The problem is that trikes don't steer with countersteering. When you transition to one wheel lifted, you have a brand new mode of operation with a misaligned rear wheel.

> especially as many trikes have solid rear axles

Do you (or anyone I guess) happen to know why? Low speed differential non-drive axles are not that complex, and would sermingly help a lot.

If they're not drive why connect them at all? Why not have them mounted independently and eliminate the need for an extra part? My only real guess is it's easier for carrying capacity.

I suspect it because with a single piece axle the torsion forces trying to twist the wheels into negative camber are taken by the axle and the forces on the two wheels negate each other, leaving the frame to only have to deal with vertical linear force.

Maybe. You can get the same effect by putting two bearing on the inside of the wheel with a disconnected axel I think. A simple axel might come out cheaper than that though.

Isn’t it the outer wheel that would lift off the ground?

it's the inner wheel with a tilt/lean. Your weight has to get out over the COG to balance. The feeling ranges from foreign to terrifying and I'm not sure why you wouldn't just go with an excellent cargo bicycle that avoids the entire issue.

You would think so but no. The inner wheel is the one that lifts.

What’s the explanation that this is different from bi-wheelers?

It wants to roll over, just like a car would if it had very sticky tires and took a sharp turn at speed.

The fun bit is that on three wheels it steers like a car, but on two wheels it steers like a bicycle.

Some cars like the Mini Cooper S do lift a rear wheel when turning sharply under braking -- I've seen this a lot in autocross racing. I normally only see front engine/FWD cars with limited suspension travel do it though. Trikes are less stable & will lift a wheel more easily overall.

The principle is the same, the distinction has more to do with suspension (or lack thereof) and the solid rear axle. The same strategy of lifting the inside rear tire is used in competitive go-kart racing: https://youtu.be/cMAtgPX6st8?t=312 . If the carts had a differential then it would be a different story (and they would be cars and not karts according to the SuperFastMatt taxonomy)

They do. Volkswagens from the 80s and 90s that have solid dead rear axles "tripod" around corners.

Automobiles have 4 wheels. The geometry of the situation is very different. This is also why cars have differentials, because otherwise the car would be fighting against the turn.

Basically when you turn your trike turns into a bike.