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How to use a slotted tungsten disc on a Pinewood Derby car. 

Example of pinewood car
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How To Add  A Slotted Disc To Your Pinewood Derby Car

Tungsten Disc Top Slotted Tungsten Disc Bottom Disc height
All disc heights are the height of the side of the disc and does not include the dome. 3.70 oz - 3/8" high
3.25 oz - 5/16" high
2.75 oz - 5/16" high

Flat top disc (no dome)
2.75 oz - 7/16" high

Slotted Tungsten Discs

These discs have a slot in the bottom which has several uses as described below.

These discs can be inserted in a 1 inch hole. The hole can be drilled with a spade bit or a forstner bit. The forstner bit is recommended as there is less chance of cracking the block and it results in a cleaner cut.
Testing center of gravity

The weight should be placed so that the car's center of gravity is one inch in front of the rear axle. To check the center of gravity, place the two front wheels and axles on the top of the car over the front axle and the weight near the rear of the car. Place a pencil across the bottom of the car one inch in front of the rear axle then move the weight forward or backward until the car balances.

Center of Gravity Adjustment

Fine tune your car's center of gravity
For this technique to work, the body of your car near the rear axle should be the thickness of your weight plus 1/4 inch to leave room for the axle slot. Your pinewood derby car will go faster if the center of gravity is as far back as possible. But, your car will tend to raise its front wheels and jump off of the track if the center of gravity is too far back. You should have a track available to adjust the center of gravity. Test tracks are available here. Use the above method to determine the position of the weight but the slot should be towards the rear of the car.  When you have determined the position of the weight, drill the 1" hole the depth of your weight. Place the weight in the hole with the slot to the front of the car. Test the car on your track. If the car wobbles excessively or jumps off of the track, rotate the weight slightly and test again. Repeat until the car is stable. Glue the disc in the block with the slot facing down. Use super glue, epoxy or gorilla glue.

Weight Adjustment

Slotted disc with additional weights
Two 1/4" tungsten cubes can be added to the disc slot for an additional 1/3 oz. The body of your car near the rear axle should be the thickness of your weight plus 1/4" to leave room for the axle slots. Drill the 1" hole then complete your car including adding the wheels and axles. Put your pinewood derby car on a scale and place the disc on top of the car. Add one or two of the cubes until the car weighs 5 oz. Tungsten putty can also be added if more weight is needed.  Glue the disc and cubes in the block with the slot facing down. Use super glue, epoxy or gorilla glue.

For Use In Cars With Minimum Wood

Slot for axles
The disc can be installed in the bottom of the car so that the slot provides clearance for the axles. One 1/4" tungsten cube or tungsten putty can be added to the slot if more weight is needed. Drill a one inch hole centered 1/4" behind the rear axle. Drill all the way through the car if the car is the same height as the side wall of the weight or drill into the bottom of the car if the car is thicker than the weight.
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