225/65R17 vs 235/65R17 — smaller than a set of tires wears

One width increment shared by two of the best-selling crossovers in North America, and a useful yardstick for what "small" means.

Drawn to scale from the size codes. Solid outline is 225/65R17; dashed outline is 235/65R17. The bars below each tire are section width at the same scale.

235/65R17 is 0.51 in taller than 225/65R17 (1.79%) and 0.39 in wider. A speedometer calibrated for 225/65R17 would under-read by 1.79%.

Measured against each other

Overall diameter
28.52 in29.03 in+0.51 in (+1.79%)
Section width
8.86 in / 225 mm9.25 in / 235 mm+0.39 in (+4.44%)
Sidewall height
5.76 in6.01 in+0.26 in
Circumference
89.6 in91.2 in+1.6 in
Revolutions per mile
707.3694.8-12.5
Ride height at the axle
——+0.26 in
Speedometer reading
——+1.79% under-read

Dimension	225/65R17	235/65R17	Change
Overall diameter	28.52 in	29.03 in	+0.51 in (+1.79%)
Section width	8.86 in / 225 mm	9.25 in / 235 mm	+0.39 in (+4.44%)
Sidewall height	5.76 in	6.01 in	+0.26 in
Circumference	89.6 in	91.2 in	+1.6 in
Revolutions per mile	707.3	694.8	-12.5
Ride height at the axle	—	—	+0.26 in
Speedometer reading	—	—	+1.79% under-read

Calibrated for 225/65R17, running 235/65R17

Dial reads 30: 30.5 mph
Dial reads 50: 50.9 mph
Dial reads 70: 71.3 mph
Odometer counts 100: 101.8 mi covered

Change either size in the comparison tool, or see the full speed table in the speedometer error calculator.

Here is the most useful way to judge a change this size: compare it not against zero, but against the diameter your existing tires will lose before you replace them.

The yardstick

A tire worn from full tread depth to its wear indicators loses roughly a third of an inch of diameter — a little over 10/32 in of tread, doubled top and bottom. This swap adds 0.51 in.

So the difference between these two sizes is of the same order as the difference between your tires new and your tires worn out, a change every vehicle undergoes twice a decade with nobody recalibrating anything. That is the correct frame for a 1.79% figure.

The numbers themselves

Section width rises 0.39 in, from 8.86 in to 9.25 in. Sidewall rises 0.26 in, because 65% of a larger casing is taller. Diameter rises 0.51 in, and the axle centre with it by 0.26 in.

The speedometer reads 1.79% low afterwards. In round terms: eighteen unrecorded miles in every thousand the odometer counts, and a shade over one mile an hour missing at motorway pace.

One pairing, two very different vehicles

Both sizes are original fitments on the sixth-generation Outback and on the fifth-generation RAV4, which between them account for an enormous number of vehicles on North American roads. The arithmetic does not care which of the two is underneath it — the tires are the same tires — and this is the reason the comparison earns a page rather than two.

Why an owner asks

Usually because the tire they want exists in one size and not the other, or because a fitment guide lists both and they want to know whether choosing the wider one has a cost. It does not have a meaningful one, which is a legitimate finding and worth stating plainly rather than dressed up.

Where the step stops being trivial

Go 20 mm instead of 10 and the same aspect ratio produces 1.02 in rather than 0.51 — exactly double, because the relationship is linear. That one crosses into territory where the speedometer error is measurable against a GPS.