235/60R15 vs 245/60R15
Going from one to the other changes the overall height by +1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/60R15 | 245/60R15 | Change |
|---|---|---|---|
| Overall height | 26.1" | 26.6" | +1.8 % |
| Sidewall | 5.55" | 5.79" | +4.3 % |
| Section width | 235 mm | 245 mm | +4.3 % |
| Circumference | 82.0" | 83.5" | +1.8 % |
| Revs per mile | 773 | 759 | -1.8 % |
| Axle height | 13.05" | 13.29" | +6.0 mm |
| Approved rim width | 6.5–8.5" | 7–9" | 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 235/60R15. Fit 245/60R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.6 mph | +1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,181 on the road, so it under-counts by 181. At a true 70 mph the first turns 901 times a minute, the second 885.