235/75R23 vs 235/80R23
Going from one to the other changes the overall height by +2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/75R23 | 235/80R23 | Change |
|---|---|---|---|
| Overall height | 36.9" | 37.8" | +2.5 % |
| Sidewall | 6.94" | 7.40" | +6.7 % |
| Section width | 235 mm | 235 mm | 0.0 % |
| Circumference | 115.9" | 118.8" | +2.5 % |
| Revs per mile | 547 | 534 | -2.5 % |
| Axle height | 18.44" | 18.90" | +11.8 mm |
| Approved rim width | 6.5–8.5" | 6.5–8.5" | overlap 6.5–8.5" |
Both are approved on a rim 6.5" 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 235/75R23. Fit 235/80R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.3 mph | +2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,251 on the road, so it under-counts by 251. At a true 70 mph the first turns 638 times a minute, the second 622.