[JUDGE3]

I believe the 15" ralley 2 wheels (15 x 7) have a 4- 1/2" backspace is this correct?

on a 1970-73 firebird would a 15 x 7 wheel with a 5" backspace fit better?

[The Champ]

I believe that the original BS on a 15x7" Rallye II wheel was 4.25". Obviously that worked fine for the OE tire.

The only reason to go to 5" BS would be to fit a much wider tire.

[JUDGE3]

well I have brown letter bf goodrich ta's :

P245 60 R15 FRONTS
P255 60 R15 REARS

really like the fit but with the 15 x 7 ralley 2's theres a slight "pooch" effect with the sidewalls. doesn't really bug me but when I go with cragar ss wheels I want to get the best backspace and possibly cure that?

wondering what backspace for curing that. so I'm guessing 5" would be the most and maybe just go 4 and 1/2 then?

waiting for a wheel sale this time of year to pull the trigger on em'

[amcmike]

The backspace itself isn't going to help the sidewall bulge. The bulge will appear the same, it'll just sit deeper in the wheel well.

You need wider rims to reduce the bulge effect, with different backspace to optimize the fit in the wheel well. A 15x8 would probably meet your wants.

If the original 15x7s had a 4.25, that'd be a +6mm offset. Don't know if that was optimum or just what they used, but in a 15x8 that would equate to a 4.75". You could take some measurements based on existing wheels, or perhaps some of the other members with 2nd gens could tell you the optimum offset. FrankieTA is running 17x9s with 275s on the front, which have a +8mm offset (about 5.25" backspacing, so the +6mm probably works pretty good).

[JUDGE3]

Originally Posted by amcmike

The backspace itself isn't going to help the sidewall bulge. The bulge will appear the same, it'll just sit deeper in the wheel well.

You need wider rims to reduce the bulge effect, with different backspace to optimize the fit in the wheel well. A 15x8 would probably meet your wants.

If the original 15x7s had a 4.25, that'd be a +6mm offset. Don't know if that was optimum or just what they used, but in a 15x8 that would equate to a 4.75". You could take some measurements based on existing wheels, or perhaps some of the other members with 2nd gens could tell you the optimum offset. FrankieTA is running 17x9s with 275s on the front, which have a +8mm offset (about 5.25" backspacing, so the +6mm probably works pretty good).

thank you for that info. needed that. I didn't think about that......the offset wont change tire fit, rim width does. I know I don't want the wide 8 inch look with the cragars, so i likely will stay with 15 x 7 and stock offset.

[The Champ]

A 255/60/15 is safely rated to run on a 7 - 9" wide rim. The 245/60 is safely rated to run on a 7 - 8.5" rim.

If I was ordering new rims, I'd probably go with the 8" rim on the back with 4.75" BS to put the tire in the exact same spot that your current wheels do. You could either go 7 or 8" on the front with 4.25" for the 7" and 4.75" for the 8".

[JUDGE3]

Originally Posted by The Champ

A 255/60/15 is safely rated to run on a 7 - 9" wide rim. The 245/60 is safely rated to run on a 7 - 8.5" rim.

If I was ordering new rims, I'd probably go with the 8" rim on the back with 4.75" BS to put the tire in the exact same spot that your current wheels do. You could either go 7 or 8" on the front with 4.25" for the 7" and 4.75" for the 8".

thinking I will go with the exact same stock size rim then.

according to the conversion chart that would be 7" wide rim is 4.25 stock backspacing, so when ordering that would be 7" wide rim with 6mm backspace?

[The Champ]

The 6mm would be the offset on a 7" rim, the 4.25" would be the backspace.