Need wheel offset/backspacing advice

vanwyk4257 · vanwyk4257's Garage

I picked up a set of BBS magnesium 20-hole centers today to build a set of wheels for my car's future widebody conversion.

It's a stock '75 911 with aluminum trailing arms, and it has the 911"S" front brakes.

I plan on going with stock turbo flares front and rear and I'd like to run as close to 17x9.5 fronts and 17x11 rears as I can.

Has anyone here built up a set of these 3-piece BBS racing wheels? I need to figure out what size inner and outer wheel halves I would need for the fronts and rears.

Thanks!

Early_S_Man · 08-26-2006, 10:09 PM

Why not just use the same offsets the factory used on the RSR Fuchs?

vanwyk4257 · vanwyk4257's Garage

#1 because I don't have that data readily available,
#2 because BBS wheel halves for their racing wheels come in half inch increments and I may not be able to precisely match the factory RSR wheel offsets.

Another thought as well, didn't the RSR's use different rear suspension pickup points and slightly modified trailing arms as well?

What I'm really looking for here are guys like Jack or Doug or others that are running these size wheels right now to give some input.

I think there are at least a few guys out there with widebodies that aren't running turbo trailing arms etc., that I can use as a baseline.

gestalt1 · 08-27-2006, 06:49 AM

i'm basically doing the same thing. unfourtunatly i do not have my car assembled yet so i can't show how my backspacing worked out. i got a set od lindsey 9.5 and 11x17 wheels all with 5.5" backspacing. the original rsr fuchs 9 and 11 x 15 had about 4 7/8" according to my tape measure. i also built a set of the bbs 20 hole wheels and the centers and the hub surface is about 1/2" out from the rim bolt surface. i have 5.5" inner and 3.5" outer rims for the front (5" back space) for the front. the rear are 6" inner and 5" outer (5.5" backspace). my suspension is stock 73 911t track width and i have turbo rear flairs and rsr fg front fenders (9" flair). hope this helps. by the way i believe jack and doug have modified front a-arms so there back spacing will be different.

vanwyk4257 · vanwyk4257's Garage

gestalt
Thanks very much, that's exactly the information I was in need of.
Now that you mention it I do recall reading that Doug's front A-arms were modified.
My wheel centers sound like the exact same ones as yours so those size inners and outers should give me a good starting point!

gestalt1 · 08-27-2006, 12:45 PM

i need to correct my info. i was just at my building where i keep my wheels and re-measured the bbs wheels. the fronts are 4" outer, 5" inner with a 5" back space. the measurement for the rims is from the bead surface to the bolt surface. the bead thickness is about 1/2". the rears are 5.5" inner and outer with a 5.5" backspace. sorry about the mis-information. also keep in mind what type of brakes you are using. some larger calipers stick out from the hub surface and you may need spacers to clear them.

vanwyk4257 · vanwyk4257's Garage

Thanks for the corrections. I'm not in a rush to build these, so I'll probably wait until I've got the flares mounted on the back and the front turbo fiberglass fenders mounted. Then I can bolt on the centers and take some additional measurements to make sure.
Thanks again for the information!

Miguel Antonett · 08-27-2006, 01:55 PM

I believe that if you go with 5.5" front and 7" rear offsets you'll be in the ballpark already, you then might need to play with "small" spacers to fine tune. I would say that every car after any modification is different.