265/65R17 vs 265/70R17 — sidewall on its own
A Colorado step that isolates the aspect ratio completely, and the cleanest way to see what a profile change is worth.
265/70R17 is 1.04 in taller than 265/65R17 (3.41%) and 0.00 in wider. A speedometer calibrated for 265/65R17 would under-read by 3.41%.
Measured against each other
Overall diameter
30.56 in31.61 in+1.04 in (+3.41%)Section width
10.43 in / 265 mm10.43 in / 265 mm0.00 in (0.00%)Sidewall height
6.78 in7.30 in+0.52 inCircumference
96.0 in99.3 in+3.3 inRevolutions per mile
659.9638.1-21.8Ride height at the axle
——+0.52 inSpeedometer reading
——+3.41% under-read
| Dimension | 265/65R17 | 265/70R17 | Change |
|---|---|---|---|
| Overall diameter | 30.56 in | 31.61 in | +1.04 in (+3.41%) |
| Section width | 10.43 in / 265 mm | 10.43 in / 265 mm | 0.00 in (0.00%) |
| Sidewall height | 6.78 in | 7.30 in | +0.52 in |
| Circumference | 96.0 in | 99.3 in | +3.3 in |
| Revolutions per mile | 659.9 | 638.1 | -21.8 |
| Ride height at the axle | — | — | +0.52 in |
| Speedometer reading | — | — | +3.41% under-read |
Calibrated for 265/65R17, running 265/70R17
- Dial reads 30
- 31.0 mph
- Dial reads 50
- 51.7 mph
- Dial reads 70
- 72.4 mph
- Odometer counts 100
- 103.4 mi covered
Change either size in the comparison tool, or see the full speed table in the speedometer error calculator.
Nothing changes here except the number in the middle of the code. Same width, same wheel, five points of profile.
What five points buys on a 265
The sidewall goes from 6.78 in to 7.30 in — 0.52 in. Five per cent of 265 mm is 13.25 mm, which is 0.52 in, and it is exactly what the code promises.
Doubled, that is 1.04 in of overall diameter: 30.56 in to 31.61 in. The section width stays at 10.43 in in both cases, because nothing in the code touched it.
Why this pairing is worth keeping in mind
Because it is the reference case. Every other comparison on this site mixes a width change into the result, and the two effects then have to be separated by inference. Here there is nothing to separate: 1.04 in of diameter, 0.52 in at the axle, and no change at all in the space the tire occupies laterally.
Anyone trying to build an intuition for tire arithmetic should read this page before any of the two-variable ones.
The consequences
A shade over two miles an hour missing at a dial reading of 60, and nothing else. It comes from a change that adds no width whatsoever — which is a good illustration of how much leverage the aspect ratio has over a figure people attribute to size in general.
What a Colorado owner gets from it
Half an inch of ride height and half an inch more sidewall, with no new demand on the space beside the tire. On a mid-size truck with limited room at the steering stop, that combination is unusually convenient, and it is why the 70-series size is the common first step rather than a wider 65.
Why the 1.04 in is unusually trustworthy
Most upgrade paths change two things at once: the casing gets wider, and how wide it actually measures then depends on the wheel it is stretched over. Here the nominal section is 265 mm on both sides and the wheel diameter is 17 in on both sides, so whatever the rim underneath does to the measured width, it does the same thing twice and drops out of the subtraction.
That is not a statement about which wheels either size is approved for — this site has no rim-width data for any size and does not infer any. It is a statement about the arithmetic: with the width term identical, 1.04 in is about as clean a difference as tire codes produce.
The width-only version
The mirror image of this page is 265/70R17 against 285/70R17 — same aspect ratio, different width — which produces a very similar 1.10 in of diameter by an entirely different mechanism, and adds 0.79 in of casing while doing it.