255/75R17 vs 245/80R17
Going from one to the other changes the overall height by +1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/75R17 | 245/80R17 | Change |
|---|---|---|---|
| Overall height | 32.1" | 32.4" | +1.2 % |
| Sidewall | 7.53" | 7.72" | +2.5 % |
| Section width | 255 mm | 245 mm | -3.9 % |
| Circumference | 100.7" | 101.9" | +1.2 % |
| Revs per mile | 629 | 622 | -1.2 % |
| Axle height | 16.03" | 16.22" | +4.8 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 255/75R17. Fit 245/80R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.6 mph | +0.6 |
| 70 mph | 70.8 mph | +0.8 |
| 90 mph | 91.0 mph | +1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,117 on the road, so it under-counts by 117. At a true 70 mph the first turns 734 times a minute, the second 725.
What drivers reported
255/75R17 carries 17 complaints. Nobody has filed one naming 245/80R17.