The Freestyle Cyclists, with fewer than a dozen core members but hundreds of supporters, are planning an act of civil disobedience next month with a helmet-free ride along Merri Creek. The group's petition has attracted more than 600 signatures, calling for bike helmets to be made optional in Australia and New Zealand.

The group's spokesman, Alan Todd, said helmets gave cyclists a false sense of security and provided only limited protection in an accident.

Before the ride on October 6, supporters will gather at CERES Community Environment Park in East Brunswick to hear from Chris Rissel, a professor of public health at the University of Sydney.

He says mountain bikers and others are capable of deciding for themselves what kind of cycling requires a helmet.

''It's hurting the people who might ride but don't,'' he said, ''and they are exactly the people we want to get more active.''

Raquel Fajardo, 27, just wants to feel the wind in her hair. She wears a helmet only to avoid a fine and says making helmets optional would help cycling shed its dangerous image.

Helmets became compulsory in Victoria on July 1, 1990, and cyclists without a helmet today risk a $176 fine.

VicRoads' director of road user safety, James Holgate, said a 1999 review found helmets reduced head and brain injuries by 88 per cent and injuries to upper and mid-facial areas by 65 per cent.

''Helmets are designed so that the foam material they are made from spreads the force of an impact and absorbs the energy, greatly reducing the risk and severity of head injury in the instance of a crash,'' he said.

The head of neurosurgery at The Alfred hospital, Professor Jeffrey Rosenfeld, said dumping compulsory helmets would be a retrograde step.

''I'm the one who sits at the hospital looking after the victims of road trauma,'' he said. ''There are many cyclists among them, and I can't help but think that if they weren't wearing helmets their injuries would be significantly worse.'' He said the idea that compulsory helmets dissuaded people from healthy exercise was ''specious'' and he called the October 6 ride a publicity stunt and a bad example.

Several studies were pending on the effectiveness of helmets in preventing more subtle brain injuries, but they indisputably protected the skull in an accident.

However, a study published last year by Norway's Institute of Transport Economics found previous research had been biased towards older stack-hats and that modern soft-shell helmets offered less protection.

City of Yarra councillor Jackie Fristacky, who will attend the rally but will not ride for fear of a fine, said mandatory helmets were largely to blame for the sluggish take-up of Melbourne's public bike scheme.

She said in Dublin and Montreal helmets remained obligatory on the outskirts but not in the centre where speed limits were usually lower. Figures from the Transport Accident Commission show that in the past decade 57 cyclists were killed in Melbourne, compared with 40 in rural Victoria.

Victoria Police were aware of the planned helmet-free ride. A spokesman said police respected people's right to protest lawfully but would monitor the situation, taking action ''when appropriate''.