215/55R21 vs 235/50R21
Going from one to the other changes the overall height by -0.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/55R21 | 235/50R21 | Change |
|---|---|---|---|
| Overall height | 30.3" | 30.3" | -0.2 % |
| Sidewall | 4.66" | 4.63" | -0.6 % |
| Section width | 215 mm | 235 mm | +9.3 % |
| Circumference | 95.2" | 95.0" | -0.2 % |
| Revs per mile | 665 | 667 | +0.2 % |
| Axle height | 15.16" | 15.13" | -0.8 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 215/55R21. Fit 235/50R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.9 mph | -0.1 |
| 50 mph | 49.9 mph | -0.1 |
| 70 mph | 69.9 mph | -0.1 |
| 90 mph | 89.8 mph | -0.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,981 on the road, so it over-counts by 19. At a true 70 mph the first turns 776 times a minute, the second 778.