17" Rear wheel scraping on wheel arch

[944Toon]

Hi, I recently replaced the D90 wheels on my 1988 8V 944 (UK RHD) - Fronts were 6" x 16" x 52.3mm offset with 205 x 50 tyres, Rears 8" x 16 x 52.3mm offset and 225 x 55 tyres

The replacement wheels I fitted (I think from a Cayman) are Front 6.6" x17" x 55mm with 205 x 50 tyres and Rears 8 x 17" x 40mm offset with 235 x 55 tyres.

All looks great and the combination fills the arches much better. I've put small spacers on the fronts as the wheels fouled on the grease caps on the hubs. However, I've noticed that the LH rear wheel occasionally scrubs on the arch (RH seems fine).

When I've looked more closely, it appears that the wheel itself is about 5mm more proud than the RH wheel (although both still within the outer extremity of the arch) - but I think the LH wheel will just be interfering with the lip of the arch when the suspension is compressed. I've read that this is a common issue with 944's when the torsion bar gets a bit tired over the years.

Anyone else aware of this problem and is there a simple fix?

I think the LH side ride height is about 5mm lower than the RH side so I'll try and fix that by adjusting the spring plate on the trailing arm, but I don't think that will solve the scrubbing problem altogether.

Much appreciate any help.

[gtgt__bangbang]

dang sound like you went a bridgestone too far.

235 on a 17 clearly wider & taller than 225 on a 16, rims widths being equal and its too early here to do the mental gymnastics regarding the offset change.

My ugly suggestion is to roll the sheet metal lip inside the wheel well up a little, but I hate to propose body work as a tire fit remedy, despite all the smash car fans that hammer there daily. It depends on the car condition I guess.

I cant recall any opportunity to offset the axle / transaxle within the body to reallocate space or to (off?) center better for your set up .

You COULD have the backside of the culprit wheel machined down a few or more mm, to seat the whole deeper on the hub. Let the next owner figure THAT one out at rotation without notes!

Re indexing the torsion bars is a very scary thought, and I have turned that thought into action... not for the time-pressed or mechanically weary.

Semi-totally off-topic, but I have heard about people cutting a hole in the body , on center with the torsion bar housing, assisting one to extract & index the torsion bar with the suspension in situ.

[flash968]

check your rear camber angles. also check the thrust angle. is the ride height correct?

an alignment may resolve your problem

[944Toon]

Thanks. Is there a quick way to approx check the camber and thrust angles before going to a specialist if alignment is required?

I think the ride height is unequal - i.e. approx. 5mm lower on the scrubbing side - so can have a go at adjusting the spring plate.

[944Toon]

Just had a further thought...

I changed the rear bearings a couple of years ago (made a puller to do this). I noticed that the rear of the trailing arm of the culprit wheel had had some 'hammer' at some point (marks on the arm -possibly as result of someone trying to knock through an old bearing perhaps). Likely that this 'abuse' of this type could have changed the geometry of the set up - or the alignment?

Just for info, the tyres on the wheels I took off had done approx. 25k miles and still have loads of tread, with no uneven wear - so this might negate my reasoning above?

[gtgt__bangbang]

I cant remember if I did a trailing arm bearing but I would have heated the trailing arm with a couple propane torches and the bearing would fall out somewhere not much over 100C.

From what I read, you put slightly bigger tires on the car, and the axle-body layout was not perfectly symmetrical ( nor should it be ?...) and the result was one tire rubbing.

Find a machinist that will skim the back side of the offending wheel (assuming there is enough metal to remove there, and check that the lug bolts wont punch out the cap of the lug nut) and good to go, easy peasy.

[9FF]

Your ride height being different on each side won't help so get that corrected with the bolt. No point in checking your camber until you do that because ride height will effect camber. You can ghetto measure camber with a level at 90deg to the wheel rims, it won't give you a figure but it will show you if they are different.

I think the main problem is you have the wrong tires on your car for 17in wheels. You need 225x45 fronts and 255x40 rears. The 225x50 you have at the back are about 40mm (1.5in) "taller" than the recommended 255x40. That's going to affect clearance, balance and your speedometer readings.

[Techno Duck]

The simple answer to your question is the offset on the rear wheels is not ideal for a late offset car.

