Rear Wheel/Tire Fitment, '81 Z28, There's something I'm missing...

Jun 5, 2017
61
Bold Springs, GA.
Hi Everyone,

I have done a great deal of research on this topic, but I am still unclear on the subject of stuffing a 12" wide tire and 10" wide wheel under a 2nd gen Camaro. From what I've read, the "safe" setup with a 15" wheel, is an 8" width with 4.5" backspacing and a 275/60-15 tire. This seems to be the ticket for no rubbing with no modifications to shock mounts, springs, or fender lips. Still, there are those running tire widths of 295, 305 and even 325 on 9" and 10" wide wheels, and they don't rub, or at least they rub very little.

The information presented is incomplete and so I am left to assume some things. I would assume that to run something larger than a 275, you must do one or all of the following:
Use a wheel with 5.5" backspacing, relocate the shocks, move the rear springs inboard, remove the exhaust pipes over the rear axle, hammer the seat belt bumps in the rear wells, roll or cut the wheel lips.

I would like to run 28x12-15 tire, roughly a 305/55-15 on a 9" or 10" wide wheel, I assume with 5.5" of backspace, but it is unclear to me what modifications are necessary to run this combination?

For those of you running this setup or something similiar, how did you do it? What did you have to move, or modify, or roll, or beat on, to make it happen?

Your comments are greatly appreciated.
 

Zspoiler

Veteran Member
May 6, 2012
4,298
Federal Way, Washington
Any wider than 10 .and sometimes thats pushing it.You need to "mini-tub" it and or flare it like the SCCA /IMSA/ IROC road racers of the 1970-81 Camaro,s
5529277575_d2325a91e8_b_26512224230_o.jpg
 
Jun 5, 2017
61
Bold Springs, GA.
Let me be clear: "I would like to run 28x12-15 tire, roughly a 305/55-15 on a 9" or 10" wide wheel, I assume with 5.5" of backspace"

I have no plans to run a wheel wider than 10 inches. When all is said and done, I may end up running a 15x8 with 4.5" backspacing and a 275/60-15 tire, but I would like a wider tire and wheel if possible. The work necessary to achieve the goal will determine whether or not I can run the wider tire. Unfortunately, I'm on a budget and I would prefer to leave the current rear spring and shock setup as is.
 

G72Zed

Veteran Member
Sep 8, 2015
3,757
Canada
Hi Everyone,

I have done a great deal of research on this topic, but I am still unclear on the subject of stuffing a 12" wide tire and 10" wide wheel under a 2nd gen Camaro. From what I've read, the "safe" setup with a 15" wheel, is an 8" width with 4.5" backspacing and a 275/60-15 tire. This seems to be the ticket for no rubbing with no modifications to shock mounts, springs, or fender lips. Still, there are those running tire widths of 295, 305 and even 325 on 9" and 10" wide wheels, and they don't rub, or at least they rub very little.

The information presented is incomplete and so I am left to assume some things. I would assume that to run something larger than a 275, you must do one or all of the following:
Use a wheel with 5.5" backspacing, relocate the shocks, move the rear springs inboard, remove the exhaust pipes over the rear axle, hammer the seat belt bumps in the rear wells, roll or cut the wheel lips.

I would like to run 28x12-15 tire, roughly a 305/55-15 on a 9" or 10" wide wheel, I assume with 5.5" of backspace, but it is unclear to me what modifications are necessary to run this combination?

For those of you running this setup or something similiar, how did you do it? What did you have to move, or modify, or roll, or beat on, to make it happen?

Your comments are greatly appreciated.

This was pretty much the exact first and second (of 3) setups during my build.
1st- BFG 325/50/15 on a 15x10 with 5.5 BS. Actual was 13.1 wide, 27.5 tall
2nd-MT ET Street Radial, 305/45/18 (28.8x12) on a 18x10 inch rim with 6.00 inch BS, in order not to have the jacked up look with a 28.8 tall tire, I needed to do most of the mods you mention StongSurvivor. (pics att.)

I did the following for both setups.
1-Trimmed and Rolled the fender lips.
2-Straighten the seat belt hump.
3- Moved front spring perch bracket inwards, gained 3/4 inch or so.
4- Moved rear frame eyelets inboard 1/2 or so (matched the front, there not perfectly inline anyway!!)
5- Stock shock location upper, and lower if the Lakewood J bolt traction bars are in a stock(ish) location. Used them for lower plates.
6- Moved spring perches on rear end to line up.
7- Had to pie cut & clearance rear inner wheel well/trunk floor for the MT 305/45/18, not the BFG's

Lots of work if you want the car to sit nice and not jacked up, JMO.
 

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Turbo70Camaro

Veteran Member
Gold Member
Jan 7, 2005
2,138
so cal
Safe = 15x8 4.5bs w/295-55 drag radial or equivalent slick


15x10 w/5.5bs works but may need work depending on tire but the 305-55 should be fine......................
 

Lowend

Administrator. .a car, a man, a maraca.
Staff member
Lifetime Gold Member
Mar 25, 1999
16,740
San Jose, CA, USA
With a 275-305 tire, you really want a 10" wide wheel. Yes, you can cram a 275 on an 8" but the sidewall won't be as well supported and traction will be worse.
 




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