Madonna

US pop star Madonna rides a bicycle on June 16, 2012 in the center of Florence. AFP PHOTO / Claudio Giovannini (Photo credit should read CLAUDIO GIOVANNINI/AFP/GettyImages)

British actress Kelly Brook

LONDON, ENGLAND - AUGUST 25: Kelly Brook launches The Mayor of London's Sky Ride on August 25, 2011 in London, England. (Photo by Ian Gavan/Getty Images)

Prince Charles

<> at Clarence House on July 27, 2011 in London, England.

Arnold Schwarzenegger

Hollywood star Arnold Schwarzenegger rides a London Cycle Hire Scheme bicycle during a photocall with London Mayor Boris Johnson, in London, on March 31, 2011. Schwarzenegger met Johnson Friday to exchange ideas on how to drive forward markets for low and zero emission technologies. AFP PHOTO/Ki Price (Photo credit should read Ki Price/AFP/Getty Images)

Elle Macpherson

<> on June 17, 2009 in London, England.

Danica Patrick

FONTANA, CA - OCTOBER 14: Race car driver Danica Patrick rides her bicycle at the California Speedway on October 14, 2005 in Fontana. California. (Photo by Frederick M. Brown/Getty Images). *** Local Caption *** Danica Patrick

Former President George W. Bush

BEIJING, CHINA: US President George W. Bush warms up before taking a bicycle ride with Chinese Olympic hopeful cyclists at a off road facility in Beijing, 20 November 2005. President Bush is on a tour of 4 Asian nations, Japan, South Korea, China, and Mongolia. AFP PHOTO/Paul J. Richards (Photo credit should read PAUL J. RICHARDS/AFP/Getty Images)

Actress Emma Thompson

British actress Emma Thompson fools around with a bicycle as she arrives at the British premiere of her latest film, Brideshead Revisited, in Chelsea, London, on September 29, 2008. AFP Photo/ Max Nash (Photo credit should read MAX NASH/AFP/Getty Images)

Sting

PARIS, FRANCE - OCTOBER 1: Sting of The Police arrives on a Velib bicycle before being inducted as 'Knights in the Order of Arts and Letters' at the Ministry Of Culture on October 1, 2007 in Paris, France. (Photo by Julien Hekimian /Getty Images)

President Barack Obama and daughter Malia

US President Barack Obama (R) and his daughter Malia ride bikes in Manuel F. Correllus State Forest in West Tisbury, Massachusetts, August 23, 2011, during their family vacation to Martha's Vineyard. AFP PHOTO/Jim WATSON (Photo credit should read JIM WATSON/AFP/Getty Images)

Actress Katharine Hepburn

ENGLAND: Photo of the American actress Katharine Hepburn riding a bicycle between scenes of the classic American movie "The African Queen" by John Huston in England in 1952. AFP PHOTO (Photo credit should read AFP/AFP/Getty Images)

Robin Williams

387619 08: Actor Robin Williams, center, and cyclist Lance Armstrong, right, wait in the starting line for the Ride for the Roses bike ride April 8, 2001 in Austin, Texas. The event raises money for the Lance Armstrong Foundation, which goes to help cancer survivors. (Photo by Joe Raedle/Newsmakers)