235/70R15 vs 225/75R15
Going from one to the other changes the overall height by +1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/70R15 | 225/75R15 | Change |
|---|---|---|---|
| Overall height | 28.0" | 28.3" | +1.2 % |
| Sidewall | 6.48" | 6.64" | +2.6 % |
| Section width | 235 mm | 225 mm | -4.3 % |
| Circumference | 87.8" | 88.9" | +1.2 % |
| Revs per mile | 722 | 713 | -1.2 % |
| Axle height | 13.98" | 14.14" | +4.3 mm |
| Approved rim width | 6.5–8.5" | 6–8.5" | overlap 6.5–8.5" |
Both are approved on a rim 6.5" to 8.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 235/70R15. Fit 225/75R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.6 mph | +0.6 |
| 70 mph | 70.8 mph | +0.8 |
| 90 mph | 91.1 mph | +1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,120 on the road, so it under-counts by 120. At a true 70 mph the first turns 842 times a minute, the second 832.
What drivers reported
235/70R15 carries 26 complaints and 1 deaths. 225/75R15 carries 258.