British princes William and Harry set off Saturday on a grueling 1,000-mile motorcycle rally in South Africa to raise money for charity.
The pair joked that they had a wager on which royal tumbles from their bike the most during the eight-day off-road adventure.
"It's going to be very challenging and we're expecting to fall off many a time," said Harry, 24, before more than 80 riders set off from the holiday resort of Port Edward on South Africa's southeast coast.
A crowd cheered the riders as they hit the winding dust road bound for the southern coastal city of Port Elizabeth.
William, 26, who next year will begin training to be an RAF search and rescue helicopter pilot, said he and his brother had decided to take part in the rally "because it's a mixture of adventure and charity."
Funds raised through the princes' participation in the Enduro Africa 08 event will be divided among UNICEF, the Nelson Mandela Children's Fund and Sentebale, a charity established by Prince Harry to help disadvantaged children in Lesotho.
Harry, an officer in the Household Cavalry regiment, said he was looking forward to spending some rare time together with his brother.
Both brothers ride high performance motorbikes when in the UK, but William said they had not trained for the event.
"We both ride bikes at the moment but on-road biking is completely different. All the off-road stuff is up hills, down slopes, across rivers and is all rocky and hilly," William said.
Questioned about which royal was the better rider, William said, diplomatically, that "we're both quite good actually," while his brother quipped: "We'll have to wait and see in a couple of days time."