Kate Middleton's younger siblings, Pippa and James have started their 3,000 mile bike journey across America to raise money for charity.

"On 14th June, my brother and I, along with six friends will be setting off on a West to East Coast Race Across America (RAAM). This relay cycling event spans 3000 miles, 12 states and 88 counties. We are aiming to complete this non-stop challenge in eight days, riding between 350 and 500 miles a day," Pippa recently wrote on her website, Just Giving.

They are riding for the charities British Heart Foundation, which Pippa is an ambassador for, and the Michael Matthews Foundation.

According to Race Across AmericaParticipants have a maximum number of nine days to complete the Race Across America and some parts are pretty rough—they will end up climbing more than 100,000 feet during the journey.

That's a pretty difficult ride even for the most expert of riders so it will be interesting to see how Kate's younger siblings handle the elements thrown their way.