I don't know why we should make a difference between dbing with bike or with car. It's true that bikes seem to be better to db because they can fire forward, but you are also more vulnerable because the vehicle itself doesn't give you any protection against the shots you receive and you lose heatlh more quickly, bikes go backwards very slowly and also you can't fire while going backwards, so dbing with bike is not easier than with car.
And specially important: some db haters say that new players leave the server because they are dbed all the time, whereas I, as a db supporter, say that it's new players (like me) who db more. So the new players can be two things: db users, or db victims. And it depends much on one simple thing: if the default spawn weapons allow to db or not. If they don't, many new players won't buy the db weapons and will become victims of db instead of users of it, whereas if the default weapons allow the player to db, he will have more of a db user than of a db victim.
Summary: if this suggestion is accepted, the default Uzi should be changed for a MP5.