215/75R20 vs 225/75R20
Going from one to the other changes the overall height by +1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/75R20 | 225/75R20 | Change |
|---|---|---|---|
| Overall height | 32.7" | 33.3" | +1.8 % |
| Sidewall | 6.35" | 6.64" | +4.7 % |
| Section width | 215 mm | 225 mm | +4.7 % |
| Circumference | 102.7" | 104.6" | +1.8 % |
| Revs per mile | 617 | 606 | -1.8 % |
| Axle height | 16.35" | 16.64" | +7.5 mm |
| Approved rim width | 6–8" | 6–8.5" | overlap 6–8" |
Both are approved on a rim 6" to 8" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 215/75R20. Fit 225/75R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.6 mph | +1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,181 on the road, so it under-counts by 181. At a true 70 mph the first turns 720 times a minute, the second 707.