PINEWOOD DERBY RULES

 

How Pinewood Derby Rules Affect Car Design:

 
For several years I explored every possible technique for increasing the speed of my pinewood derby cars. Unfortunately, many of these, like super-light lathed wheels, are illegal except in outlaw races. Since the goal of the pages I've written on how to improve pinewood derby car performance for cars that can actually be raced, I decided it would be more useful to shift my focus to those techniques that are legal in any pinewood derby race... and there-in lays a problem.

Boy Scouts of America allows every pack and district to write their own sets of rules for their races. While most sets agree on the basics, in the all important area of wheel treatments there is a great deal of variation. This makes the job of defining a legal car almost impossible. To resolve this problem I surveyed the rule sets from 14 packs and districts to develop a consensus of what the average legal pinewood derby car looks like. All future research will be limited to cars that follow these rules.

To develop this consensus I used the 2014 Pinewood Derby Rules from the following organizations:

1. North Florida Council
2. Redwood District
3. Gateway District
4. Timberline District
5. New Horizons District
6. Patriot District
7. NNJ Ramapo Valley District
8. Samoset Council Rib Mountain District
9. Nashua Valley District
10. Thunderbird District
11. North Star Council Championships
12. Vancouver District
13. Pack 3371 - Lafayette, Indiana
14. Northeast Georgia Council

 
All state that the cars must be made from official BSA pinewood derby car kits or approved BSA parts and that cars must weigh a maximum of 5 ounces. They also state that the cars must be new for the year in which they are raced and that the cars must be made by the scout with a minimum of adult help. Either by implication or direct statement, lightened or lathed wheels, narrowed wheels, professionally prepared wheels or axles and prebuilt cars are prohibited. These rules are intended to prevent someone to simply "buy" a victory. In most cases, precut cars bodies are prohibited. Any lubricant must be of a nature and applied in such a way that it doesn't not foul the track. Springs, bearings and bushings are prohibited. The car must be freewheeling and the only source of power is gravity.

 

The Most Important Pinewood Derby Rules:

Where they differ the most is in what can be legally done to the wheels, how many wheels have to be on the car, how many have to contact the track and where the wheels can be placed. Axles treatments are also carefully defined, though because of their limited affect on performance these are not as critical as the limitations on wheels. Because wheel treatments have the greatest impact on car performance, rules limiting them are the most important. Here's how the 14 rule sets dealt with this all-important issue:

 
Number of wheels on the car:

Five organizations state that the car must have 4 wheels and that all 4 must be in rolling contact with the track.

Four state that the car must have 4 wheels but only three must be in contact with the track.

One states cars must have 4 wheels but doesn't specify how many have to touch the track.

One fails to state how many wheels the car must have but does state that 3 have to touch the track. (This opens the door for a three-wheeled car where the fourth wheel is replaced with a guide fin.)

Three fail to mention how many wheels the car must have or how many have to touch the track. (Again, this allows guide fins.)

 
Ten of the rule sets state that the car must have four wheels. Nine state or imply that only three need to touch the track. Therefore the consensus is that the average legal pinewood derby car has four wheels of which only three need to touch the track. Note that this implies that using guide fins in place of one of the front wheels is illegal.

Anyone organizing a pinewood derby race has my sympathy. On one hand you want a level playing field so everyone has an equal chance at winning. Adopting a very limiting sets of rules prevents someone from creatively interpreting the rules to build a car with what may seem like unfair advantages. But, very limiting rule sets also penalize builders who have taken the time to research the physics of fast cars and are willing to put in the extra work to make use of the knowledge they've collected. One way to satisfy both is to define different classes of cars. The price for this is a more complicated race and the expense of more trophies.

 

Amount of allowed machining:

All 14 rule sets state that the wheel surface that touches the track must be flat. Any form of reshaping such as rounding, grooving or edging to reduce the area in contact with the track is prohibited. They all also stated that the width of the wheel cannot be reduced. Additionally, no machining of the inside of the wheel tread or the outside to reduce weight is allowed.

