225/75R15 vs 205/85R15
Going from one to the other changes the overall height by +1.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/75R15 | 205/85R15 | Change |
|---|---|---|---|
| Overall height | 28.3" | 28.7" | +1.5 % |
| Sidewall | 6.64" | 6.86" | +3.3 % |
| Section width | 225 mm | 205 mm | -8.9 % |
| Circumference | 88.9" | 90.2" | +1.5 % |
| Revs per mile | 713 | 702 | -1.5 % |
| Axle height | 14.14" | 14.36" | +5.5 mm |
| Approved rim width | 6–8.5" | 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 225/75R15. Fit 205/85R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.1 mph | +1.1 |
| 90 mph | 91.4 mph | +1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,153 on the road, so it under-counts by 153. At a true 70 mph the first turns 832 times a minute, the second 819.
What drivers reported
225/75R15 carries 258 complaints. Nobody has filed one naming 205/85R15.