235/85R23 vs 245/80R23
Going from one to the other changes the overall height by -0.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/85R23 | 245/80R23 | Change |
|---|---|---|---|
| Overall height | 38.7" | 38.4" | -0.8 % |
| Sidewall | 7.86" | 7.72" | -1.9 % |
| Section width | 235 mm | 245 mm | +4.3 % |
| Circumference | 121.7" | 120.7" | -0.8 % |
| Revs per mile | 521 | 525 | +0.8 % |
| Axle height | 19.36" | 19.22" | -3.8 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 235/85R23. Fit 245/80R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.8 mph | -0.2 |
| 50 mph | 49.6 mph | -0.4 |
| 70 mph | 69.5 mph | -0.5 |
| 90 mph | 89.3 mph | -0.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,924 on the road, so it over-counts by 76. At a true 70 mph the first turns 608 times a minute, the second 612.