The original poster's event has come and gone, and so has the poster himself, so I'll just leave general comments.
I photograph bicycle races at least every other week. Wide angle lenses are pretty much useless, even on crop sensor cameras. They capture too much, even if up close. The choice of lenses, of course, depends widely on how you frame it, and how close you are.
When I've been able to get within feet of the cyclists, and they're winding through an S Curve, a medium telephoto will work on a crop sensor camera. I use a 24-70 on a 7D. This accounts for the wide frame you'll want for cropping, as well as a minimum amount of distance. You'll need something with a fast frame rate, or you'll likely miss the shot you want to get.
I've been downhill on a mountain side during mountain bike races, shooting up to capture mountain peaks in the background. I shot between 24mm and 30mm on a 7D, and you don't want to get much closer!
The best lens, BY FAR, for bicycle races is the 70-200mm 2.8 IS I or II, in combo with a crop sensor camera. I've shot both lenses. On a crop sensor camera, which also allows faster frame rates than the 5D, the lens is fast, and just the right focal length. I shoot it 90% of the time. If gives enough distance, and the 70-200 range is great. If I had to pick, an 80-220 is what I'd normally shoot at. Again, this gives enough room for cropping. If you want tighter shots, you'd have to go with a 300mm or 400mm, if you're at a distance.
The 70-200 2.8 is great, because it's also sharp enough and fast enough to support a 1.4x teleconverter. I've only shot with a teleconverter a couple times, but if I wanted tighter shots, that's the best of both worlds, without too much extra baggage.
Being at longer distances with a 300mm or 400mm is too long. It compresses your subjects too much. But if you don't have an option to be closer, or need absolute separation between subject and background, that's one way to do it.
In either case, you won't want to shoot at 2.8. You only have one chance to get a shot of the lead racers. My colleage, who has shot hundreds of races, recommends f/5.6 to f/8.0.
As far as flash is concerned, if you haven't experimented extensively, your results will be disappointing. Cyclists are moving far too fast, at far to great of a distance to be of much use. Yes, they could use a flash in the face below the visor, but you'd need an off-camera flash, with an assistant holding it, and zoomed, for it to be of much use.
High-speed sync is not valuable when the flash to subject distance is too great. The range is too short.
There are some ways you can do this, especially if the cyclists are run through a choke point, where you have a very definable range. Recycle time is also an issue. You'd likely need several flashes to combat recycle and power issues.
Check out Syl Arena's "Speedliter's Handbook". Very good guide and reference.
