wheel and tire size limits - Pontiac GTO Forum
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post #1 of 12 (permalink) Old 05-17-2011, 12:18 PM Thread Starter
 
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wheel and tire size limits

Hello. I have a 69 GTO convertible fresh off a complete powertrain rebuild and want to put some shiny new rims on her for the summer. Anyone know if 18x8 wheels with 4.5 inches of backspacing work? I am thinking that it will clear suspension and brake parts but am worried about rubbing on the body lip and wheel well.

Any reccomendation for tire sizes? Would like to keep a good profile - maybe 245/45 - but am worried about rubbing. Anyone run successfully with something like this or bigger? Thanks for the help.
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post #2 of 12 (permalink) Old 05-18-2011, 09:03 PM
 
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it will rub on the front. Buddy has that problem.
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post #3 of 12 (permalink) Old 05-18-2011, 10:21 PM
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Here are a few measurements to find the perfect fit,

A 245/45-18" tire breaks down like this;

245 X .03937 = 9.64" at the widest part of the tire,

9.64" x .45 aspect ratio = 4.3" sidewall height,

4.3" x 2 = 8.6" + 18" wheel = 26.6" total tire height,

measure total distance between wheel well and body lip, then subtract the widest part of the tire (9.6") and divide that number by 2, (example 13.6" total space minus 9.6" tire width= 4" divided by 2 = 2".

now measure the rear space in the wheel well, place a flat edge against the tire mounting surface, measure from the flat edge to the inside of the wheel well where the tire rides and allow for travel (13 to 18 inches from the center of the wheel) then subtract the 2", that number should be the back space. (verify with the wheel manufacture)

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post #4 of 12 (permalink) Old 05-19-2011, 08:53 AM
 
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Randy, Great math! I'm going to buy one of those "Percy's Wheelrite" gauges. It bolts on the wheel studs and is adjustable to find height and width, back space.....pretty cool tool. E



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post #5 of 12 (permalink) Old 05-19-2011, 09:26 AM
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It does sound like a cool tool, Eric. Where would a guy buy it?



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post #6 of 12 (permalink) Old 05-19-2011, 10:28 PM
 
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www.Speedway Motors.com sells them.....$89......better than making a size mistake!!!!



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post #7 of 12 (permalink) Old 05-19-2011, 10:34 PM
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I dug up some info on that Wheelrite tool. Considering all the questions about "how big" about tire/wheel fitment, it would be a good tool to have. Here's some info:
Wheel Rite - Wheel and Tire Fitment Tool

Looks like Jegs, Summit, Autozone and Street Side carry it. Summit has it for $69.99, the only place I looked. Could be cheaper elsewhere.

Percy's High Performance 01201 - Percy's WheelRite Wheel and Tire Fitment Tools - Overview - SummitRacing.com

EDIT: Looks like Uncle E and I was on the same train of thought at the same time......



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post #8 of 12 (permalink) Old 05-19-2011, 10:45 PM
 
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I have seen these tools advertised before. The only thing I'm not certain about is how it accounts for the actual ride height and the suspension as it works thru its range of motion. Once you jack it up and pull a wheel off its not a good representation of ride height? Maybe I'm missing something here.
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post #9 of 12 (permalink) Old 05-19-2011, 11:04 PM
 
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If you jack the rear at the axle tube and/or the front at the lower ball joint, the suspension remains loaded at ride height..... you can have a chubby chick push down on the front or rear bumper to simulate bumps in the road !



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post #10 of 12 (permalink) Old 05-20-2011, 08:20 AM
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Quote:
Originally Posted by onetwomany View Post
I have seen these tools advertised before. The only thing I'm not certain about is how it accounts for the actual ride height and the suspension as it works thru its range of motion. Once you jack it up and pull a wheel off its not a good representation of ride height? Maybe I'm missing something here.
I went to their web site and read what was there, also viewed the video. There were two ideas mentioned. One was to support the chassis with one jack(or jack stand) then use another jack under the suspension to put it back at ride height. Another idea (easier for the rear) was to remove the springs and let it settle down on the stops to be able to measure at the point of maximum suspension travel.

I just ordered myself one from Summit.

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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Wheels & Tires

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