235/70R18 vs 225/75R18
Going from one to the other changes the overall height by +1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/70R18 | 225/75R18 | Change |
|---|---|---|---|
| Overall height | 31.0" | 31.3" | +1.1 % |
| Sidewall | 6.48" | 6.64" | +2.6 % |
| Section width | 235 mm | 225 mm | -4.3 % |
| Circumference | 97.2" | 98.3" | +1.1 % |
| Revs per mile | 652 | 645 | -1.1 % |
| Axle height | 15.48" | 15.64" | +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 235/70R18. Fit 225/75R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.5 mph | +0.5 |
| 70 mph | 70.8 mph | +0.8 |
| 90 mph | 91.0 mph | +1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,108 on the road, so it under-counts by 108. At a true 70 mph the first turns 760 times a minute, the second 752.
What drivers reported
235/70R18 carries 1 complaints. Nobody has filed one naming 225/75R18.