Apprentice jockey Harry Coffey has a unique reason for adding to his winning tally at Caulfield on Saturday.

Coffey will ride Clang And Bang who will be chasing a hat-trick of wins - but it is this Saturday which holds strong significance for the teenager.

He has defied the odds to become a jockey while fighting cystic fibrosis.

The 17-year-old will climb aboard Clang And Bang in the CFV Great Strides Handicap (2000m) on what will be Caulfield's Cystic Fibrosis Victoria Summer Race Day.

As well as the normal fitness regimen any jockey must endure, Coffey must undergo 45 minutes of physiotherapy every day and spend a fortnight in hospital every three months for monitoring.

But the progressively debilitating illness has been relegated to the back of his mind as he concentrates on backing up from his recent Ararat Cup win on trainer Darren Weir's gelding.

Weir is impressed with the determination of Coffey, who will speak about his illness at a function at Caulfield.

"He's been on medication all his life but it doesn't affect his riding," Weir said.

"I've never asked about his health. They just say he's healthy and that's the main thing."

As for Clang And Bang, Weir has no plans to spell him despite a preparation which stretches back to March and includes two wins in the winter.

"He's going really well but, geez, he's been in work forever," Weir said.

"He won a couple here in the winter and he's been racing ever since.

"He's a six-year-old gelding so there's not much future for him."

Weir described Clang And Bang as a reliable but limited horse.

"He's no star but he's been making his own luck by going forward.

"You certainly wouldn't have thought he'd be running in a $100,000 race on a Saturday though."

Weir will be going into the race with "an open mind".

"He gets no weight, he has 51 kilos and he'll go forward so he'll give them something to chase."

Clang And Bang will get a rest "as soon as he puts in a bad run" according to Weir.

The gelding will be one of two rides for Coffey along with Littleriver Ruby for Terry and Karina O'Sullivan in the fifth event.

It will mark Coffey's first day riding at a Saturday metropolitan meeting.