215/70R21 vs 235/65R21
Going from one to the other changes the overall height by +0.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/70R21 | 235/65R21 | Change |
|---|---|---|---|
| Overall height | 32.9" | 33.0" | +0.5 % |
| Sidewall | 5.93" | 6.01" | +1.5 % |
| Section width | 215 mm | 235 mm | +9.3 % |
| Circumference | 103.2" | 103.8" | +0.5 % |
| Revs per mile | 614 | 611 | -0.5 % |
| Axle height | 16.43" | 16.51" | +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 215/70R21. Fit 235/65R21 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 10,054 on the road, so it under-counts by 54. At a true 70 mph the first turns 716 times a minute, the second 712.