225/50R21 vs 235/50R21
Going from one to the other changes the overall height by +1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/50R21 | 235/50R21 | Change |
|---|---|---|---|
| Overall height | 29.9" | 30.3" | +1.3 % |
| Sidewall | 4.43" | 4.63" | +4.4 % |
| Section width | 225 mm | 235 mm | +4.4 % |
| Circumference | 93.8" | 95.0" | +1.3 % |
| Revs per mile | 675 | 667 | -1.3 % |
| Axle height | 14.93" | 15.13" | +5.0 mm |
| Approved rim width | 6–8.5" | 6.5–8.5" | overlap 6.5–8.5" |
Both are approved on a rim 6.5" to 8.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 225/50R21. Fit 235/50R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 70.9 mph | +0.9 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,132 on the road, so it under-counts by 132. At a true 70 mph the first turns 788 times a minute, the second 778.