05-03-2013, 09:53 AM
Grand Superpatriot Sport+
Join Date: Mar 2006
Location: Southern California
My Ride: M54B30
Again, why did you do it? If the rubber bushings could be installed just as easy, would you?
Originally Posted by Grande D
Never said it made the car faster. But I do think you're over-thinking it. Plenty of respected people who've made track cars out of their M3s use poly, so they must see some advantage or they would not do it. Neither is wrong, but I do not think stock or limited stock RTABs are worth the effort at all. Two people I know who did stock RTABs with limiters agree with me.
Properly greasing them is key, you can't use the supplied grease. You have to use copper anti-sieze.
Having said that, I've never heard a single noise from either car with the PF RTABs. If you want softer, buy the AKG Poly RTABs which have roughly the same deflection characteristics as the OEM RTABs (based on eyeballing them both).
Furthermore, the CSL is still a compromise. It's not a race car no matter how great it may be.
What method did you use to remove your stock RTABs?
I'm sure you didn't do it because you think it would make your car faster--I have more faith in you than that. But you've got to admit there's probably plenty of people out there blindly thinking that "stiffer is better" on everything suspension related. Or just because they want to be "modded."
I'm also well aware of the grease thing. Lots of "track guys" have also are of the consensus that rubber/limiters is superior to poly. I'm sure you're aware of that too.
Again, I know it's preference but if anything, I'd rather use poly in the FCABs or subframe bushings if at all where tiny bushings don't have to take rapid or drastic load changes in multiple directions. But never at the RTAB location. my personal take on it.
I think it just gives the car consistency in the way it's tuned from bumper to bumper. What would stop you from going poly engine/trans/fcabs/steering guibo/drive shaft coupler/diff mounts/brass caliper bushings, poly everything? just a thought.
These bolded parts really hits home from Vorshlag: Yeah I know
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.
OK I guess all of it hit home. You don't want to damage those RTAB pockets or subframe mounts. Careful.