Cyclists who wear helmets are more likely to be knocked down by passing vehicles, research suggests.
A study found that drivers tended to pass closer when overtaking cyclists wearing helmets than those who were bareheaded, by 8.5cm on average.
Dr Ian Walker, a lecturer at Bath University, used a bike fitted with a computer and an ultrasonic distance sensor to analyse 2,500 overtakings in Salisbury and Bristol. He was struck twice during the experiment, by a bus and a lorry, while wearing a helmet.
The average car passed 1.33m (4ft 4ins) away from the bicycle, whereas the average lorry got 19cm (7.5in) closer and the average bus 23cm (9in) closer.
There was no evidence of 4x4s (SUVs) getting any closer than ordinary cars.
Dr Walker said: "This study shows that when drivers overtake a cyclist, the margin for error they leave is affected by the cyclist's appearance. By leaving the cyclist less room, drivers reduce the safety margin that cyclists need to deal with obstacles in the road, such as drain covers and potholes, as well as the margin for error in their own judgements.
"We know that helmets are useful in low-speed falls, and so definitely good for children, but whether they offer any real protection to somebody struck by a car is very controversial. Either way, this study suggests wearing a helmet might make a collision more likely in the first place."
Dr Walker thinks the reason drivers give less room to cyclists wearing helmets is because they see them as "Lycra-clad street-warriors" and believe that they are more predictable than those without.
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