295/30R17 vs 275/30R17
Going from one to the other changes the overall height by -2.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 295/30R17 | 275/30R17 | Change |
|---|---|---|---|
| Overall height | 24.0" | 23.5" | -2.0 % |
| Sidewall | 3.48" | 3.25" | -6.8 % |
| Section width | 295 mm | 275 mm | -6.8 % |
| Circumference | 75.3" | 73.8" | -2.0 % |
| Revs per mile | 841 | 858 | +2.0 % |
| Axle height | 11.98" | 11.75" | -6.0 mm |
| Approved rim width | 8.5–11" | 7.5–10" | 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 295/30R17. Fit 275/30R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.0 mph | -1.0 |
| 70 mph | 68.6 mph | -1.4 |
| 90 mph | 88.2 mph | -1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,803 on the road, so it over-counts by 197. At a true 70 mph the first turns 982 times a minute, the second 1001.