When one person is being followed by a couple (Its usually an awkward couple).
-The first wheel on a tricycle is being followed by two wheels, real bikes have two wheels
My friend took this chick out to a dance and they just followed me around. OMG this must be a first wheel!
First wheel is the person that is the lonely wheel in the front of a tricycle and the happy couple are represented as the back two wheels. Being the first wheel usually puts you in an uncomfortable position given then fact that you are forced to be around your friend and her/his mate. But remember, a tricycle can't function without the front wheel so the first wheel is a necessary component of the back two tires relationship.
Me: "Gosh Sammy, you are such the first wheel of this tricycle...look at Robby and Natalie that happy couple of tires back their and you're up here in the front such a lonesome tire...the first wheel"
Sammy: "Yea *sighs* it sucks being the first wheel...:("