235/40R14 vs 215/40R14
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 | 235/40R14 | 215/40R14 | Change |
|---|---|---|---|
| Overall height | 21.4" | 20.8" | -2.9 % |
| Sidewall | 3.70" | 3.39" | -8.5 % |
| Section width | 235 mm | 215 mm | -8.5 % |
| Circumference | 67.2" | 65.3" | -2.9 % |
| Revs per mile | 942 | 971 | +2.9 % |
| Axle height | 10.70" | 10.39" | -8.0 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 235/40R14. Fit 215/40R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.5 mph | -1.5 |
| 70 mph | 67.9 mph | -2.1 |
| 90 mph | 87.4 mph | -2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,706 on the road, so it over-counts by 294. At a true 70 mph the first turns 1099 times a minute, the second 1133.