315/60R20 vs 295/65R20
Going from one to the other changes the overall height by +0.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/60R20 | 295/65R20 | Change |
|---|---|---|---|
| Overall height | 34.9" | 35.1" | +0.6 % |
| Sidewall | 7.44" | 7.55" | +1.5 % |
| Section width | 315 mm | 295 mm | -6.3 % |
| Circumference | 109.6" | 110.3" | +0.6 % |
| Revs per mile | 578 | 575 | -0.6 % |
| Axle height | 17.44" | 17.55" | +2.8 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 315/60R20. Fit 295/65R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.3 mph | +0.3 |
| 70 mph | 70.4 mph | +0.4 |
| 90 mph | 90.6 mph | +0.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,062 on the road, so it under-counts by 62. At a true 70 mph the first turns 675 times a minute, the second 670.