Helmets worn by cyclists could save their lives, particularly in collisions with slower moving cars, a university study has found.
Debate rages among safety campaigners and cyclists about how effective headwear really is in a crash.
But the latest academic study, which looked at 37 road deaths involving cyclists over 10 years, firmly backs the "significant protection" of helmets.
Professor Michael Gilchrist, of University College Dublin (UCD), staged computer reconstructions of all the fatal collisions to determine whether headgear would have changed the outcomes.
The research included eye witness testimonies from drivers and bystanders, vehicle damage reports for the bicycles and motor-vehicles as well as post-mortem examination reports and on-site measurements and photographs.
His findings show bicycle helmets offer "effective protection at low speeds of less than 50km/h (31 mph)".
Helmets also offer cyclists protection against secondary impacts against ground after the initial collision, it concluded.
But it also suggests headgear become less protective the faster cars are travelling, and were of "minimal" use in crashes with cars travelling at more than 50km/h (31 mph).
Nonetheless, Prof Gilchrist, head of UCD's School of Mechanical and Materials Engineering, recommends the wearing of helmets.
"The results indicate helmets should be worn as they do provide significant protection," he said.
The study concluded that some deaths could be prevented with helmets while the severity of injuries could also be reduced.
Prof Gilchrist called for better headgear to be designed and manufactured.
Last year, a leading neurosurgeon came under attack from safety campaigners after he controversially claimed that cyclists who wear helmets are wasting their time.
Henry Marsh, an eminent doctor and keen cyclist, said helmets were "too flimsy" to offer much protection.
Speaking at the Hay Festival, Mr Marsh, a consultant at St George's Hospital in Tooting, south London, said: "I ride a bike and I never wear a helmet. In the countries where bike helmets are compulsory there has been no reduction in bike injuries whatsoever.
"I see lots of people in bike accidents and these flimsy little helmets don't help."
A previous study by the University of Bath claimed cyclists who wear helmets are more likely to be hit by overtaking vehicles.
Drivers get more than 8cm (3.1in) closer to cyclists wearing helmets than they do to bare-headed riders, because they are seen as being more experienced, the research found.
It also showed female cyclists are given more room on the road than their male counterparts.