225/60R17 vs 245/65R17 — a truck-sized step on a car-based platform
The all-terrain size Foresters end up on, and the largest jump anything car-derived in this set makes.
245/65R17 is 1.91 in taller than 225/60R17 (6.91%) and 0.79 in wider. A speedometer calibrated for 225/60R17 would under-read by 6.91%.
Measured against each other
Overall diameter
27.63 in29.54 in+1.91 in (+6.91%)Section width
8.86 in / 225 mm9.65 in / 245 mm+0.79 in (+8.89%)Sidewall height
5.31 in6.27 in+0.95 inCircumference
86.8 in92.8 in+6.0 inRevolutions per mile
729.9682.8-47.2Ride height at the axle
——+0.95 inSpeedometer reading
——+6.91% under-read
| Dimension | 225/60R17 | 245/65R17 | Change |
|---|---|---|---|
| Overall diameter | 27.63 in | 29.54 in | +1.91 in (+6.91%) |
| Section width | 8.86 in / 225 mm | 9.65 in / 245 mm | +0.79 in (+8.89%) |
| Sidewall height | 5.31 in | 6.27 in | +0.95 in |
| Circumference | 86.8 in | 92.8 in | +6.0 in |
| Revolutions per mile | 729.9 | 682.8 | -47.2 |
| Ride height at the axle | — | — | +0.95 in |
| Speedometer reading | — | — | +6.91% under-read |
Calibrated for 225/60R17, running 245/65R17
- Dial reads 30
- 32.1 mph
- Dial reads 50
- 53.5 mph
- Dial reads 70
- 74.8 mph
- Odometer counts 100
- 106.9 mi covered
Change either size in the comparison tool, or see the full speed table in the speedometer error calculator.
Nearly two inches of extra diameter on a unibody crossover is a big number, and it arrives from two changes that look small written down.
Two variables, compounding
- 225 mm to 245 mm: 0.79 in more section width
- 60-series to 65-series: the sidewall becomes a larger fraction of a larger casing
Sidewall height goes from 5.31 in to 6.27 in — nearly an inch — and it counts twice. Hence 1.91 in of diameter from what reads on paper like a modest specification change.
6.91% is a real number, and it cannot be corrected here
Seven per cent is visible against a phone's GPS on any journey. Over the twelve thousand indicated miles a family crossover covers in a typical year, 12,829 have actually gone under the wheels — and the service intervals, the lease allowance and the resale mileage are all counting the smaller number.
There is no remedy available on this kind of vehicle. Restoring the original engine speed at a given road speed from a 3.73:1 final drive would take 3.99:1, but almost nothing car-derived has a serviceable ring and pinion, so the error is carried rather than corrected.
Where the other half of the diameter goes
Half of the 1.91 in ends up under the axle. The other half goes upward, into whatever gap sits above the tread and below the arch liner — which on a car-derived platform is exactly where there is least of it.
Width is the smaller proportional change at 8.89% but it is the one that meets the strut and the liner at full lock. On this class of vehicle, that is usually the constraint people actually find.
Compared with the cautious option
The alternative is 225/60R17 to 235/60R17, which is 0.47 in and 1.71% — roughly a quarter of the change described here. There is nothing stocked between the two, so the decision is genuinely binary rather than a matter of degree.
What is not answered above
Whether the assembly clears at full lock and full compression on a lifted or unlifted car, and whether the tire you are looking at carries the rating the placard asks for. Both belong to a particular vehicle and a particular product rather than to a size code.