The rider was travelling along College Road, B2052 on his blue Suzuki GSF 600 when he was involved in a collision with a black BMW 320i in Millmead Road.
The rider of the bike, a man in his 20s, was flown by air ambulance to a London hospital with serious injuries which are described as life threatening.
Officers from the Serious Collision Investigation Unit would like to talk to anyone who witnessed the incident or has dash cam or mobile phone footage. Anyone with CCTV is also asked to get in touch.
Investigators are also keen to talk to the driver of a black Audi estate which was seen travelling in the opposite direction of the motorbike prior to the collision on Millmead Road.
Road closures are in place while the investigation continues.
Anyone with information can call the SCIU appeal line on 01622 798538 or email [email protected] quoting reference MM/SW/091/20.