What size tires do you really have?
- Thread starter bobthetj03
- Start date
Real versus stated tire size has been used by folks forever to try and cheat the requirements of axles and lift heights forever. At the end of the day it is pretty simple. 37's are bigger than 35''s which are bigger than 33's which are bigger than 31's. I've had 20 folks try to get me to sign off on a build with the wrong crap on it using the logic that they are going to run X brand in a 37 because it runs smaller than what the sidewall says. Sorry, that isn't how it works in real life. If I build it for 35's, it won't work for 37's. If I build it for 37's, it won't work for 40's.
That and the only way to measure a tire unless you're trying to decide on gearing is horizontally.
That and the only way to measure a tire unless you're trying to decide on gearing is horizontally.
sgtjdgelinas
TJ Enthusiast
egclassic
TJ Enthusiast
I don't take credit (or responsibility for this) but I found this article explaining how to "read" tire sizes:
"Let's use 285/70R17 as an example.
285 is the section width. It's the width of the tire in millimeters.
70 is the aspect ratio. It indicates the height of the sidewall in relation to the section width. An aspect ratio of 70 means that the sidewall's height is 70% of the section width.
17 is the rim diameter in inches. The R simply means that the tire is a radial tire, which is what you want.
So, to find the overall diameter of a tire we have to do a little converting.
Overall Diameter = [(Section Width/25.4) x .Aspect Ratio x 2] + Rim Diameter
First, you convert the section width to inches by dividing by 25.4, because there are exactly 25.4 millimeters in 1 inch.
285 / 25.4 = 11.22 in.
So, the tire is 11.22 inches wide. Now we multiply by the aspect ratio to find how tall the sidewalls are.
11.22 x .70 = 7.85 in.
Since we have two sidewalls, we have to multiply by 2.
7.85 x 2 = 15.7 in.
Then add the diameter of the rim.
15.7 + 17 = 32.7 in.
So the overall diameter of a 285/70R17 tire is approximately 32.7 inches (without the weight of the vehicle sitting on it)."
"Let's use 285/70R17 as an example.
285 is the section width. It's the width of the tire in millimeters.
70 is the aspect ratio. It indicates the height of the sidewall in relation to the section width. An aspect ratio of 70 means that the sidewall's height is 70% of the section width.
17 is the rim diameter in inches. The R simply means that the tire is a radial tire, which is what you want.
So, to find the overall diameter of a tire we have to do a little converting.
Overall Diameter = [(Section Width/25.4) x .Aspect Ratio x 2] + Rim Diameter
First, you convert the section width to inches by dividing by 25.4, because there are exactly 25.4 millimeters in 1 inch.
285 / 25.4 = 11.22 in.
So, the tire is 11.22 inches wide. Now we multiply by the aspect ratio to find how tall the sidewalls are.
11.22 x .70 = 7.85 in.
Since we have two sidewalls, we have to multiply by 2.
7.85 x 2 = 15.7 in.
Then add the diameter of the rim.
15.7 + 17 = 32.7 in.
So the overall diameter of a 285/70R17 tire is approximately 32.7 inches (without the weight of the vehicle sitting on it)."
BendLarry
TJ Addict
egclassic
TJ Enthusiast
I use a tape measure, no math needed...
Glad that works for you!
But this was meant for someone who is considering different tires, not already on the vehicle, to decipher the metric sizing.
Kinda hard to use a tape measure on something you don't physically have, that is all.