235/80R14 vs 225/85R14
Going from one to the other changes the overall height by +0.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/80R14 | 225/85R14 | Change |
|---|---|---|---|
| Overall height | 28.8" | 29.1" | +0.9 % |
| Sidewall | 7.40" | 7.53" | +1.7 % |
| Section width | 235 mm | 225 mm | -4.3 % |
| Circumference | 90.5" | 91.3" | +0.9 % |
| Revs per mile | 700 | 694 | -0.9 % |
| Axle height | 14.40" | 14.53" | +3.3 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 235/80R14. Fit 225/85R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.4 mph | +0.4 |
| 70 mph | 70.6 mph | +0.6 |
| 90 mph | 90.8 mph | +0.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,089 on the road, so it under-counts by 89. At a true 70 mph the first turns 817 times a minute, the second 810.