tyre size for Magnums
#1
NewSorry if this has been covered before. I'm new to the site and still finding my way around. Anyway, I'm restoring a 72 Q code Mach 1 and have purchased some new magnum rims. 15 x 7 for the front and 15 x 8 for the rear. I understand the factory 7" rims had 225/60 15 tires. What i want to know is what is the best size for 7' and 8" rims without getting that balloon tire look. Photos would be great. I'm looking at BFG's to get the retro look. Also what impact will it have on my speedo if i change from the factory 225 tire. Currently running the factory 3.25 posi diff.A110103_confused_prv
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#2
Mr. Pistol, I just put 15x7 and 15x8 on my '73 mach 1, with 235/60 in front and 275/60 on the rear.

[Image: DSC00435.jpg]
[Image: DSC00437.jpg]
[Image: DSC00433.jpg]
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#3
To be perfectly honest. The 225/60 x15 didn't exist back then, We used letters in front of the 60, such as F 60 15 which in all actuallity would be pretty close to the same general size as the 225/60x15, remember tire size flucuates with each manufacturer, So 2 different brands could have the same size on the side of the tire and be very different in actual size! Icon_shrug The next question is width? the old school way is to measure the width of the tread section of the tire and size it approximately 1" wider then the rim it's going on. This wont give you the baloon look and it will keep it from looking to small for the rim. So, you said the fronts were 15x 7. you should need about an 8" tread width. The rears being 15x8 should need about a 9" wide tread section. I would also stay with the 60 series. Do remember that these cars originally had Bias ply tires and looked totally different then the radials of today. but this formula as I stated should produce the look you want and provide excellent wear and traction. Please be assured this is from experience and not some text book. As for the speedo it should be fairly close, it all depends on the tires circumference, (distance around the tread) with out knowing exactly what size was originally on the car and that exact measurement. There is no way to tell for sure. there are places that can recalibrate the speedo, (change the gear in the trans) Most transmission shops can help if you can find one willing to do it. Hope this helps. Just off the top of my head 225/60's up front and 235/60's in the rear. JTS 71 Mach1
"We built these cars to drive the "HELL" out of them, not to be museum pieces!"  Carroll Shelby

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1994 Ford F150 Shortbed
1986 Honda 450 Rebel
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#4
(08-05-2011, 12:55 PM)Jeff Quinn Wrote: Mr. Pistol, I just put 15x7 and 15x8 on my '73 mach 1, with 235/60 in front and 275/60 on the rear.

[Image: DSC00435.jpg]
[Image: DSC00437.jpg]
[Image: DSC00433.jpg]

Looks great. Your tires are so new the still have the blue on the white lettering. You probably already know but soapy steelo pads will bring the white lettering up brilliant. The lettering on BFG's is solid white so you won't wear it off.
(08-05-2011, 01:18 PM)JTS71 Mach1 Wrote: To be perfectly honest. The 225/60 x15 didn't exist back then, We used letters in front of the 60, such as F 60 15 which in all actuallity would be pretty close to the same general size as the 225/60x15, remember tire size flucuates with each manufacturer, So 2 different brands could have the same size on the side of the tire and be very different in actual size! Icon_shrug The next question is width? the old school way is to measure the width of the tread section of the tire and size it approximately 1" wider then the rim it's going on. This wont give you the baloon look and it will keep it from looking to small for the rim. So, you said the fronts were 15x 7. you should need about an 8" tread width. The rears being 15x8 should need about a 9" wide tread section. I would also stay with the 60 series. Do remember that these cars originally had Bias ply tires and looked totally different then the radials of today. but this formula as I stated should produce the look you want and provide excellent wear and traction. Please be assured this is from experience and not some text book. As for the speedo it should be fairly close, it all depends on the tires circumference, (distance around the tread) with out knowing exactly what size was originally on the car and that exact measurement. There is no way to tell for sure. there are places that can recalibrate the speedo, (change the gear in the trans) Most transmission shops can help if you can find one willing to do it. Hope this helps. Just off the top of my head 225/60's up front and 235/60's in the rear. JTS 71 Mach1

Thanks for the well thought out answer. I already have 2 x BFG's 235's in good shape so I think I may use them.
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#5
Thanks for helping out Jeff with the pictures. Your car looks sharp with those new slippers!

Thanks for the facts JTS71 Mach1.
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Southern Arizona
Current Mustangs:
1973 Mach 1

1971 Mustang Grande
1965 Mustang
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