275/30R18 vs 295/30R18
Going from one to the other changes the overall height by +1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/30R18 | 295/30R18 | Change |
|---|---|---|---|
| Overall height | 24.5" | 25.0" | +1.9 % |
| Sidewall | 3.25" | 3.48" | +7.3 % |
| Section width | 275 mm | 295 mm | +7.3 % |
| Circumference | 77.0" | 78.4" | +1.9 % |
| Revs per mile | 823 | 808 | -1.9 % |
| Axle height | 12.25" | 12.48" | +6.0 mm |
| Approved rim width | 7.5–10" | 8.5–11" | overlap 8.5–10" |
Both are approved on a rim 8.5" to 10" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 275/30R18. Fit 295/30R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.0 mph | +1.0 |
| 70 mph | 71.4 mph | +1.4 |
| 90 mph | 91.7 mph | +1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,193 on the road, so it under-counts by 193. At a true 70 mph the first turns 961 times a minute, the second 942.