285/30R19 vs 305/30R19
Going from one to the other changes the overall height by +1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/30R19 | 305/30R19 | Change |
|---|---|---|---|
| Overall height | 25.7" | 26.2" | +1.8 % |
| Sidewall | 3.37" | 3.60" | +7.0 % |
| Section width | 285 mm | 305 mm | +7.0 % |
| Circumference | 80.8" | 82.3" | +1.8 % |
| Revs per mile | 784 | 770 | -1.8 % |
| Axle height | 12.87" | 13.10" | +6.0 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 285/30R19. Fit 305/30R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.7 mph | +1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,184 on the road, so it under-counts by 184. At a true 70 mph the first turns 914 times a minute, the second 898.