This article is dedicated to and also written for the fans in the stands that
always wanted to know a little more about the cars they watch on the racetrack
every Saturday night. It’s you that allow us to race and enjoy ourselves. We
couldn’t have this much fun if you didn’t spend your hard-earned money to
come out and watch. We probably don’t thank you enough for all that you do. I
tried to keep it simple but some technical stuff found it’s way in. The idea
is to edumacate the average fan in the stands and have a little fun while doing
What is a midget/sprint car/Silver Crown
All three cars use the same basic layout and the primary differences are in
physical size as well as engine size. All use components whose basic design has
been around for 4 decades or more. You may find it interesting (I did anyway) to
go to the Indianapolis Speedway’s museum and look at the racecars displayed in
If you look closely, you will see many components that are still used today
on midgets/sprints/Silver Crown cars (to make things easier I’ll just call the
conglomeration of the three, spridgets). I’ll get into an explanation of these
terms later, but you’ll see things like torsion bars with adjustable stops and
torque tubes on both those cars in the museum and today’s spridget.
It’s rather amazing to me that today’s spridget uses most of the same
components used by racecars 4 decades ago. It’s my opinion that most of
today’s mechanics/engineers can’t hold a candle to the guys who designed
these components years ago. How often do you see something that has used the
same basic design for that many years, much less in a sport like racing? They
thought up and perfected by hard work the basic components without computers or
anything like that. Just plain old American ingenuity. You may hear somebody say
that they have a “revolutionary” new car, but in reality nothing is
revolutionary on a spridget these days. The “new” ideas more likely are
evolutions of past ideas. Anyway, I’ll get on with it now. I’ll go into the
component similarities first, then the differences unique to each car.
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Chassis and Front Axle
The basic chassis (frame) designs are similar on all three types of car. The
chassis is constructed from welded tubular steel. The type of construction used
is called “space frame” and it’s similar to how road cars used to be made.
Most of today’s road cars use a “Unit body” where the individual fenders
and such are bonded together in such a ways that a separate chassis is not
needed. Indy cars use a variation of the “unit body”. The front axle of a
spridget is a solid beam axle (just like on grandpa’s old Ford truck) with the
wheels attached on each end. The design has been around as long as cars have, so
there’s nothing fancy here. You might notice that there are usually 3 rods (1
on the left side or “driver’s side” and 2 on the right side) that attach
the front axle to the chassis. These “rods” are called radius rods. Their
purpose in life is to keep the front axle from moving forward or backwards
within the chassis while also allowing the axle to move up and down as the
wheels hit bumps. There are 2 radius rods on one side of the axle (1 top & 1
bottom) to keep the axle from spinning around within the chassis (that would not
be a good thing). Why 3 radius rods and not 4? 3 radius rods allow freer
movement of the axle. On cars where there are 4 radius rods (2 on each side)
like I noticed on Stevie Smith’s WoO car a year ago or some pavement cars, the
4th radius rod likely is there to create an “engineered” bind or
tightness. They want the bind there to lock down the front end, but I’m a
little too dumb to figure all that out. At the end of the radius rods are
“heim joints”. These are similar to the ball joints on your car but have
tighter tolerances so that the spridgets don’t go down the straightaways
wandering around like the old Dodge you had in high school with worn out ball
A “panhard” bar (sometimes also called a “sway” bar) connects the
axle laterally to the chassis. It’s there so that when you turn left, the axle
doesn’t shoot out the right side of the chassis. A spridget panhard bar is
essentially a short radius rod that runs crosswise in the chassis whereas all
the radius rods run lengthwise down the chassis. Both radius rods and panhard
bars are roughly parallel with the ground and changing the location point of one
end either up or down is one of the million ways to “tune” the chassis to
make those fussy drivers happy. There are also other adjustments that may be
made with radius rods to make the car travel straighter. Ever notice that the
front wheels on some spridgets at low speeds look like those annoying wobbly
wheels on the shopping cart you always seem to get stuck with at the
supermarket? That problem is adjusted out with the front radius rods. Funny, I
know how to quickly fix that problem on a sprint car yet I seem to put with it
during hour-long grocery shopping trips. I must remember that the next time a
driver complains about that.
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Okay, how do you steer a spridget? I’ll start at the tires and move back to
where the steering wheel is located. There’s a long rod called the “drag
link” that runs from the side of the cockpit (where the driver sits, funny how
they named it that) to a lever attached to one of the front wheels. Dirt cars
have the drag link connected to the left front wheel. Pavement cars sometimes
connect the drag link on the right front wheel. The drag link pushes or pulls on
that one wheel which is connected to the other wheel by a “tie rod”. The two
front wheels are connected to each other with a “tie rod”. The tie rod is
there to make sure that when the left tire turns left, the right front turns
left too. If you see a car with the wheels pointed in different directions, the
tie rod is broken.
The non-wheel end of the drag link is connected to the “pitman arm”. The
pitman arm is a short bar that connects the steering box to the drag link. The
guy in the cockpit (giggle) turns the steering wheel right which causes the
lower end of the pitman arm to move towards the back of the car. As the pitman
arm moves backward it pulls on the drag link which causes the left front wheel
to turn right. As left front wheel is turned left, it pulls on the tie rod which
pulls on the right front wheel causing it also turn right. Whew, the ankle bone
is connected to the foot bone....... The opposite occurs when the steering wheel
is turned left and also on a right steer pavement car.
