10" wheel backspacing question
 

Probably one of the more easy and basic questions in the tech section so here goes. 1st will a 15" x 10" wheel work without rubbing or frame/fender interference on the rear of a 1970 Pontiac GTO? If it will, #2 what backspacing will I need to make it all work. I'm looking at a 275/60/15 BFG for a tire. The fronts would be a 15" x 8" with a 215/70/15 BFG as well.

a day 2 mod of Cragar SS wheels.

I had a 10 inch with 275/50 15 on my 71 lemans with 4.25 BS and it would rub occasionally on the really bad ramps or bumps. I started with 295's and they got chewed up really quickly. I am pretty sure you can fit the 275 on a 15X8 rim with no problem and that is what I had on my Lemans for a long time.

If your set on running the wider rim then take advantage of wider tire profiles. On my 70 I have 15 X 10's custom BS 5.5" IIRC, don't quote me it's been over 10 years on the car. Been running M & H DR's 325/50/R15's. The same profile numbers vary some between brands. This same MT DR is an inch wider which would never work on my car because the M & H's are already shoe horned in there.

..
....

Somewhere in the 5.5" to 6" range ought to do it.

However for a true 'day 2' look they need be sticking out past the fenders, with air shocks for that rock-hard ride and to keep the tires from hitting the wheel opening. That would require a wheel with about 3" of backspace, for that super deep-dish look everyone craved back then.

Don't let anyone ride in the back seat either. ;)

15x10 draglites with 5.5 bs,295-65 MT drag radials.
John
http://i1067.photobucket.com/albums/...sbcfza7ko.jpeg

http://i1067.photobucket.com/albums/...syk6pi6vq.jpeg

I know this is a firebird, but this will show a 275x60x15 on 15x8 snowflakes.

have even ran them on 15x7 ralleys, but they work better on 8-10s.

I know this isn't a 10" wheel, but on my 70 GTO with rear discs I needed a 5.25" backspace to center 275/60-15 tires with 15"x8" wheels. If I was using drums instead of discs I think a 5" backspacing would have worked.

If my math is correct, then subtracting 1/4" of backspace from my 5.25" (if you are using drum brakes) and then adding 1" (which is 1/2 of the 2" difference of 10" vs. 8" rims), brings you to a 6" backspace which is in the ballpark of what Bart suggested.

Just another data point that may help.

I think those Centerlines you have now may be 11" wide, may want to check the back spacing on those. I used to squeeze 295s on using those wheels. I think they may be 6" BS, but honestly forget...

.

I'm looking at a set of new Cragar's with these tire sizes already mounted at a good price.
The owner of the wheels doesn't know the back spacing but says they will fit my car with no issues. He said he purchased these wheels to go on an 82 Pontiac Grand Prix and the previous owner had them "on an old Chevelle."

Well, if the guy who's trying to unload them is telling you they'll fit then it's a sure thing.

Right? ;)

I suppose he either doesn't own a measuring tape or can't operate one, to get those simple but most important and possible deal-breaking measurements you need.

A shame. :(

If it's local, then see if he can let you take 1 wheel home for a fit test. Maybe work out a deposit or some sort of arrangement where he feels comfortable that you won't steal his wheel.

I sent him a YouTube video last night that shows how to measure backspacing, lol. I agree I shouldn't be doing all the legwork, hes the seller, right?

That's a good call Squidward, I mentioned that to him when he said he didn't know the backspacing.

I haven't gotten confirmation yet that a 10" wheel will work or not in my application. I guess my real question is what backspacing will I need to get a 10" wheel with a 275/60/15 tire on it if even in fact a 10" wheel width will work without any frame contact or fender rubbing?

Don't know if it makes a difference but I have rear drum brakes at the moment.

That's a pretty wide wheel.

I tucked 18X9" wheels with 6.57" of backspace both front and rear on my '64 Tempest, it's lowered a bit too. Up front I used a pair of 1.063" thick wheel spacer/adapters, effectively making the front backspacing 5.507". I know a '70 has a bit more room towards the outside, so that's in your favor.

However the sidewall 'bulge' on low-profile 40 and 45-series 18" tires is a bunch smaller than the sidewall 'bulge' of a 60 or 70-series 15" tire. So even if the rim can fit in the confines of the wheelwells (without jacking the car up for fender clearance), getting the tire to fit is another story.

I'd be very wary of the fit of any 15X8" front wheel, especially with that fairly tall (26.85") 215/70-15 tire.

Most off-the-shelf Cragar SS wheels have shallow backspacing, somewhere around 3.75", which is totally wrong for proper fitment on our cars.

It's all about the backspacing. If it's wrong, you'll kick yourself for buying those wheels and tires.

OK B-Man, I'll defiantly take this to heart. Much appreciated.

http://i263.photobucket.com/albums/i...izeRender1.jpg

275/60/15....15x8....4.5" bs

http://i263.photobucket.com/albums/i.../IMG_27731.jpg

close up

Don't the '70s have larger rear wheel wells than the earlier cars?

Probably not too helpful - but I got a 10" wheel inside both front and rear of my Formula with 5.5" back spacing. Tire occasionally rubs on the exhaust pipe in the rear under hard cornering.