Drag Racing Suspension Setup and Tuning using Digital Video by John Heard with contributions from Mike Canter, Scott Smith & Pat Musi
Videotaping your Race Car
A video camera may turn out to be one o your best performance investments if you use it to help diagnose what your car is doing. No matter how many buddy's you have watching your car launch, you're not likely going to get a very good idea of what the car is doing without video.
Taping the launch
Since getting a car to hook good is one of the most important things to do in order to go fast, you'll likely want to film the car launching to see how the suspension is reacting. Here's a few tips for recording the launch.
Use a shoe marker and paint a mark on the side of the rear tire so you can watch to see if the tire is spinning. You might also want to paint a thin mark all the way around the outside edge of the tire to help view the contact patch length.
If you have wheelie bars, coat the wheels with wheelie bar chalk. You can get the chalk from Jerry Bickle Race Cars (and probably Summit or Jegs), it's made by either VHT or Geddex and costs about $10 a can. Have the person shooting the video shoot the starting line after the pass so you can see the tire pattern laid down and what the chalk marks the wheelie bars made.
Avoid shooting into the sun, try and choose a lane that will let you tape with the sun behind the camera if at all possible.
Have the person video taping the car stand behind and to the side of the car. Ideally you want to capture the left front and rear of the car. Have them fill the screen as much as possible without zooming. This will mean they will have to stand most likely about 10-12 feet or so behind and to the left of the drivers door.
Avoid using the zoom feature if possible. Zooming in tends to magnify hand movement and results in a really shaky video.
Try to include the tree in the background because it's a lot easier to cue
the video by watching for the tree to start down.
What to watch for...
There is a standard progression of events that occur as a doorslammer launches. Watching each of these events and at what point in time they occur gives you the clues you need to dial in your suspension. The key is to making these events all happen at the right "time" is your shock valving controls.
Mike Canter of Outlaw Pro-Mod fame had this jewel of a post post years ago that I saved where he detailed the following sequence that you should watch for:
"This should be the sequence of events seen on the video. Right at launch the front should start to come up before any forward movement or the car.
The rear of the car with this added weight transferred from the rising front will lift very little but it should not go down (squat). An inch or two is normal and can be best seen by looking at the relationship between the top of the slicks and the rear fender lip.
This one or two inches of rise will indicate that the rear of the car is lifting and pushing harder on the tires while the front weight is being transferred (for every motion there is an equal and opposite motion).
If the front of the car does not rise first then the front shocks are too stiff or the rear shocks are not stiff enough.
If the rear of the car squats right away then the rear shocks are too loose.
I have found through slow motion video tape that if the rear shocks are too loose the rear tire actually bounces on the initial hit and will break loose almost right away. I stood next to the car pointing the camera right at the rear tire. It was amazing to watch. I kept on tightening the rear shocks until it stopped which was just below mid point of the adjustment. From all that I have seen the rear shocks should never be adjusted less that half way because of rear squat and tire bounce."
Pat Musi's Tips On Adjusting Wheelie Bars & Reading Chalk Marks
(from Feb 06 Fastest Street Car Magazine, reprinted with permission)
There are two different heights, measuring center-to-center, from the back to the ground. The first is the cold tire pressure height, You should always be on the flattest ground you can find, so if you're setting them with the tires cold, you know where you want to be. "Every driver, every crew knows where they want to be at what we call cold tire pressure."
The second is the height after the burnout. When the tires get hotter, they grow and the height changes. So, after the burnout they see how much the wheelie bar moves up. "We have a measurement that we use and we'll go up or down on one or both, it just depends. We're talking very slight adjustments at that point. Generally we know where we want to be within an eighth of an inch."
"We read many things by the chalk. Chalk is used for two reasons. You'll have two strikes. You're going to strike them immediately, and then the car is going to get up on the tire. It'll come off them, the front end will start to come up, and it gets on them again. So, we're looking at the distance of those two marks. The first strike is very short. We run stagger. You have to run the driver's side 1/4 inch higher, typically, than the passenger side because that's the side that is going to hit first."
"You can also tell by the width of the chalk how hard they struck. If the chalk is wide, meaning you hit hard, you'll want to raise them up a little bit. Also, you can control the car from going left to right, I mean you shouldn't steer the car with the wheelie bars, that should be done with the suspension, but if the wheelie bars are off left to right, you have to adjust them."
Fast vs. Slow Motion
Let's take a look at this video of one of a launch and see how much more information you can see when the video is slowed down. This video was slowed down substantially using Microsoft Movie Maker "Half Speed" effect.
Notice how much more detail you can observe when you have time to observe everything going on? Would you like to venture a guess at what is causing this car to unload? Psss - if you know who this is don't tell him <evil grin>
On Board Video Cams
This is where the input jacks on your video camera can come in handy. For example on my car, I was trying to figure out what was causing "camel humps" in the accelerometer data in first gear. I knew it was spinning a little bit, but it appeared to be a cyclic pattern to the spin. So I decided to try and video tape what was going on under the car. Here's what we found...
Yes, new rear shocks are on order!
But also look at the other details we noticed - we also found A) Shock Bracket almost hitting the shock B) Upper mount is flexing. Both problems are going to be addressed soon, and I would bet the 60' times are going to improve!
The camera we used for this test was a 12vdc security camera from our office. If I was going to go out and buy a new one for projects like this I would look for something like the Adventure Cam II Bullet camera that www.viosport.com sells.
If your lucky enough to have a serious budget for your video equipment, also make sure to check out the remote cameras and micro recording equipment at stableimaging.com for some really cool hardware used by many big teams.
In Car Camera Roll Bar Mounts
If you want to mount the camera in-car so you can see what the driver is doing, watch gauges or just for fun there are a lot of ways to mount the camera. One of the first roll bar mounts I used was this mount, one of those quicky things I made in a few minutes that's nothing more than a couple muffler clamps with a piece of steel strap welded between them. It worked pretty good, but had limited adjustability.
Then I ran across this mount that Creative Flow Management sells that is really a cool setup. Talk about adjustability, it has a ton, and it's very sturdy compared to many other mounts. The picture here on the left shows the clamp on features and how much adjustment it has.
After playing around with this mount for a while, I can see where you could mount it in a lot of different positions in the car - you could even rig it up to point out the window so you can catch yourself passing the competition!
The way this thing works is neat, it has this quick release for the camera that screws right to the bottom and fits into a mating feature on the clamp which makes it easy to undo without upsetting the camara position.
A video camera may turn out to be one o your best performance investments if you use it to help diagnose what your car is doing. No matter how many buddy's you have watching your car launch, you're not likely going to get a very good idea of what the car is doing without video. 
In Car Camera Roll Bar Mounts
Then I ran across this mount that 
The way this thing works is neat, it has this quick release for the camera that screws right to the bottom and fits into a mating feature on the clamp which makes it easy to undo without upsetting the camara position.