315/30R23 vs 295/30R23
Going from one to the other changes the overall height by -1.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/30R23 | 295/30R23 | Change |
|---|---|---|---|
| Overall height | 30.4" | 30.0" | -1.6 % |
| Sidewall | 3.72" | 3.48" | -6.3 % |
| Section width | 315 mm | 295 mm | -6.3 % |
| Circumference | 95.6" | 94.1" | -1.6 % |
| Revs per mile | 663 | 673 | +1.6 % |
| Axle height | 15.22" | 14.98" | -6.0 mm |
| Approved rim width | 8.5–11.5" | 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 315/30R23. Fit 295/30R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.9 mph | -1.1 |
| 90 mph | 88.6 mph | -1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,845 on the road, so it over-counts by 155. At a true 70 mph the first turns 773 times a minute, the second 785.