235/40R17 vs 225/45R17
Going from one to the other changes the overall height by +2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/40R17 | 225/45R17 | Change |
|---|---|---|---|
| Overall height | 24.4" | 25.0" | +2.3 % |
| Sidewall | 3.70" | 3.99" | +7.7 % |
| Section width | 235 mm | 225 mm | -4.3 % |
| Circumference | 76.7" | 78.5" | +2.3 % |
| Revs per mile | 827 | 808 | -2.3 % |
| Axle height | 12.20" | 12.49" | +7.3 mm |
| Approved rim width | 6.5–8.5" | 6–8.5" | overlap 6.5–8.5" |
Both are approved on a rim 6.5" 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 235/40R17. Fit 225/45R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.2 mph | +1.2 |
| 70 mph | 71.6 mph | +1.6 |
| 90 mph | 92.1 mph | +2.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,234 on the road, so it under-counts by 234. At a true 70 mph the first turns 964 times a minute, the second 942.
What drivers reported
Nobody has filed a complaint naming 235/40R17. 225/45R17 carries 122.