why do people use different #s on tire sizes? for example

265 70 17 i know fiest is how wide, second tall, and third is rim

and 31"" tires or what ever.

and how can you tell exactly what size a 31" - 38" tire is in the 295 85 17 way?

if that makes any sence.

can some one please explain the mathmatical portion of the problem? thanks mike

 

metric sizes are designated as

width in millimeters & aspect ratio (as a % of width) & rim diameter

inch sizes are designated as

diameter of tire (height) & width of tire & rim diameter


They are related by math as follows:

1. to obtain the width of an inch tire in mm (metric)

width in inches * 25.4

2. to obtain the aspect ratio of the corresponding metric tire size from an inch sized tire

aspect ratio = (inch height - rim diameter) / [ 2 * (width in inches ) ]

3. The rim is measued in inches in almost every case for both metric and inch sized tire designations.


LT31x10.50R16 is about an LT265/70R16
LT33x12.50R16 is about an LT315/70R16 (I think most are called an LT305/70R16)
LT35x12.50R16 is about an LT315/75R16
LT38x15.50R15 is about an LT390/75R15