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FEATURE ARTICLE
Modifying the Pinewood Derby Wheelbase


It is not entirely clear to me how the various organizations established the
location of the axle slots on their kits. Years ago, the BSA wheel base(1)
was longer than the current 4-3/8 inches of today's kits. Choosing to be
different, Awana kits use a wheel base of about 4". Other organizations and
kit makers use slightly different measurements.

Unfortunately, none of the current standard wheel bases are really the best
for speed and alignment. The best wheel base for going straight is always
the longest possible wheel base. Top fuel dragster competitors know this,
as is evident from the design of the rail-type dragster. Not only is the
wheelbase very long, but the car is made very long as well.



WHY EXTEND THE WHEELBASE

For pinewood derby cars, extending the wheelbase provides an advantage due
to the following reasons:

1. On Ramp-flat tracks(2) best speed is attained by locating the center of
gravity (COG) of the car as far back as possible while still maintaining
stability (typically this is between 1" and 1-1/4" in front of the rear
axle. If the rear axle is moved as far backwards as possible, the COG can
also be moved backward, thus increasing performance.

2. The longer the wheel base, the greater the turning distance (a short car
turns much more quickly than a long car). A pinewood derby car should go as
straight as possible, so a longer wheel base is an advantage.

Assuming a 7" maximum length and 1-1/4" diameter wheels the best placement
for the axles is 5/8" from the front and back of the car. If you are allowed
to use this long wheel base, then I will describe how to modify the block to
attain that wheel base under 'Method 2' below.

CHECK YOUR LOCAL RULES

But before making any modifications to your wheel base, make sure to check
your local rules. Generally, the rules will offer one of the following:

No choice - The wheel base on the kit must be used, and the location of the
slots on the block must be retained. If this is the case, make sure to use
the slot that is closest to the end of the block as the rear axle slot.

Choice 1 - Wheel Base Restricted: The wheel base on the kit must be
maintained, but the location of the slots on the block is not restricted.
That is, the spacing between the axles must be retained, but the slots can
be relocated as desired.

Choice 2 - No Restrictions: The wheel base may be adjusted as desired.

If choice one is available, then consider Method 1. If choice two is
available, then consider Method 2.

METHOD 1

Method 1 retains the existing wheel base but moves the wheel base as far to
the rear of the car as possible. This can be accomplished by drilling new
axle holes, cutting new axle slots, or using the existing slots. If you
choose to drill new holes or cut new slots, locate the rear axle 5/8" from
one end of the car. Then locate the front axle at a distance from the rear
slot equal to the wheel base on the original block (see the following
sections for tips on drilling/cutting new axle holes/slots).

If you choose to use the existing slots, then measuring from an axle slot
towards the closest end of the car, make a line 5/8" from the axle slot.
Use a saw to cut through the car on that line. Then glue the removed piece
onto the opposite end of the car.



The block will now have the rear axle slot at a distance of 5/8" from the
rear of the car, which will allow the COG to be moved further backward.

METHOD 2

Method 2 creates the optimum wheel base by creating new holes/slots a
distance of 5/8" from the ends of the car.

Cutting New Axle Slots

In the absence of power tools, new axle slots can be cut using a ruler, a
square (Combination or Carpenter's), and two hacksaw blades.

1. With the ruler, make marks on the block a distance of 5/8" from each end
of the block. You will probably want to do this on the side of the block
opposite of the existing slots.

2. Using the square, at the pencil marks draw a line across the block.

3. On the sides of the block even with the pencil marks made in step 2, make
a pencil mark at the depth of the original axle slots.

4. Clamp the block in place, with the axle lines facing up.

5. Holding the two hacksaw blades tightly together saw the new axle slots.
Make sure the cuts are exactly on the axle lines, and the cuts go no deeper
than the marks on the side of the block.

Drilling New Axle Holes

A more accurate method for creating an extended wheel base is by drilling
axle holes. This can be done with a drill press, or with the Pro-Body tool
and a hand drill.

-- Drill Press Method --

The following tools are required for the drill press method:

- Drill Press

- Drill Bit (#44 for BSA axles, 3/32" for Awana axles, other kits will be
similar but always drill a test hole on a scrap piece of wood to make sure
your axles fit properly)

- Ruler

- A flat piece of wood (placed under the block. This will keep the wood
block from chipping when the drill bit goes through the block. Make sure the
piece of wood is flat and square).

To ensure that the slots are square to each other, the rear hole (and the
front if a raised wheel is not desired) will be drilled all the way through
the block. But since drill bits are flexible, one-half of each hole will be
drilled first, and then the remainder of the hole will be drilled.

1. On the right side of the block, make a pencil mark 5/8" from each end of
the block and 1/8" from the bottom of the block. If one front wheel will be
raised, then on the left side of the block make a pencil mark 5/8" from the
front of the block and 3/16" from the bottom of the block.

2. Insert the drill bit into the drill chuck with about 1" exposed and set
the drilling depth to about 7/8".

3. Place the block of wood with the right side facing upwards on the flat
piece of wood on the drill platform. Drill the front and rear axle hole on
the right side of the block. If a front wheel will be raised, turn
the block over and drill the front-left axle hole.

4. Stop the drill press and extend the bit so that at least 1-3/4" is
exposed. Make sure the bit will go all the way through the block into the
flat piece of wood.

5. On the right side of the block, drill into the existing rear hole and
continue all the way through the block. If a front wheel will not be
raised, then repeat for the front axle hole.

-- Pro-Body Tool Method --

The following tools are required:

- Hand Drill

- Drill Bit (#44 for BSA axles, 3/32" for Awana axles, other kits will be
similar but always drill a test hole on a scrap piece of wood to make sure
your axles fit properly)

- Ruler

- Clamp - 'C' or bar type

- Optional - Square (combination or carpenter's)

1. Identify the tool parts - The hole with the larger countersink is sized
for Awana kits and requires a 3/32" drill bit. The hole with the smaller
countersink is sized for BSA and PineCar kits and requires a #44 drill bit.
The index marks are used to align the tool with the axle slots or with the
desired axle hole position.

2. Test Fit - Test fit the Pro-Body tool on the bottom of the block with the
two 'ears' positioned on the sides of the block. If the block is too wide
for the tool, use coarse grit sandpaper to reduce the width of the block
until the tool fits snuggly onto the block. If the block is too narrow for
the tool, insert a piece of paper - folded as many times as needed - between
one ear of the tool and the block such that the tool fits snuggly onto the
block.

3. Mark the Block - Make a pencil mark 5/8" in from each end of the block.
Extend the marks from the bottom of the block to the top of the block using
a square (or measure and mark near the bottom of the block and near the top
of the block, and then join the line with a pencil and ruler).

4. Clamp Tool and Drill - Position the tool on the bottom of the car with
the two 'ears' on the sides of the block. Align the index mark for the
desired hole with the line on the block. Clamp the tool in place, using
paper if necessary to ensure a snug fit (see step 2). Hold the block firmly,
position the drill bit in the desired hole, and drill 3/4" into the block.
Without releasing the clamp, turn the tool and block over, and drill the
second hole. Repeat for the other 2 holes.

CONCLUSION
Extending the wheelbase can be a distinct advantage for your car. So if
allowed by your local rules, don't miss out on this performance advantage.

Notes:
(1) Wheelbase - The distance from the center of the front wheel to that of
the rear wheel in a motor vehicle, usually expressed in inches - from The
American Heritage® Dictionary of the English Language.

(2) A Ramp-flat track starts on a slope, then transitions to a long flat
section.

From Pinewood Derby Times Volume 2, Issue 6

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