215/40R18 vs 235/35R18
Going from one to the other changes the overall height by -1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/40R18 | 235/35R18 | Change |
|---|---|---|---|
| Overall height | 24.8" | 24.5" | -1.2 % |
| Sidewall | 3.39" | 3.24" | -4.4 % |
| Section width | 215 mm | 235 mm | +9.3 % |
| Circumference | 77.8" | 76.9" | -1.2 % |
| Revs per mile | 814 | 824 | +1.2 % |
| Axle height | 12.39" | 12.24" | -3.8 mm |
| Approved rim width | 6–8" | 6.5–8.5" | overlap 6.5–8" |
Both are approved on a rim 6.5" to 8" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 215/40R18. Fit 235/35R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.4 mph | -0.6 |
| 70 mph | 69.2 mph | -0.8 |
| 90 mph | 88.9 mph | -1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,881 on the road, so it over-counts by 119. At a true 70 mph the first turns 950 times a minute, the second 961.
What drivers reported
215/40R18 carries 2 complaints. Nobody has filed one naming 235/35R18.