235-75-15 = 717 revs per mile at 45mph
31-10.5-15 = 677 revs per mile at 45mph

 

how u do that?!?!?
lol

 

you can go to tire rack... or use a converter and find the overall height then find the circumference, convert to feet and multiply by a mile.

 

also BFG has it on their site for every tire they sell

 

a 235/75 15 tire is 28.9" in diameter

63360 in/mi / Pi*D = 697.85 rev/mile

and for the 31 = 650.58 rev/mile

and the speed doesn't matter

 

That's the theoretical revs/mile. The true revs/mile is usually different because actual computed circumference is not necessarily the same as rolling circumference. Also, most "31-inch" tires are actually a little smaller than the sidewall size designation might imply.

For the most accurate number, it is best to use the measured data from the manufacturer's website. BFG site lists 30.7" diameter and 677 revs/mile for the 31x10.50R15 A/T KO used on the LII and 677 is exactly the number that my LII had in the PCM from the factory.

 

The circumference of a tire is simply the diameter times PI.

A 31" tire has a circumference of 31 * 3.142 = 97.4 inches.

97.4 inches is 8.17 feet more or less. A mile is 5280 feet so the number of revolutions is 5280 / 8.17 = 646. It's not really speed dependent in any great measure though tires do "expand" due to centrifugal force.

You can get more accurate measurements by substituting the exact diameter from manufacturers specs. A 31" tire for example, might only be 30.4 inches in diameter.

As far as metric sizes, I have a shortcut to tire height.

Take the first two numbers of the size and multiply them together. Then divide by 1270. Take that result and add the third number (rim size) and you have diameter.

In your example, a 235-75-15 would be done like this:

(235 * 75) = 17625
17625 / 1270 = 13.88
13.88 + 15 = 28.88 (or about a 29" tire)

I know that seems like a lot, but it's how it's done. I've reduced the method to convert the metric sizes by basically getting rid of all the brough-ha-ha about aspect ratio and metric to english conversion by consolidating the math.

 

thats what i did

 

where did you have it flashed? i need mine done to 631

 

hahahaha I AM SORRY, i wouldnt wish there service dept on my worst enemy, I worked there for several months ya screw that... and have fun with getting money back form Doug that would be a once and a life time....


just FYI if ANYONE goes there for oil changes STOP NOW.. per DOUG they where suppost to put 4.5qt in if it called for 5... and so on.. because the extra would save them money... ya um ya no

 

When i worked at tom holzer we were told to put 5qts MAX in every gasoline engine. Wait a minute....the 3 valve 5.4 takes 7.25......not good