275/40R20 vs 275/35R20
Going from one to the other changes the overall height by -3.8 %. That is past the 3% band — expect rubbing, and a speedometer that is properly wrong.
Side by side
| Measure | 275/40R20 | 275/35R20 | Change |
|---|---|---|---|
| Overall height | 28.7" | 27.6" | -3.8 % |
| Sidewall | 4.33" | 3.79" | -12.5 % |
| Section width | 275 mm | 275 mm | 0.0 % |
| Circumference | 90.0" | 86.6" | -3.8 % |
| Revs per mile | 704 | 731 | +3.8 % |
| Axle height | 14.33" | 13.79" | -13.8 mm |
| Approved rim width | 7.5–10" | 7.5–10" | overlap 7.5–10" |
Both are approved on a rim 7.5" to 10" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 275/40R20. Fit 275/35R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 28.9 mph | -1.1 |
| 50 mph | 48.1 mph | -1.9 |
| 70 mph | 67.4 mph | -2.6 |
| 90 mph | 86.6 mph | -3.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,622 on the road, so it over-counts by 378. At a true 70 mph the first turns 821 times a minute, the second 853.
What drivers reported
275/40R20 carries 14 complaints. Nobody has filed one naming 275/35R20.