Hundreds of cyclists are expected to take part in a ride across the Cotswolds in memory of a physicist and cycling fan who died after being knocked off his bike.

The 105-mile Circuit of the Cotswolds event, starting in Witney on Sunday, has been organised to commemorate the life of Oxford University graduate Dr David Ryan.

Dr Ryan was killed on June 29, 2004, after being struck by a speeding car while riding his bike in America. He was 32.

The driver responsible for the crash, Joshua Paniccia, was sentenced to up to three years in a New York prison for negligent homicide.

After studying for a DPhil at Oxford University's department of physics where he achieved the highest finals mark in his year Dr Ryan worked at Eynsham-based Oxford Instruments, before being headhunted by US company General Electric. He had been in New York for three years and had just been awarded a £2m grant by the US government to develop a new generation of high-resolution MRI scanners, which help detect cancer, when he died.

Fellow Oxford graduate Jim Henderson - an engineer and member of the university's Dark Blue Cycling Club - has organised the Cotswolds ride for the second year running.

He said: "The ride recalls the cycling he enjoyed while a student at Oxford long, hard and hilly. Dave was the ideal clubmate, always ready for a ride, never complaining about the weather or the hills and just as happy touring or racing. The ride that commemorates him is in that spirit."

The cyclists will set out from Witney's Langdale Hall from 7.30am on Sunday, before setting off on a route that will take them through Charlbury, Shipston-on-Stour, Chipping Campden, Broadway, Winchcombe and Burford and back to Witney. Some will take a shorter 71-mile route.

Money raised by the event will go to Yorkshire Cancer Research. Dr Ryan was originally from North Yorkshire and was a supporter of Cancer Research UK, Britain's biggest medical research charity.

The first Circuit of the Cotswolds last year attracted 250 cyclists and raised £3,000 for the charity.

Entry numbers are expected to more than double for this year's event and Mr Henderson - five times the National Hill Climb Champion - is hoping the ride will raise about £6,000. For more details and to make a donation, log on to www.circuitofthecotswolds.org