225/35R20 vs 215/40R20
Going from one to the other changes the overall height by +2.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/35R20 | 215/40R20 | Change |
|---|---|---|---|
| Overall height | 26.2" | 26.8" | +2.2 % |
| Sidewall | 3.10" | 3.39" | +9.2 % |
| Section width | 225 mm | 215 mm | -4.4 % |
| Circumference | 82.3" | 84.1" | +2.2 % |
| Revs per mile | 770 | 753 | -2.2 % |
| Axle height | 13.10" | 13.39" | +7.3 mm |
| Approved rim width | 6–8.5" | 6–8" | overlap 6–8" |
Both are approved on a rim 6" to 8" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 225/35R20. Fit 215/40R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.1 mph | +1.1 |
| 70 mph | 71.5 mph | +1.5 |
| 90 mph | 92.0 mph | +2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,218 on the road, so it under-counts by 218. At a true 70 mph the first turns 898 times a minute, the second 879.
What drivers reported
225/35R20 carries 2 complaints. Nobody has filed one naming 215/40R20.