These are long distance rides - in the UK typically 200km, 300km, 400km and 600km (but can be shorter or longer) - that must be completed within a specific time. The maximum time allowed to complete the ride is measured from the time you set off, to the time you finish. There are no allowances for breaks, meals, rest, sleep or mechanical breakdown. So in practical terms this means you have to ride fast enough to generate your own time buffers, especially on the longer events where you will need to rest or even sleep for a while. (This is not as tough as it may sound, as the maximum time limits are quite generous, with this in mind). Audax United Kingdom (known as Audax UK or AUK) is the foremost long-distance cycling association in the UK, and the biggest in the world. It was established in 1976 and oversees the running of long-distance cycling events, and, using a system of timed checkpoints, validates and records every successful ride. They have an extensive FAQ on their website, so rather than re-hash it all here I will offer the following links for anyone who is interested in challenging themselves with an Audax event: Audax FAQ: http://www.aukweb.net/aboutauk/faq/ Membership FAQ: http://www.aukweb.net/aboutauk/membershipfaq/ For anyone who is interested there is also a brief history here: http://www.aukweb.net/aboutauk/history/ Enjoy!