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Largest Rear Tires I Can run on the Rear

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Hey guys, i'm new to this site and I was wondering if some of you could answer a question I have been debating about. I've got a 69 factory mach 1 car with a set of factory replacement springs from mustangs unlimited and I am wanting to run the largest tire possible on the rear with out any fender rolling issues or cutting. I am thinking of going with 15x8 magnum 500s (which I believe has a 4.5in backspace) on the rear and maybe a bfg 255/60/15. Do any of you guys know if i can go any wider?

Thanks,

Drew

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I have 17X9 on the rear, with 285/40/17 tires, and no rub issue. The wheels have a 5.5" backspace. I know there are guys here with larger tires, and wider wheels. It all depends on your budget, and the look you want.

 

You will be limited to the size rear tire you want to run with the Magnum 500s, simply because the wheels don't have any/many optional offsets available.

 

 

Oh! And welcome to the site!!

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I am in the same boat as you. I have been reaserching the same issue. It seems that you should be able to run the Magnum 15 x 8 rim, 4.5"bs, with the 255/60/15 BFG in the rear without rubbing pending rear spring condition. Some have run the 275/60/15 without rubbing but some do rub. I am having my car painted in the summer so Im gonna have them roll the fenders and run the 275/60. When you are ready it seems Summitt has the best price going with mounting included. I like the fact when they show up at the door all you have to do is put em on.

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Do you have rear sway bar? It may limit you. Mine did on my 70 Mach. I am still fitting tire sizes but am targeting 315/35-17 on 11" wide wheels. Check your backspace and check the spec on the tire width before you buy. You can get some variation in width from tire maker to tire maker. I would bet for your 255 you will be fine.

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Mine is a 15X8 5.5 bs with a 275/60/15 on it. I think a 4.5 BS would rub the fender because mine rubbed on great big bumps, until I installed Caltracs. They seem the keep the rear located better, and they don't rub anymore.

Edited by sportsroof69

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thanks for all the info! no my car does not have a rear sway bar even though I think one would be a good idea. I also wish I would have seen that other thread earlier. I believe I am going to go with 15x7 with 235/60/15 in the front and 15x8 with 255/60/15 in the rear. I would go bigger in the rear I would go bigger in the rear but i just replaced the whole right rear quarter panel from the top of the roof down! Inner outer fender and all! Took a ton of time and i just got it painted 2 weeks ago so i think it would hurt my feelings a little to much to roll that lip of the rear fender under.

Thanks again for all the input guys!

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I currently am looking into a custom sizes myself. My current wheels (Shelby Cal 500 14"x  7) are 4.5" offset with 3.3/8"back space on the front and have a nice profile. The backs are the same and just touch the inner lip with a passenger in the rear. So I called Wheel Vintiques for same offset for their Magnum 500's 15x8 front and the rears at 4.00" to 4.25" offset 15x10. They charge $50.00 per wheel for the mods though.

 

 

 

 

 

 

 

 

v

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I am running 255/40/18s, with no issue.   I am using 18x9.5" Foose Knuckle Wheels with a 5.5" backspace.  I cut the axle bumper brackets off of the inner fender, and had the fender well edges rolled.  I have at least 1 inch clearance left.

 

 

B984900C-9D45-40BB-981C-E9EBB3D55FC7.thumb.jpeg.1c840b6a0bfb031b49ee3a6a13eae8df.jpg

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This is how my 4.5" positive offset, 3 3/8" back space looks. 

I'm going to pull all the wheels and use a L square ruler to figure max offset with rim width to tire specs off the net. 

The specs for these cars really focus on back space mostly which for me is half the info.

IMG_0813.JPG

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I'm running a 275/40/18 in the rear.

Wheels are Rambler U111's and are 18x9.5.

I do however have a 66 length rear end in the car LOL.

My best friends 69 was running Mickey Thompson 275/60/15's on Mag 500s with no fender roll, but on really big bumps the tire would rub.

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