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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.
Next - Choosing a Digital Video
Camera
or skip forward to Video Software
