245/35R17 vs 225/40R17
Going from one to the other changes the overall height by +1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/35R17 | 225/40R17 | Change |
|---|---|---|---|
| Overall height | 23.8" | 24.1" | +1.4 % |
| Sidewall | 3.38" | 3.54" | +5.0 % |
| Section width | 245 mm | 225 mm | -8.2 % |
| Circumference | 74.6" | 75.7" | +1.4 % |
| Revs per mile | 849 | 837 | -1.4 % |
| Axle height | 11.88" | 12.04" | +4.3 mm |
| Approved rim width | 7–9" | 6–8.5" | overlap 7–8.5" |
Both are approved on a rim 7" to 8.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 245/35R17. Fit 225/40R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 71.0 mph | +1.0 |
| 90 mph | 91.3 mph | +1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,141 on the road, so it under-counts by 141. At a true 70 mph the first turns 991 times a minute, the second 977.