295/70R22.5 vs 305/70R22.5
Going from one to the other changes the overall height by +1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 295/70R22.5 | 305/70R22.5 | Change |
|---|---|---|---|
| Overall height | 38.8" | 39.3" | +1.4 % |
| Sidewall | 8.13" | 8.41" | +3.4 % |
| Section width | 295 mm | 305 mm | +3.4 % |
| Circumference | 121.8" | 123.5" | +1.4 % |
| Revs per mile | 520 | 513 | -1.4 % |
| Axle height | 19.38" | 19.66" | +7.0 mm |
| Approved rim width | 8.5–11" | 8.5–11" | overlap 8.5–11" |
Both are approved on a rim 8.5" to 11" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 295/70R22.5. Fit 305/70R22.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 71.0 mph | +1.0 |
| 90 mph | 91.3 mph | +1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,142 on the road, so it under-counts by 142. At a true 70 mph the first turns 607 times a minute, the second 599.