285/45R19 vs 305/40R19
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 | 285/45R19 | 305/40R19 | Change |
|---|---|---|---|
| Overall height | 29.1" | 28.6" | -1.7 % |
| Sidewall | 5.05" | 4.80" | -4.9 % |
| Section width | 285 mm | 305 mm | +7.0 % |
| Circumference | 91.4" | 89.9" | -1.7 % |
| Revs per mile | 693 | 705 | +1.7 % |
| Axle height | 14.55" | 14.30" | -6.3 mm |
| Approved rim width | 8–10.5" | 8.5–11" | overlap 8.5–10.5" |
Both are approved on a rim 8.5" to 10.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 285/45R19. Fit 305/40R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.5 mph | -1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,831 on the road, so it over-counts by 169. At a true 70 mph the first turns 809 times a minute, the second 823.
What drivers reported
285/45R19 carries 2 complaints. Nobody has filed one naming 305/40R19.