305/25R19 vs 285/30R19
Going from one to the other changes the overall height by +2.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/25R19 | 285/30R19 | Change |
|---|---|---|---|
| Overall height | 25.0" | 25.7" | +2.9 % |
| Sidewall | 3.00" | 3.37" | +12.1 % |
| Section width | 305 mm | 285 mm | -6.6 % |
| Circumference | 78.6" | 80.8" | +2.9 % |
| Revs per mile | 807 | 784 | -2.9 % |
| Axle height | 12.50" | 12.87" | +9.3 mm |
| Approved rim width | 8.5–11" | 8–10.5" | 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 305/25R19. Fit 285/30R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.5 mph | +1.5 |
| 70 mph | 72.0 mph | +2.0 |
| 90 mph | 92.6 mph | +2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,291 on the road, so it under-counts by 291. At a true 70 mph the first turns 941 times a minute, the second 914.
What drivers reported
Nobody has filed a complaint naming 305/25R19. 285/30R19 carries 1.