I would like to know how to convert the measurements for tire sizes. For example my truck has 32x11.50r15 BFG's, thats in inches, and is easy to decipher. Now, how do I convert the 285/75r16 to inches? I know that the first number is the diameter, the second is the width, and the last is the rim size. Now, is the 285/75r16 one just in centimeters or something?

 

The first number, 285, is the width ot the thread in milimeters. The second number is the aspect ratio, ie ratio of sidewall height to thread width, so in this case the sidewall height is 75% of 285mm. The last figure is the rim diameter in inches.
To convert mm to inches divide by 25.4

 

Maurice is right on.

So roughly a 285/75R16 is a 33x11.50R16

265/75R16 is a 32/10.50R16

265/70R16 is a 31/10.50R16

 

there are a bunch of calc's on the internet, do a search for metric tire size conversion...that is if you dont want to do the math

 

Or go to www.tirerack.com and select a Light Truck tire (pick one, say BFG AT) click on through to Specs, and look over the chart.

 

Best bet is to look up the spec sheets on the mfg website, as there is considerable leeway in each of those measurements.

 

http://www.csgnetwork.com/tireinfo4calc.html

 

Very true, heck there is huge leeway with standard measurments... My 33 TSL's were as big as some cheap 35's, i have seen 32's shorter that 31's... This is the main reason I run a 35.. I had 33 TSL Bias, didnt want to do bias again, but since its the tallest 33 made ( by over .5") I couldnt buy a "shorter" tire.. :-)

 

Extremely good point to add about manufacturer's specs!