225/75R18 vs 235/70R18
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 | 225/75R18 | 235/70R18 | Change |
|---|---|---|---|
| Overall height | 31.3" | 31.0" | -1.1 % |
| Sidewall | 6.64" | 6.48" | -2.5 % |
| Section width | 225 mm | 235 mm | +4.4 % |
| Circumference | 98.3" | 97.2" | -1.1 % |
| Revs per mile | 645 | 652 | +1.1 % |
| Axle height | 15.64" | 15.48" | -4.3 mm |
| Approved rim width | 6–8.5" | 6.5–8.5" | 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 225/75R18. Fit 235/70R18 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 | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,893 on the road, so it over-counts by 107. At a true 70 mph the first turns 752 times a minute, the second 760.
What drivers reported
Nobody has filed a complaint naming 225/75R18. 235/70R18 carries 1.