equivalent spring without tbars.

I've read numerous threads, including the often copied email that Patrick posted regarding Karl's (Racers Edge) advice on what Porsche specified as the wheel rate (0.42 x spring). BUT, Porsche didin't use the lower Racers Edge shock mounts that change the angle of the spring.

To satisfy myself I measured the wheel movement and spring compression at around a dozen positions and found that the measured motion ratio was about 0.59 and therefore wheel rate = 0.59^2 = 0.35. This actually makes perfect sense, as if you change the mount position by the 30mm standoff and calculate the theoretical motion ratio (as the shock mount is more inboard) it changes from 0.65 to 0.59. So it appears to me the lower shock standoff mount has a reasonable effect on the motion ratio and of course greater effect on wheel rate and is something to consider.

In my case I'm changing from 350F 137tbar + 225helper rear to 350F, 525lb/in rear. The current rear setup has a wheel rate of 215, proposed is 184 lb/in.

Cheers

333pg333

Eric I think that's a fair question and one I'd shoot in an email to Karl. You can quote my discussion with him as far as I'm concerned. Totally in context as you're actually using one of his parts and this is where your question is centered. If you do so, report back your findings.

Eric_Oz_S2

Have sent an email Patrick. Will see if I get a response. I'm pretty confident the 30mm standoff shock mount have the effect I've documented though. What it means is if you run the standoffs you need 15-20% stiffer springs than without for the same wheel rate.

Dougs951S

Interesting...Thanks for posting this.