The owners of California Chrome are putting all their hopes into the chestnut colt to win the Kentucky Derby.

After all, he is the only horse they own.

California Chrome, based at Los Alamitos racetrack in suburban Los Angeles, is the early 5-2 favourite for the 140th Derby with good reason.

He has won four straight races by a combined 24 lengths under Victor Espinoza who won the Derby in 2002 on War Emblem.

"He's so light on his feet," Espinoza said. "He just does things so easy and makes my job easy."

California Chrome's owners, Steve Coburn and Perry Martin, are blue collar rather than blue bloods.

A trainer called them "dumb asses" for getting into the racing game, inspiring the duo to put the letters DAP on their silks, which stands for Dumb Ass Partners.

"We're going to go down in history," Coburn said.

California Chrome is the product of an $8000 mare and a $2500 stallion. He has already earned more than $1 million, making it somewhat easier for Coburn and Martin to turn down a pre-Derby offer of $6 million for a 51 per cent stake in the horse.

"We've been blessed with this colt," Coburn said. "The first time we saw him, we knew it was going to be something special."

At 77, Art Sherman, who oversees California Chrome, would be the oldest trainer to win. His colt would be the first California-bred to wear the garland of red roses in 52 years.

"He's feeling good and he's doing good," Sherman said. "He's coming up to this race right."

Wicked Strong is the early 6-1 second choice. The colt is named for the victims of last year's Boston Marathon bombings and is trained by Jimmy Jerkens, who has his first Derby horse.

Trainer Todd Pletcher has four horses in the Derby - Danza and Intense Holiday are both 8-1 while his other two are longer shots, 30-1 Vinceremos and 50-1 We Miss Artie.

Three-time Derby winner Bob Baffert is down to 20-1 shot Chitu after being forced to scratch early second favourite Hoppertunity because of a minor foot problem.

"California Chrome has proven he's a really good horse," Baffert said. "(But) there's a lot of parity in this field. Everybody might have a chance."

The forecast for Saturday (Sunday AEST) is for sunny skies and a high of 73 degrees (23C), with a crowd of at least 140,000 expected.