Police last year handed out half the number of fines in Whanganui for cycling without a helmet than three years ago.
The number of cyclists penalised by police for failing to wear a helmet dropped from 1141 in 2014 to 493 last year in the wider Central District region - a decrease of 57 per cent.
A cyclist could be fined $55 for not wearing a helmet and it has been mandatory in New Zealand since 1994.
Owner of The Bike Shed in Whanganui Doug Rennie said he thought it was a combination of more people complying with the law and maybe a touch of police turning a blind eye.
He said in the last 18 months he has noticed more people buying helmets - but that number would plateau at some point.
"I would say the people who are not wearing helmets are always going to be the ones not wearing helmets," Mr Rennie said.
"We used to get a lot of that [in the store] but I certainly haven't seen that in the last 18 months.
"Everyone should wear a helmet. Helmets definitely save lives."
Police however, denied turning any blind eye. Superintendent Stephen Greally said safety on the road was a priority for police, whether the road user was in a car, on a bike, or using some other form of transport.
"There has been no change in the way police enforce laws for bicycle related offences," he said.
"When an officer attends a job, they are responsible to assessing the situation and providing an appropriate response to ensure the safety of the public.
"The response from an officer could range from an infringement notice to a warning or prevention advice, this decision is made at the officer's discretion."
Mr Rennie, who is also president of Whanganui Mountain Bike Club, said Whanganui's cycling culture was developing, and he praised council efforts to build cycle lanes and welcomed plans to construct more.
Cycling Action Network's Patrick Morgan also said he believed the fall in helmet infringements seemed to be a result of changing police priorities.
"I think it's just police have better things to do than stop people on bikes and fine them for helmet use or misuse," Mr Morgan said.
"I welcome police resources going into higher priorities."
Mr Morgan says there is "thin" evidence that mandatory helmet use laws work, and that Australia and New Zealand are the only two countries that have such a law.
"There's enough evidence that mandatory bicycle helmets hasn't worked as intended, and that's why it's our policy to review the law, to see if it's working as intended - but it's not our top priority."
He said CAN's position was not a call for making helmets optional, but to review the wider effects of helmet-wearing legislation.
Mr Morgan said he doesn't normally wear a helmet when cycling on the road. He has a legal exemption - on medical grounds as he said helmets gave him headaches and migraines. He said he was stopped three or four times per year.
"I wear it if I do something dangerous, like mountain biking or something risky like that. But [not if I'm] just riding around my neighbourhood or on a separate New Zealand cycle trail."