245/50R18 vs 225/50R18
Going from one to the other changes the overall height by -2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/50R18 | 225/50R18 | Change |
|---|---|---|---|
| Overall height | 27.6" | 26.9" | -2.8 % |
| Sidewall | 4.82" | 4.43" | -8.2 % |
| Section width | 245 mm | 225 mm | -8.2 % |
| Circumference | 86.9" | 84.4" | -2.8 % |
| Revs per mile | 730 | 751 | +2.8 % |
| Axle height | 13.82" | 13.43" | -10.0 mm |
| Approved rim width | 7–9" | 6–8.5" | overlap 7–8.5" |
Both are approved on a rim 7" 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 245/50R18. Fit 225/50R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.4 mph | -2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,715 on the road, so it over-counts by 285. At a true 70 mph the first turns 851 times a minute, the second 876.
What drivers reported
Nobody has filed a complaint naming 245/50R18. 225/50R18 carries 15.