gwatson said:
How did it feel different out of interest? I don't track my car so can't comment about how it feels on the limit.
For the road I'm very happy with it and car feels a lot more planted, but obviously that's comparing old vs new, not poly vs OEM plus limiters.
It's a difficult one to explain but I found a loss in confidence in the car in high speed cornering, it didn't feel as predictable let's say.
The part I've highlighted in bold below perhaps gives a qualified explanation of what I was feeling, taken from Vorshlag website.
"In the Rear Trailing Arm Bushing (RTAB) location on the rear suspension of an E36 or E46 BMW the bushing has to pivot on two axis. Unlike other suspension bushing locations that only have one axis of rotation, swapping in excessively stiff replacement bushings using materials such as Polyurethane can and will cause suspension bind. The stock rubber M3 bushing is fairly compliant and effective when brand new but wears quickly over time, and doesn't cope with the added forces from race tires in perfect condition. Added wear adds excessive toe change under suspension movement, acceleration and braking. It is compounded greatly with additional power and grip from racing compound tires. If your stock RTABs have more than 20K miles and/or you've used the car for more than a season of racing, they are likely shot.
We've seen some significant toe change on some cars with stock (and/or worn) RTABs - usually evidenced by toe induced tire rub where there shouldn't have been any. These Limiters do work - they limit the deflection of the rubber mounts but they do not add additional noise or bind, and will extend the life of a rubber RTAB bushing considerably.
Many racers just blindly install polyurethane into this and all bushing locations as a "fix" for a worn OEM rubber RTAB bushing. Polyurethane is a bad choice for a bushing material if it has to deflect - such as in a multi-axis suspension bushing location like the RTAB. Rubber bushings + limiters or a complete replacement with a custom steel spherical bearing are the only two textbook choices for this location. We cannot count the number of times we have seen RTAB or front LCA failures on BMWs that were using poly in these areas - an expensive repair and dangerous racing situation.
At the very least poly will add bind during significant suspension movement, and this can make the handling feel odd (unexplained oversteer) as well as add significant stress to the suspension-to-chassis mounts (which is how they can fail over time).
That said, some folks with fully track prepared race BMWs have had OK results with polyurethane RTABs. This is due to the much higher spring rates and smoothness of tracks they tend to run with - higher spring rates and smooth tracks limit suspension travel, and thus limits the potential for bind from a polyurethane bushing at this bushing location. So even though you may hear good results from one racer, it doesn't necessarily mean that poly RTABs are the right choice for you. If you have a street car or dual purpose BMW you should always stick with OEM bushings and RTAB limiters, and even many race prepped BMWs use this setup with excellent results."
Think we even met in Italy in 2006..?