951 8's on Rear?

[KTL]

I've seen 944 Turbo 16x8's on the rear of SC-flared cars and it looks okay (looks just like a 16x7 actually).

Just curious if anyone's done this and does a 245/45-16 tire fit with the +23.3mm offset of this wheel?

I know the outboard clearance is fine, but for some reason my calculations show the inboard side of the wheel/tire combo being tighter than that of a 16x9 with a 245/45?

Any info. is much appreciated.

[Bill Verburg]

The outboard side of the +23.3mm o/s 944/951 wheel will sit 12.7mm further inboard than a +10.6mm 911 8

The inboard side will, of course, sit the same distance further inboard.

the 245/45 will work on the 8's but not as well as on 9's

to me it would look very odd having the wheel sit that much further inboard(there will be no rubbing problems inboard because they do not sit as far inboard as 9's)

[nestorjw]

That 16x8 is mostly used to put on the front of the car and use 9"s on the rear. I just got a set back refinished. They basically look bad on the rear, unless u used a spacer maybe. Most people use it for the front.

[KTL]

I don't think it looks too bad from the outside. Pretty much looks like a 16x7 with a spacer.





The inboard side is what I was thinking would be tight. Here's why:

951 16x8 Fuchs has backspacing of

23.3 mm (+o/s)+ 4 in. (1/2 rim width) + 0.3 in. (rim flange thk.) = 5.22 in.

16x9 Fuchs has backspacing of

15mm + 4.5 in. + 0.3 in. = 5.39 in.

Makes sense to me. Simple math.

The tire size is what concerned me. Using a 245/45-16 Bridgestone S-03 with a 9.6 in. section width (based on a 8 in. rim width) , I get a distance from the mounting surface of the wheel to the inboard tire sidewall:

951 16x8 Fuchs

23.3mm (+o/s) + 4.8 in. (1/2 of sect. width) = 5.72 in.

16x9 Fuchs

15mm + 4.8 in. = 5.39 in.

Note how this calculation ignores wheel width. This cannot be a good thing to do!

From the above numbers, it would seem that the 8 in. wheel/tire combo. would have less inboard clearance. This doesn't make sense considering the backspacing numbers- and I know these are right. I know the 16x9 is going to make the section width a bit wider. So I assume it makes a big difference and you can't compare the two wheels with the same tire this way (using the same section width dimension)?

Any clue as to the error of my ways is greatly appreciated. I'm not the sharpest knife in the drawer.............

[Bill Verburg]

Forget backspacing the 2 critical #s are width and o/s. If you use the advertised width the actual edge of the rim will be a displaced a bit more(~5 - 6mm) due to the flange thickness.

Here is a nice graphic developed by Andy in England posted here a while ago



Here are the #s for some wheels I have messed with, neglecting flange thickness


This graphic from my website shows where the #s come from


For the outboard distance from the hub mounting face the formula is
width(inches)*25.4/2 - o/s

For the inboard distance from the hub mounting face the formula is
width(inches)*25.4/2 + o/s

[KTL]

Thanks as always Bill. Especially for the extra effort of posting the diagrams

I too thought that graphic posted awhile ago by Andy was excellent. Printed it out the first time I saw it! With this diagram, I knew the 23.3mm 8 was similar to the 9 on the inboard side. But the tire width was what concerned me. Still, it's obvious from that diagram that the same tire that is used on the 9 will most certainly clear when used on the 23.3mm 8.

What threw me off was the section width of the tire on different width rims. The cross section of the wheel and tire assembly shows where my error in judgment lies. The rim width obviously has an impact on the section width of the tire (duh!). Advertised section width numbers should only be associated with the advertised measured rim width!

[Bill Verburg]

What threw me off was the section width of the tire on different width rims. The cross section of the wheel and tire assembly shows where my error in judgment lies. The rim width obviously has an impact on the section width of the tire (duh!). Advertised section width numbers should only be associated with the advertised measured rim width!

Exactly, but the 1" of extra rim = 0.2" of extra section width rule of thumb is fairly useful.

The other thing that is often forgotten is that as the tire carcass is stretched axially it is also compressed radially giving a bit shorter tire w/ a bit better torque multiplication.

wider is better!

[KTL]

Originally posted by Bill Verburg
Exactly, but the 1" of extra rim = 0.2" of extra section width rule of thumb is fairly useful.

The other thing that is often forgotten is that as the tire carcass is stretched axially it is also compressed radially giving a bit shorter tire w/ a bit better torque multiplication.

wider is better!

Understood.

Thanks again!