255/55R17 vs 245/60R17
Going from one to the other changes the overall height by +1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/55R17 | 245/60R17 | Change |
|---|---|---|---|
| Overall height | 28.0" | 28.6" | +1.9 % |
| Sidewall | 5.52" | 5.79" | +4.8 % |
| Section width | 255 mm | 245 mm | -3.9 % |
| Circumference | 88.1" | 89.8" | +1.9 % |
| Revs per mile | 719 | 706 | -1.9 % |
| Axle height | 14.02" | 14.29" | +6.8 mm |
| Approved rim width | 7–9.5" | 7–9" | overlap 7–9" |
Both are approved on a rim 7" to 9" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 255/55R17. Fit 245/60R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.7 mph | +1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,190 on the road, so it under-counts by 190. At a true 70 mph the first turns 839 times a minute, the second 823.