245/40R17 vs 235/40R17
Going from one to the other changes the overall height by -1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/40R17 | 235/40R17 | Change |
|---|---|---|---|
| Overall height | 24.7" | 24.4" | -1.3 % |
| Sidewall | 3.86" | 3.70" | -4.1 % |
| Section width | 245 mm | 235 mm | -4.1 % |
| Circumference | 77.6" | 76.7" | -1.3 % |
| Revs per mile | 816 | 827 | +1.3 % |
| Axle height | 12.36" | 12.20" | -4.0 mm |
| Approved rim width | 7–9" | 6.5–8.5" | 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 245/40R17. Fit 235/40R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.4 mph | -0.6 |
| 70 mph | 69.1 mph | -0.9 |
| 90 mph | 88.9 mph | -1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,873 on the road, so it over-counts by 127. At a true 70 mph the first turns 952 times a minute, the second 964.
What drivers reported
245/40R17 carries 6 complaints. Nobody has filed one naming 235/40R17.