Calculating Tire Size
Junior Member
Joined: Nov 2013
Posts: 9
Likes: 0
I often see people inquiring about metric tire sizes and what they are equivalent to in inches. For those who do not know how to convert a metric tire size to an inch equivalent I wanted to post this. Hopefully you can find it helpful.
Let’s use a common stock tire found on the F150:
275x65x18
275 = width in mm
65 = aspect ratio, this is the side wall height as a percentage of the tires width
18” = rim size in inches
To convert this tire to standard units (inches) use the following steps:
(NOTE: I round to the 100th place)
1. Convert the width in mm to inches: 275/25.4 = 10.83" (25.4 mm = 1 inch)
2. Calculate the sidewall height: 10.83 x .65 = 7.04" (don’t forget the decimal as this is a %)
3. Calculate final tire height: (total sidewall = sidewall x 2) 7.04" x 2 = 14.08". Now add your total sidewall height to your rim size, 14.08"+18" = 32.08"
This means a 275x65x18 is ~32.08x10.83x18
Hope this helps.....
Let’s use a common stock tire found on the F150:
275x65x18
275 = width in mm
65 = aspect ratio, this is the side wall height as a percentage of the tires width
18” = rim size in inches
To convert this tire to standard units (inches) use the following steps:
(NOTE: I round to the 100th place)
1. Convert the width in mm to inches: 275/25.4 = 10.83" (25.4 mm = 1 inch)
2. Calculate the sidewall height: 10.83 x .65 = 7.04" (don’t forget the decimal as this is a %)
3. Calculate final tire height: (total sidewall = sidewall x 2) 7.04" x 2 = 14.08". Now add your total sidewall height to your rim size, 14.08"+18" = 32.08"
This means a 275x65x18 is ~32.08x10.83x18
Hope this helps.....
Junior Member
Joined: Dec 2013
Posts: 1
Likes: 0
Tires
I have a 2005 F150 Lariat 2WD with a 2.5 inch leveling kit on it. I am inquiring about buying new tires. I am unsure of what size will fit. Right now my tires are p275/r18 michelins but I am hoping to get a more aggressive looking tire that is still good for a lot of on road driving. How much bigger of a size do y'all recommend for my situation? Can I go up to 285?
Junior Member
Joined: Aug 2014
Posts: 6
Likes: 0
From: Ohio
Yeah. Those will fit. I have the 17" rim without the leveling kit, and I have 285/70R17s on mine which is basically the same tire/rim height of the 285/65R18s. They don't rub at all either. They're both 32.7" tires. I wouldn't go bigger than that though without leveling the truck, and putting aftermarket rims on it too.
Last edited by EdBurns; Dec 20, 2014 at 01:20 AM.
Member
Joined: Nov 2016
Posts: 14
Likes: 0
I have a 13 supercrew xlt with stock 18s. i am leveling it this week. i want to get 20s and the biggest tire i can get without rubbing. I'm lost on reading rim sizes and need help. if i want the tire to stick out the fenders about an inch what would i need? i really like the moto metal MO970 if that helps