185/50R18 vs 185/55R18
Going from one to the other changes the overall height by +2.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/50R18 | 185/55R18 | Change |
|---|---|---|---|
| Overall height | 25.3" | 26.0" | +2.9 % |
| Sidewall | 3.64" | 4.01" | +10.0 % |
| Section width | 185 mm | 185 mm | 0.0 % |
| Circumference | 79.4" | 81.7" | +2.9 % |
| Revs per mile | 798 | 775 | -2.9 % |
| Axle height | 12.64" | 13.01" | +9.3 mm |
| Approved rim width | 5–6.5" | 5–6.5" | overlap 5–6.5" |
Both are approved on a rim 5" to 6.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 185/50R18. Fit 185/55R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 72.0 mph | +2.0 |
| 90 mph | 92.6 mph | +2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,288 on the road, so it under-counts by 288. At a true 70 mph the first turns 931 times a minute, the second 905.
What drivers reported
Nobody has filed a complaint naming 185/50R18. 185/55R18 carries 1.