Being a strong cyclist in a temperate climate does not mean you can climb mountains in Bali. The tropical heat can sap strength, making even shallow hill climbs an arduous endeavor. Moreover, the heat can have more serious consequences than the embarrassment of puffing and panting up a seemingly easy grade.
Like the chill factor, which indicates the aggregate cooling effect of both cold and wind, the heat index measures both air temperature and humidity: factors affecting the body's ability to cool itself through perspiration. Daytime heat index in Bali ranges between 30-40 C, and can reach 50 C on an exceptionally hot, humid day.
In these conditions, experienced cyclists and rank novices alike must take care to avoid dehydration and heat exhaustion, which can lead to heat stroke, a serious medical emergency. You should wear loose-fitting, light-colored clothing or a cycling jersey and shorts, and avoid riding between ten AM and two PM.
Signs of impending distress are easy to spot: muscle cramps or light-headedness are clear signals that you should stop and rest in the shade for a few minutes. However, profound weakness and fatigue, nausea or vomiting, or cold, clammy skin mean that your cycling adventures are over for the day. Riders losing consciousness for more than a few seconds, suffering mental confusion or a severe, throbbing headache, or with red, hot, and dry skin need immediate medical attention.
As any holiday maker in Bali will tell you, the key to having a good time is to drink a great deal, though in this case the beverages should be water, diluted fruit juices, or sports drinks. Starting a ride fully hydrated by drinking a few glasses of water or juice the previous evening and again at breakfast will greatly reduce the risk of heat-related distress during a ride.
On the road, your water bottle is your best friend. Thirst is not a reliable indicator of dehydration, so you should drink a mouthful of water at frequent intervals, whether thirsty or not. For rides lasting longer than an hour, sports or isotonic drinks are highly recommended. Fortunately, these drinks are readily available almost anywhere on the island.