265/60R21 vs 245/60R21
Going from one to the other changes the overall height by -2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/60R21 | 245/60R21 | Change |
|---|---|---|---|
| Overall height | 33.5" | 32.6" | -2.8 % |
| Sidewall | 6.26" | 5.79" | -7.5 % |
| Section width | 265 mm | 245 mm | -7.5 % |
| Circumference | 105.3" | 102.3" | -2.8 % |
| Revs per mile | 602 | 619 | +2.8 % |
| Axle height | 16.76" | 16.29" | -12.0 mm |
| Approved rim width | 7.5–9.5" | 7–9" | overlap 7.5–9" |
Both are approved on a rim 7.5" to 9" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 265/60R21. Fit 245/60R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,718 on the road, so it over-counts by 282. At a true 70 mph the first turns 702 times a minute, the second 722.