265/30R18 vs 245/35R18
Going from one to the other changes the overall height by +2.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/30R18 | 245/35R18 | Change |
|---|---|---|---|
| Overall height | 24.3" | 24.8" | +2.0 % |
| Sidewall | 3.13" | 3.38" | +7.9 % |
| Section width | 265 mm | 245 mm | -7.5 % |
| Circumference | 76.2" | 77.8" | +2.0 % |
| Revs per mile | 831 | 815 | -2.0 % |
| Axle height | 12.13" | 12.38" | +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 265/30R18. Fit 245/35R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.0 mph | +1.0 |
| 70 mph | 71.4 mph | +1.4 |
| 90 mph | 91.8 mph | +1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,203 on the road, so it under-counts by 203. At a true 70 mph the first turns 970 times a minute, the second 951.