Many people rent small motorcycles to get around the countryside or the islands. A Thai city is not the place to learn how to drive a motorcycle. Phuket in particular is unforgiving to novices—don't think of driving one around there unless you are experienced. Motorcycles skid easily on wet or gravel roads. On Koh Samui a sign posts the year's count of foreigners who never made it home from their vacations because of such accidents. In the past people often did not bother to wear a helmet in the evening, but government crackdowns have made it common practice to drive as safely at night as during the day. Shoes, a shirt, and long pants will also offer some protection in wrecks, which are common. When driving a motorbike, make sure your vehicle has a rectangular sticker showing up-to-date insurance and registration. The sticker should be pasted somewhere toward the front of the bike, with the Buddhist year in big, bold numbers. You can rent smaller 100cc to 125cc motorcycles for only a few dollars a day. Dirt bikes and bigger road bikes, 250cc and above, start at about $25 per day.
Two-wheeled vacations are a growing segment of Thai tourism, especially in the north. With Thailand's crazy traffic, this is not a good option for first-time tourists to the area. That said, Golden Triangle Rider has a fantastic website (www.gt-rider.com) on biking in the area, with information on rentals and routes.