215/50R18 vs 225/45R18
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 | 215/50R18 | 225/45R18 | Change |
|---|---|---|---|
| Overall height | 26.5" | 26.0" | -1.9 % |
| Sidewall | 4.23" | 3.99" | -5.8 % |
| Section width | 215 mm | 225 mm | +4.7 % |
| Circumference | 83.1" | 81.6" | -1.9 % |
| Revs per mile | 762 | 777 | +1.9 % |
| Axle height | 13.23" | 12.99" | -6.3 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 215/50R18. Fit 225/45R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.7 mph | -1.3 |
| 90 mph | 88.3 mph | -1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,814 on the road, so it over-counts by 186. At a true 70 mph the first turns 889 times a minute, the second 906.
What drivers reported
Nobody has filed a complaint naming 215/50R18. 225/45R18 carries 61.