"The 27:02 reported for Haile Gebreselasie (ETH) at Doha QAT on 11 Dec 2002 was illegally aided by a sizeable lead vehicle that provided drafting for the lead men's pack. At times, Gebreselasie was reported to be within one meter behind this vehicle. A statistical analysis of the race provides an estimate that this drafting produced times that were 47 seconds faster than had the lead runners not had this advantage. IAAF Rule 143 clearly prohibits such assistance. This mark has been recognized by the IAAF."
as quoted by the Road Racing Statisticians making Sammy Kipketer's 27:18 the world road 10K best (I believe)