One of the warmest Manx Telecom Parish Walks in recent times faces the 1,304 who registered.
It started at the National Sports Centre at 8am.
Organisers are advising competitors to slap on the sunscreen, wear loose clothing and drink plenty of fluids.
The pace could be slower than recent years due to the forecast hot sunshine.
Added to that, champion Michael George is rumoured to have an injury niggle and Jock Waddington and Vinny Lynch recently competed in the 100 mile race in Holland.
Could that mean Richard Gerrard starts as favourite or will someone else come to the fore?
Drivers are urged to be extra vigilent and be prepared for delays - there are a number of road closures, temporary one-way systems and no stopping zones along the 85 mile course.
And organisers are urging support vehicles to act responsibly and park sensibly.