235/50R17 vs 245/45R17
Going from one to the other changes the overall height by -2.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/50R17 | 245/45R17 | Change |
|---|---|---|---|
| Overall height | 26.3" | 25.7" | -2.2 % |
| Sidewall | 4.63" | 4.34" | -6.2 % |
| Section width | 235 mm | 245 mm | +4.3 % |
| Circumference | 82.5" | 80.7" | -2.2 % |
| Revs per mile | 768 | 785 | +2.2 % |
| Axle height | 13.13" | 12.84" | -7.3 mm |
| Approved rim width | 6.5–8.5" | 7–9" | 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 235/50R17. Fit 245/45R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.9 mph | -1.1 |
| 70 mph | 68.5 mph | -1.5 |
| 90 mph | 88.0 mph | -2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,783 on the road, so it over-counts by 217. At a true 70 mph the first turns 896 times a minute, the second 916.