235/45R20 vs 225/50R20
Going from one to the other changes the overall height by +1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/45R20 | 225/50R20 | Change |
|---|---|---|---|
| Overall height | 28.3" | 28.9" | +1.9 % |
| Sidewall | 4.16" | 4.43" | +6.4 % |
| Section width | 235 mm | 225 mm | -4.3 % |
| Circumference | 89.0" | 90.7" | +1.9 % |
| Revs per mile | 712 | 699 | -1.9 % |
| Axle height | 14.16" | 14.43" | +6.8 mm |
| Approved rim width | 6.5–8.5" | 6–8.5" | 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 235/45R20. Fit 225/50R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.7 mph | +1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,188 on the road, so it under-counts by 188. At a true 70 mph the first turns 831 times a minute, the second 815.
What drivers reported
235/45R20 carries 2 complaints. Nobody has filed one naming 225/50R20.