You will notice that on a left steer (dirt) car that when turning right the
drag link and tie rod are being pulled not pushed. Control type rods like to be
pulled rather than pushed as how they react can be more easily predicted when
they are pulled. Dirt cars typically slide in the turns and are turned right to
correct the slide. Pavement cars are not supposed to slide and are steered left.
To make sure that the control rods are being pulled, they locate the drag link
on the left side on a dirt car and the right side of a pavement car. The idea is
to be pulling all the steering rods in the more frequently used direction. All
this may sound complicated, but in practice the front axle and steering on a
spridget is about as sophisticated in design as a soap box derby car. The
difference is that spridget steering is much more refined (and costs mucho
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Rear Axle Assembly
Since we are talking about axles I’ll move to the back axle. A spridget
uses what’s called an “open tube” axle. What this means is that the axle
is right out in the open for all your snooping neighbors to see. Your standard
road car commonly uses a closed tube axle meaning a closed tube encloses the
axles within it. A closed tube axle keeps grease, oil and other icky stuff
inside and your family cat outside, out of harms way of the spinning axles. The
spridget axle is solid from one end to the other which causes both rear wheels
to turn at the same speed.
In the middle of the axle is the rear end. If you look into the cockpit
(giggle) you will see a small “T” handle sticking up somewhere. Pulling up
or pushing down on that handle moves a cable connected to the rear end. That
cable moves a lever attached to a coupling on the lower shaft of the rear end.
The lower shaft is in two pieces. Moving the coupling one way connects the two
shafts together, putting the car in gear and ready to go. Moving the coupling
the other way disconnects the two shafts and the car is out of gear and can be
rolled by hand. Those are the basic components of the rear axle.
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Are radius rods used on the rear of the car to locate the rear axle in much
the same way as the front axle? Yes. There are two radius rods (1 on each side
of the car) running from the rear axle towards the front of the car. There are
also 2 torsion arms (1 on each side of the car) running from the axle towards
the back of the car. The radius rods and torsion arms are mounted in such a way
to allow the axle to move up and down in the chassis. So if your arm was a
radius rod, the shoulder end of your arm would be the end connected to the
chassis (uh, you) and the hand end (likely connected to your little brothers
throat or something) would be the end connected to the axle. Torsion arms
operate in the same fundamental way.
So how do you connect radius rods and torsion arms to an axle that’s an
open spinning tube? They are connected to the axle by what’s called a birdcage
because in the good old days that’s what they looked like. This method of
giving things obvious names keeps cropping up, which I like. The birdcage is
basically a bearing with a plate attached to it allowing the axle inside to spin
on the bearing without the plate outside spinning with it. The radius rods and
torsion arms connect to the plate, the radius rod on top of the axle and the
torsion arm on the bottom.
This radius rod/torsion arm mess is what keeps the rear axle from moving forward
and backward in the car. You will also note that most all the forward motion
generated by the rear wheels is transmitted to the chassis through the rear
radius rods. This is why moving the end of the radius rod that connects to the
chassis up or down is another chassis “tuning” adjustment.
So what keeps the rear axle assembly from moving from side to side in the
chassis? Good question George, but a hard answer. The short answer is the
“Jacobs Ladder” (aka “W” link or Watts link) as used on dirt or the
“panhard bar” as used on pavement. The panhard bar is attached to the
birdcage on the left rear wheel and runs across to be connected on the right
side of the chassis. The connection point on the chassis can be moved up or down
to tune the chassis. If you watch the NASCAR races on TV, you will sometimes see
someone turning a wrench that goes into the rear window of the car. One of the 2
holes in the rear window on the passenger side of the car is an adjustment for
the rear panhard bar (the NASCAR boys call it a track bar)
On dirt, a jacobs ladder is used. This funky deal looks like a “W” laid
on its right side when you are looking at it from the back of the car. The
middle point of the “W” is attached to the right side birdcage. The two
outside points are attached to the chassis.
The points connected to the chassis and the two points pointing to the left
of your laid over “W” are hinged so that this whole mess can move up and
down. A Jacob’s ladder is used for two reasons. One is to laterally locate the
rear axle in the chassis to keep the rear axle from sliding out from under the
car. Two, it moves what’s called the Roll Center upwards as the car rolls to
the right. It’s a pretty slick piece from an engineering point of view. (You
will also see jacobs ladders on the early 60’s type Indy cars in the museum)
I’ll do a little discussion about roll centers because they are very
important to the handling of these racecars. Feel free to skip ahead if this
stuff doesn’t interest you. I will not grade you down on your test if you get
these questions wrong. Think of roll centers this way. A roll center is an
imaginary line running the length of the chassis. This imaginary line is the
point around which the chassis leans laterally.
The location of the roll center is set by a bunch of complicated
circumstances and I can’t think of an easy or funny way to describe it, but
suffice it to say that where it is located is set by the suspension geometry. On
dirt, you want the roll center to be in a variable location so that you can tune
the car to changing track conditions allowing the car to “lean” and transfer
weight onto the tire of your choice.
