TeeLew
Well-Known Member
I think those rates are correct. It's about the best info we have.@TeeLew, I have 2019 PP1 Magneride, and GT350R bars front & rear. I am unsure of the OEM spring rates. The spreadsheet in the 6g sticky thread is getting rather dated. If it is correct for my car then I am at only 165#/inch front rate, and 728 rear.
The M1 owner's manual publishes (page 339) 211#/in front and 742 rear for the handling package. So the rear is already pretty close between the two cars.
I switch several things converting my car from street to track and back again. So inserting spring rubber donuts would be easy enough to add.
Which hardness donut do you recommend for me to attempt to mimic the M1 front spring rate? Which sets if I ordered two pairs of different hardness?
Would be nice if there was a chart to help choose which donuts.
The spring rubbers will act a little different in each spring, so the only way to really know is a test with a spring rate machine.
For a back-of-the-envelope guess, count the coils of the spring. 1 spring rubber partially cancels a coil.
If you have 6 coils in a spring and cancel one, then only 5 are left deflecting and "active". The math works like this:
New rate= old rate x (coils/active coils)
K = 165 x (6/5) = about 198 #/in
The stiffer the spring rubbers are, the closer this estimate will be, but the really stiff ones can be tough to fit on certain springs. Shore 70 hardness is a good compromise.
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