245/70R17 vs 235/75R17
Going from one to the other changes the overall height by +1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/70R17 | 235/75R17 | Change |
|---|---|---|---|
| Overall height | 30.5" | 30.9" | +1.2 % |
| Sidewall | 6.75" | 6.94" | +2.8 % |
| Section width | 245 mm | 235 mm | -4.1 % |
| Circumference | 95.8" | 97.0" | +1.2 % |
| Revs per mile | 661 | 653 | -1.2 % |
| Axle height | 15.25" | 15.44" | +4.8 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 245/70R17. Fit 235/75R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.6 mph | +0.6 |
| 70 mph | 70.9 mph | +0.9 |
| 90 mph | 91.1 mph | +1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,123 on the road, so it under-counts by 123. At a true 70 mph the first turns 771 times a minute, the second 762.