245/50R18 vs 235/50R18
Going from one to the other changes the overall height by -1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/50R18 | 235/50R18 | Change |
|---|---|---|---|
| Overall height | 27.6" | 27.3" | -1.4 % |
| Sidewall | 4.82" | 4.63" | -4.1 % |
| Section width | 245 mm | 235 mm | -4.1 % |
| Circumference | 86.9" | 85.6" | -1.4 % |
| Revs per mile | 730 | 740 | +1.4 % |
| Axle height | 13.82" | 13.63" | -5.0 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 245/50R18. Fit 235/50R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.3 mph | -0.7 |
| 70 mph | 69.0 mph | -1.0 |
| 90 mph | 88.7 mph | -1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,858 on the road, so it over-counts by 142. At a true 70 mph the first turns 851 times a minute, the second 863.
What drivers reported
Nobody has filed a complaint naming 245/50R18. 235/50R18 carries 25.