265/30R21 vs 245/35R21
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 | 265/30R21 | 245/35R21 | Change |
|---|---|---|---|
| Overall height | 27.3" | 27.8" | +1.8 % |
| Sidewall | 3.13" | 3.38" | +7.9 % |
| Section width | 265 mm | 245 mm | -7.5 % |
| Circumference | 85.6" | 87.2" | +1.8 % |
| Revs per mile | 740 | 727 | -1.8 % |
| Axle height | 13.63" | 13.88" | +6.3 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 265/30R21. Fit 245/35R21 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 863 times a minute, the second 848.