Shearer and Chiles set off from St James' Park this morning at 8.40am. There's video on the BBC.
Newcastle FC gaffer Kevin Keegan said: "Good luck, guys, it was good knowing you."
Shearer and Chiles have been joined on the ride to London by Mark Willey, a reporter for The Sun. His reports on the prep for the ride started yesterday.
No other newspaper will be allowed access to the star pair.
Willey - like Shearer and Chiles - is riding a Specialized Roubaix. Specialized has also supplied a support van and mechanic.
Sponsor the stars here.