Twelve rule sets state that only a light sanding of the wheel is allowed. At first this sounds like a simple enough rule, yet it has many ambiguities. What is a "light" sanding? One racer might think it's a few thousandths of an inch. Another 20 thousandths. The difference can give the second a 6-inch advantage at the end of the race. Sanding is defined as using an abrasive to remove unwanted material. The tool in a lathe can be considered as as a sander with a single piece of grit. I grant that this is extreme but it does open the door to lathing wheel treads, which imparts an enormous advantage.

Four rule sets address this by defining how much the original 1.194 wheel diameter can be reduced: 1.16 inches in one case, 1.18 inches in another and two state that the small, decorative ring of bumps (tread marks) on the outside of the wheels face must be visible and untouched - 1.14 inches.

Two state that wheels may be "trued," and term used for lathing wheels to make sure the wheel surface is perfectly coaxial with the wheel bore.

One rule set stated that wheels must weigh at least 2.6 grams. The problem with this rule is that to determine it a car's wheels would have to be removed and weighted. Since this would almost certainly throw off the car's alignment when the wheels are replaced, this amounts to destructive testing.

The most demanding rule was from the Thunderbird District, which stated that wheels had to be used as they come out of the box. No polishing or lathing of any type was allowed.

 
While there appears to a consensus that only light sanding is to be permitted, the complete lack of any definition of how much material can be removed and still be considered "light" makes this rule worthless. Defining a minimum diameter sounds better but has a practical problem. It requires someone at the impound desk to have and know how to use a micrometer. Properly measuring the diameter of each wheel takes time and risks scoring the wheel surface. I believe the best solution is to adopt the criteria of the two districts that stated that as long as the ring of wheel bumps on the face of the wheel are untouched, the wheel is legal. This is quick and easy to access and permits the racer willing to put in the extra work to sand it down that far a reward for doing so. As far as trying to prohibit lathing, it's an impossible rule to enforce. After sanding and polishing all lathe marks are removed so it's impossible to tell if it was done. As long as the wheels have not been reduced in diameter beyond the limit, there is no difference between lathing and sanding. Some people may complain that lathing unfairly "trues" the wheels (a process allowed either explicitly or implicitly by 11 of the 14 rule sets.) The fact is that there is a much greater chance that improper use of wheel mandrels will result is wheels coming out of the process worse than when they went in.

 

Wheel location:

Seven rules sets did not make any mention of where the wheels were to to be located.

Seven stated the wheels must be mounted either in the original slots or separated by a distance close to the original slot separation.

One prohibited staggered wheels.

 

This rule isn't important enough to worry about. Longer wheel bases reduce drag on the guide rail. Shorter bases reduce a car's moment of inertia. These two effects tend to cancel each other so the advantages one way or the other are negligible. I recommend the fairest rule is one that allows the wheel base to be extended not because it imparts any significant advantage but because it allows the car's builder more creativity in what the car looks like. I do not believe the rules should state that only the original slots can be used. Many blocks have slots that are so crooked that they make aligning the car impossible. Forcing one racer to use such a block, or buy additional blocks until he's lucky enough to get a good one, is unfair to him and a financial burden on his parents.

 

Wheel Bore Treatments:

Only one rule set prohibited filling then redrilling the wheel bore to use a smaller diameter axle. The advantage this is supposed to gain is that while the drag is the same, it acts of a wheel through a smaller radius thereby reducing torque.

 
This rule is important, but almost always covered by the prohibition against using reduced diameter axles. The problem with abdicating the control of this process to axle treatments is that they are hard to verify. My belief is that filling and redrilling should be specifically prohibited.

 

Axle treatments:

Because pinewood derby car kits all use nails, which have many surface imperfections that have to be removed so the car can roll, all rule sets allow filing, sanding and polishing the nails.

 

Six stated that narrowing or putting grooves in axles was prohibited. For many years it was thought that cutting grooves in axles reduced the area in contact with the wheel bore and thereby reduced drag. Many tests by independent researchers have refuted this idea but it persists to this day. In most cases axle grooves actually cause cars to run slower. This is a difficult rule to enforce because it requires the car to be disassembled to verify.

