My friend - we'll call him Mr. RT - often goes on rides with another person I know, Mr. GS. He mentioned when talking bikes the other day that Mr. GS seems to him to be less leaned over than he is, in the same turn.
I argued to Mr. RT that this is an optical illusion. Bikes make coordinated turns (I claimed) unless you are leaning off, and so for a given turn (speed, radius) there is a lean angle that goes with it, regardless of bike. Mid turn, in your reference frame, the bike ahead of you is also above and leaned towards you, making his lean angle difficult to judge.
He however argues that Mr. GS is indeed at a different lean angle, and that this is due to the difference in steering geometry between the two bikes. I tend to agree that the GS is insanely easy to ride at any speed, but this seemed to me like hooey.
What do you think? (Exhaustive proofs encouraged).