According to many seasoned skaters, larger wheels offer more speed than smaller ones. You can test this with a simple experiment by skating with both 50-mm- and 60-mm-in-diameter wheels along the same distances. Get a partner with the same level of skill as yourself and time both of your speeds across 10-, 50- and 100-meter distances with a stop watch. Change your wheels and time yourselves again. Repeat the process on a sloped surface as well as a flat one.
The friction between the wheel and the surface below it is hugely important to maintaining control of a skateboard. In this experiment, take five people of similar skating abilities to skating venues with different surfaces such as asphalt, concrete or wood. Record how many times you fall over the course of an hour and what you were doing each time you fell. Also make sure you and your partners have wheels and boards of similar style.
Some people claim that because you are just pushing yourself around on a board skateboarding is not real exercise. Test this with yourself and two other partners in similar physical condition. Weigh yourselves beforehand and have one partner skateboard for an hour a day, one perform 15 minutes of aerobic exercise and one do no strenuous exercise for a week. Weigh yourselves at the end of the week and compare the skateboarder's weight to that of the other two partners.
Skateboarding is a relatively dangerous sport and requires a good deal of concentration. But does this mean skateboarders are better at concentrating in general? Test this by showing a skateboarder and a non-skateboarder a list of several items, removing the list and seeing how many they can recall afterward. This will test their abilities to concentrate on things they have recently learned. Follow this up by doing the same experiment with a different set of items, but while playing a loud or annoying noise in the background. If possible, perform the test on multiple skaters and non-skaters to gather a broad sample.