285/35R18 vs 265/40R18
Going from one to the other changes the overall height by +1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/35R18 | 265/40R18 | Change |
|---|---|---|---|
| Overall height | 25.9" | 26.3" | +1.9 % |
| Sidewall | 3.93" | 4.17" | +6.3 % |
| Section width | 285 mm | 265 mm | -7.0 % |
| Circumference | 81.2" | 82.8" | +1.9 % |
| Revs per mile | 780 | 765 | -1.9 % |
| Axle height | 12.93" | 13.17" | +6.3 mm |
| Approved rim width | 8–10.5" | 7.5–9.5" | 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 285/35R18. Fit 265/40R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.0 mph | +1.0 |
| 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 10,190 on the road, so it under-counts by 190. At a true 70 mph the first turns 910 times a minute, the second 893.
What drivers reported
Nobody has filed a complaint naming 285/35R18. 265/40R18 carries 1.