285/30R19 vs 305/25R19
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 | 285/30R19 | 305/25R19 | Change |
|---|---|---|---|
| Overall height | 25.7" | 25.0" | -2.8 % |
| Sidewall | 3.37" | 3.00" | -10.8 % |
| Section width | 285 mm | 305 mm | +7.0 % |
| Circumference | 80.8" | 78.6" | -2.8 % |
| Revs per mile | 784 | 807 | +2.8 % |
| Axle height | 12.87" | 12.50" | -9.3 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 285/30R19. Fit 305/25R19 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 | 68.0 mph | -2.0 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,717 on the road, so it over-counts by 283. At a true 70 mph the first turns 914 times a minute, the second 941.
What drivers reported
285/30R19 carries 1 complaints. Nobody has filed one naming 305/25R19.