930 rim offset values/backspacing recommendations
 

I have a general question for the racers running aftermarket rims on their 930's

I am looking at making a set of Forgeline rims in the following size widths for my 1979 930 turbo:

Front = 17 by 8.5 wide
Rear = 17 by 10 wide

I want to select the best rim backspacing when ordering these but also am aware of the fact that I dont want to alter the front scrub radius too much and screw up the handling. If I could increase track width a little and still maintain clearance to the front and rear fender well and oil lines is another priority.
Throwing all this out there.....can you guys chime on what backspacing you have used and recommend in these particula rim widths?

I hope these widths are a pretty typical set up for alot of you though I know the car probably is not that common....

Thanks,
Fred

A little more info is needed,
still have the stock floating rotors and spacer? Do you wish to retain the front spacers if they are still there?

do you wish to retain the rear spacers?

8.5/10 is an odd choice for a 930, 9/11 is the more usual fitment, Do you really want 8.5/10?

Talk to David Schartd at Forgeline, that's what I'd did and I could not be happier with the fitment.

hi Biill,
I would like to remove the front and rear spacers since it would be better to run without them if I am customizing rims to my size.
I have the stock floating rotors and calipers.
I chose 8.5 and 10 because of available racing rubber that I would be purchasing to fit. These rim widths fall right in the range of tire widths that I would be mounting allowing me the widest selection.
9 and 11 did not seem to fit the bill in this regard according to the tire chart I was using as a guide. Maybe you can elaborate more on what tire widths would range for 9 and 11 rims so i could change my mind.

Fred

What tires did you want to use? brand/size/model line

I asked if you would tell me what tire widths would run on 9 and 11 inch rims.....brand and type should not matter.

there has to be a range of tire sizes for those rim widths correct?

Anything from 225/275 to 275/335 in 17" Hoosiers can be fit and are recommended by Hoosier on 9"/11" wheels with a slight amount of discrepancy depending on sidewall height.

Only reason I can see to go with 8.5"/10" is if class rules ding you for wheel width increase. POC has a rule like this and thus 245/275 on 8"/9" or 10" has become the best use of points.

yes, it does matter, especially if you want to optimize for a particular situation.

Please elaborate.

Its not productive asking me to respond one question at a time. If you would explain what you mean and all the questions you have for me in one message then we would be making positive progress, otherwise its frustrating.

Thanks for the info Evan.

Ok thanks.
Can you tell me what sizes you are running and the backspacing or offsets for each as I can calulate backspacing from that number?
I am assuming you have stock fender flares on your 86 turbo and not using any spacers with your rims right?

Fred

It's not productive for me either, so answers aren't forthcoming, talk to Dave

255 front and 315 rear

Front 17x9 +31 offset 255/40ZR17 Kumho

Rear 17x11 +06 offset 315/35ZR17 Kumho

Stock fenders with no rubbing and I removed the rear spacers. No front spacers on 86 930.

I hope this helps.

Regards, Dave

wheels
 

I track a 79 930 and have run a variety of rims sizes, 17 x 9 and 11 with 255 x 40 x 17 and 315 x 35 x 17. Currently run smaller sizes due to class rules. I run factory spacers so my offsets are not relevant. i suggest calling John at Complete Custom Wheel in Florida. he knows the data for all the options you may need, with or without spacers,tire sizes etc.
Willy

an '86 930 has a wider hub which is used from 'mid '80 on, it serves the same purpose as the older 21mm front spacer. So yes, your car has a spacer it's just not separable as on the '78-80 930.

Yup that helps alot.
I can use this info to calulate what I need in a 8.5 and 10 inch set up if I go that way too.

Thanks for the info on the using max wheel and tire on 930 without spacers

Bill or Dave, would you happen to know what the best offset to use on the front of an 85 Carrera (stock setup) with 930 fenders (wide body conversion) using a 17"x9" wheel and 255/40R17 tire?