235/65R18 vs 215/70R18
Going from one to the other changes the overall height by -0.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/65R18 | 215/70R18 | Change |
|---|---|---|---|
| Overall height | 30.0" | 29.9" | -0.6 % |
| Sidewall | 6.01" | 5.93" | -1.5 % |
| Section width | 235 mm | 215 mm | -8.5 % |
| Circumference | 94.3" | 93.8" | -0.6 % |
| Revs per mile | 672 | 676 | +0.6 % |
| Axle height | 15.01" | 14.93" | -2.3 mm |
| Approved rim width | 6.5–8.5" | 6–8" | 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 235/65R18. Fit 215/70R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.8 mph | -0.2 |
| 50 mph | 49.7 mph | -0.3 |
| 70 mph | 69.6 mph | -0.4 |
| 90 mph | 89.5 mph | -0.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,941 on the road, so it over-counts by 59. At a true 70 mph the first turns 784 times a minute, the second 788.
What drivers reported
235/65R18 carries 10 complaints. Nobody has filed one naming 215/70R18.