I am not looking for any complex bike physics math system, just a simple, no suspension, no wheelspin / traction, bike model that can handle jumping off ramps and landing on a sloped surface. any ideas or help would be appreciated!

Are you using an engine or doing it all yourself? Do you need to account for tipping and rolling the bike, or are you assuming it is locked upright on both axis? How do you intend to handle the fact that in jumps the front and back leave ground at different times? Do you need to account for each wheel independently, or are you considering treating it as single object locomotion?

If you're leveraging an existing engine you can use their physics system and constrain the bike so it stays upright and mostly straight, but any time a player hits those constraints it won't look right. You can add animations to work around it, but then you're exchanging the complexity of a physics system with the complexity of an animation system.

If you were trying to actually physically simulate the bike, without constraints to ensure it always remains upright, you would need to use a physics engine that supports gyroscopic/Coriolis forces. These forces will maintain the orientation of a rotating object the same way a real bike works. As far as I know, Newton is the only game physics engine (aside from my own) that supports this force. How well this would work in practice is hard to say. Without Coriolis forces your best bet is probably to do as frob says, and use some kind of constraint to maintain orientation vertical (or maybe aligned with the ground slope).