I've been fortunate enough over the years to participate in shooting quite a few rolling, or car-to-car shots. While most have taken place on closed circuits, I do recall at least one shoot taking place on a public road. I don't recommend that unless you have an isolated location and a genuinely deserted road.
The rolling shot, when executed properly, gives a really exciting look to the vehicle you're shooting. For me, I find the rolling shot much more pleasing and less surreal than the rig shots that seem to be popular these days... especially with the import tuner car set. I guess it's just a matter of personal taste, but for me, there's something powerful and real about the car-to-car rolling shot.
So... how do you go about it? Well, the process is fairly straight forward. However, things happen pretty quick and there are lots of things that can creep in and spoil the final image. Hopefully, I can give you some pointers on what to watch out for.
Obviously, you need a good DSLR with constant focus and a pretty good burst rate. You'll also want a fairly wide angle lens... preferably a zoom. In my last shoot I used a Canon 40D with a Sigma 12-24mm zoom. I have also used my Canon 16-35mm, but there's a reason I went with the Sigma.
I should also add that you'll want to throw in a good sized compact flash card. You're going to want to shoot with reckless abandon. Stopping to load a new card is not a good use of your time.
Next, you'll want to find a chase vehicle that will open at the back and allow you to comfortably (not going to happen) lie on the floor. Mini vans with side doors can be nice too. They give you the option of doing a rolling side shot.
In addition to the vehicle, you need a driver that understands what you're doing and an assistant to help keep you in the vehicle and to communicate with the chase vehicle driver. DO NOT ATTEMPT THIS WITHOUT AN ASSISTANT.
Before you head out, sit everyone down and discuss the objectives of the shoot and give everyone their specific instructions. One of the first things I do is have the driver of the subject car... the car we're shooting, look at the car through the camera at the widest focal length. I want him to have an idea of what the camera can see and have him understand how close I need him to get.
I'll then explain to both the chase vehicle driver and the subject car driver what I want them to do. And, I will establish some hand signals with the subject car driver. The key for both drivers is understanding where I need them on the track and what speed they need to maintain.
Typically I will have the chase car driver maintain a top speed of 50 mph unless I give my assistant instructions that I want to go faster. I also want him to follow the racing line as smoothly as possible. Other than the fact I don't want to be rolling around in the back (it's happened), I want him to be predictable to the driver of the subject car since he'll be giving new meaning to the term tailgating.
Once we roll out, I'll have the camera set to the widest focal length. Using shutter priority, I'll set the shutter speed at 1/40th sec. If your camera as a "Live view" setting and will allow you to use the LCD preview screen while you shoot, a car-to-car shot is the perfect opportunity to use it. In the past, I've shot blind using a wide angle. While that worked OK, Live view works spectacular. It does cancel the preview while the shutter is open... but for the most part, you have a much better reference of your composition. Furthermore, I think you have better control steadying the camera compared to holding the view finder up to your eye.
Just to clarify the shutter setting and, for that matter, the car speed. I've found 1/40th sec. at 50 mph gives me adequate blur, excellent wheel spin and a little more control over camera shake and vibration. Of course, shooting at 12 - 24mm also helps with the equation too. You might experiment with other settings, but those have become baseline for me and combined with Live view, my keeper rate on the last shoot was spectacular. I should also warn you... CLEAN YOUR SENSOR. Chances are at a slower shutter you're going to be stopped down pretty good... any sensor dirt will certainly rear its ugly head. You might also want to consider a neutral density filter. This will help you get the shutter speed down if it's a particularly bright day. Even if it isn't, it can help you manage a more desirable f/ stop and shutter speed combination.
Try to shoot early in the morning or late in the day. If you're on a closed circuit and doing laps, you're going to be dealing with lighting that rotates around you through out each lap of the cricuit. With that in mind, you'll need to keep an eye out for shadows... yours and the chase vehicle's. Most important, if your chase vehicle's back door opens up and overhead, there will be times it will throw a shadow onto the road in front of the subject car and your camera.
The other problem with lapping the track is changing backgrounds. Again, try to plan ahead of where you're going to want the subject car positioned as you pass through different sections of the track. Move the subject car in close then shift it off to the left and right. Also, change the vertical position of your camera... shoot high, looking down, low looking up and straight ahead. If you're shooting a roadster with the top down, you'll want to shoot a few shots higher and looking down. Most of all, get a variety of looks. Oh, and when you shoot low and to the side, keep an eye on your viewing frame to make sure you're not picking up the chase vehicles bumper.
If you're shooting a passenger car, make sure the windows are up, the visors are up and your subject car driver knows to keep two hands positioned properly on the wheel... eyes straight ahead. You don't want the driver looking at you or the camera.
To help give your shots a greater sensation of speed, try to keep the car in close. There are more "streaks" in the road surface closest to the camera. Also, on a race track, try to use the gator strips or curbing. Tree lines will also add blur and give the sense of motion.
Lastly, SHOOT A LOT. This is one of the few occasions that it's OK to "spray and pray." Blowing off a dozen frames or so once you've moved the subject car into position makes a lot of sense. You're going to bounce, you're going to miss and you're going to want variety as the subject car pulls up and drops back from the desired position. Shoot. A few hundred frames don't mean a thing when you consider what you've put into arranging the shoot. Fire away and give yourself choices.
One last word of caution. BE SAFE. Don't hang your shoulders out of the car. I make sure my chin is behind the bumper at all times. And have your assistant hold on to your belt at the back of your waist. The shot isn't worth getting injured. You're probably going to get bruised and I've even been burned (another story)... just be safe.
Thanks for listening...