255/60R17 vs 235/65R17
Going from one to the other changes the overall height by -0.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/60R17 | 235/65R17 | Change |
|---|---|---|---|
| Overall height | 29.0" | 29.0" | -0.1 % |
| Sidewall | 6.02" | 6.01" | -0.2 % |
| Section width | 255 mm | 235 mm | -7.8 % |
| Circumference | 91.3" | 91.2" | -0.1 % |
| Revs per mile | 694 | 695 | +0.1 % |
| Axle height | 14.52" | 14.51" | -0.3 mm |
| Approved rim width | 7–9.5" | 6.5–8.5" | overlap 7–8.5" |
Both are approved on a rim 7" to 8.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 255/60R17. Fit 235/65R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.0 mph | -0.0 |
| 50 mph | 50.0 mph | -0.0 |
| 70 mph | 70.0 mph | -0.0 |
| 90 mph | 89.9 mph | -0.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,993 on the road, so it over-counts by 7. At a true 70 mph the first turns 810 times a minute, the second 811.