255/35R16 vs 245/40R16
Going from one to the other changes the overall height by +3.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/35R16 | 245/40R16 | Change |
|---|---|---|---|
| Overall height | 23.0" | 23.7" | +3.0 % |
| Sidewall | 3.51" | 3.86" | +9.8 % |
| Section width | 255 mm | 245 mm | -3.9 % |
| Circumference | 72.3" | 74.5" | +3.0 % |
| Revs per mile | 876 | 850 | -3.0 % |
| Axle height | 11.51" | 11.86" | +8.8 mm |
| Approved rim width | 7–9.5" | 7–9" | overlap 7–9" |
Both are approved on a rim 7" to 9" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 255/35R16. Fit 245/40R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.5 mph | +1.5 |
| 70 mph | 72.1 mph | +2.1 |
| 90 mph | 92.7 mph | +2.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,299 on the road, so it under-counts by 299. At a true 70 mph the first turns 1022 times a minute, the second 992.