Front wheels 15x7 with 3.750 backspace. Rear wheels 15x8 wtih 3.875 backspace. Stock suspension front and rear. No tubs.

#1: P225/70R15 27.4 diameter front and P255/70R15 29.1 diameter rear.

# 2: P235/60R15 26.1 diameter front and P255/60R15 27.0 diameter rear.


From my research I think either front will fit but I am not sure about the rears with that backspacing.

Many thanks,

I would recommend option #2.

P195/75/R14 is also 26.1" OD....This was the OEM size in the bias to radial equivalent and then radial only on many Camaro's...P195/75/R14 also came on Regals, Ventura's, Nova's & Cutlass. P235/60/R15 is as you know 26.10 in OD.

The 15x7 4.25" backspacing fits the rears nicely. You gain an inch in width but lose some in backspacing. I still like option 2 better as it gives you a wider aspect ration which will improve your cornering, handling & dry traction.

FWIW, the P225/70R15 was OE on Z28's in the late 1970's Trans AM's the Corvette & many Police Cars used that size as well back in the day with a Good Year Eagle GT which later became the GT +4

Still like option #2

It all depends how much space you are comfortable with from the top of the tire to the top of the wheel well opening.

There's no way I'd put a 27" tall tire on the front. It's gonna hit something. Try gor under 26, even as little as 25. (mine are 23 1/2"!)

A 215-65-15 is a good choice, as is a 225-60-15.

On a 7" rim, you want 4" BS in front. 3.75" may be ok with a short tire. Mine are 3 7/8" The tires are out a lil, but don't scrape cause they are so short, and because I've done other mods to the front suspension that help.

On the back, a 29" tire is barely gonna fit in there, it's just too tall, will probalby scrape the rocker in the front. The 255-60-15 is perfect though.
Again, not enough backspace. With an 8" rim, 4 1/2" of backspace will center the tire in the available space.

*** note I don't know the year of your car. What I say is true of 67 & 68's, I'm no expect on 69's, but what I've read hear holds it true as well.

The 68 and 69 Z28 camaro's had 26.73" overall diameter on front and back according to the Kelsey tire site.http://www.kelseytire.com/pages/preformancetires.html try a 215/70 R15" BFG tire on front and 235/70 R15 on back for a stock look.

Jim,

I was feeling pretty good about the 60 series tires til your post. The wheels I want to use are Keystone Klassics and I can't get a 4.5 backspace for the rears. I rechecked the specs on the rears with 3.875 backspace. They show a negative .63 inch offset so am I correct in that this will add .63" to the backspace bringing it to 4.505? If so, then this wheel should work.

Thanks,

I really wish they still used "offset" simple, elegant and to the point.
"backspace" is a real crappy term cause it's dependant on the rim width.

Yes, negative offset moves the tire into the car.

Half an 8" rim is 4" plus .63 = a schosh more than 4 5/8 BACKSPACE.

Yes, those wheels will fit and will hold a 255 tire nicely.

so where the heck does the 3.875 come in?

so where the heck does the 3.875 come in?

Jim,

I got the specs from Summit's site which says the following:

Brand: Cragar
Product Line: Cragar Keystone Klassic Wheels
Part Type: Wheels
Rim Diameter (in): 15 in.
Rim Width (in): 8.00 in.
Backspacing (in): 3.875 in.
Offset (mm): -16.00mm
Wheel Material: Steel
Wheel Finish: Chrome

I assumed from this that you would add the offset to backspacing.

Hey Jim,

I looked at this again this morning and am now confused. If you take an 8' wheel with the centerline at 4" then subtract .63 for negative offset then don't you now have a backspace of 3.37" and not 3.875 as shown in the specs? Am I missing something?

Thanks,

I'm missing it too. Maybe call keystone and see what the deal is?
Make sure you are armed with the keystone part # from summit's site when you make the call.

Jim,

I sent an e-mail to Cragar inquiring about this offset issue. Here is the response:

"NO NO NO when measuring backspacing it is based on the overall width of the rim outter most edge to outter most edge, when mesuring offset it is from bead seat to bead seat."

I still didn't get it. I sent another e-mail asking if I am correct in thinking the offset as shown in their specs does not have any bearing on the backspace and asked them to confirm the backspacing on this particular wheel. No reply yet.