215/70R20 vs 235/65R20
Going from one to the other changes the overall height by +0.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/70R20 | 235/65R20 | Change |
|---|---|---|---|
| Overall height | 31.9" | 32.0" | +0.6 % |
| Sidewall | 5.93" | 6.01" | +1.5 % |
| Section width | 215 mm | 235 mm | +9.3 % |
| Circumference | 100.1" | 100.6" | +0.6 % |
| Revs per mile | 633 | 630 | -0.6 % |
| Axle height | 15.93" | 16.01" | +2.3 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 215/70R20. Fit 235/65R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.3 mph | +0.3 |
| 70 mph | 70.4 mph | +0.4 |
| 90 mph | 90.5 mph | +0.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,056 on the road, so it under-counts by 56. At a true 70 mph the first turns 739 times a minute, the second 735.