215/70R17.5 vs 205/75R17.5
Going from one to the other changes the overall height by +0.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/70R17.5 | 205/75R17.5 | Change |
|---|---|---|---|
| Overall height | 29.4" | 29.6" | +0.9 % |
| Sidewall | 5.93" | 6.05" | +2.2 % |
| Section width | 215 mm | 205 mm | -4.7 % |
| Circumference | 92.2" | 93.0" | +0.9 % |
| Revs per mile | 687 | 681 | -0.9 % |
| Axle height | 14.68" | 14.80" | +3.3 mm |
| Approved rim width | 6–8" | 5.5–7.5" | overlap 6–7.5" |
Both are approved on a rim 6" 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 215/70R17.5. Fit 205/75R17.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.4 mph | +0.4 |
| 70 mph | 70.6 mph | +0.6 |
| 90 mph | 90.8 mph | +0.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,087 on the road, so it under-counts by 87. At a true 70 mph the first turns 802 times a minute, the second 795.