255/35R17 vs 245/40R17
Going from one to the other changes the overall height by +2.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/35R17 | 245/40R17 | Change |
|---|---|---|---|
| Overall height | 24.0" | 24.7" | +2.9 % |
| Sidewall | 3.51" | 3.86" | +9.8 % |
| Section width | 255 mm | 245 mm | -3.9 % |
| Circumference | 75.5" | 77.6" | +2.9 % |
| Revs per mile | 839 | 816 | -2.9 % |
| Axle height | 12.01" | 12.36" | +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 255/35R17. Fit 245/40R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 72.0 mph | +2.0 |
| 90 mph | 92.6 mph | +2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,287 on the road, so it under-counts by 287. At a true 70 mph the first turns 979 times a minute, the second 952.
What drivers reported
Nobody has filed a complaint naming 255/35R17. 245/40R17 carries 6.