235/85R14 vs 225/85R14
Going from one to the other changes the overall height by -2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/85R14 | 225/85R14 | Change |
|---|---|---|---|
| Overall height | 29.7" | 29.1" | -2.3 % |
| Sidewall | 7.86" | 7.53" | -4.3 % |
| Section width | 235 mm | 225 mm | -4.3 % |
| Circumference | 93.4" | 91.3" | -2.3 % |
| Revs per mile | 678 | 694 | +2.3 % |
| Axle height | 14.86" | 14.53" | -8.5 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 235/85R14. Fit 225/85R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.9 mph | -1.1 |
| 70 mph | 68.4 mph | -1.6 |
| 90 mph | 88.0 mph | -2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,775 on the road, so it over-counts by 225. At a true 70 mph the first turns 791 times a minute, the second 810.