225/40R18 vs 245/35R18
Going from one to the other changes the overall height by -1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/40R18 | 245/35R18 | Change |
|---|---|---|---|
| Overall height | 25.1" | 24.8" | -1.3 % |
| Sidewall | 3.54" | 3.38" | -4.7 % |
| Section width | 225 mm | 245 mm | +8.9 % |
| Circumference | 78.8" | 77.8" | -1.3 % |
| Revs per mile | 804 | 815 | +1.3 % |
| Axle height | 12.54" | 12.38" | -4.3 mm |
| Approved rim width | 6–8.5" | 7–9" | 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 225/40R18. Fit 245/35R18 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 | 69.1 mph | -0.9 |
| 90 mph | 88.8 mph | -1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,867 on the road, so it over-counts by 133. At a true 70 mph the first turns 938 times a minute, the second 951.
What drivers reported
225/40R18 carries 39 complaints. Nobody has filed one naming 245/35R18.