California - Three-time defending Tour of California champion Levi Leipheimer will be hoping for a repeat performance when the 2010 Tour of California begins Sunday.
Leipheimer will head up favourites Team RadioShack along with seven-time Tour de France winner Lance Armstrong who is using the Tour of California to prepare for another run at the Tour de France.
They will be joined by RadioShack teammates Chris Horner and Spaniard Jose Luis Rubiera in the most prestigious cycling event in the USA which begins in Nevada City, California before finishing in the hills above Los Angeles on May 23.
This is the fifth running of the event which was moved from February to May because of conflicts with the Giro d'Italia. This year's California race is longer and more difficult than past versions and features the first finish at a notable altitude.
"There's a lot different about this year's Tour of California," Leipheimer said. "We're here in May, not in February, and the whole feeling of it is different."
There will be 16 teams with more than 125 riders from 23 countries, including Belgium, Finland, Spain, France, Germany, New Zealand and Sweden.
"We are proud of the powerful and talented group of international and domestic cyclists set to participate in the 2010 Amgen Tour of California," said Andrew Messick, president of organizers AEG Sports.
"From Tour de France champions to Olympic medalists and world champions, this field is one of the best that has ever competed on American soil. The growing reputation of the Amgen Tour of California has resulted in a very accomplished field of cyclists, which should make for a great race."
Besides RadioShack other well-known teams include Team HTC-Columbia, Quick Step, Team Saxo Bank and Garmin-Transitions.
"This is a big race for us with Radio Shack involved," Armstrong said. "There so many retail outlets in the around the country and particularly in California. It's no secret this is a priority for us."
Belgian national champion Tom Boonen of Quick Step is one of the world's best single-day racers.
The 2005 world champion has won the spring classic Paris-Roubaix three times, but he was banned from the Tour de France last year after testing positive for cocaine for the second time in less than a year.
British cyclist Mark Cavendish, of Team HTC-Columbia, is the best sprinter in the world. He has won six stages at the Tour de France, three at the Giro d'Italia and two at the Tour of California.
Tour de France runner-up and Luxembourg champion Andy Schleck of Saxo Bank should also be in contention.