235/75R15 vs 225/80R15
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 | 235/75R15 | 225/80R15 | Change |
|---|---|---|---|
| Overall height | 28.9" | 29.2" | +1.0 % |
| Sidewall | 6.94" | 7.09" | +2.1 % |
| Section width | 235 mm | 225 mm | -4.3 % |
| Circumference | 90.7" | 91.7" | +1.0 % |
| Revs per mile | 698 | 691 | -1.0 % |
| Axle height | 14.44" | 14.59" | +3.8 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 235/75R15. Fit 225/80R15 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 | 70.7 mph | +0.7 |
| 90 mph | 90.9 mph | +0.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,102 on the road, so it under-counts by 102. At a true 70 mph the first turns 815 times a minute, the second 807.
What drivers reported
235/75R15 carries 219 complaints and 3 deaths. Nobody has filed one naming 225/80R15.