I have run a 17x9 with a 47mm rear offset and it rubbed when i stepped up to a 275 width tire. I was able to rectify this by rolling the rear fenders. Ideally the offset should be in the 50mm+ range depending on width for a rear wheel on a late offset car.

You will primarily get rubbing inbetween the tape marks..



Other than evening out the ride height, I would try rolling the fenders in the back or putting on a different size tire; maybe something like a 205/45/17 and 245/40/17.

[944Toon]

Thanks for that feedback. Very useful.

Just noticed a typo in my original note after your post - it's the front tyres that have the 55% wall / width ratio. The rears (235's not 225's) are 50% - and not the other way round - so I guess that will help a little.

I'll give the spring plate adjustment a go.

In terms of the height measurement, I was simply going to level up both sides to the highest part of the arch from a flat floor (with the same pressure in both tyres). Is there a better way or is that okay as a start?

[944Toon]

Just seen your feedback Techno Duck. Thanks for that also. Will give the tyre size some thought if the height adjustment doesn't work. Basically, I took he wheels because I had the opportunity for a good deal from a local seller. Idea was that I could sell them on if they didn't work. As it happens, I tried them before buying - but only on the 'good' side where there is visibly more clearance.

When you say roll the fender, do you mean roll / bend up the lip?

[flash968]

you can use a framing square to quickly look at camber.

[968 GUY]

Good call Duck! Always check the obvious.

[mytrplseven]

I put the same wheels on my '87 944 N/A and the tires that came with the wheels rubbed on the left outer lip when accelerating in a right turn. Since the tires were shot when I bought the wheels, I decided to use TireRack's tire comparison information tools and came up with a tire that met not only the proper performance requirements and reviews but also had a tread width 1/8 inch narrower that the stock tires. I chose the 225/45/17 tires for the rears. I chose the BFG G-Force radial. Here in Florida where we get a lot of standing water when it rains, the tires work great and handle very well in the dry.

[944Toon]

Thanks for that. Exactly the same wheels as in your picture. Glad to see that I'm not the first and only to see this problem. Tyres may be the only option if other things don't work, but would be a shame as all have good tread.

Anyone got any ideas about why it's always the rear left that sticks out more? Tired torsion bar?

Thanks.

[emoore924]

This might sound stupid, but it might be a case of "they all do that".

It has been known for some time in the 924 world that the LEFT rear tends to be closer to the wheel well and more likely to rub than the RIGHT rear tire. Like the whole rear is shifted to the left. Don't know why. Its just the way it is...

[mytrplseven]

I think it has something to do with the coriolis effect.

[jhowell371]

Originally Posted by mytrplseven

I think it has something to do with the coriolis effect.

Best explanation yet.

[azbanks]

Originally Posted by Techno Duck

The simple answer to your question is the offset on the rear wheels is not ideal for a late offset car.

I have run a 17x9 with a 47mm rear offset and it rubbed when i stepped up to a 275 width tire. I was able to rectify this by rolling the rear fenders. Ideally the offset should be in the 50mm+ range depending on width for a rear wheel on a late offset car.

You will primarily get rubbing in between the tape marks..



Other than evening out the ride height, I would try rolling the fenders in the back or putting on a different size tire; maybe something like a 205/45/17 and 245/40/17.

Rolling the fenders should fix the issue. I've got wheels and tires on my 90 cab that everyone told me are impossible to get to fit on my car. It took aggressive fender rolling and stretching but they do fit and as of this week, there is no more rubbing.

To roll the fenders, I recommend a 4-5 lb hammer. Go slow, working from the center of the area you want to roll and go out. Heat the area with a heat gun to soften up the paint to keep it from cracking. Go slow and it should turn out great.
TD's tape marks are at about 1:00 to 2:45, I would recommend rolling from about 11:00 to 3:00

[flash968]

before making some permanent modifications, i would seriously look at the alignment. 3/4 degree negative camber is about 1/2". if the alignment is off, it would be easy for wheels to hit.

thrust/toe angle will mess with this too. if things are set forward, it can easily hit up there. the wheel looks stuffed fully forward.

occam's razor

[gtgt__bangbang]

his rears are rubbing. he stepped up too far