The roll center also interacts with the Center of Gravity to determine how
easily the car can tip over. The higher the “Center of Gravity” is located
above the Roll Center, the more likely you will tip over. The Center of Gravity
(CG) is also an imaginary line running the length of the chassis. This next
explanation will have some of you tearing your hair out, but it’s the best my
peanut head could come up with. If you were to stand a spridget on end with it
resting on the imaginary line that is the Center of Gravity and gave it a spin,
it would spin around perfectly balanced like a top. The motor is the single
heaviest component in these cars so where it sits pretty much determines where
the center of gravity will be. If you move the motor up higher in the chassis,
the CG moves up. Move it down, the CG goes down.
For a practical explanation of how roll centers work, grab your cousin Joey
and go out on the front lawn. Call the neighbor kid Billy over because he’s
not too bright and will sit still during your experiment. Engage Billy in a
conversation to distract him and have Joey lie flat on the ground right behind
Billy’s feet. Give Billy a push. Billy’s body will rotate over Joey and fall
on the ground. Try not to laugh because this is a scientific experiment. Help
Billy back up on his feet and engage him in conversation again. This time have
Joey get on his hands and feet behind Billy. Once again give Billy a push and
watch as Billy’s body rotates backwards and fall over. Note that it took a
harder push to tip him over this time. Now take Joey and clear out because Billy
will go get his mom and it’s best not to be around when she’s mad.
Joey’s positioning behind Billy set where the roll center was located on
Billy’s body. In the first experiment, Billy’s ankles were his roll center
and in the 2nd experiment Billy’s roll center was higher up his
legs towards his backside. Where Joey was positioned in relation to Billy set
Billy’s roll center You may have
noticed that it was a lot easier to push Billy over when Joey was laying flat on
the ground and when Billy’s roll center was low around his ankles. This little
experiment showed you that as outside forces caused Billy’s roll center to
move higher, it became harder to tip Billy over.
What does all this have to do with spridgets and jacobs ladders? The design
and movement of the jacobs ladder create a situation where as the chassis goes
around a corner and leans to the outside of the turn, the roll center rises
within the car. Our experiment with Billy showed that as the roll center moved
higher that it required more force to tip Billy over. Again, finding the
delicate balance between chassis roll and tipping over can be a highwire act.
How does Roll Center apply to mechanics and drivers? Let’s assume that the
average person’s Roll Center is located at their waist. Your average bigheaded
driver has a very low roll center. Why? The driver’s low roll center comes
from having his CG located higher than his roll center. With that big rock on
top of the body, there is a lot of weight above the waist causing them to have a
high CG. Your average mechanic (like me) has a big backside and therefore a high
roll center. Why?
Because most of our weight is located below our waist and causes our CG to be
located low on our bodies and also below our roll centers (waist). In people,
having most of your weight below your roll center can be a good thing as you are
less likely to tip over. That’s why Weebles wobble but they don’t fall down.
They have a high roll center. These differences between drivers and mechanics is
also why you always see drivers tipping over on the track and us mechanics never
being able to figure out why those drivers keep tipping over. It’s an
If you’ve read to this point without stopping, I think you should take a
break for a minute. No, really. You are way too much into this and need to do
something else, like watch “When Animals Attack 27” on TV or something to
get a little more grounded in reality. Pick this back up later and read on.
One last component attached to the axle/rear end that we will talk about is
the “torque tube”. The torque tube is a tube that connects the axle/rear end
assembly to the chassis. Within the tube is the driveshaft that transfers the
drive from the motor to the rear end. One end of the torque tube is bolted on
the rear end housing that contains the axle, gears and stuff. The other end’s
connection is a lot more complicated. Since the torque tube is bolted to the
rear end assembly, which moves up and down as the wheels hit bumps, the other
end must be hinged. The other end of the torque tube is connected to the
“motor plate” where it can move up and down. The motor plate is a flat plate
that is bolted in the chassis in front of the driver’s feet. It is also bolted
to the motor, which is a good thing since without it the motor would fall out
the bottom of the car. Connecting the torque tube to the motor plate is a ball
and socket arrangement.
I’ll talk about the old style of ball and socket first, then talk about the
“Buckley” type. If you cupped your hands in a circle like you are yelling at
the neighbor next door for letting his dog poop on your lawn, your hands would
look like the outer housing or socket for the “ball”. This housing is bolted
to the motor plate. The ball portion fits inside your cupped hands but has an
extension that sticks out through the hole in your hands kind of like a
megaphone does when you hold it with both hands. This extension would be
sticking back towards you in this example. The ball can rotate freely within the
housing. The part of the ball sticking out between your hands slides either
inside or outside of the torque tube (depending on manufacturer’s style). The
“Buckley” type looks like a “Y” with the end with the two points
connected to the motor plate and the end with the one point sliding inside the
torque tube. In both cases, the driveshaft sits inside all of this mess.
I think this is the correct application of this, but if you hark back to your
days in school, you remember might remember one of Newton’s Laws of physics.
