235/45R17 vs 215/45R17
Going from one to the other changes the overall height by -2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/45R17 | 215/45R17 | Change |
|---|---|---|---|
| Overall height | 25.3" | 24.6" | -2.8 % |
| Sidewall | 4.16" | 3.81" | -8.5 % |
| Section width | 235 mm | 215 mm | -8.5 % |
| Circumference | 79.6" | 77.3" | -2.8 % |
| Revs per mile | 796 | 819 | +2.8 % |
| Axle height | 12.66" | 12.31" | -9.0 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 235/45R17. Fit 215/45R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,720 on the road, so it over-counts by 280. At a true 70 mph the first turns 929 times a minute, the second 956.