285/40R21 vs 265/45R21
Going from one to the other changes the overall height by +1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/40R21 | 265/45R21 | Change |
|---|---|---|---|
| Overall height | 30.0" | 30.4" | +1.4 % |
| Sidewall | 4.49" | 4.69" | +4.6 % |
| Section width | 285 mm | 265 mm | -7.0 % |
| Circumference | 94.2" | 95.5" | +1.4 % |
| Revs per mile | 673 | 664 | -1.4 % |
| Axle height | 14.99" | 15.19" | +5.3 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 285/40R21. Fit 265/45R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 71.0 mph | +1.0 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,138 on the road, so it under-counts by 138. At a true 70 mph the first turns 785 times a minute, the second 774.
What drivers reported
Nobody has filed a complaint naming 285/40R21. 265/45R21 carries 2.