315/35R21 vs 295/35R21
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 | 315/35R21 | 295/35R21 | Change |
|---|---|---|---|
| Overall height | 29.7" | 29.1" | -1.9 % |
| Sidewall | 4.34" | 4.06" | -6.3 % |
| Section width | 315 mm | 295 mm | -6.3 % |
| Circumference | 93.2" | 91.5" | -1.9 % |
| Revs per mile | 679 | 692 | +1.9 % |
| Axle height | 14.84" | 14.56" | -7.0 mm |
| Approved rim width | 8.5–11.5" | 8.5–11" | overlap 8.5–11" |
Both are approved on a rim 8.5" to 11" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 315/35R21. Fit 295/35R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.7 mph | -1.3 |
| 90 mph | 88.3 mph | -1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,814 on the road, so it over-counts by 186. At a true 70 mph the first turns 793 times a minute, the second 808.
What drivers reported
Nobody has filed a complaint naming 315/35R21. 295/35R21 carries 1.