Mongo

I currently have the following wheels on my car:

Boxster S II

Front 7x17 ET55 225/45/17 Tires
Rear 8.5x17 ET48 255/45/17 Tires

After reviewing some threads in the archives, I have found that the lowest offset for the front would be 50mm. One of my thoughts was to square the car all the way around with 8.5x17 wheels and run 245/45/17 all the way around. Since the 8.5" wheels are 48mm with a 2mm lower offset than the recommended 50mm, would there be any significant disadvantage to this lower offset on the front such as tramlining or inner fender and wheel well rubbing?

Mongo

Below is a screenshot of what the following link shows:

http://www.rimsntires.com/specspro.jsp

It compares the factory original 7x16 ET65 up front against the Boxster S 8.5x17 ET48 (rear wheel) mounted in the front. Now, to me it looks like there could be an issue with fender rub and a possible handling issue, hence why I'm inquiring about this.

terry gt

I am running 245/45/17 on the front of my GT . The rims are 3 piece OZ rims 8.25 x 17 . just misses the outside of the fender lip , and no rub lock-lock on the inside even with DR front sway bar. My 81 runs 275/40/17 on 9.5 " rims with good clearance on the fender and will rub lock-lock on the inside (parking)

Mongo

Do you recall what the front wheel offset is on the OZ?

FredR

With that offset you can just about run a 225 section but not a 245 section- it is not even close on a S4 I would suggest.

To run a 245 on the front you need an offset of 60mm I would say- that or call Mark Kibbort to pop round with his baseball bat.

Regards

Fred

Alan

Has anyone ever tried this kind of solution for fit evaluation: Wheelright

Not sure how good it is ? But conceptiually it seems good & in combination with wheel specs and tire specs seems it could give you better idea of how close you are with different configs... esp if you have mods like sway bars, non-standard springs etc.

This gives more detail on application

Alan

joejoe

I had 8.5x17 et55 with 225/45 on an 86.5 (996 twists) rear was 275/40 on 9" et 50 rim. For myself it was a bit close to outside fender, although it never did rub. I do not see 245 tire fitting without rubbing. Not sure what I will do with the rims.

Tom in Austin

With a lower ET you lose the negative scrub radius designed into the suspension for stability under certain adverse conditions ...

Mongo

I need to read up on negative scrub and the suspension design on these cars. I suspected a possible handling issue with such a low offset, but never a compromise in handling in addition to fitment issues brought to my attention.

FredR

A lot depends on how you are using the car. When you are pushing the limits of the car I believe it is wise to retain the correct offset or close to it. Some time ago I had some very nice 18 inch reverse spoke offtakes on my 928 with ET50/ 225x40x18 tires. We had an autocross track day and I struggled to beat a ratty 928S on stock wheels so I flogged them to a friend who put them on his 993 4S. Then I purchased some real wheels with suitable rubber- 5 seconds lap time reduction on a 1 minute lap.

Regards

Fred

Mongo

This car is a garage queen and will never see track. Mostly, I use it to commute a mile down to work 2 days out of the week and as a weekend cruiser on Sunday.

If a 245/45/17 would rub in the front, what about a 235/45/17? Going with anything less sort of defeats the purpose of an 8.5" Boxster wheel up front.

FBIII

I think putting a 48 offset on the front is a bad idea. I'd think twice about using anything less than 55. As others have stated your messing up the geometry. There are a lot of other Porsche wheels that interchange with more favorable offsets. If you are hell bent on going this direction I would first try the 235 on an 8.5 inch wheel. I suspect that the tire might look a bit narow.

dr bob

Andy--

Try bolting one of your existing rears onto the front, and see how it fits. The tire you are using now (255 width) sticks out 5mm, a little less than 1/4" more than the 245 on each side. So with that wheel on the front, will it --just-- touch the fender lip? If so, your answer is yes, it will fit with the 245 tire.

From experience running the same size fronts on my car for a while, you'll do yourself a big favor upgrading to a 225-section tire on the front wheels you have. 205's are too narrow.

And... the colloquial 50mm 'limit' on front offset is marginal at best. IIRC, 52 or 53 is when the scrub radius is zero. So 55 is barely OK, 50 is barely not so OK.

Mongo

Hey Dr. Bob, I apologize - the fronts do have 225s on them, dang typo.

Considering what is marginal as far as offset goes, my 8.5" rims definitely will not fit the front.