It said that for every action, there is an equal and opposite reaction. A common
example of Newton’s Law is when you talked back to your mom, you got whacked
across the face. Action = talking back. Reaction = Smack! How does Newton’s
Law apply to a spridget? As the rear wheels are being rotated forward by the
motor (Action>the rear end assembly trying to rotate in the opposite
direction (Reaction). The torque tube is connected to the rear end and
Newton’s Law is forcing the front of the torque tube upwards. This is why you
see the chassis of spridgets rising up when the driver is on the gas. The torque
tube is driving the motor plate and everything else attached to it upward. This
is what causes wheelies. Newton also sticks his head in here because as the
motor plate is driven upward, an equal reaction is that the rear end assembly is
driven downward causing more traction or friction between the tires and the
ground. See, ain’t science fun? Now all of this science stuff goes kaput when
a bind occurs in the torque tube area. A bind is when all of these complicated
linkages cannot move freely in relation to each other, sort of like my body the
morning after a big night on the town. If a bind is present, then the desirable
upward forces are spread out in different directions instead of the direction
you want. If the torque tube is trying to push sideways as well as upwards,
that’s not a good thing as the car will not have as much forward drive than
when there are no binds present. Driver types always seem to complain the
loudest about this type of thing. When binds are present is when a perfectly
good racecar becomes a piece of poop.
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Okay, we can now steer this thing and it has axles that move up and down, but
what holds it up off the ground? It certainly is not Flubber. Spridgets use
either torsion bars or coil springs for their suspension. Torsion bar suspension
has been around for years. VW bugs all had it, as did most 911 Porsches. A
torsion bar is a bar that is twisted.
As the bar is twisted, it stores energy. That stored energy is the bar
wanting to untwist itself. If you grab your little brother by the underwear and
twist it around real tight, it wants to unwind once you release one end of it.
This is the basic principal behind torsion bars. In a spridget, the torsion bars
are located at the extreme ends of the chassis and
run side to side in the chassis. The torsion bars spin around freely within
torsion tubes, which are part of the chassis. Bolted on one end of the torsion
bar is a torsion arm. In the front of the car, the other end of the torsion arm
is resting on top of the axle whereas in the back of the car, the torsion arms
are bolted to the birdcages.
So we have a torsion bar spinning freely within a torsion tube bolted to a
torsion arm, which is either bolted to or resting on an axle. So far we don’t
have anything holding the car off the ground. The end of the torsion bar
opposite the arm has a “torsion stop” bolted onto it. A “torsion stop”
is a little lever that has an adjustment bolt running through one end of it. The
end of the adjustment bolt rests against the chassis. By turning the bolt one
way or the other, we can raise or lower the chassis. Let’s get back to our
little brother’s underwear. By twisting the underwear tighter, we are creating
a bigger “wedgie” right? By twisting the adjustment bolt tighter, we are
twisting the torsion bar more which is trying to push down harder on the torsion
arm and raise that corner of the car. The adjustment bolts are used as a
suspension-tuning device. A byproduct of trying to make raise one particular
corner of the car is that we are also making that particular wheel push down
harder on the ground. (That Newton dude again) You can change the way the car
reacts by having one tire press down on the ground harder than another. The
magic of having a fast car is to balance the needs of each wheel with each other
to achieve harmony (while ignoring the whining needs of the driver). This whole
balance is called set-up. In Indy type cars they use high falutin words like
“package” but it’s all basically the same.
Coil springs are springs that are coiled. Duh. In a typical spridget
installation, they are coiled around the shock absorbers and called coil-overs.
They operate under the same basic principal as torsion bars but with different
characteristics. For a semi-technical explanation of the difference in
characteristics, coil springs are generally linear in compression whereas
torsion bars have a rising rate. The more you twist a torsion bar, the harder it
wants to twist back whereas a coil spring will push back just as hard when you
compress it 1” as when you compress it 4”. Remember that this is all in
general terms here before you jump on me about variable rate springs.
The torsion bars can be easily changed as a way to tune the chassis. They
come in different diameters, which changes the amount of force that they push
back when they are twisted. Generally on a sticky track you run bars that are
harder to twist (stiffer) and on a slick track you run bars that twist easier
(softer). Shock absorbers are used to slow down the suspension movements.
Without shocks, the wheels will bounce up and down wildly. To the driver a car
with no or bad shocks will feel like one of those beds in cheap hotels that you
put a quarter in. Shocks come in different types. By changing shocks, you can
change how quickly or slowly the chassis responds to wheel movements. Again, a
stickier track will want “stiffer” shocks that slow down the suspension
movement and slicker tracks will want “softer” shocks. That’s suspension
in a nutshell.
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I suppose this would be the logical time to talk about wings and why they
make a car faster. But I don’t like wings on midgets or sprints so I’m not
gonna talk about them. I will tell you this. It really hurts when you bang your
head on them. You may be asking yourself, how can you not see something that is
big as a barn door? Well let me put it this way. If you walk into a barn 999,999
times and it doesn’t have a barn door on it I guarantee you that if it has a
door on it the 1,000,000th time you walk into it, you will walk right
into that barn down. Why? Because it was never there before. Besides if that
barn got along without a door on it for that long, it doesn’t need one now.
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Okay we’ve covered axles, steering and suspension. Now we’ll talk about
tires (tars for those of you in the south). If you are slightly perceptive, you
may have noticed that the rear tires on a spridget appear to be different sizes.
