205/70R20 vs 205/75R20
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/70R20 | 205/75R20 | Change |
|---|---|---|---|
| Overall height | 31.3" | 32.1" | +2.6 % |
| Sidewall | 5.65" | 6.05" | +7.1 % |
| Section width | 205 mm | 205 mm | 0.0 % |
| Circumference | 98.3" | 100.9" | +2.6 % |
| Revs per mile | 644 | 628 | -2.6 % |
| Axle height | 15.65" | 16.05" | +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 205/70R20. Fit 205/75R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.3 mph | +2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,258 on the road, so it under-counts by 258. At a true 70 mph the first turns 752 times a minute, the second 733.
What drivers reported
205/70R20 carries 2 complaints. Nobody has filed one naming 205/75R20.