Cyclists are being warned by Avon and Somerset Police to take better security measures when they leave their bikes in Bath city centre.
Nearly 80 bikes have been stolen in the past four months and police believe an organised gang could be responsible.
Sixty-five per cent are mountain bikes but road, stunt and hybrid models have also been taken.
City centre beat officers have been carrying out undercover patrols in an attempt to catch the thieves in action, and are now calling on cyclists to make their property more difficult to steal.
PC Roger Parker said: “It’s frustrating that some owners fit an inferior lock – and sometimes none at all – when they leave their bikes and think they will be safe.
“We recommend that people buying a bike spend at least another ten per cent of the price on a solid thief-proof lock. Also, they should remove their quick-release wheels and lock them to the frame of the bike and to cycle racks.”
Officers have asked bike shops throughout the city to co-operate and spread the security message.
Anyone with information about bike thefts is asked to contact the police on 0845 456 7000. Or call the charity Crimestoppers anonymously on 0800 555 111 or via www.crimestoppers-uk.org. They never ask for your name or trace your call.