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for Building Pinewood Derby Cars
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There isnít one tip or secret that will make a fast pinewood derby
car. There are several things that need to be done to make a fast
pinewood derby car, (see below). Also the type of track, how the
track is setup, and how the winner is determined affects the
relative importance of the tips given below. A car that wins on one
track may not win on another track or the same track setup on a
different day. Also there is luck. I have heard of blocks of wood
that win pinewood derby races. I have my own a little pinewood
derby story to illustrate luck.
For several years I have helped
make 3 or 4 cars for my four kids and we are always finishing them
the day of the weigh-in. One year, as usual we were having trouble
getting my oldest son car aligned. It never seemed to run straight
enough. We were tweaking it right before the weigh-in. Finally we
had to go. My son was bringing the car up the basement steps when
HE DROPPED HIS CAR!! Nothing broke and nothing looked bent
but the axles are not very sturdy. We couldnít check the alignment
so we took the car as is to the weigh-in. At the weigh-in we
checked the alignment again by rolling it along a table. It seemed
to be about the same, so we checked it in. He won every race, which
was the first time we had won 1st place. To this day I
donít know whether dropping the car fixed our alignment problem.
NOW, I DO NOT RECOMMEND DROPPING YOUR CAR
TO IMPROVE ITS ALIGNMENT!!!!!
The most important tip is to
work with your son and have fun. Most kids remember the time spent
working with their parent on their car; not the actual race. Also
every year we have OUTLAW races for dads, siblings, and cub scouts
with illegal cars. It is just for fun and no prizes are awarded,
but you are allowed to violate the rules (as long as the car doesnít
damage the track so keep the weight reasonable and donít use razor
thin wheels that would cut into the track). Then if there is time
we open up the track for anyone to race.
Pack 88 uses a six lane, plastic
track called SuperTrack. We got the complete system: track,
electronic finish, and race manager software. Go to
http://www.supertimer.com/track/supertrack.html for more
information. Besides being plastic instead of wood, one difference
is that this track uses side rails instead of a center guide strip.
So cars with a front wheel lifted too high and with a lot of weight
in the back or cars that have very poor alignment tend to
cross-lanes. We have a procedure to handle these cases, see the
official rules at
http://www.cubpack88.org. We also have the bought the
electronic finish, so all the races are timed. Each car goes done
each lane once (a total of six races for each car) and the carsí
times are recorded for each race. The cars are actually racing
against the clock not against other cars. The final winners are
determined by the fastest average times, so it is possible for a car
to win every race but not be an overall winner if it is racing slow
cars. The race manager software records the times automatically (so
there wonít be a manual recording error). Also the race manager
software schedules the races and tends to race slower cars against
slower cars and faster cars against faster cars as the racing
progresses. This way the individual races tend to be more
Every year our Pack has a
Pinewood Derby Help session please check the calendar for the date
and time. Several experienced pinewood derby dads and tools will be
available to help you and your son build your car. I will bring my
little drill press to help drill out the axle slots. My tips below
are not a step-by-step guide to building a fast pinewood derby car,
since two very good step-by-step guides exists. The first is free
http://www.lastufka.net/lab/cars/html/index.htm. The second
cost ~$7 or $8 at
http://www.maximum-velocity.com/speed_tips.htm. However, if you
use these guides there are several suggestions that are not legal in
our race, so donít use them. See the first tip below.
Obey all the rules;
see the Pack 88 website,
http://www.cubpack88.org, for the official rules. If you
want to use trimmed wheels, longer length between axles or other
improvements that violate the rules, build an ďoutlawĒ car and
race it in the outlaw race.
Make suggestions to your
son, but have him make decisions. Also let your son do as much
work as possible. (Car shape/aerodynamics does not affect
performance very much so let him choose the shape/style of the
car; however, most of the fastest cars have a flat or wedge
shape). However, donít make your car too tall or it wonít go
into the stopping garage or fit under the finish gate on other
tracks. Since every finish gate and garage are different, as a
general rule I would keep the total height under 2.75Ē.
Check your pieces. Make
sure that the axle slots are square and that the wheels and
axles donít look damaged. If they are damaged contacted the cub
master or me and we will get you a replacement.
My first step while I still
have a block of wood is to drill out the axle slots to allow the
nails to go in easier. Then we cut the carís shape, sand,
paint, etc. Then one of the last steps is to epoxy the axles
with their wheel in place. I use a small drill press with a
3/32Ē drill bit. 3/32Ē is actually a little large, a #44 is
better, but I donít have one. If you donít have a drill press
you can do it by hand or you can go to
www.maximum-velocity.com for a ~$11 tool to aid in drilling
the holes. Note: many items at
www.maximum-velocity.com will violate the Pack88 rules so
donít use them on your sonís official car. You can use them for
your outlaw car.
Align your car so it travels
straight. A car that is pulling to one side will be pushing
against the side rails or bouncing between the rails, which will
slow it down. This is by far the hardest thing to do. I test
alignment by pushing the car on a flat surface to see which way
it curves. The alignment is usually done by slightly bending
the axles, but be careful you can break the wood very easily.
