215/70R18 vs 235/60R18
Going from one to the other changes the overall height by -2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/70R18 | 235/60R18 | Change |
|---|---|---|---|
| Overall height | 29.9" | 29.1" | -2.5 % |
| Sidewall | 5.93" | 5.55" | -6.3 % |
| Section width | 215 mm | 235 mm | +9.3 % |
| Circumference | 93.8" | 91.4" | -2.5 % |
| Revs per mile | 676 | 693 | +2.5 % |
| Axle height | 14.93" | 14.55" | -9.5 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 215/70R18. Fit 235/60R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.7 mph | -1.3 |
| 70 mph | 68.2 mph | -1.8 |
| 90 mph | 87.7 mph | -2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,749 on the road, so it over-counts by 251. At a true 70 mph the first turns 788 times a minute, the second 809.
What drivers reported
Nobody has filed a complaint naming 215/70R18. 235/60R18 carries 30.