IT comes naturally to most firefighters to have exceptional physical fitness, but for these Liverpool crew members, fitness will mean the difference between taking the easy or the hard road literally.

Right now they are on their bikes, somewhere between Sydney and Wagga Wagga, on a 400-kilometres-in-four-days challenge, called ``400 in 4'', to raise money for the burns unit at The Children's Hospital at Westmead.

The charity cycle has been running for five years under the management of Liverpool firefighter Scott Hanley.

He said the only real challenge during the four days was possible wet weather.

``Everyone's champing at the bit,'' he said, just before the crew set off.

Twenty-four NSW firefighters are involved in this year's cycle, and have so far raised $95,000 towards their $150,000 goal.

With four in the support crew and an ex-Olympic cyclist turned firefighter leading the pack, the gang will pass through Goulburn, Yass, and Gundagai, visiting schools and community groups and taking fire safety messages and demonstrations with them.

``The towns all pitch in and even try to out-do each other with donations,'' Mr Hanley said.

To track their route, make a donation or find out more about the cycle, visit 400in4.org.