How many revolutions per mile is 265/70R17?
Answer
638.1 revolutions per mile
265/70R17 has a circumference of 99.3 in. A mile is 63,360 inches, so it turns 638.1 times to cover one — a geometric figure, computed from the size code rather than measured on a rolling road.
The working
- Revolutions per mile
- 638.1
- Revolutions per kilometre
- 396.5
- Circumference
- 99.3 in
- Overall diameter
- 31.61 in
The baseline almost everything else is measured against
638.1 turns per mile. This figure recurs more than any other in the arithmetic on this site, for a dull but decisive reason: it is the count a very large number of 17-inch trucks were calibrated around before anything was changed. Every "how much error will I get" answer for such a truck is a ratio between 638.1 and whatever went on instead.
The comparisons, worked
- To a 33x12.50R17 at 611.2 — 26.9 fewer rotations per mile, which is 4.41%.
- To a 285/70R17 at 616.6 — 21.5 fewer, 3.49%.
- To a 35x12.50R17 at 576.2 — 61.9 fewer, 10.74%.
Each percentage is simultaneously the speedometer error, the odometer error and the multiplier on the axle ratio required to undo the change. One number, three consequences.
A high count means a small tire
638.1 is a large figure next to a 35's 576.2 and a small one next to a 195/65R15's 807.4. It moves inversely with diameter, which is worth holding on to when reading a specification sheet: the tire with the bigger rotation count is the smaller tire, every time, and a rotation count is often the only dimension a control module ever sees.
The circumference behind it
99.3 in. That is the distance this tire covers in one unhurried turn, and 638.1 of them fit inside a mile. A 265/75R16 comes out at 637.2 — nine-tenths of a rotation away, on a wheel an inch smaller — which is a useful reminder that the count belongs to the tire's overall height and not to anything printed before the slash.
Geometric, not measured
The figure comes from the circumference the size code implies, not from rolling a tire on a drum. A manufacturer's published count for a real 265/70R17 will read a little higher, because a loaded tire deflects and covers marginally less ground per turn than its free radius suggests. Use the geometric number for comparisons between sizes, which is what it is good at, and a measured number when one is available for the specific tire. Load two sizes here to see the count and the percentage together.