Velocity is velocity, the first law holds true where it is angular or linear.
Acceleration occurs when fight gravity, not in the flats.
Unless you disagree with Newton.
Leave Newton out of this. I disagree with iab.
But, while we're on the subject, here's the first law:
1) Every object persists in its state of rest or uniform motion* in a straight line unless it is compelled to change that state by forces impressed on it.
(emphasis is mine; notice how that directly contradicts your assertion above.)
I don't know what wheelset you're running, but mine spins in circles, which leads to my
bike traveling in a fairly straight line. And, the other funny thing is, both my bike and myself are subject to gravitational pull whether we're on flatground or in the hills. It's a shame, b/c I bet floating around on a bike would be fun.