295/40R23 vs 305/35R23
Going from one to the other changes the overall height by -2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 295/40R23 | 305/35R23 | Change |
|---|---|---|---|
| Overall height | 32.3" | 31.4" | -2.7 % |
| Sidewall | 4.65" | 4.20" | -9.5 % |
| Section width | 295 mm | 305 mm | +3.4 % |
| Circumference | 101.4" | 98.7" | -2.7 % |
| Revs per mile | 625 | 642 | +2.7 % |
| Axle height | 16.15" | 15.70" | -11.3 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 295/40R23. Fit 305/35R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.1 mph | -1.9 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,726 on the road, so it over-counts by 274. At a true 70 mph the first turns 729 times a minute, the second 749.