The 'context' meaning that the picture must be able to tell a story ... like what aspect of the race are you depicting here ? Someone trying to breakaway, someone struggling ? Someone having a strong race ? Or just the pure pace of the event ?
Panning in sports is more often than not under-estimated by most people. It takes a pretty fair level of skill to snap good panning shots. In my example "_MG_0570.jpg" was shot at 1/160, on a slow lens. Would suggest using what's available for lighting and tweak your shooting to it. I've shot as low as 1/50 but only if I have the space to move freely.
Note though, learn the idiosyncrasies of your camera's AF. I used to own the 40D and now I shoot with the 5DII. (the shot examples were on a 5DII). They both behave somewhat differently given similar situations and same lenses used. I find its easier to shoot in manual at night as lighting is never even, and can result in erratic exposure readings. But.. do that if you know what you're doing. Else, AV, TV is preferred by most.
If you can't get high shutter speeds, do more panning. Do more head-on shots. Get up close.
If you must use flash, please don't flash into their faces/eyes. A side fill flash from a distance is perfectly fine though. As its hazardous in tight criterium races for cyclists if they even lose concentration for a split second from a head-on flash.
Here's 'Tinker' Juarez with the setting sun in the background and dim, dim evening light. Flash was used for fill and this was shot using an ultrawide 12-24mm on the 5DII. ISO was 1600, at 1/125 shutter. Just to illustrate the 'slight flash fill' ...
http://i235.photobucket.com/albums/ee89/KangSw/Tinker%20Juarez/Tinker-Sunset-background.jpg?t=1242795211