Wheel Fouling Wheel Arch

[Guest]

Over the past couple of hundred miles I have noticed occasionally a graunching (sp?) noise from the left rear wheel when accelerating hard. I got it again a couple of times this morning when accelerating away from the lights 'in an enthusiastic manner'. When I parked up at work I could see some damage to the the outside shoulder of the left rear tyre, so I'm pretty convinced that the tyre is fouling the wheel arch. So the questions are, is it to do with the non-original tyres and wheels or is it the suspension sagging?

The tyres I have got on are the same size as when I bought it, but I have just replaced them. They are 255/40 17". The wheels have got 8.5 and 50 written on either side of the valve (I guess that the sages will know what that signifies). I did a track day on the previous tyres (worn but nominally exactly the same as the new ones I have put on) and there was no fouling under those circumstances.

If it is likely to just be the suspension getting on a bit, what would it cost to replace and would the recommendation be to replace with like-for-like or take the opportunity to change?
Cheers,

Graham

 

[jr2015]

Hi Graham,
You don`t mention if you changed tyre brand, the tyres may have the same nominal sizes, but the shoulder of the tyre can vary in size, causing contact with the wheelarch. The 8.5 (ins) is the wheel jaw width and the 50 (mm) refers to the offset ( the ammount of the wheel inboard of the hub).
regards,
jr.

 

[Guest]

Hi - I had Continental SportContacts and have now changed to SportContact2s - so not too much change there then!

 

[jr2015]

Maybe your rear dampers (shock absorbers) are shot then.
jr.

 

[Alpine]

I think that the standard wheels (Design 90's) are 16", so maybe that has something to do with it ?

 

[Mark_Bennett]

I seem to recall my old 944S had been fitted with 255 16's on the rear by the previous owner, and in spite of it having factory rolled arch returns it they rubbed if I went through dips on the road (not under acceleration though).

Fitted the corrct 245 tyres and the problem went away...

 

[Diver944]

Hmmm, something odd here. I also have 255/40 on 8.5/50 rear wheels and have no fouling whatsoever and I know that plenty of other owners have the same setup. There are even some of us with 265 tyres on 18" wheels.

Are you sure the tyre fitters haven't fitted 255/45 in error?

 

[Hilux]

They are 255/40 17".

Check that the overall diameter of the tyre is the same with the taller wheels, if the aspect ratio is the same as the 16" then the rolling circumference will be greater, may cause rubbing and will put your speedo out as the wheels will be gaining ground for the same revolutions.

ie: 255/45/16 has a 25" diameter as does 255/40/17 ergo if your tyres were not rubbing on the originals then it must be a wider shoulder or the wrong wheel offset.

 

[Fen]

The rub will be the forward part of the arch - about 10 o'clock as you look at it from the side. It could be the suspension softening or a fractionally broader shouldered tyre or both. If you get the arch rolled either with a proper tool for the job (OPCs used to be able to borrow one from Porsche Cars GB or a bodyshop might have one) or with something like a baseball bat or rolling pin then you'll have enough clearance and even if it should touch it will be smooth and won't slice strips out of the tyre sidewall.

 

[Big Dave]

Graham.
It could be the way the car was made..
On my S2 ive fitted 9-17" et 55 wheels + 255-40-17 Goodyears...No probs with them...

BUT

When i fitted a set of copy 17" wheels 9-17" et 49, [ the lower the ET number, the farther out the wheel will be.], the left rear tyre rubbed on the arch...I checked the clearance from right to left + found the drivers side had more clearance than the passenger side....
The car hasnt been crashed at any time, so i just put it down to "large" tolerences. I believe the last of the 944,s that came off the production line had large panel gaps + "strange" tolerences...[8|][8|][8|][8|]

 

[Fen]

They are all out passenger side compared to driver's side and it's always the passenger side that rubs. Given that it was fine with the previous tyres though something must have changed rather than this car is just a tight clearance.

 

[Guest]

Mine does it too Continental 245/45ZR16/BBS wheels, only on bad nearside bumps.

 

[Guest]

I have just checked this morning and I notice that at about the 10 o'clock position, as mentioned by Fen, the clearance is the tightest, with about one and a bit finger's width of clearance, whereas there is a couple of finger's width on the driver's side. Am I right in thinking that the suspension is provided by a torsion bar and that therefore this is not a broken spring (there being none)? Is it possible that the torsion bar weakens with time? If it is not that the suspension geometry has changed in some manner the only other change is that I have got newer tyres which are (obviously) a bit larger than the worn ones that came off.

 

[Fen]

I suspect the rear shocks are going soft. I had the same happen on my current Turbo with 18's and it got significantly worse over a period of only a few weeks. I replaced them with new Konis and the problem disappeared.

 

[lali]

If it is your shock then get it sorted before your next track day, I had a soft drivers side rear shock and it resulted in me exiting craner curves backwards!