The Island of Bali is 8 degrees south of the equator, so the climate is tropical. Although the temperature stays pretty constant all year round — 28 to 30 degrees C at sea level during the day, the humidity varies throughout the year. It is highest during the rainy season which is from December to March and gradually reduces to it's lowest level from May to September, when there is a beautiful dry cooling breeze blowing across from Australia.
From a mountain-biking perspective all of the trails start between 500 and 1700 metres where the temperatures are cooler. At 1700 meters the temperatures can be below 20 degrees C and at 500 m the temperatures can be as high as 26 or 27 degrees C, but are usually less. Although a lot of the trails end at sea-level, at this stage in the trail you are predominantly going down-hill and therefore hopefully not generating much heat.
Up in the mountains, which is where we spend at least 3 or 4 nights, there is an increased chance of rain at any time of the year, however, in the dry season these are usually short showers and because it is so warm, it is not usually necessary to wear a water-proof jacket (a personal preference). It is cool in the evenings, so you will need a fleece and long trousers.
You may well find that it takes a few days to acclimatize to the heat and initially you may feel more tired than you expected for comparable trails in your own country, but on the longer tours our holidays start in the coolest areas so you will be well acclimatized by the time we reach the warmer trails!
Like anywhere in the world the weather can be very unpredictable, however, the one thing that is entirely predictable and extremely comforting is that it is never cold — biting winds and horizontal sleet and hail are definitely not on the agenda.
Here are some average temperatures and rainfall figures taken from the Washington Post. Please note that ‘Average Temperature' information averages temperature over 24 hours. The temperatures are in degrees centigrade and I assume the rainfall is in inches (?).