Cycling stars Lance Armstrong and Robbie McEwen will take part in a flood fundraising ride in Brisbane a day after they finish the Tour Down Under in South Australia.

Participants in the 25-kilometre charity ride will each contribute a $50 donation fee towards the flood relief appeal.

It is hoped the ride will raise up to $500,000 for the Premier's Disaster Relief Appeal.

The route starts at the RNA showgrounds, then runs over the Story Bridge and through Brisbane's eastern suburbs, before returning to the showgrounds.

It will be the second fundraiser the cycling legends have organised since floods devastated Queensland this summer.

Hundreds rode along Adelaide's coast from Glenelg to Semaphore and back before the Tour Down Under began last weekend.

Seven-time Tour de France champion Armstrong suggested Monday's fundraiser to his Brisbane-born team-mate McEwen on Twitter on Thursday morning.

"I think a Twitter ride in Brisbane would go down very well. Show our support for Qld. Let's do it!" McEwen replied.

Armstrong has used the social networking site to announce several "Twitter rides" around the world in recent years, which sometimes attract thousands of other cyclists.