265/75R23 vs 245/85R23
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 | 265/75R23 | 245/85R23 | Change |
|---|---|---|---|
| Overall height | 38.6" | 39.4" | +1.9 % |
| Sidewall | 7.82" | 8.20" | +4.8 % |
| Section width | 265 mm | 245 mm | -7.5 % |
| Circumference | 121.4" | 123.8" | +1.9 % |
| Revs per mile | 522 | 512 | -1.9 % |
| Axle height | 19.32" | 19.70" | +9.5 mm |
| Approved rim width | 7.5–9.5" | 7–9" | overlap 7.5–9" |
Both are approved on a rim 7.5" to 9" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 265/75R23. Fit 245/85R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.0 mph | +1.0 |
| 70 mph | 71.4 mph | +1.4 |
| 90 mph | 91.7 mph | +1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,194 on the road, so it under-counts by 194. At a true 70 mph the first turns 609 times a minute, the second 597.