Traffic psychologist Dr Ian Walker's previous research said beware of White Van Man, his new work - carried out by himself with a sensor strapped to his rear carrier - suggests that motorists of all kinds driver closer to cyclists wearing helmets and further away from female cyclists.
This echoes research carried out by the Transport Research Lab which found that motorists think helmet-wearing cyclists are "protected" and "better cyclists" so drive closer to them when over-taking.
According to Dr Walker's new research, motorists get more than 8cm closer to cyclists wearing helmets than they do to cyclists without helmets.
Dr Ian Walker used a bicycle fitted with an ultrasonic distance sensor to record data from overtaking motorists in the South West of England.
He found that motorists were twice as likely to get skim him when he was wearing a helmet.
"Drivers think, 'He knows what he's doing, he won't do anything surprising'. But that's really quite a dangerous thought, particularly as so many cycling novices are told to wear helmets," said Dr Walker.
His research will be published in the journal Accident Analysis & Prevention.
Dr Walker found that the average motorist gave cyclists 1.33m of room, the average truck got 19cm closer and the average bus 23cm closer.
He must have looked quite a picture when conducting his next test. The bearded academic rode with a long blond wig to see if there was any difference in passing distance when motorists thought they were overtaking a woman. Vehicles gave 'her' an average of 14cm more space when he was pretending to be a female cyclist.
So, here's an idea for helmet manufacturers: make some models with long pony-tails sticking out the back...