Wheel offset question
 

Hi All,

I've searched and read through many posting regarding wheel offset for my 964 C2. There was a good diagram showing offset measurement, basically distance betwen the center of the wheel to the wheel hub.

My question is that as I upgrade my wheel to a +1 or +2, ie. from 16" to 18" on my C2. I must keep the offset value the same right? Or do I have to change the offset depending on the width of the wheel.

Let's say, the stock rear wheel is 16x8 with a 52mm offset. Now if I want to upgrade to a 18x10, the offset should still stay at 52mm in order not to cause problem for the wheel bearing right?

thanks,
anthony

You need to find the "sweet spot" answer....such that:
- there is no interference on the "outside" surface of the wheel with ( say) the fender lip
- there is no interference on the inside surface...say...an oil line as is often the case with the RR location on 911's.
- it fits altoghether ( maybe the new "wider" wheel is simply too wide).
- Maintaining ( or not)...the original "Scrub radius"...if the application if for the front of the car.

You need to relate "offset" ...to the new/old "backspace". If you have the Bill Verburg drawing in front of you which shows all this...it'll become a bit more clear.

So the answer is ....maybe...maybe not.

It's best to draw a picture of the original wheel ...and the proposed new wheel ..toghether, on graph paper. It'll show you exactly where the new wheel "sits-in-space" compared to what you're running now. Intereferences will likely become very clear to you, but even then you'd need to know the inside/outside points of possible rubbing based on the car body you have.

Wil

Re: Wheel offset question
 

Anthony-
No, since offset is related to the centerline of the wheel, a 52mm offset 10" wheel will have an inch more backspacing than a 52mm offset 8" wheel. This may push the wheel and tire inboard so much it will interfere with the suspension. As you go wider on the rim, the offset will have to change to keep backspacing within acceptable clearances.

Check Bill Verburg's wheel and tire page to see what may work for your car.

TT

Cool site. Took me a while to understand it. THANKS!!!!

For the same width wheel, where you want to keep the outer face plane of the wheel in the same position relative to the fender, yes

This one is a good example of keeping the same o/s but w/ a 1" wider wheel
http://members.rennlist.com/1976c38/..._wheel_fit.jpg

You can see that both face planes were moved, the outer ~13mm outboard and the inner ~13mm inboard.

To keep the outer face place in the same place w/ the 9" wheel the o/s would need to be ~75mm

Good explanation Bill.

I guess it's then a trial and error in fitting the wheel so that there is no rubbing on the strut housing and wheel well edge huh?

---
anthony

Not really, you should have a good idea of what you have and how much empty space can be used.

The fitment of the extreme sizes often involves mods to inner and outer pieces, but for a modest increase you have more play.

Now I happen to know that 964 Cup cars used the following
<pre>Carrera cup x17
8.0 52.0
9.5 68.0
92 euro cup
8.0 52.0
9.5 68.0
Kinesis x17
8.0 51.0
10.0 54.0</pre>

18s would want to be pretty much the same, the tire size you use is also critical to fitment

ok partial high jack of thread here but same topic. If I have 7 and 9 inch fuchs on my 77 911 with a newly added turbo body should I be added 2 inch rear spacers and 1 inch front spacers? or am I screwing up my offset

wil, Bill? I do realize that no spacing is required for inside cleareance but track will be wider in rear or is it not really as the stock turbos were 1 inch wider at the rear hubs along with a 1 inch spacer? Please clarify sorry for moving off topic!

1" front and 2" rear is about right unless you also changed to late 930 hubs and rotors and trailing arms

bill no change on suspension as of yet who knows maybe next winter