How low can you go?

[rw229]

Assuming new rubber bushings, proper alignment and rack spacers, how low can an '86 911 with stock suspension and wheels/tires be lowered before having to add stiffer torsion bars and address bump steer? 25.5 front, 25 rear? How about 25 front, 24.5 rear?

[Dave Colangelo]

I just did my spring plate bushings and was thinking the same thing. I imagine that it cant be much I have what I think is stock torsion tubes and unloaded they move quite a bit.

[Oh Haha]

If you added rack spacers then bump steer has been addressed already.

24 rear, 24.5 front when measured at the fender lips is about as low, IMO, as practical for the street.

[will hung]

My ROW SC is on stock torsion bars and I have rack spacers. I lowered it 0.5" front and rear (25" front, 24.5" rear) and I'm running on 7's and 9'. I'm running I believe -1 degree of camber of front and -1.5 degree camber in the rear. I rubbed at the front left on the way home from the alignment shop, so I rolled my front fenders. I don't have a concernable amount of bump steer, but looking at the control arm and tie rod angle, if I lowered it much more I would.

[Bill Verburg]

Originally Posted by rw229

Assuming new rubber bushings, proper alignment and rack spacers, how low can an '86 911 with stock suspension and wheels/tires be lowered before having to add stiffer torsion bars and address bump steer? 25.5 front, 25 rear? How about 25 front, 24.5 rear?

stiffer suspension only addresses bump steer issues in so far as it limits the range of suspension motion, less motion = less total toe and camber change from suspension motion.

Bump steer is addressed by changing the geometry of the suspension. In front the easiest change is rack spacers that raise the steering rack, also available are o/s tie rods, both are intended to restore the stock relationship between steering and A arm travel arcs

more involved steps are raising the spindle height on the strut and decambering ball joints

[rw229]

Will - your car looks like what I'm thinking

Bill - Thanks, I understand there are all sorts of ways to correct the suspension geometry, raising the spindles, etc. My goal is ~25/24.5 and want to make sure that I'm not getting in to that territory.

At this height, will I be OK with suspension travel and tie rod angles? (using rack spacers) Will the stock t-bars be stiff enough to prevent bottoming?

[Bill Verburg]

Originally Posted by rw229

Will - your car looks like what I'm thinking

Bill - Thanks, I understand there are all sorts of ways to correct the suspension geometry, raising the spindles, etc. My goal is ~25/24.5 and want to make sure that I'm not getting in to that territory.

At this height, will I be OK with suspension travel and tie rod angles? (using rack spacers) Will the stock t-bars be stiff enough to prevent bottoming?

When I used to track my C3 I ran it t 25/24.5" w/ 16" wheels and 205/55 & 245/45 tires, stock t-bars & sways, Bilstein sport and a rack spacer. There was never any bottoming issue. The difference today is that tires are much stickier but I think you will be fine w/ just a rack spacer.

Some of the SC era cars came w/ shock bumpers that would need to be removed, and Bilsteins do provide a little more spring rate than other shocks

[rw229]

Thanks for the confirmation. Now to figure out what the actual measurements/angles need to be to get that height.

The car actually has new Bilstein HDs all around.

Originally Posted by Bill Verburg

When I used to track my C3 I ran it t 25/24.5" w/ 16" wheels and 205/55 & 245/45 tires, stock t-bars & sways, Bilstein sport and a rack spacer. There was never any bottoming issue. The difference today is that tires are much stickier but I think you will be fine w/ just a rack spacer.

Some of the SC era cars came w/ shock bumpers that would need to be removed, and Bilsteins do provide a little more spring rate than other shocks

[will hung]

Originally Posted by rw229

Thanks for the confirmation. Now to figure out what the actual measurements/angles need to be to get that height.

The car actually has new Bilstein HDs all around.

Here you go.

911 Spring Plate Angle Calculator

To get my ride height, I used the angle midway between "Euro" and "Race" ride height.