https://www.gov.im/categories/travel-tra...-and-rail/

The government operate all public transport with the exception of taxis. Buy direct every time. TT is sadly a time when pirates pop up to take a slice from visitors. I have no knowledge of what you have bought so this could be a good deal - but if it isn't direct from the Gov, then potentially a middle man could take a slice. Many locals of course will tell you that the gov are in fact the biggest pirates of the lot, but that is a different story altogether

The timetables are reachable through the link however in TT and Grand Prix, there are extra services called "race specials". Additionally, the system has spare bus capacity and a radio network. If a bus leaves Ramsey and gets full by Sulby, the driver can and will radio back to depot and get an extra bus tom follow on behind. This system has its limits but generally means you're sorted.