Downhill mountain biking photography can be very challenging. The lifts only run during the worst hours of sunlight (midday), and the shadows of the trees cause very complex and shadowy situations to deal with. My advice for mountain bike photography: Purchase a powerful flash (such as the SB-800 from Nikon), a quantum turbo battery pack (allows for ultra fast flash reloads for multiple shots of one trick), and a set of wireless radio triggers (Mine are Pocketwizards, but I also highly recommend the Alienbees Cybersyncs). Better yet, purchase two of these complete setups! These are very expensive though, and if you are just starting out and a Nikon user, you only need the SB-800 or SB-600, and can control them from your camera's pop-up flash. The flash will have to be line-of-sight, and you will have to time out your shot just right since midday light generally means 1/2 to 1/1 power.
This setup allows you to properly deal with those spotty forest lighting situations. I generally place the flash around 10 feet from the rider, aim it higher than you might think you have to, and set it to 85mm or 105mm zoom for more kick. It appears I've gotten ahead of myself though, and must now backtrack to the start of the whole process... First off, you need a talented mountain biker that is willing to stop repeatedly, and climb back up the trail for multiple attempts. Before shooting with said biker, you must build up a good rapport as this will make the whole process a lot easier, and make them more comfortable with having a camera in their face all the time like paparazzi.
From there, I choose to ride ahead of the model/rider, and scout the best locations for my vision. I find that although knowing a trail in advance can help you get to locations faster, if you don't know it all you won't overlook certain parts of the trail. This, in turn, leads to great shots that had you known the trail, may have never come into being. Once I have found something that may work, I have the rider roll through it once to become familiar with it, and so that I will know the best spot to setup my shot. I then setup my flash like I discussed above and have the rider stand on the corner for a quick test shot. At this point I can adjust all my camera settings and make sure everything is just right! Usually a shutter of 1/250th to avoid high speed sync, an aperture right around f/7.1 to ensure the sharpest image possible and keep highlights from washing out, and an ISO of 200. These are only rough guidelines, but the aperture is usually the only thing I change.
The rider climbs back up for the shot and yells when ready. I confirm my focus (almost always pre-focus on the key spot), and the rider hits the feature. Sometimes things will go wrong, or you will be disappointed with the results. If this happens, show the rider the image, and ask if they are willing to hit the feature again. Don't get too hung up on it if they aren't interested in making that climb back to the top again, you will have plenty more opportunities in other locations.
My best advice for a stock shoot like this: SHOOT EVERYTHING THAT HAPPENS!! From when the rider is unloading the bike off the car, lunch time, riding the gondola, staring into the distance while they wait for you to finish setting up on a berm. Shoot anything and everything that happens. You will be surprised by the resulting images. Always remember that when shooting any sport or activity, there is more than just the action that makes that sport mean so much to people.
Above are some shots that I captured from this short day of photography. If you have any questions please contact me at email@example.com, or comment below this post. I am trying to create a strong following on this blog so if you enjoy my posts, please add yourself as a follower!