Originally Posted by laura*

If the angle is too extreme, it could tear the inner tube.

Remove the wheel from the bike.
Deflate it fully (but do not take the tire off.)
Place the wheel on the ground with the valve stem at the very bottom (pointing up).
Observe which way the valve stem is leaning.
Gently roll the tire for exactly one revolution in the direction that the leaning stem points.
If the stem is still leaning the same way, roll another revolution but push down slightly.
If the stem is leaning the other direction, roll the other way but push down less.
Once the stem is vertical, inflate, reinstall, and ride!