215/75R17.5 vs 225/70R17.5
Going from one to the other changes the overall height by -1.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/75R17.5 | 225/70R17.5 | Change |
|---|---|---|---|
| Overall height | 30.2" | 29.9" | -1.0 % |
| Sidewall | 6.35" | 6.20" | -2.3 % |
| Section width | 215 mm | 225 mm | +4.7 % |
| Circumference | 94.9" | 93.9" | -1.0 % |
| Revs per mile | 668 | 674 | +1.0 % |
| Axle height | 15.10" | 14.95" | -3.8 mm |
| Approved rim width | 6–8" | 6–8.5" | overlap 6–8" |
Both are approved on a rim 6" to 8" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 215/75R17.5. Fit 225/70R17.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.5 mph | -0.5 |
| 70 mph | 69.3 mph | -0.7 |
| 90 mph | 89.1 mph | -0.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,902 on the road, so it over-counts by 98. At a true 70 mph the first turns 779 times a minute, the second 787.