The apparent stability of a mechanical system: a bike on railroad tracks

[Spinnor]

I watched a video of a rail bike and if I had to I would have guessed that what I saw in the video was not a stable mechanical system, stable to the rear wheel coming off the railroad track. Please watch from 1:54 to 2:30 to understand the setup of this rail bike below,



I would have guessed that the back wheel would be constantly be coming off the rail track. In the comment section it was asked,

"I am surprised that the back wheel stays on the rail even more so since the rail is slightly crowned. Does it ever come off while you ride?"

The owner of the rail bike replied,

"The long story is that it never came off...ever. until my last trip where the wheel was off center, the rails were very worn, and it was raining. That's caused us a lot of grief."

It seems there is some inherent stability in this particular setup to the rear wheel coming off the track, without giving it away does anyone see it?

Thanks.

 

[Baluncore]

It is explained at 28:30 in the original video. Read the transcript.
"One of the most common questions I get asked about the rail bike, is how does the rear tire stay on the rail, and that's because it's not fixed, it actually sways back and forth. I usually respond in the comments, and tell people it just follows the front fork, but they keep asking over and over and over again, and I think they know that I'm lying.
Let me tell you the truth the way that the rear wheel stays on the railway track is through a technology known as Insanotron 5 million, it's a patent pending, unreleased system, that uses a circumferential electromagnetic pulse, to keep the tire attached to the railway. It's powered by the crankshaft of the bike, so as you pedal, it sends power to the device in the center of the wheel, transfers it out to the perimeter, to the circumferential magnet, and that's what attracts the metal to the tire, now you're probably wondering, Steve, with such a high rotational mass, how do the poles not reverse and resist each other? That's easy, what we do is we fill the tire with an inert gas, such as helium or hydrogen, it's a very safe system, it's never let me down, and now you know the truth. "

 

[Spinnor]

I eventually watched most of the video, must have missed that part, thank you.

 

[Baluncore]

If you analyse it for long enough, you will eventually reach an explanation.
https://en.wikipedia.org/wiki/Pursuit_curve