235/55R20 vs 215/65R20
Going from one to the other changes the overall height by +2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/55R20 | 215/65R20 | Change |
|---|---|---|---|
| Overall height | 30.2" | 31.0" | +2.7 % |
| Sidewall | 5.09" | 5.50" | +8.1 % |
| Section width | 235 mm | 215 mm | -8.5 % |
| Circumference | 94.8" | 97.4" | +2.7 % |
| Revs per mile | 668 | 651 | -2.7 % |
| Axle height | 15.09" | 15.50" | +10.5 mm |
| Approved rim width | 6.5–8.5" | 6–8" | 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 235/55R20. Fit 215/65R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 71.9 mph | +1.9 |
| 90 mph | 92.5 mph | +2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,274 on the road, so it under-counts by 274. At a true 70 mph the first turns 780 times a minute, the second 759.
What drivers reported
235/55R20 carries 3 complaints. Nobody has filed one naming 215/65R20.