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SupaPursuit

Member
Joined
Jan 17, 2020
Messages
9
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7
Location
Canberra Australia
My Car
1971 Grabber Yellow 351 BOSS
Hello All,

Need some guidance. I believe backspace on early Mustang Rims need to be 4" does this apply to 71-73? It seems most rims for early Mustangs now have 4.5".

Will a 9.5" rim fit under the rear of a Fastback or best to stick with 8"?

All assistance greatly appreciated.

Regards

 
The backspace on the rims is dependent on the rim width. For the most part the stock rims have zero offset, which means the backspacing is one-half of the rim width.

For our cars a good rule-of-thumb for backspacing is 1/2 the wheel width plus 1/2". Others have used wheels that wide on our cars, you should be able to find out the specifics by searching the forum, but 5" to 5-1/2" backspacing should work.

You can use the spreadsheet in this thread to estimate the clearances of various wheel sizes (clearance tab)

Tire Sizes - Suspension, Handling, Brakes, Wheels and Tires - 7173Mustangs.com

 
A 10” wide rim with 5 1/2” backspacing will work 

 
Then, you have to take into consideration the width of the tire you plan on using. It's the tire that will hit the springs or inner or outer fenders.

 
Last edited by a moderator:
Make sure your look at the tires Aspect Ratio. This will determine ride quality and harshness.

Ride comfort is a function of spring and dampening, and that can come from the tire, the springs, a shock, or any combination of the three. A car riding on lower profile tires will have less sidewall-flex capacity to absorb bumps, and will either require softer springs to accomplish the same results, or be bumpier.

 
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