Correct Tire Size
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Senior User
Joined: Jan 2009
Posts: 134
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From: Nor Cal
Correct Tire Size
My tires are getting pretty worn on the back and I'm not sure what size tires these trucks are supposed to run. Right now I have 275/60R15 on the rear and 255/60R15 in the front. The fronts are still in really good shape, so I was thinking of putting some new 255/60's on the rear. However, I'm hesitant to do that because I know that the 275/60's that I have on the rear are a taller tire. My truck is 1973 F100, 2WD, 390, 3-Spd manual, w/ 9" rear. I'm not sure what the gearing is in the rear.
1. Will it hurt to go with the 255's?
2. What is the original size tire that came on these trucks?
1. Will it hurt to go with the 255's?
2. What is the original size tire that came on these trucks?
Laughing Gas
Joined: Apr 2001
Posts: 868
Likes: 3
From: New Glasgow, Nova Scotia
Most came with a 235/75 15, a 275/65 will give you the same height tire, just wider. The 255 will be shorter and effect the speedo.
Here the tire size formula. widthXsidewall percent gives sidewall height.
275/65 X15 works like this
275mmX0.75 equals 178mm tall sidewall
Original
235/75X15 equals 176mm tall sidewall, 2mm is not noticable.
Go with the 275, they look great on the rears.
Here the tire size formula. widthXsidewall percent gives sidewall height.
275/65 X15 works like this
275mmX0.75 equals 178mm tall sidewall
Original
235/75X15 equals 176mm tall sidewall, 2mm is not noticable.
Go with the 275, they look great on the rears.
Certified Thread Hijacker
Joined: Aug 2001
Posts: 14,441
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275/60-15 = 27.99"
255/60-15 = 27.04"
Now that is theoritical height, measured height on the truck is always slightly less. In reality going to the smaller tire will raise the cruise RPM about 100.
Josh
255/60-15 = 27.04"
Now that is theoritical height, measured height on the truck is always slightly less. In reality going to the smaller tire will raise the cruise RPM about 100.
Josh
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
If I remember correctly, original equipment tire size should be on the White lable below the driver door striker bolt.
Most of these earlier trucks came with a SAE tire size.
When the industry switched to metric, the original SAE size, was converted to the nearest metric equivelent.
235/75/R15 is a metric tire size.
Most of these earlier trucks came with a SAE tire size.
When the industry switched to metric, the original SAE size, was converted to the nearest metric equivelent.
235/75/R15 is a metric tire size.
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