Quote:
Originally Posted by John_01
In a stock 135i, the rear subframe bushings are *very much* a part of the suspension.
1) They are used to absorb the road vibrations transmitted through the RFT tires.
2) They are claimed to place an upper limit on the maximum rear spring rate that can be used. (reference from TC Kline)
Only after you replace the bushings with a hard rubber/elastomer or solid metal component, then it can behave like a structural component.
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Can vouch for your second point from experience. If you upgrade to stiffer spring + coilovers, say 700#, you will notice with this setup that the rear suspension will feel like it's moving around when you're cornering. The energy from the spring is too much for the bushing to handle. M3 subframe bushings got rid of that. I would like to see the difference between these and aluminum, if they ever wear out I'll be going aluminum, i know that much.