You could just have one event for all your vehicles, just triggering a vehicle model. 
addEvent ( "spawnVehicle", true ) 
addEventHandler ( "spawnVehicle", root, 
    function ( model ) 
        local x,y,z = getElementPosition ( source ) 
        local vehicle = createVehicle ( tonumber ( model ), x, y, z ) 
        if ( vehicle ) then 
            warpPedIntoVehicle ( source, vehicle ) 
        end 
    end 
) 
 
For the bike: 
triggerServerEvent ( "spawnVehicle", localPlayer, 509 ) 
 
For the BMX: 
triggerServerEvent ( "spawnVehicle", localPlayer, 481 )