Wheel insight

snotrocket71

Greasemonkey
Feb 20, 2011
218
12
18
29
Wading River Long Island
#1
hey guys, i'm looking into ditching the factory 15x7 rallye wheels in favor of a set of weld prostars, i'm looking into stuffing a 275/60/15 or a 275/50/15 tire in there. I've looked high and low at pictures and posts but most don't have backspacing and I know each car really is different than the next. currently I run 255/60/15 on the factory 7" wheel with 4" of backspace (factory) and its tight to the frame rail, maybe a 1/4" at most of a gap. I was thinking that a 15x8 wheel with 3.5" of backspace would properly place the tires further out towards the fender lip, any thoughts on this logic? i'm stuck with either 4.5" or 3.5" backspace and would prefer not to run spacers or notch but also would like to get the widest drag radial I can in the stock well to help harness the power the big block will put down. anyways, any thoughts and insight is always appreciated. I know i'm asking for the world!
 

UNGN

Comic Book Super Hero
Sep 6, 2016
2,525
974
113
53
Southlake, TX
ungn.net
#2
With an 8" wheel you want 4" BS. This puts the center of the tire 1/2" further out than a 7" wheel with 4" BS.

3.5" will likely need the Fender lips rolled, but still should work unless the car is low. 4.5" will need 1/2-3/4" spacers/adapters, which is too much for a spacer and not enough for an adapter.
 

lilbowtie

Royal Smart Person
Jan 7, 2006
1,960
900
113
Canton Mi
#3
Figure it out mathematically - You have aprox 5.5 inches from the face of the drum to the frame. your 275/60/15 drag radial has a cross section width of 11.4 inches on an 8 in rim. This means the tire is 3.4 inches wider that the rim or 1.7 inches wider per side. If you have 4 inch back space plus the 1.7 inch (5.7)you will hit the frame with the tire. 3.5 back space with 1.7 = 5.2 inches . I run 3.5 bs on mine

IMG_5646.JPG
 

UNGN

Comic Book Super Hero
Sep 6, 2016
2,525
974
113
53
Southlake, TX
ungn.net
#4
Section width is highly dependent on MFG, so be sure to check the exact tires you plan to use.

The BFGDR section width for a 275/60 on an 8" wheel was 11.0 and the Nitto DR 275/60 section width was in the 10's on a 8" wheel. Both would clear frame with Lilbowties measurements with an 8" with 4" BS.

Hoosier 275/60 section width is 11.5 and won't clear.

Same size tires, different mfg's.
 

lilbowtie

Royal Smart Person
Jan 7, 2006
1,960
900
113
Canton Mi
#5
Not trying to be confrontational but an 11.0 in cross section on an 8 inch rim is 3.0 inches wider than the rim or 1.5 inches per side. 4 inch backspace plus 1.5 inches is 5.5 - problems. Rocket - take some measurements on your car and see where your at and do the math. The biggest tire I can fit is a 29.5 / 9 /15 (11.4 sec)
 

snotrocket71

Greasemonkey
Feb 20, 2011
218
12
18
29
Wading River Long Island
#7
thank you guys for the insight, i'm gonna take some measurements on both sides just to make sure it should clear, i'm hoping the aluminum drums don't cause any issues either. more than likely Id be running MT ET street S/S tires, I have them in 235/60/15 on my gray 442 and they seem to hold up well all around. its incredible how the fitment varies from car to car on g-bodys, I had an 87 cutlass with a set of 15x7 (4" BS) 442 wheels that had 245/60/15 bfg's and there was next to no clearance between the tire and frame
 

lilbowtie

Royal Smart Person
Jan 7, 2006
1,960
900
113
Canton Mi
#8
383 your running a rear end from a 75 Monte which is wider than the g-body so you need more offset. Section width will change with rim width and as UNGN brought up, tire manufacture.
 

UNGN

Comic Book Super Hero
Sep 6, 2016
2,525
974
113
53
Southlake, TX
ungn.net
#9
Not trying to be confrontational but an 11.0 in cross section on an 8 inch rim is 3.0 inches wider than the rim or 1.5 inches per side. 4 inch backspace plus 1.5 inches is 5.5 - problems. Rocket - take some measurements on your car and see where your at and do the math. The biggest tire I can fit is a 29.5 / 9 /15 (11.4 sec)

Most people (including wheel mfgs) measure backspacing to the outside of the rim, not the inside of the rim (where the tire mounts) On an AL rim this gives another 1/4" from your math. If you measure backspacing to the rims flange, another 3/8".
 

ham1974

Greasemonkey
Oct 6, 2012
242
50
28
#10
394E4925-8D4F-4500-92E5-8E3CB3687D90.jpeg
I run a 275/60/15 on an 8 inch ralley nitro 555 dr. There right but don’t rub. Not sure of the bs on the ralley.
 

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