Creator Sets Information 31015 Emerald Express I bought this for the pulley wheels that are used as the driving wheels of the loco. Free-running pulley wheels are useful on cranes where the rope (string) goes several times between the hook and the jib. 3 sets make a nice little train. 31030 Red Go Kart I bought this primarily for the wheels, for use in my monorail: http://www.brickshelf.com/cgi-bin/gallery.cgi?f=517847 The wheels have a Technic cross axle hole so they can be driven. The tyres have good grip on tile-topped 2M-wide monorail track. The 2x3 plates with hole are useful too. 3 sets make a variety of vehicles. 12 wheels is enough for 2 monorail trains. These are not the cheapest sets considering most of the parts are fairly basic, but they make good stocking fillers for LEGO fans of all ages!