I think an ideal controller would be something like the one mentioned above, however, since we are talking about motorcycles and the need to be able to 'lean' into a turn from a riders perspective, also make the controller tiltable from left-to-right as opposed to what just looks like a solidly mounted "T" bar with just a throttle/brake added. This way here, you not only control both gas/brake but also the angle in which the bike enters/exits turns! 👍
This should add the needed 'realism' of actually riding a motorcycle to games such as TT and MotoGP!