Actually, the fronts are slightly different too. The reason for this difference
in size is to allow the car to turn easier. Since spridgets only turn left, the
tires are smaller on the left side of the car.
This difference in size is called “stagger” (or “rollout” for you
older folks or “tire wedge” for you NASCAR types). To give an example of how
stagger works, I need you to break out a pencil. I don’t want to hear any
groaning out of you just because you have some homework to do. Take your pencil
and sharpen it until it is short and sharp. Roll the pencil on a table and you
will notice that it tries to roll around the sharper end. Why? Because that end
has a shorter diameter. So if you had a small desk you would want to have a
greater diameter difference between the eraser end and the pointy end so that
the pencil turns in a tighter circle and doesn’t fall off the desk. A bigger
desk would want a small diameter difference between the two ends so that you
could make big circles on your big desk. This same theory works on racetracks.
Small tracks, big stagger difference, Big tracks, small stagger difference. If
you have too much stagger, then you tend to want to go in circles smaller than
the actual track size and you spend your time doing little circles inside the
racetrack or just plain spinning out. Again, drivers don’t like to have this
happen because it makes them look bad so they scream at the poor mechanics to
have the correct stagger in the car.
During driver interviews, you may have heard a driver say something like
“On the red flag, we moved the tire in a little to tighten it up”. What does
this mean? First of all, have you ever seen a driver get out and do anything to
a tire during a red flag? Heck no! I don’t know where they get this “we”
stuff from. A properly trained
driver should say something like “On the red flag, the guys who worked their
butts off on the car all week and all night moved the tire in because I was
whining to them about the car being loose
and they wanted to shut me up”. Okay, what happens when you move the tire in?
Well first of all, more weight presses down on a tire the closer to the
chassis it is moved. That weight has to come from somewhere so it comes off of
the other tires on the car. The more weight pressing down, the more traction
that the tire has. There’s other things going on here, but we’ll leave it
alone for now. On a sticky track however, you want the right rear tire as far
out as possible to act as an outrigger to help hold the car up and to take
weight off the tire. So you have to find the delicate balance between keeping
the car upright and going fast. As a practical experiment, have your little
brother stand with his feet spread apart. Try and push him over onto his side.
It’s not easy, right? Next have him stand with his feet together and see how
easy it is to push him down. Now try it again. Repeat until the reason why this
is happening becomes clear to you but before mother comes along and demonstrates
Newton’s Law. See how fun learning can be?
How is the tire moved in or out? The axle sticks through a splined hole in
the wheel. The tire and wheel are held onto the axle with a nut. On the axle
behind the wheel are spacers (they look like metal donuts) between the axle and
the birdcage. The spacers are usually of different width so if you take spacer
out, you are moving the wheel in by the same amount as the width of the spacer.
Moving the wheel in or out is accomplished by removing the wheel nut, then
removing the wheel and either taking off an existing spacer (in) or adding an
additional spacer (out). It’s so easy that even I can’t screw it up. Moving
the right rear wheel out “loosens” the car up by making it slide sideways
You may also hear a driver say “we picked the wrong tire compound” as an
explanation for why he didn’t win. What does this mean? Nothing, other than a
driver whining. No, really it means that you guessed incorrectly as to what the
track conditions would be. Tires come in different compounds (or softness). On a
dirt track, racecars draw the moisture up out of the track causing the track to
dry out and the racing conditions change. I think I heard Danny Lasoski say
sometime that a hard track (slick) requires a hard tire and a soft (sticky)
track requires a soft tire. That pretty much sums it up. You want to run as soft
a tire as the conditions allow because soft tires generally provide more
traction. Too soft a tire and it will either wear out, blister or the rubber
will get torn off the tire. Too hard a tire and it will not provide as much
Another common driver whine is the old “my tire sealed over”. What this
means is that the tire heated up during the race, cooled during a caution
period, “sealed over” and no longer provided as much traction when the race
restarted. What happens is the very top layer of the tire becomes hard due to
heating and cooling cycles and sometimes will even get shiny. Tires get hot
because there is friction between the tire and track. Remember the old “Indian
Rub”? That’s where the street bully rubbed his hand back and forth really
fast across your arm and how much it hurt because your arm got hot? That’s
friction. In short terms when a tire seals over, the compound of the tire
changed from soft to hard.
And last but not least, that famous whine “my tire blistered”. What
happens is that the rubber in the tire gets so hot it actually turns to liquid
under the tire surface. What causes this? Friction again. You will note that the
tread on a dirt tire is separated into individual blocks. What happens is that
as the wheel spins and each block comes into contact with ground it is forced
into the ground. As the tire continues to roll these blocks reach a point where
part of the block is still in contact with the ground and part of the block has
left it’s contact with the ground. As part of the block is on the ground and
part has lost contact with the ground, the block stretches. As the last part of
the block loses its grip to the ground it “snaps” back into its normal
position and shape.
This “snapping” creates a tremendous amount of localized heat. As the
tire spins each block spends most of its rotation traveling through the air,
cooling it. However if it does not get cooled enough, the block will continue to
gain & retain heat until the rubber turns to liquid and bursts through the
surface of the block. It looks just like theblister you got when you where two
and put your hand on the stove after your mom told you not to. Blistering is
contagious as once one block starts to do it eventually most of the rest will
too. Since you are losing surface of the tire as it blisters, you do not get as
much traction as an unblistered tire. Again, there’s more going on here, but
I’ve just plum run out of funny explanations so I’ll leave it alone.
