215/40R20 vs 235/40R20
Going from one to the other changes the overall height by +2.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/40R20 | 235/40R20 | Change |
|---|---|---|---|
| Overall height | 26.8" | 27.4" | +2.4 % |
| Sidewall | 3.39" | 3.70" | +9.3 % |
| Section width | 215 mm | 235 mm | +9.3 % |
| Circumference | 84.1" | 86.1" | +2.4 % |
| Revs per mile | 753 | 736 | -2.4 % |
| Axle height | 13.39" | 13.70" | +8.0 mm |
| Approved rim width | 6–8" | 6.5–8.5" | overlap 6.5–8" |
Both are approved on a rim 6.5" to 8" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 215/40R20. Fit 235/40R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.2 mph | +1.2 |
| 70 mph | 71.6 mph | +1.6 |
| 90 mph | 92.1 mph | +2.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,235 on the road, so it under-counts by 235. At a true 70 mph the first turns 879 times a minute, the second 859.