Jordan Childs is counting on a commitment to ride Surprise Baby at a weight below his comfort zone will pay off in the Melbourne Cup.

Childs won The Bart Cummings on Surprise Baby at Flemington a month ago which clinched the lightly raced stayer his spot in Tuesday's Cup.

And when Surprise Baby was given a 1kg penalty for that win to take his Melbourne Cup weight to 53.5kg, Childs set about the task of getting down to the weight.

He hopes it will all be worth it.

"That's what I'm doing it for," Childs said.

"The horse is going very well. I think we're in with a live chance. In racing you just always need a bit of luck. But if we can get a bit of luck we should be right there.

"I've had systems in place and the diet's going really well. I'm within striking range now.

"It's been hard but I guess it's good to know you're doing it for a good chance."

For the past two weeks Childs has had fitness guru Ron Johnson living with him, helping him with his diet and training.

"He's been a big help," Childs said.

"When I first found out Surprise Baby was getting 53.5kg I started doing it myself and I got him to come down the last two weeks. He's been training my arse off, it's been hard work but it's really starting to show now.

"It's all just clean eating and lots of exercise really. I pretty much train twice a day if I'm not race riding. Or if I'm race riding just once a day. It's pretty relentless."

Childs was around 54.5kg at Flemington on Saturday during the Derby Day meeting.

"It's all about probably just maintaining that weight until probably Monday and then just shred the last little bit off," he said.

The 23-year-old's biggest win has been the Group One Blue Diamond Stakes on Written By last year.

He will be having his second Melbourne Cup ride on Tuesday, having finished 18th on the Mike Moroney-trained Sound last year.

"You start out and you just want to ride in the Cup and I had that experience last year and the whole lead-up to that. So I know what to expect this year," he said.