Fitting wider tires on OEM Porsche 17" RIMs

[gfrnndz]

I'm having to buy new tires for my 2005 Porsche Boxster.  The wheel size are 17 inches.  The front wheels are 6.5 inches wide and rear wheels are 8.0 inches wide.  I currently have tires 205/55R17 on the fronts and 235/50R17 on the rears.

 

I would like to install wider tires to help with autocrossing without having to buy new wheels.  

 

Has anyone installed wider tires for these size of wheels?  I would like to install 225/45R17 for the fronts and 255/40R17 for the rears.

I know that the front and rear overall diameter need to be the same.

 

Thanks,

  Gilbert

[teaberry]

I have the same question as well. According to TireRack.com I thought OE wheels are 7.5x17 and 8.5x17? Will 225/45/17 and 255/40/17 work w/o messing up balance nor the ABS/PSM?

 

[Hilux2400]

I don't know what the tolerance is, but the handbook gives wheel and tyre sizes for road use in winter and summer.  It's easy to calculate the rolling comparison.

 

The second figure in the size gives the aspect ratio of the tyre as a percentage of the overall width.  For example a standard 911 996 C2 fit would have 225/40 tyre on the front with a height of 90mm  (225 X 0.40 = 90) and a 285/30 on the back with a height of 85.50mm (285 X 30 = 85.50).  The tyre height off the rim back to front is within 5% and therefore the rolling circumference difference back to front is within about 0.6%.  (Circumference = 3.142 x Diameter).  It would seem from this that a 5% difference in tyre height is tolerable in terms of rolling circumference.   

 

Hope this helps you.

 

H

[teaberry]

Thx for the info, but based on a few forums I've read, for 987, people say 3% is tolerable to not have issues with ABS/PSM. I simply want to know what others have tried aside the standard 17in on 987 which is fronts: 205/55/17 (unusual size), back: 235/50/17 (normal and plenty options). I've also read you want to front/back to go in both directions (both up or both down). I also read on another forum for autoX some are running 225/45/17 front and 255/40/17 rear but I think those are on 986S wheels which I'm not sure are same as 987 OE wheels.

I don't know what the tolerance is, but the handbook gives wheel and tyre sizes for road use in winter and summer.  It's easy to calculate the rolling comparison.

 

The second figure in the size gives the aspect ratio of the tyre as a percentage of the overall width.  For example a standard 911 996 C2 fit would have 225/40 tyre on the front with a height of 90mm  (225 X 0.40 = 90) and a 285/30 on the back with a height of 85.50mm (285 X 30 = 85.50).  The tyre height off the rim back to front is within 5% and therefore the rolling circumference difference back to front is within about 0.6%.  (Circumference = 3.142 x Diameter).  It would seem from this that a 5% difference in tyre height is tolerable in terms of rolling circumference.   

 

Hope this helps you.

 

H