You may have noticed that there is a bunch of bolts running in a circle
around the outside of the wheel rim. These are “beadlock bolts”. There is a
circular plate (beadlock) with the beadlock bolts in it that clamps the tire to
the rim. The rear tires have such low air pressure in them (4 or 5lbs in the
left rear tire and 7 -12lbs in the right rear tire) that extra help is needed to
keep the tires on the rim.
The words “tire rule” or “spec tire” have been bounced around a lot.
Basically this means that the organizers of the race specify the brand of tire
that can be used. They may also specify the compound. The idea is to make racing
a little cheaper as the specified tires are usually harder than what is
available on the open market and as such may last longer. The racing organizers
usually also get paid some money by the tire manufacturer to run their brand of
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We’ve spent a fair amount of time talking about going forward, let’s slow
this thing down a little. How? With brakes of course. Spridgets all use disk
brakes to slow down. How does a disk brake work? Take your bicycle and turn it
upside down. Spin the front wheel and hold both hands like you where playing an
accordion. Press bothhands together on each side of the spinning tire. If you
are a “slower” reader, feel free to press them together on the spokes. This
is how disk brakes work. Attached to the wheel or axle of a spridget is a disk
(the bicycle wheel) that has a “caliper” (your hands) with brake pads inside
that press against the disk when the guy in the cockpit (giggle) steps on the
brake pedal. On dirt, most midgets and sprint cars have either two or three
brakes. One brake works on the left front wheel and the other one or two work on
the back axle (remember both rear wheels are hooked together on the same axle)
Why only one front brake on the left front? This helps turn or pull the front
of the car left into the corner as the brakes are applied. On pavement and on
Silver Crown cars both front wheels have brakes because you don’t want to make
abrupt left hand turns on pavement or the big mile tracks. Why two brakes on one
common axle in the rear?
Because the brakes are marginal at best on these cars and for some silly
reason the drivers want good brakes when everyone is wrecking in front of them.
A lot of guys get by with only one brake in the rear. On double rear brake
applications, one brake is mounted on the left side up against the rear end
assembly with the right side brake mounted out by the wheel on the birdcage. The
right side brake is the one normally left off when only one rear brake is used.
Why do they run only one brake? Mostly to reduce weight but also because the
right side brake changes the handling of the car.
The less weight that the motor has to spin around (driveshafts, axles,
wheels, etc), the quicker it can accelerate. That means better acceleration off
the corners. For a demonstration of this effect, let’s go into the backyard.
Take a 10-foot piece of rope and tie a rock onto the end of it. Spin it around
your head. Keep spinning until the rock flies off the end and through Mrs.
Winterbottom’s kitchen window. See how much easier it is to accelerate the
rope now that the rock is gone? Now find another rock and tie this one on better
and repeat spinning. Shorten the rope to 5 feet and spin it around again. See
how much easier it is to get the rock spinning with the rope shorter? Keep
spinning until you get dizzy and fall on the ground. Now class, let’s laugh at
the guy laying on the ground. This little demonstration showed us two laws of
physics whose names escape me. Ideally, we would have all the motor driven
components as light as possible and what weight that does exist on those
components would be located as close as possible the spinning axis.
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What’s left? I guess the motor. I’ll go into the motor differences
between the three types of car below, so I’ll talk about a few things on the
motor that are common to all three. One is fuel injection. The fuel injection
these cars use is an offshoot of the fuel injection used on WWII fighter planes.
The fuel injection used on spridgets is a pretty rudimentary system, but it’s
simple and effective for these cars. The fuel pump (usually driven off the back
of the motor and located in the cockpit) is supplied with fuel from the fuel
tank and pumps the fuel to a valve located on the engine. This valve is called
the “barrel valve” If you’ve been following the naming of parts on these
race cars you can figure out why it’s called the barrel valve. The accelerator
pedal opens the barrel valve and also opens air valves as it is pushed on. The
fuel is injected into individual cylinders of the motor. As the valves open,
more fuel and air are allowed to go into the motor. The air and fuel enter from
different paths, meet, mingle and do-se-do into the combustion chamber where
they are ignited. All this is not any different than the way it occurs on your
family Buick. What makes this fuel injection different is that on your family
car the fuel is timed so that a short burst is delivered just as it is needed,
whereas on a spridget the fuel is constantly pouring in and not delivered in
bursts. Your family car is much more economical with fuel because just the right
amount is delivered as needed.
Your family car also uses gasoline and a spridget uses methanol type fuel.
What’s the difference? Well, gasoline comes from oil and methanol is produced
from alcohol. Gasoline powered cars are much more economical with fuel but more
power can be developed with methanol. Engines want a certain mixture of fuel and
air to produce optimum power. This is called the stochiometric amount meaning
the mixture amount needed to obtain perfect combustion. Hey, we’ve talked
about physics, now we’re talking about chemistry. In a gasoline engine, this
mixture is about 15 parts of oxygen to each part of gas. Sort of like baking,
huh? Methanol wants a mixture of about 7 parts oxygen to each part of methanol.