One trick if you are running on three wheels is as follows.
Assuming that one of the front wheels is raised, very slightly
bend the axle of the wheel on the ground, donít glue the axle
yet, test the alignment, then rotate the bent axle until the car
goes straight. For
2008, the District Pinewood derby rules require that all four
wheels touch the ground, so this tip cannot be used.
Slightly raise 1 wheel so it doesnít touch the ground. (If the
weight is toward the back, raise a front wheel.) Donít raise
the wheel too much, (1/16Ē to 1/8Ē is enough), if it is too high
then the wheel may go over the side guard rails and the car will
For 2008, the District
Pinewood derby rules require that all four wheels touch the
ground, so this tip cannot be used.
Add weight to get close to 5
oz. You can add the final weight at the weigh-in to get to 5
oz. Since all scales are slightly different, being a little
under 5 oz at the weigh-in is better, since it is usually easier
to add weight than to remove weight. We will have the official
Pack 88 scale at the help session.
Adjust the center of gravity
so that it is 0.75Ē to 1.5Ē in front of the rear axle. The
center of gravity is the location where a car will balance. I
check the center of gravity by balancing the car on a square
edge ruler. Before I figured out about the square edged ruler I
used my finger. The location of the center of gravity involves
a trade-off between stability (weight towards front) and maximum
speed or potential energy (weight towards back). Basically the
optimal position depends on the car and the track. I feel that
cars with poor alignment will do better with the center of
gravity closer to 1.5Ē in front of the rear wheels, while cars
with excellent alignment will do better with the center of
gravity closer to 0.75Ē in front of the rear wheels. I wouldnít
go less than 0.75Ē in front of the rear axle because the front
end will become very ďlightĒ, which makes it easier for the
front wheels to go over the side rails and for the car to cross
lanes. So your car could be very fast, but if it canít stay in
its lane it will be disqualified. The primary way to adjust the
center of gravity is by positioning the weights. You can also
remove weight by drilling or cutting away wood.
Rear axle as far back as
possible, since you want the weight as far back as possible
while keeping the center of gravity in front of the rear axle.
At a minimum have the axle slot closest to the end be the back
of the car. For a further improvement cut off part of back end
and add it to front to get to 7Ē since you have to use the
original slots that came with the car. You canít drill new
holes or cut new slots. This trick allows you to move the
center of gravity farther back while allowing it to be in front
of the rear axle.
Donít shorten the car (i.e.
keep length at 7Ē). Make sure the car length including wheels
and accessories (like tail lights or tail pipes) is at most 7Ē.
Remember if you cut off the back of the car and the rear wheels
stick past the body, then total length includes the wheels.
Remove the burs on the axle
and polish them. I place the axle in a drill press which spins
the axle so it can be sanded and polished easily. You can also
clamp a hand drill in a vice instead of using a drill press.
Lightly sand the wheels to
remove the little stubs on the other edge. (Donít reshape the
wheels, which is against the Pack88 rules). Some of the
original ďtread marksĒ must remain visible to the inspector at
weigh-in. You can get a special axle/hub at the scout shop or
www.maximum-velocity.com that can be mounted in a drill to
spin the wheel to make sanding it easier. Special wheels can be
purchased but that is against the Pack88 rules.
Use graphite, preferably
with moly (Donít use the White Teflon sold at the Scout
Shop). I work graphite into the axles and rub it around the
wheels. I also graphite the spot on the body where the wheel
After adding graphite to the
wheel axles, the graphite needs to be worked in. Spin the
wheels several times or roll it gently along a table several
times before turning your car in at check in. The Weigh-in will
be the last chance to add graphite before the race. You cannot
add graphite during the races. I donít know exactly how much to
add or how long to spin the wheels. I put about two or three
puffs into each wheel before spinning them.
Raising the front end may or
may not be helpful on our track since we have an automatic
starting gate and a strip sensor that extends from the bottom of
the track. It is usually is helpful on tracks with LED diodes
at the finishing line and manual starting gates. Donít raise
the front end to much, since if the front end goes over the
starting peg the car will be disqualified for having a lead at
the start of the race.
Donít make the front end too
pointed. It doesnít significantly help with aerodynamics and it
may disqualify your car if it canít stay on the starting peg.
At the District Pinewood derby race one year, a carís front end
had a sharp point and the starting peg was rounded. The car
always slid forward before the race started, so it had a lead
and was disqualified. Another reason not to do it is that if
the car is over to one side of the lane at the finish line, a
car with a pointed front may pass the finish sensor in the
center of the lane without triggering it. The sensor wonít be
trigger until a wider part of the car crosses the sensor.
Another car whose front end is behind the other carís pointed
front end but trips the sensors first will have a faster time.
Most packs with electronic timers use the official time from the
electronics and wonít re-run races based upon what people saw at
Finally I suggest going to
http://www.maximumvelocity.com and sign-up for their free
newsletter. They were offering a free car plan if you signed up.
Visit our website,
http://www.cubpack88.org, which list lots of links for
additional information on building pinewood derby cars.