There are six major factors that influence the speed of a Pinewood Derby car. Pay close attendtion to all six of these and you can build a winning car.
Major Speed Factors:
1. Body Design
2. Weight Placement
3. Wheel Preparation
4. Axle Preparation
Advanced Speed Techniques:
1. Rail Rider Alignment
2. Rear Wheel Canting
3. Advanced Friction Reduction
How to Build a Rail RiderTM
Most instructions manuals will have you to align your car so that it rolls perfectly strait with absolutely no deviation for at least six feet. The theory, or myth, is that if the car rolls strait down the track it will not make contact with and rub against the center guide strip. Believing that the breaking effect caused by rubbing the rail will slow the car down, many builders insist on a perfectly strait running car. The only problem is this adjusting technique is doomed from the start.
WHAT DO THE EXPERTS SAY?
Experts agree that controlled rail riding will produce a much faster car. Yes, that’s right; if your car consistently rubs against the inside rail all the way down the track it will be faster.
It is nearly impossible to have a track that will allow a perfectly aligned car to run straight and not hit the rail. Invariably, any car will drift into the rail causing it to bounce back toward the other side. This generates a side to side movement, causing the car to repeatedly slam into the rail. This is actually the number 1 enemy of a speedster.
Therefore, knowing that you will definitely be hitting the rail (evidenced by almost every video of a fast car that you study in slow motion) we want to bias the car to hit the rail on the front dominant wheel side, as opposed to the raised wheel side, which incidentally is yet another kiss of death.
HOW MUCH IS ENOUGH?
Now, the real trick is to determine how much bias towards the center rail to create. According to most the optimal is about 1" to the rail over a 4' distance. However, every car is different. Some require more.
HOW TO DO IT
You need several tools to properly build a Rail Rider. The DERBY MONKEY ULTIMATE RAIL RIDER KIT is a great kit to help you develop a rail riding speedster. BEST KIT
This kits contains:
- Derby Worx Pro Axle Press
- Derby Worx Pro Rail Rider Tool
- Rail Rider Instructions
You will need some additional items such as pliers for adjusting the steer. We recommend the Pro Axle Pliers. Another option will require a Dremel Tool and a small screwdriver (we will discuss this later)
The absolute best kist for building a Rail Rider is Derby Monkey's Advanced Rail Rider and Wheel Canting Kit. This kit includes the tools and instructions on not only how to build a Rail Rider but how to also cant your rear wheels in order to build a near friction free and super fast Pinewood Derby racing machine.
It’s important to plan ahead when building a Rail Rider car. There are several things you must do to the car body and axles before we ever get to the Rail Rider alignment procedures. Its best to read this entire section before starting the work on your car.
RAISE ONE WHEEL
In order to have a Rail Rider, you must construct the car so that one front wheel does not make contact with the track like the car in photo. The best was to do this is to drill new axle holes placing one front hole about 1/16” higher than the other. Most builders raise the left front wheel so that the right front becomes the dominant wheel (the front wheel that touches the track) and that is how we will proceed with the instructions.
If your rules force you to use the stock axle slots then you must cant (bend) the left front axle up so that it raises the wheel off the track.
You need to drill a glue hole in the bottom of the car body for each axle. You can use a 1/16” drill bit. Position the glue hole directly above the axle hole so that when the axle is inserted you can see it through the hole. You will later glue the axles in place through these holes in hopes to maintain your car’s alignment.
If you are using the original axle slots then no holes are needed.
NARROW THE FRONT
Remember, we want the right front wheel to migrate in toward the center rail and make contact with the rail. The right front will maintain this rail contact for the entire run. We do not want the right rear wheel to ever touch the rail. So, you must now narrow the front wheel spacing 1/16” less than the rear. The best way to do this is to simply sand off 1/16” on the right front side of the body where the dominant front wheel will be attached.
This diagram shows the right front of the car body narrowed by 1/16"
FINISH THE CAR
The next step is to completely finish your car including painting, weighting and fine polishing your axles and wheel bores.
