205/80R18 vs 225/70R18
Going from one to the other changes the overall height by -1.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/80R18 | 225/70R18 | Change |
|---|---|---|---|
| Overall height | 30.9" | 30.4" | -1.7 % |
| Sidewall | 6.46" | 6.20" | -4.0 % |
| Section width | 205 mm | 225 mm | +9.8 % |
| Circumference | 97.1" | 95.5" | -1.7 % |
| Revs per mile | 652 | 663 | +1.7 % |
| Axle height | 15.46" | 15.20" | -6.5 mm |
| Approved rim width | 5.5–7.5" | 6–8.5" | overlap 6–7.5" |
Both are approved on a rim 6" to 7.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 205/80R18. Fit 225/70R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.5 mph | -1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,834 on the road, so it over-counts by 166. At a true 70 mph the first turns 761 times a minute, the second 774.
What drivers reported
Nobody has filed a complaint naming 205/80R18. 225/70R18 carries 7.