225/35R20 vs 205/40R20
Going from one to the other changes the overall height by +1.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/35R20 | 205/40R20 | Change |
|---|---|---|---|
| Overall height | 26.2" | 26.5" | +1.0 % |
| Sidewall | 3.10" | 3.23" | +4.1 % |
| Section width | 225 mm | 205 mm | -8.9 % |
| Circumference | 82.3" | 83.1" | +1.0 % |
| Revs per mile | 770 | 762 | -1.0 % |
| Axle height | 13.10" | 13.23" | +3.3 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 225/35R20. Fit 205/40R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.5 mph | +0.5 |
| 70 mph | 70.7 mph | +0.7 |
| 90 mph | 90.9 mph | +0.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,098 on the road, so it under-counts by 98. At a true 70 mph the first turns 898 times a minute, the second 889.
What drivers reported
225/35R20 carries 2 complaints. Nobody has filed one naming 205/40R20.