Bus drivers/mechanics: what's this knob?

I went on a tour of Sicily/Southern Italy over the summer and watched the driver of our tour bus make the most amazingly tight turns onto narrow streets. Then one day I watched him closer. Every time he had to make a really tight turn, he pulled out (or pushed in, I can’t remember) some sort of large knob on the dashboard. What the hell does this knob do? I thought it might be some sort of steering unlock button, something that might make the front wheels turn tighter than usual. Problem with that, though, is that there’s no real reason to leave it locked in a restricted state. Even if there was, the smart thing to do is have an automatic unlock that kicks in at low speeds. So as I see it, a steering unlock mechanism is out.

That brings me to some sort of front drive mechanism. It seems to me that a front drive mechanism would allow tighter turns more easily (the bus is obviously otherwise rear-engine and rear wheel drive). A mechanical front wheel drive mechanism seems far too cumbersome, but how about a low power (maybe a couple horsepower) electric front wheel drive mechanism? Anyone know?

Note to Southern Italians: damn, your food is good.

Maybe it allows the rear wheels to steer. WAG.

Hmmmmm, me likey. Did a search on rear wheel steering on buses, though, and most mentioned were articulated buses (the tour bus was not). So, do they make unarticulated buses with rear steering, and is that what that knob activates?

I must reiterate: Southere Italians, damn, your food was good…

I was on a bus in Ireland in which the driver did something that obviously made the rear wheels turn too in order to go around a very tight turn, but I wasn’t close enough to the front to see what he did.

For safety, vehicles are made with a limited turning circle. Maybe the knob released a limiting block, and enables the wheels to turn in a tighter circle.

You say it comes into play during very tight turns. Could it have something to do with the differential?

Local long distance buses here in Scotland have obvious rear wheel steering- probably switched off on the open road for safety.

If the bus had three axles, the knob may have lifted the rearmost axle.

Rear steering … which is to steer oppositely to the front.
You definitely only want that activated for the sharp corner that needs it !
If you didn’t a simple lane change left would see the rear of the coach go into the lane to the right the same amount. !