245/35R15 vs 265/30R15
Going from one to the other changes the overall height by -2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/35R15 | 265/30R15 | Change |
|---|---|---|---|
| Overall height | 21.8" | 21.3" | -2.3 % |
| Sidewall | 3.38" | 3.13" | -7.3 % |
| Section width | 245 mm | 265 mm | +8.2 % |
| Circumference | 68.3" | 66.8" | -2.3 % |
| Revs per mile | 927 | 949 | +2.3 % |
| Axle height | 10.88" | 10.63" | -6.3 mm |
| Approved rim width | 7–9" | 7.5–9.5" | 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 245/35R15. Fit 265/30R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.9 mph | -1.1 |
| 70 mph | 68.4 mph | -1.6 |
| 90 mph | 88.0 mph | -2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,774 on the road, so it over-counts by 226. At a true 70 mph the first turns 1082 times a minute, the second 1107.