Originally Posted by Dackelone
because... most have found out (the hard way) that when you install a thicker rear sway bar... you loose traction when the inside wheel lifts off the ground. You really should not install a thicker rear sway bar without having an LSD.
From the research I've done on this forum, that appears to be the majority consensus but I'm still not convinced.
I managed to find these articles.
The guy who installed it has an E88. He tried a few difference combinations of sway bars including front and rear, UUC and M3. With the M3 E93 23.5mm rear sway bar he experienced a lot of oversteer but with the smaller E90/E92 20mm rear sway bar he said all was good with the handling. This was in combination with the E93 M3 FSB and no LSD.
Another option could be trying to go with the 1M coupe's 20mm rear sway bar. I'm not sure what the difference is between the two as the bar itself has a different part number but maybe that is more suited to our 1ers somehow.
This article, http://www.mwerks.com/artman2/publis...-_Part_2.shtml
has MWerks put a 20mm H&R rear sway bar into a stock 135i coupe. Their findings were that it reduced understeer whilst increasing their average speed on a short slalom course.
Of course I don't have any first hand experience with this but I'm planning on doing the rear 1M 20mm RSB when I do the rear bushings and I'm happy to let you all know how it goes when I do.
As for the OP, I believe that a 20mm RSB would definitely help with the body roll issue he's having. The jury's still out on how it will affect the under/oversteer.