275/35R17 vs 255/40R17
Going from one to the other changes the overall height by +1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/35R17 | 255/40R17 | Change |
|---|---|---|---|
| Overall height | 24.6" | 25.0" | +1.8 % |
| Sidewall | 3.79" | 4.02" | +6.0 % |
| Section width | 275 mm | 255 mm | -7.3 % |
| Circumference | 77.2" | 78.6" | +1.8 % |
| Revs per mile | 821 | 806 | -1.8 % |
| Axle height | 12.29" | 12.52" | +5.8 mm |
| Approved rim width | 7.5–10" | 7–9.5" | overlap 7.5–9.5" |
Both are approved on a rim 7.5" to 9.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 275/35R17. Fit 255/40R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.7 mph | +1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,184 on the road, so it under-counts by 184. At a true 70 mph the first turns 957 times a minute, the second 940.
What drivers reported
Nobody has filed a complaint naming 275/35R17. 255/40R17 carries 3.