Carboy

Does anyone know the bolt pattern and offset for a standard 993?

Ray Calvo

Has a 5-bolt pattern; quick lit check can't uncover the bolt distance or bolt circle diameter.

RE offset; depends on wheels and body (regular or fat-body C4S). My '95 with 7" front and 9" rear width 17" wheels has 55mm front and rear offset (altho some wheel nos. have a rear 70 mm offset - no other info).

Viken

Porsche bolt pattern: 5 on 130 mm

Offsets for 7" and 9" by 17" wheels (all models): 55 mm front and rear

Offsets for 8" and 10" by 18" wheels for narrow body: 52 mm front and 65 mm rear

graham_mitchell

Why are the offsets different for different wheel diameters?

I have spent 8 - 10 hours looking into wheels and tires. Boy, is it hard work (read: impossible) trying to find accurate information on bolt patterns, offsets, wheel weights, tire weights, maximum wheels and tire sizes that will fit 993, and whether different combinations alter the suspension geometry requirements.

Very confused...

STLPCA

Graham
It's the different widths that requires the offset variations.

graham_mitchell

Dan, that makes sense but if a 7" and 9" take a 55mm offset, why does the 8" (which is in between) take a 52mm offset? That threw me...

Is there a resource with all this information? (Other than Viken )

viperbob

Hi Dan, your back. Hope you had a nice Vacation. Did the check arrive OK??

Thanks
Bob

ApexL8

It is kind of hard to sift through, but there is a lot of information on Robin's P-Car site about factory wheel size/width/offset:

Tires approved by Porsche - By Ray Calvo

There was a thread here at Rennlist about wheel weights:

Wheel Weight Thread

The thread included a pointer to a web site which may not be 100.00% accurate or complete, but still worth a look nevertheless:

www.wheelweights.net

Good luck with your future research, it does seem like the information should be easier to find, especially tire weights.

graham_mitchell

ApexL8, thanks that is some help but it would be nice to know how to calculate the correct ET for any wheel width rather than relying on the width being in a table.

Does that not exist?

I tried the wheelweights.net site too. Not only are my wheels not in there but the entire manufacturer is missing! The battle continues...

SLVR

Graham,
It is true, most websites are miserable when it comes to providing data. Even major manufacturor and the Tirerack don't provide much help.

However, if you mount non-std wheels on any car, I understand that regardless of the wheel's width, your ET should be the same to maintain the same suspension geometry (or for my tast within say five mm in practical terms) for street apps.

ApexL8

Graham,
I've never seen a formula for calculating offset, not to say that one doesn't exist. I guess for aftermarket wheels the safest thing to do is stick with a configuration that Porsche offers as a factory option. I went with a (sort of) non-standard fitment by using 18" 996 wheels, after being assured the did indeed fit on a 993 narrow body.

What manufacturer made your wheels? I'm surprised they didn't show up at all on wheelweights.net.

graham_mitchell

Brock. See http://www.brock.de

Edward

... that makes sense but if a 7" and 9" take a 55mm offset, why does the 8" (which is in between) take a 52mm offset? That threw me...

Remember that the 7s and 8s are intended for front and 9s and 10s for the rear...one can't compare offsets between front/rear ; only front to front or rear to rear. The scant 3mm difference in offset for the 8" rim is probably to maintain the same relative dimensional relationships of the 8" in comparison to the 7" wheel within the wheelwell. Apart from aesthetics, maintaining this relationship, regardless of wheel widths, also probably keeps handling and wear to suspension joints similar should you swap rims. Besides, as we all already know, it's not like one MUST ALWAYS use Porsche's numbers; it's just that deviation form their design parameters will alter (to the benefit or detriment) the characteristics of the car.

Edward