295/65R23 vs 305/60R23
Going from one to the other changes the overall height by -1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 295/65R23 | 305/60R23 | Change |
|---|---|---|---|
| Overall height | 38.1" | 37.4" | -1.8 % |
| Sidewall | 7.55" | 7.20" | -4.6 % |
| Section width | 295 mm | 305 mm | +3.4 % |
| Circumference | 119.7" | 117.5" | -1.8 % |
| Revs per mile | 529 | 539 | +1.8 % |
| Axle height | 19.05" | 18.70" | -8.8 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 295/65R23. Fit 305/60R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.7 mph | -1.3 |
| 90 mph | 88.4 mph | -1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,819 on the road, so it over-counts by 181. At a true 70 mph the first turns 618 times a minute, the second 629.