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Canted Axles Revisited

The term "canted" means setting an object at an angle. Thus, "canted
axles" are axles which are attached to the car at an angle. Sometimes
this is done accidentally, but usually car builders cant axles in an
attempt to reduce the amount of contact between the wheel tread and
the track.

When discussing canted axles, the following questions must be asked:

1. Is there an advantage to canted axles? We will attempt to
determine this with an experiment.

2. Which type of canting (up or down) would provide the most benefit?
(see Figure 1) Generally, up canting is chosen as the wheel to car body
contact is eliminated, and the car body is lowered. However, the guide
rail contact is increased with up canting.

3. What is the optimum canting angle? We will attempt to
determine this with an experiment.

Figure 1 - Canting

Back in December of 2003 I conducted an experiment measuring the
effect of canted axles (see Pinewood Derby Times, Volume 3, Issue 6,
"The Big Debates Part 4: Canted Axles", December 10, 2003). The
results of that experiment were that, in general, up-canted axles were
not beneficial. These results were supported by an experiment from
another person, as well as from mathematical models.

Since then, I have had many discussions with various people regarding
the results of this experiment versus the anecdotal support for canting.
So I decided to rerun the experiment with some key changes. The main
changes to the experimental method were:

Original experiment
1. Four wheels on ground,

2. Front and back canted equally,

3. Cant angle adjusted by using multiple axle holes (axles had to be
pulled and then reinserted to try a different angle. Unfortunately, this
introduced experimental error.

New experiment
1. Three wheels on the ground,

2. Front dominant wheel not canted, but shimmed to cause rail-riding,

3. Cant angle of rear axles synchronously adjusted with a mechanism
(eliminates error introduced by pulling axles, and using multiple axle


The main equipment for this experiment is a car with an adjustable rear
cant. Figures 2 through 4 show this car.

Figure 2 - Full Car

Note the fork of brass protruding out of the car. The fork is held in place
by a screw into an L-bracket mounted on the car. When the screw is
loosened, the fork can be moved up or down, adjusting the cant angle.

Figure 3 - Undercarriage

The fork from Figure 1 is connected to two aluminum tubes, which are
press fitted into a slot milled into the bottom of the car. As the fork is
moved up and down, the aluminum tubes synchronously move up and
down. The axles are pressed into the aluminum tubes.
(Note that the chip on the upper left is cosmetic; it doesn't affect the

Figure 4 - Side support

To force the aluminum tubing to move up and down at an angle, the end
of each tube is supported by a washer. The screws hold the washer in
place (I wasn't sure if epoxy alone would hold the washer). The washer
has a close fit with the tubing, so it does limit the amount of cant that
can be applied to approximately 6 degrees down or up.

To set the desired cant angle, a little trigonometry is used. First, the
length of one aluminum rod is measured (L). Then the up-down offset of
the center part of the rod is measured (O). With this information, the
following formula provides the cant angle:

Angle = arcsin(O/L)

This can also be worked in reverse to calculate the desired offset:

O = sin(desired angle) x L

Additional equipment for the experiment includes:

- 32 Foot Aluminum Freedom Track, the track was leveled with a bubble
level and shims.

- Rear weighted extended wheelbase wedge weighing five ounces, front-
left wheel raised

- Max-V-Lube Graphite

- Ultralight Speed Wheels from DerbyWorx

- Speed Axles from Maximum Velocity

The car was first aligned to rail-ride (see Volume 8, Issue 4), and then a
few break-in heats were run. Then the following sequence was followed.

- 5 runs, 0 degrees cant
- 5 runs, 3 degrees up cant
- 10 runs, 5 degrees up cant
- 5 runs, 3 degrees up cant
- 5 runs, 0 degrees cant

After the heats were run, the high and low times were removed and the
remaining heats averaged.

The results of the experiment are shown in Figure 5.

Figure 5 - Experiment Results

Note the time scale on the left is in milliseconds. The results indicate
that there is a very small improvement in performance by up-canting the
rear axles. However, note that this is not an absolute conclusion as the
statistical variation of the heat times is greater than the 3 milliseconds
absolute difference in times. So, there may actually be no real

We can certainly say that accurately up-canting the rear wheels on a
smooth aluminum track is not a disadvantage, and may provide a slight
advantage. However, the benefit of canting on a rough track is unknown,
but may provide a more noticeable advantage.

Read More at: Pinewood Derby Times Volume 8, Issue 8

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