If you didn't understand where 849 revs/mile came from why didn't you ask?

It's no mystery. If you look at any tire at The Tire Rack and click on "specs" the revs/mile and a lot of other data is displayed. The tire manufacturer's web sites also list similar data for every model and size tire they offer.

Don't most guys look at these sites and check out the specs when they are looking to buy tires? I have to assume some basic level of knowledge on the part of other members of this forum.

I assume that most guys can look up specs as easily as I can, and since tires are often discussed it seems that most would know about basic specs such as revs/mile.

If you don't, just ask, and I can explain as I have several times over the years, already - or maybe I'll refer you to the archives.

I find it a little irritating that a guy drags up a six month old post where the question was answered and then gives a bum answer. This happens (bum answers) way too often.

The above applies to "tire calculator" links that are offered up. They use "rigid body" dimensions to calculate revs/mi like you were driving on solid steel "tires" like on a railroad wheel. These calculations will not give accurate results if you are trying to compute revs at a given speed in any gear.

And correct information is only a few clicks away. If your make and model tire is out of production and specs are no longer listed, just look at the specs for a couple of same size tires. The revs/mi and other dimensional data for each size usually vary no more than one percent from high to low even across manufacturers. For each size group there are industry standard dimensions and other characteristics that are promulgated by The Tire and Rim Association, so the basic dimension and revs/mi data is nearly the same for all tires of a given size.

The 849 revs/mile data I quoted is the Michelin spec for the 185/65VR-15 MXV tire that were OE on my car, and other makes/models/speed rating tires that were OE are essentially the same as are replacement tires of the same size.

Another tidbit you may want to file away is that revs per mile increases about 2 percent by the time the tread depth gets down to the wear indicators. If you don't know what those are, The Tire Rack has some good tire tutorial pages that explains tire basics.

Duke