So it requires roughly twice the amount of methanol as gasoline to run a
methanol-powered motor. That’s why you don’t see Toyotas and Escorts running
on methanol because it ain’t good for fuel mileage. One other interesting side
effect of methanol is that methanol motors run cooler than gasoline motors. The
fuel draws heat from the motor out the exhaust. This is why you see alcohol
dragsters and funny cars running without radiators.
The motors use what’s called a “dry sump” system to provide oil to all
the parts of the motor that want slippery stuff. Your family Gremlin uses
what’s called a “wet sump” system. The difference is that in a wet sump
system, the stuff inside the motor is spinning around is a pool of oil. Sounds
icky, huh. The problem is that all those motor parts spinning around in that oil
are being slowed down by the liquid in which they are spinning. A dry sump
system draws all unneeded oil out of the motor so it does not slow down the
spinning parts inside. A wet sump motor keeps all its icky oil in the oil pan
down underneath the motor where it’s out of sight and out of mind. Dry sump
systems are also much better at providing a constant supply of oil to the motor
during heavy cornering, flips and the like. In a wet sump system, the oil tends
to run away from the pump under these circumstances. A dry sump system keeps its
oil in a round tank that looks like a miniature beer keg on most spridgets and
holds about twice as much oil as the family road car.
I guess that last thing that is common on most spridgets, but different from
your road car is the ignition. Your road car uses the car’s battery as the
source of electricity to create a spark in the spark plugs. This is done via the
“distributor”. A spridget uses a form of distributor called a “Magneto”
(or mag for short). The magneto contains it’s own source for generating
electricity so that a battery is not needed. When a magneto starts losing it’s
ability to generate electricity, that’s when spridget motors misfire. The
sound they make when they misfire sounds like gunfire and somebody will usual
comment that “so and so is out there shooting ducks”. So next time you hear
that noise, go right down to the fence line and yell at the idiot mechanics to
change the mag. They will appreciate your input and expertise.
Well that’s all that I can think of to talk about on the basic components
of a spridget. Now, I’ll go into the details that separate a midget from a
sprint car and a Silver Crown car.
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Midgets, Sprints and Silver Crown Cars
The 3 types of car are different in wheelbase (the distance from front axle
to rear axle) by about a foot each. A midget’s wheelbase is about 6 feet, a
sprint car about 7 and a Silver Crown car about 8 feet. The overall lengths of
each car differ a little more than that because of fuel tank size and placement.
By the way, the fuel tanks on these cars are those big blobs hanging off the
back of the car with numbers on them.
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I’ll start with a midget. I’m amazed that in today’s politically
correct environment that the term “midget” has not been attacked by the
“height challenged” but so be it. As stated above, the midget is the
smallest of the other two type of racecar. Midgets weight about 1000lbs. The
motors in a midget come in a variety of types. You will typically see them with
either a 4 cylinder or 6 cylinder motor. Depending on engine layout, midget
motors range in size from 120 cubic inches to 166 cubic inches. The cubic inch
measurement refers to the size of the combustion chambers inside the motor if
you combined the maximum amount of all the cylinders combined. So if you took
all the cylinders in the motor and combined them into one large cylinder, it
would have a hole that 166 cubic inches of air would fit into (for a 166 cubic
The reason why the motors vary in size is that the various racing clubs try
to come up with a formula that will equalize the different types of motor used.
This is so that a VW engine can compete “equally” with a hybrid specially
built for racing motor. I’m not up on my midgets, but I would guess a good one
makes about 350 horsepower and is about 3 feet tall. Okay, the last part I made
up. The fuel tank on a midget carries a maximum amount of about 27 gallons. The
wheels and tires are smaller on a midget than a sprinter or SC car because they
do not have as much power and do not need that entire tire. On all three types
of car the maximum width of the wheels/tires is limited by rules. You will find
a much more diverse collection of motor and chassis combinations in midgets than
in sprints or Silver Crown cars. I love to watch the midgets race as they are
very exciting. The economics of the midget division have gotten all out of whack
with the amount of money spent by some owners far outpacing the amount of purse
money. It’s very tough to make money racing for purses, but the midgets have
gotten out of hand cost/benefitwise. I’m not against midgets, but I just
scratch my head over the economics when a sprint car is so much cheaper to run.
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A sprint car is the middle child of this group. Sprint cars weigh between
1100 and 1300 lbs. The motors do not come in as big a variety as midgets.
Basically there are three types. The most common is based on the Chevy V8, a
less common one is based on the Ford V8 and a rare creature is based on the
Chrysler V8. I say based, because you cannot run down to your local dealer and
buy one of these motors. They have all been modified from their original form.
The biggest difference is that they have most of the parts made out something
lighter than the original steel, like aluminum. As an aside, a lot of racers
drink beer because most sprint car pieces are made out of aluminum.
They are recycling. For every aluminum beer can that is emptied, another can
may be melted down into sprint car parts. So when you see a bunch of guys in a
pit area sitting around drinking beer with their heads hanging down because
their motor blew up, go over and help them create enough aluminum pieces so that
they can put their motor back together. It’s all in the name of ecology.
