Negative Camber/Wheelarch Rolling/Tyre Rubbing

[TopCarrera]

Please can anybody help?

Had suspension on my car stiffened and lowered about six months ago. After a couple of track days and about 500 miles later the nearside rear arch is just rubbing the upper part of the outer sidewall of the tyre when the car is at maximum acceleration in the lower three ratios (i.e. squatting under power).

I am running about 1 deg negative camber on the front and 1.5 deg negative on the rear. I am on Fuchs 7s&8s with 205/55s & 225/50s Bridgestone S02s. Have been advised that adding another 0.25 to 0.5 degrees of negative camber will enough to stop the rubbing. Is this reasonable?

I will roll the arches if I have to but would prefer to leave alone and rely on geometry if I can. Is wheelarch lip rolling straightforward for a garage with a recent bodyshop to do as a quick job? Is it easy to do as a home job? The lips on the front arches are much bigger than the rears; will rolling romove the profile of this lip completely on the front of the car?

 

[Siggy]

If you are happy with the handling as it is, I would not change it. Unless by increasing the camber the handling will improve.

If its only rubbing on hard acceleration, then surly its the ride hight that needs addressing or roll the archs.

Dave

 

[Guest]

First a question - are you absolutely sure you have just 8x16s with 225/50 SO2s and no spacers? Reason for the question is that I had just this rear wheel/tyre combo with std torsion bars and similar 1.5 degree neg camber on my car about 4+ years ago and even with 7mm of spacers it never rubbed on lots of track days. My ride height looked very similar (assuming your picture shows squatting under acceleration). I currently have 2.5 degrees neg camber in the rear with 29mm rear torsion bars plus 14mm of spacers per side and my road tyres are the same 225/50 on 8s and their is a massive amount of clearance, to the point where I am thinking of adding more spacers. My track wheels with 245/45s on 9s that sit about 7mm further "out" also have just enough clearance with 14mm of spacers in place. It is certainly worth checking if there is a spacer between the hub and the wheel - you should be able to see thru the wheel spokes but it might be best to take off the wheel. I have never heard of rubbing with 225s on 8s unless there is something else non-standard in the set-up even with less rear camber than your 1.5 degrees.

So, assuming no spacers, what do you do to fix it?

1. Rolling arches will not help IMHO because the rear wheels do not usually catch the arches - they rub further up the guard about an inch above the arch usually. Is this the case with your problem?
2. Raising the ride height will work, but if you like the stance of your car then you will probably want to keep it as it is - I certainly would. Your ride height does not look excessively low but maybe you could post a picture side on static.
3. Negative camber will certainly help. If the rubbing is minor then perhaps another 0.25 degrees is enough. The camber also helps a lot with handling on the track, the only penalyt being a little inner shoulder tyre wear. The only thing to watch is that you want something like 0.5-1.0 degree difference beteen the front and the rear camber and no more - you already have a 1.0 degree differential. Why? Too much rear camber without a corresponding increase in front camber will move your handling balance towards understeer. This means that to maintain your 1.0 degree differential, you will have to realign the front as well and this starts to get tricky once you have half a degree of negative in the front already. Getting more neg camber out of the rear is easy as there is a lot of adjustment in this direction once you get the ride height down. Typically the front can only get about 0.75-1.0 degrees without other measures. A strut brace will let you wind the strut towers together a little - maybe an extra 0.25 degrees - but it usually pulls one strut more than the other and not the two equally as one will probably be slightly weaker (sod's law). Further lowering helps you get more camber and after that its monoball strut mounts, camber plates etc. Ask me how I know !
4. Getting into the realms of expensive, but bigger torsion bars will solve the problem. Either a "fast road" set-up using turbo t-bars in the rear (1mm bigger diameter)and std fronts or a "track day" set-up with say 21mm/28mm or 22mm/29mm bars or "race" set-up with even bigger rear bars (up to 33mm). You can use the std shocks for the fast road set-up but the other two really demand revalving if you have Bilsteins already or replacement if you have Boge. While you are in there a full set of polybronze bushings would be nice. Told you it would be expensive.

Hope that helps. The easiest fix is a little more rear neg camber and see if you like the handling. If not, then try to get a little more front camber as well and you should be good to go.

Richard

 

[TopCarrera]

Richard,

Thanks for your reply, informative as ever!!

Photo above taken a few weeks ago shows stance of car.

The front wheels are at 1deg negative camber now and the rears at 1.5 deg negative. Does the variance between front and rear in this case mean 0.5 deg or 1 deg ? (i.e. is it per side or the sum?).

I will check the wheels again but am 99% sure that the rears are stamped as 8s (strangely I have sometimes thought myself that they look a little deeper). I do not have spacers. The wheelarch lip just kisses the upper part of the sidewall at the top of the arch.

I have read elsewhere about the potential restrictions regarding the adding of more necative camber on the fronts. Interestingly though before I had the geometry set (at 9M) the before measurements showed the nearside front with exactly 2 deg negative camber!! (have checked the printout). The tyre on the wheel at the time did show accelerated wear on the inner shoulder.

I will check again later this week that my rears really are 8s.

 

[Guest]

Well, 8s or 9s shouldn't make much difference - about 7mm. The interesting thing is that I have 21mm more track per side, assuming 8s (or 14mm assuming 9s) and a wider tyre and I have no clearance issues. Yes, I have more camber, about 2.5 degrees, and stiffer torsion bars, but you can see below I have visible room between tyre and arch - see below. I have run this wheel/tyre/spacer set-up with std torsion bars and closer to 1.75 degrees camber with no issues.

I think your ride height looks spot on but you could get a slight 5-10mm tweek either side without making it look silly. This should be possible on the eccentric adjusters on the spring plate without having to pull out the torsion bars. I misread your front camber, so you actually have 0.5 a degree to play with on the rear, which should give you all the clearance you need. A 1.0/2.0 front/rear camber set-up is still ok. JAZ set up their classis race cars with 1.0+ degrees more camber in the rear, I just like a bit more front bite.

I wonder if some early 3.2s had a slightly narrower rear, or if perhaps the shape of the flare altered slightly at some point? Otherwise, I don't quite understand the discrepancy between cars. Please double check that there is nothing between the hub and the wheel when you check the rim width - no shims or spacers. I think you have 8s from the photo as the 9s have recessed lug nuts, which I cannot see, but my curiousity is certainly tweeked.

 

[franklin]

ORIGINAL: TopCarrera

the nearside rear arch is just rubbing the upper part of the outer sidewall of the tyre when the car is at maximum acceleration in the lower three ratios (i.e. squatting under power).

I am running about 1 deg negative camber on the front and 1.5 deg negative on the rear.

You are running about 30minutes more negative than standard, so another 1deg to 1deg 30minutes is achievable at the expense of..... (hoary old chestnut ..tyre wear)

The 930 uses shorter control arms and modified fulcrums (suspension pickup points) aka the RSR which as also supposed to reduce the squat. (10mm up, 22mm-25mm away from the centre of the car and 47.5mm towards the rear of the car).

 

[937carrera]

The back end looks a little low, relative to the front, to my eyes. If you really want the best handling, particularly for track use I would lower the front a little. Again, for track use, adding some more rear camber should not be a problem, but you should check if any spacers are fitted. Reducing the track a little will help with the rubbing.

However, I am a little surprised to hear you say the contact is being made under accelleration. I would have expected it to occur under cornering. The right hander into the Mountain at Cadwell is where I burnt the paint on my carrera 3. Do you know what size torsion bars you are running - they seem to be a little soft to me?