305/40R23 vs 295/45R23
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/40R23 | 295/45R23 | Change |
|---|---|---|---|
| Overall height | 32.6" | 33.5" | +2.6 % |
| Sidewall | 4.80" | 5.23" | +8.8 % |
| Section width | 305 mm | 295 mm | -3.3 % |
| Circumference | 102.4" | 105.1" | +2.6 % |
| Revs per mile | 619 | 603 | -2.6 % |
| Axle height | 16.30" | 16.73" | +10.8 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 305/40R23. Fit 295/45R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.3 mph | +2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,260 on the road, so it under-counts by 260. At a true 70 mph the first turns 722 times a minute, the second 703.