225/70R18 vs 245/65R18
Going from one to the other changes the overall height by +0.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/70R18 | 245/65R18 | Change |
|---|---|---|---|
| Overall height | 30.4" | 30.5" | +0.5 % |
| Sidewall | 6.20" | 6.27" | +1.1 % |
| Section width | 225 mm | 245 mm | +8.9 % |
| Circumference | 95.5" | 95.9" | +0.5 % |
| Revs per mile | 663 | 660 | -0.5 % |
| Axle height | 15.20" | 15.27" | +1.8 mm |
| Approved rim width | 6–8.5" | 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 225/70R18. Fit 245/65R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.2 mph | +0.2 |
| 70 mph | 70.3 mph | +0.3 |
| 90 mph | 90.4 mph | +0.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,045 on the road, so it under-counts by 45. At a true 70 mph the first turns 774 times a minute, the second 770.