AXLE HEAD SLOT
This is an optional technique that you can perform on your dominant front axle in order for you to easily adjust the steer of your car. At this time you should determine which axle will go where on your car (RF, LF, RR and LR) and mark them or keep them in separate locations. Then use a Dremel and diamond cutting wheel or a smal file to place an axle head slot on the head of the right front axle. (see photo) This slot will be used later in the fine tuning of your new Rail Rider.
NOTE: If you are going to cant the rear axles, you should cut a slot in those heads also. But that is another topic and is not required for rail riding.
BEND THE RIGHT FRONT AXLE
In order to force the car to drift toward the rail you must bend the front axle 1.5 degrees. You will then insert and turn the axle to the exact location to give you the desired amount of inward drift. Using your Derby Worx Pro Axle Press and Pro Rail Rider Tool you will bend the right front axle 1.5 degrees using the following method:
A. With a permanent marker, place a dot on top of the axle close to the edge. From this point forward the dot must always point up to the 12:00 position.
B. Insert the right front axle into the Pro Axle Press with the axle head extended out about ½”.
C. Turn the axle so that the head dot is located exactly at the 12:00 position. Your axle head slot should be in the vertical position.
D. Place the 1.5 side of the Derby Worx Pro Rail Rider Tool over the top of the axle press and rest on the axle shaft in the groove on the tool.
E. Press the axle head against the Pro Rail Rider Tool.
F. Keep your dot in the 12:00 position.
G. Hold the assembly with one hand and gently place it on a solid surface.
H. Gently tap the top of the tool two to three times. This will accurately bend the axle to 1.5 degrees.
If your rules require using the original axle slots then you must repeat the above procedure on the left front axle using the 2.5 degree side of the Derby Worx Pro Rail Rider Tool. Keep your dot in the 12:00 position. Install left front in the car at the 6:00 position.
INSERT WHEELS AND AXLES
After applying lubrication to the wheels and axles, install them with the location dot of the dominant front axle (right front) at the 12:00 position and axle head groove in the vertical position. This will create Positive Camber (the top of the wheel will lean out father from the car body than the bottom).
You want the bend portion in the front right axle to be just inside the wood body so that the hub will never ride on the bend, only the straight part that resulted from the bend.
Next, you will need to make some type of tuning board. This can easily be made with any 8” wide board that is 4 or 6 feet long. Mark a strait center line all the way down the length of the board. Prop one end up about 3”. Level the tuning board as well as possible. (see image below)
RAIL RIDER TESTING AND ALIGNMENT
1. Place the car at the top of the tuning board straddling the center line and point the car perfectly strait down the board.
2. Let the car roll down the tuning board and observe which way the car drifts (left or right) and by how much.
3. Your goal is to have the car’s dominant front wheel (right front) drift toward the center line at about 1” over a 4’ distance.
4. This means the car will have a slight left turn. (see above image)
5. To make adjustments to the drift, slightly turn the axle with your screwdriver or pliers.
6. If the car migrates too much to the left, then turn the axle clockwise to give it more right steer.
7. If the car does not migrate enough to the left (or if it turns right) then turn the axle counterclockwise to give it more left steer.
8. Continue testing and tuning until you achieve the desired results (1” over a 4’ distance).
9. As soon as you achieve the desired results, glue the axles in place so that your adjustment will not change.
To make adjustments to the drift, slight turn the axle with screwdriver or pliers:
- Clockwise to migrate right
- Counterclockwise to migrate left
NOTE: Some cars run better being set up less aggressive (less migration) while others perform best being more aggressive (more migration). This is where you really need a test track so that you can compare speeds at various alignments.
You now have a Rail Rider and are ready race. Now, don’t monkey with it until race day. This is a very important factor that you should really discuss with your young scout well before the car is finished. All too often, some boy will impatiently decide to start playing with their car on the floor before the race. This is disastrous. The car will lose graphite, get knocked out of alignment, pick up dust, or even worse… get broke.
You should explain that this Pinewood Derby car is a fine tuned instrument and that any unnecessary handling can easily slow the car down. There will be plenty of time to play with the car after the race.
Rail Rider is a registered trademark of Derby Worx, Inc.