245/45R18 vs 235/50R18
Going from one to the other changes the overall height by +2.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/45R18 | 235/50R18 | Change |
|---|---|---|---|
| Overall height | 26.7" | 27.3" | +2.1 % |
| Sidewall | 4.34" | 4.63" | +6.6 % |
| Section width | 245 mm | 235 mm | -4.1 % |
| Circumference | 83.8" | 85.6" | +2.1 % |
| Revs per mile | 756 | 740 | -2.1 % |
| Axle height | 13.34" | 13.63" | +7.3 mm |
| Approved rim width | 7–9" | 6.5–8.5" | 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 245/45R18. Fit 235/50R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.1 mph | +1.1 |
| 70 mph | 71.5 mph | +1.5 |
| 90 mph | 91.9 mph | +1.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,214 on the road, so it under-counts by 214. At a true 70 mph the first turns 882 times a minute, the second 863.