Stationary bicycles need support to stop from falling over because they lack gyroscopic stabilization. Right?
If you ride a free bicycle on a treadmill (so both wheels are spinning) will it fall over or stay upright?
If you fall over on a treadmill, does it matter if this treadmill bicycle combo is on a train?
That would be wise, as well as having an assistant or a wall/doorway nearby to steady you.