Larger Rear ARB

[Jakg]

My Z4 has a 25mm front and 19mm rear anti-roll bar.

I've seen a lot of talk recently around larger front ARBs - whether from an E46 cab, an M3 or even an aftermarket one.

My understanding is that stiffer front ARB = more understeer.

I'd like to introduce a little more oversteer, so I was wondering about a rear ARB upgrade.
I know the M3 rear one doesn't fit, but RealOEM suggests that some of larger engined E46 cabs, when specced with sports suspension, got a 20mm rear ARB - 33556751267
Based on the fact that the 19mm ARB is cross-compatible with E85 / E46, I'd assume the 20mm is too.

 

[Liam22]

Ultra Racing do a 21mm rear ARB and there are 21mm bushes readily available from the E46 M3.

But be careful - you may not get what you wanted. Stiffer rear ARB will move the balance *towards* oversteer but only in the mid-part of the corner. If you're looking for oversteer (or to reduce understeer) on turn-in or power-slidey exits then it won't help.

 

[DaveD]

Agree with Liam. I actually bought a 19mm sport bar off him a while ago to replace the 18mm SE one on my car. The front SE bar remains untouched so it’s shifted the balance away from understeer in the corners. As Liam says, it doesn’t affect initial turn in but makes a noticeable difference when settled into the corner. With pins pulled on the front shock towers for just under 2 degrees camber, there is now very little understeer and will tighten the line nicely lifting the throttle. The thing I would be most paranoid about is putting too big a bar on the back, needing to back off sharply in a corner and then snap over steering off the road.