245/65R15 vs 235/65R15
Going from one to the other changes the overall height by -1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/65R15 | 235/65R15 | Change |
|---|---|---|---|
| Overall height | 27.5" | 27.0" | -1.9 % |
| Sidewall | 6.27" | 6.01" | -4.1 % |
| Section width | 245 mm | 235 mm | -4.1 % |
| Circumference | 86.5" | 84.9" | -1.9 % |
| Revs per mile | 732 | 746 | +1.9 % |
| Axle height | 13.77" | 13.51" | -6.5 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 245/65R15. Fit 235/65R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.7 mph | -1.3 |
| 90 mph | 88.3 mph | -1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,814 on the road, so it over-counts by 186. At a true 70 mph the first turns 854 times a minute, the second 871.