215/65R18 vs 235/55R18
Going from one to the other changes the overall height by -2.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/65R18 | 235/55R18 | Change |
|---|---|---|---|
| Overall height | 29.0" | 28.2" | -2.9 % |
| Sidewall | 5.50" | 5.09" | -7.5 % |
| Section width | 215 mm | 235 mm | +9.3 % |
| Circumference | 91.1" | 88.5" | -2.9 % |
| Revs per mile | 695 | 716 | +2.9 % |
| Axle height | 14.50" | 14.09" | -10.5 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 215/65R18. Fit 235/55R18 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 811 times a minute, the second 835.
What drivers reported
Nobody has filed a complaint naming 215/65R18. 235/55R18 carries 49.