315/40R22 vs 305/45R22
Going from one to the other changes the overall height by +2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/40R22 | 305/45R22 | Change |
|---|---|---|---|
| Overall height | 31.9" | 32.8" | +2.8 % |
| Sidewall | 4.96" | 5.40" | +8.9 % |
| Section width | 315 mm | 305 mm | -3.2 % |
| Circumference | 100.3" | 103.1" | +2.8 % |
| Revs per mile | 632 | 615 | -2.8 % |
| Axle height | 15.96" | 16.40" | +11.3 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 315/40R22. Fit 305/45R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 71.9 mph | +1.9 |
| 90 mph | 92.5 mph | +2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,278 on the road, so it under-counts by 278. At a true 70 mph the first turns 737 times a minute, the second 717.
What drivers reported
Nobody has filed a complaint naming 315/40R22. 305/45R22 carries 2.