Anyway, there are different classes for sprint cars based on their motor size. A
410 class means that the engine size is limited to 410 cubic inches. A 360 class
is limited to 360 cubic inches and so on. A strong 410 motor makes around 800hp
and about 700 ft lbs of torque. I’ll go into torque a little later. A Sprint
car holds about 35 gallons of fuel. The right rear wheel is roughly 18” wide
and the left rear wheel roughly 14” wide. Both fronts are roughly 10” wide.
The right rear tire circumference is about 100”. What’s circumference?
It’s the distance around a circle. The people who went around the world in 81
days traveled the circumference of the earth. Left rear tires come in different
circumferences so that you can change the stagger amount in the car. They range
from 86” to 100”. So you can see that you can change the stagger in the car
from 14” (100 minus 86) to 2” (100 minus 98) by changing the left rear tire.
The sizes are not exact but you the idea. Roughly 60% of a sprint car’s weight
is sitting on the back tires. When you put the driver in that number goes up
even more. A 410 makes a lot of power and even though those big rear tires have
most of the car’s weight sitting on top of them they still produce lots of
wheelspin. That’s part of what makes them so fun to watch, especially on dirt.
I can’t think of anything else, so I guess that’s all I have to say about
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Silver Crown Cars
Silver Crown cars (currently called “Silver Bullet” cars and still called
“dirt champ cars” by others) are the biggest of the three cars. These cars
owe their heritage directly to pre 1970 Indy cars. Up until 1971 I believe, you
still had to run these cars on dirt to win the USAC “Indy” car championship.
You would see AJ Foyt run the Indy 500 in a sleek Indy car and soon thereafter
see him slinging a big bulky “champ car” around mile dirt tracks. The Indy
car of today has evolved over the years, but these Silver Crown cars have stuck
close to their heritage of years past. They share a lot of components with
sprint cars, including wheels, rear & front end assembly, steering and
various motor parts. They are limited to 355 cubic inches (by rule) and must use
a steel engine block whereas most sprint cars are allowed to have aluminum
engine blocks. It’s my understanding that they twist these motors pretty hard
and so they don’t make much less horsepower than a 410 sprint car. 750
horsepower is a stout SC motor. While they make nearly as much horsepower as a
sprint car, they don’t make nearly as much torque due to the smaller engine
size. I would say they make about 600 to 650 foot lbs of torque.
What is torque? Let’s see.... how do I explain this one. I’ll probably
not be technically correct here, but let’s give this a shot. Say you are
riding your bicycle. Torque is how hard you are pushing on the pedals.
Horsepower is that pushing force multiplied by how fast you are turning the
pedals. I’m guessing here, but I would imagine that if you were put on a
dynamometer (that’s a machine they use to measure torque and horsepower) with
your bicycle you would produce relatively high torque amounts at slower pedal
speeds and not much horsepower. At a high pedal speed, your torque rating would
not be that high. Your horsepower rating would shoot up because you are
producing about the same amount of torque but because the torque rating is
multiplied by the higher pedal speed, your horsepower rating is higher. Clear as
I thought so. Think of a 410 motor as a big fat strong guy on a bicycle who
can turn the pedals real fast. A 355 SC motor is a skinny triathlete type who
can turn the pedals as fast or faster than the fat guy but who cannot push as
hard on the pedals. Oh yeah, I can tell by all your faces that you understand
Well then lets get back to talking about the car. Silver Crown cars must
weigh a minimum of 1500lbs? after the races (I forget exactly how much, you can
see I spent lots of time on research here) The fuel tanks hold about 70 gallons.
70 gallons you say? Why twice as much fuel as a sprint car? Well, an average
midget or sprint car race is 30 laps on a track that is a ½ mile or less in
size. Silver Crown car races last 50-100 laps on tracks that are at least a ½
mile in size and most are 1 mile or bigger.
They have to go farther so they carry more fuel. All that of fuel weighs 450
lbs or more and it’s all hanging off the back of the car. Because 25% of the
car’s weight is burned off and disappears during the race the handling of the
car changes drastically from the beginning of the race to the end. Midgets and
sprints don’t carry as high a proportion of their weigh in fuel (midgets come
closer) and so don’t have the drastic handling changes that SC cars do. Since
set-ups in general are compromises, you really have to compromise when setting
up a Silver crown car. The Silver Crown division seemed to be dying off a few
years ago, but has been revitalized by the IRL.
Jeff Gordon (of NASCAR fame) won the title 7 or so years ago and I doubt many
people even remember. Since then, car counts and car quality has gone up and
they are well on their way to making a comeback.
Well, I guess that I’ve written enough about this subject. If you want to
learn more about the technical side of these cars or are starting out racing
sprint cars and really need more help, there is a publication put out by Steve
Smith Motorsports. I may not agree with everything he says as far as setups go,
but otherwise the book is excellent.
I hope some of you learned a little. The rest can print this out and line the
bottom of their birdcages with the paper. I can spend my days looking up the
business end of your parakeet. Either way, I was of some use to you.
If you have an interest in hearing more about the types of things mechanics
do to prepare the racecars or repair them after the drivers wreck them (you’d
think they’d learn after the first wreck), let me know and I’ll see what I
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