Centred or offset CABs?

[vking]

Hey R3v,

I'm installing some H&R Race and Bilstein sports in my E30. I'm refreshing the CABs too, but do I go with centred or offset?

Cheers

[MR 325]

It's really up to you. I usually install the OEM E30 M3 offset bushings anytime I do control arms.

[vking]

It's really up to you. I usually install the OEM E30 M3 offset bushings anytime I do control arms.

Sorry, I'm a bit of a novice at this and am still trying to wrap my head around the caster correction that comes with offset CABs. If I install H&R race springs will there be any detrimental effects if I just go with centred CABs? Why do people use offset CABs to 'correct' caster on lowered cars? What about the caster needs to be corrected when a car is lowered?

[broach328]

Sorry, I'm a bit of a novice at this and am still trying to wrap my head around the caster correction that comes with offset CABs. If I install H&R race springs will there be any detrimental effects if I just go with centred CABs? Why do people use offset CABs to 'correct' caster on lowered cars? What about the caster needs to be corrected when a car is lowered?

When you lower the car with stock cabs, the wheel essentially is moved back a little bit in the wheel well. To correct this on the slightly lower m3s, they just used offset bushings to pull the back of the control arm toward the outside of the car. By doing that, it moves the wheel farther forward to where it should be or even farther than it was stock. With the wheel farther forward, it changes the angle of the strut which in this case means a greater caster. The right amount of caster+camber is important as it maximizes surface area of tire on the ground around corners and in a straight line. Some others here may be able to go more in depth about the relationship of caster and camber but I think thats the overall idea of it.

I vote either m3 cabs or treehouse eyehole cabs. They allow for more caster and they are a solid bushing as apposed to the stock e30 bushings which offer some flex to absorb bumps and vibrations but in turn makes the front feel mushy. I currently have stock ones while my brother has m3s and I can tell a big difference in the two as far as precision and stability. Hope that helps a little.

[cleanasse30]

I just installed the Bimmerworld trackCAB and they make turn in way more precise. As others have mentioned, both the trackCAB and the m3 offset bushings will add caster to the front suspension.

From tirerack.com:

Increasing the amount of positive caster will increase steering effort and straight line tracking, as well as improve high speed stability and cornering effectiveness. Positive caster also increases tire lean when cornering (almost like having more negative camber) as the steering angle is increased.

What's the downside to positive caster? If thevehicle doesn't have power steering, a noticeable increase in steering effort will be felt as positive caster is increased. Other than that, the effects of positive caster are pretty much "positive," especially increasing the lean of the tire when the vehicle is cornering while returning it to a more upright position when driving straight ahead.

Hope that helps clear some things up.

[vking]

Thanks a bunch guys. I understand now.