Newbie: Need help with wheel offsets, please!

[PorschePRH]

I'm looking to get some new wheels with the following spec's:

Size (front) 18 x 8.5

Size (rear) 18 x 10

Offset 52MM-F, 48MM-R

I have a 03 C2 Coupe with the 030 sport chassis option...

A 48MM rear offset looks about 17MM less than the stock Turbo Look 2 18's that I have on the car.

Is this reasonable? Will it look odd or rub?

I was planning on using the current tires which are 225/40 and 265/35. Will these look ok on those rims?

Here's a pic of the car with it's stock rims. Doesn't really look like I would have room for less offset, but then I'm new to this...

Thanks in advance!

PRH

Edited March 15, 2005 by PorschePRH

[LVDell]

Search is your friend. ......as this topic has been asked quite often.

The quick and easy answer is that the front wheels will fit fine, it is the rear wheels you will have a problem with. The offset for the C2 is 65 (63 will work as well). The rear has no chance of fitting.

[PorschePRH]

I am good friends with the search already, but I am not sure I'm interpreting the posts correctly.

Some people seem to be putting spacers on their wheels. I have seen people talking about spacers of 15MM up to 21MM on the rears. But I don't know what they were starting with in terms of wheel width and offset.

[LVDell]

Ah, that makes more sense. Here is an article link to help explaint he offset to you a bit better. People using the spacers are for example wide body 996's (C4S, TT) using the wheels off of a C2 and need to push them out closer to the fender so they will fit properly.

http://www.tirerack.com/wheels/tech/offset.jsp

[PorschePRH]

Looks like the wheels may work afterall. I got a message from someone using these exact wheels on their 911 narrow body. He says they don't rub and look good. Someone suggested I could shave some of the hub from the wheel to fine tune the fit... Not sure about that...

[LVDell]

You would be better off rolling your fenders if you are going to purchase wheels that are made for a widebody. When it comes to offests and wheels, etc., I don't mess with the geometry of the car. You are changing the center of the wheel and then accomodating it to fit. IMHO, do it right and get the PROPER offsets for your car.

[ar38070]

You would be better off rolling your fenders if you are going to purchase wheels that are made for a widebody.  When it comes to offests and wheels, etc., I don't mess with the geometry of the car.  You are changing the center of the wheel and then accomodating it to fit.  IMHO, do it right and get the PROPER offsets for your car.

<{POST_SNAPBACK}>

Rolling the fenders and putting bigger wheels on is also going to change the geometry. In any case, any geometry change is small or well within the limits of the car. As long as the wheel/tire fit, the geometry changes are okay.

Even Porsche put 5mm spacers all the way around on the 550 edition.

[PorschePRH]

We are talking about .68" in this case, which considering this is a street car with tip, I doubt I will notice.

I saw some pics of cars with up to 1.18" more outward on a narrow body and it looked ok from the pics. That's a lot though. I wouldn't mind doing some shaving to get the difference down below .5"...

[Coaster]

Some things to consider:

1. The tire you want to reuse on the rear (265/35) is not an OE 18" size for that year C2 (285/30 is the correct size). Dependent on the manufacturer that tire is likely meant for a 9" wheel and may fit a 10" wheel at most.

2. The tire you want to reuse on the front (225/40) is an OE 18" size and if it is an OE model tire it will fit on an 8.5" wheel (even though the OE wheel width is 8").

3. The combination of increased offset (from 50mm) with a wider front wheel means that you will reduce inside clearance by 9mm a side (.4"), extend outward 5mm more a side, and have a net 10mm increase in front track.

4. The decreased offset (from 65mm) for the rear means that you will increase inside clearance by 17mm a side, extend outward 17mm more a side (.7"), and have a net 34mm increase in rear track.

5. The overall effect of this change (aside from clearance issues) will be an increase in understeer.

I labored over a wheel/tire change recently for this same MY C2 and this doesn't sound like a good change to me. I can't imagine that the rear is going to look right or fit inside the fender.

Edited March 16, 2005 by Coaster

[Loren]

Even Porsche put 5mm spacers all the way around on the 550 edition.

... and 5 mm spacers were standard on the GT3 mk1's (RoW version).

[Loren]

1.... Dependent on the manufacturer that tire is likely meant for a 9" wheel and may fit a 10" wheel at most.

The MY01 and older Carrera's had 265/35 tires as standard on the 18 x 10 wheels. The 285/30 were not introduced as standard until MY02 - when they also increased the front wheel size to 8" (from 7.5").

[LVDell]

Loren, any idea why they changed the front wheel size but kept the tire size constant?

Also, they kept the front size constant (225) yet increased the rear from 265 to 285 so wouldn't it make logical sense (siince Porsche deemed it better as a 225/285 setup) to change the size on your rear to 285 on the next tire change for those with the 10" rears?

[Loren]

There was no "official" explaination that I could find. Using 8" front wheels will still give a slightly wider tire contact patch (over a 7.5" wheels) with the same size tires.

[PorschePRH]

Just speculating that it could have been a supplier issue...Either on the tire or wheel side....

[LVDell]

I am guessing that the 10" sport designs (like the ones you have) that are 10" rears that orginally had 265 can now accomodate the 285 rubber?

Edited March 17, 2005 by LVDell

[PorschePRH]

My 03 manual shows summer tires as 285/30 and snow tires as 265/35 on the same rim....So that must mean you can go either way...

[Loren]

I am guessing that the 10" sport designs (like the ones you have) that are 10" rears that orginally had 265 can now accomodate the 285 rubber?

Yes.

[LVDell]

Thanks Loren.