205/75R20 vs 205/70R20
Going from one to the other changes the overall height by -2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/75R20 | 205/70R20 | Change |
|---|---|---|---|
| Overall height | 32.1" | 31.3" | -2.5 % |
| Sidewall | 6.05" | 5.65" | -6.7 % |
| Section width | 205 mm | 205 mm | 0.0 % |
| Circumference | 100.9" | 98.3" | -2.5 % |
| Revs per mile | 628 | 644 | +2.5 % |
| Axle height | 16.05" | 15.65" | -10.3 mm |
| Approved rim width | 5.5–7.5" | 5.5–7.5" | overlap 5.5–7.5" |
Both are approved on a rim 5.5" to 7.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 205/75R20. Fit 205/70R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.7 mph | -1.3 |
| 70 mph | 68.2 mph | -1.8 |
| 90 mph | 87.7 mph | -2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,749 on the road, so it over-counts by 251. At a true 70 mph the first turns 733 times a minute, the second 752.
What drivers reported
Nobody has filed a complaint naming 205/75R20. 205/70R20 carries 2.