305/65R23 vs 295/70R23
Going from one to the other changes the overall height by +1.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/65R23 | 295/70R23 | Change |
|---|---|---|---|
| Overall height | 38.6" | 39.3" | +1.7 % |
| Sidewall | 7.81" | 8.13" | +4.2 % |
| Section width | 305 mm | 295 mm | -3.3 % |
| Circumference | 121.3" | 123.3" | +1.7 % |
| Revs per mile | 522 | 514 | -1.7 % |
| Axle height | 19.31" | 19.63" | +8.3 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 305/65R23. Fit 295/70R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.2 mph | +1.2 |
| 90 mph | 91.5 mph | +1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,168 on the road, so it under-counts by 168. At a true 70 mph the first turns 609 times a minute, the second 599.