245/40R17 vs 255/35R17
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 | 245/40R17 | 255/35R17 | Change |
|---|---|---|---|
| Overall height | 24.7" | 24.0" | -2.8 % |
| Sidewall | 3.86" | 3.51" | -8.9 % |
| Section width | 245 mm | 255 mm | +4.1 % |
| Circumference | 77.6" | 75.5" | -2.8 % |
| Revs per mile | 816 | 839 | +2.8 % |
| Axle height | 12.36" | 12.01" | -8.8 mm |
| Approved rim width | 7–9" | 7–9.5" | 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 245/40R17. Fit 255/35R17 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 9,721 on the road, so it over-counts by 279. At a true 70 mph the first turns 952 times a minute, the second 979.
What drivers reported
245/40R17 carries 6 complaints. Nobody has filed one naming 255/35R17.