265/35R17 vs 285/30R17
Going from one to the other changes the overall height by -2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/35R17 | 285/30R17 | Change |
|---|---|---|---|
| Overall height | 24.3" | 23.7" | -2.3 % |
| Sidewall | 3.65" | 3.37" | -7.8 % |
| Section width | 265 mm | 285 mm | +7.5 % |
| Circumference | 76.4" | 74.6" | -2.3 % |
| Revs per mile | 830 | 850 | +2.3 % |
| Axle height | 12.15" | 11.87" | -7.3 mm |
| Approved rim width | 7.5–9.5" | 8–10.5" | overlap 8–9.5" |
Both are approved on a rim 8" 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 265/35R17. Fit 285/30R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.8 mph | -1.2 |
| 70 mph | 68.4 mph | -1.6 |
| 90 mph | 87.9 mph | -2.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,765 on the road, so it over-counts by 235. At a true 70 mph the first turns 968 times a minute, the second 991.