One prohibited coning the axle head. Some filing and polishing of the head is necessary to eliminate flanges created during the nail manufacturing process. Physically, it's impossible to eliminate this flange without introducing some some coning. Since the amount of coning required to achieve the coning effect is too small to be detected this rule is impossible to enforce except in extreme cases. The outside faces of modern stock pinewood derby wheels are shaped so that coning has a minimum effect so this rule really doesn't serve much purpose.

One prohibited canting or angling axles. This is a serious problem because it could be interpreted to included bent axles. Without this most cars cannot be aligned to roll straight.

One stated that the minimum axle diameter was 0.084 inches. This is a difficult rule to enforce for the same reasons applying to defined wheel diameters.

One allowed axle grooves.

 

I believe the fairest rule is to state that axles may be filed, sanded and polished and leave it at that. Grooving probably won't help and is difficult to verify. One possible advantage is that the grooves could be packed with graphite to create a reservoir so the wheels maintain a higher level of lubrication as the race progresses. But, successfully doing this is so difficult and the advantage so minor that if a racer succeeds in pulling it off I believe any victory he achieves has been earned.

 

"Spirit" Rule:

Eleven of the districts/packs had an additional statement that all racers are expected to abide by the spirit of the rules and not look for loopholes that can be exploited to gain a performance edge. The problem with this statement is that it discourages creative thinking, research and initiative - all of which are otherwise endorsed by the BSA. If the rules do not clearly state that a car must have four wheels and one contestant has the imagination to realize this means he can race on only three wheels and a guide fin, then I believe he's earned the right to take advantage of it. On the other hand, if the rules prohibit axle grooves and a racer does it anyway because they are hidden and he can get away with it, then this is cheating and goes against the "spirit" of the rules.

 

Pinewood Derby Rule Recommendations:

 
After carefully considering the 14 sets of pinewood derby rules researched for this page, their implications, intents and consideration of what's fair to the racers, I recommend the following rules, which are easily adapted to AWANA Grand Prix and Pinecar races by simply changing the names of the approved kits:

 

Overall: Cars must be built using only approved BSA Pinewood Derby kits and BSA approved accessories. All cars must be built for the current Pinewood Derby Racing Season. NO REPEATS or REPAINTS. (The goal of promoting father-son interaction is thwarted if the son simply uses the same car year after year.) Cars must be designed, built and aligned by the racer with minimal adult supervision. (The intent is to develop a child's motor skills, patience and creativity. All these are compromised if the adult does most of the work. Also, the child will experience little pride if he wins with a car he didn't make himself.) Cars may not be sent to third party facilities for construction, tuning or other performance enhancements. No cars purchased completed may be used. (This is to prevent someone from simply "buying" a win.)

 

Body: The main body shall be made from the wood block provided in a BSA approved kit. If the builder lacks the resources to cut out a car from a stock block of wood, attendance at a workshop(den/pack/district/council) is strongly encouraged. Alternately, a BSA approved pre-shaped block may be purchased to be used with the stock BSA Wheels and approved Axles.

Car Specs:

A. Width - Not to exceed 2 & 3/4 inches

B. Length - Not to exceed 7 inches

C. Weight - Not to exceed 5.0 ounces (141.7 grams) as measured on a scale. (It is the responsibility of the judges to have a certified 5-ounce calibration weight available at the check-in table to make sure the scale is accurate and to prevent arguments from parents concerning the accuracy of the scale. Many dens permit cars to pass if they are over by as much as 10-percent. Because the same scale is often used year after year, racers may learn they can take advantage of this by building heavier cars. This gives them an unfair advantage. One gram equates to a 0.006 second (1-inch) lead by the end of the race. Passing cars that are even just 5-percent over weight (7 grams) means they have a 7-inch advantage over all the other legal cars.) Lead is permitted and need not be completely contained so that it can not come in contact with skin. (Some rule sets are counter to this. However, in practical terms this means no one could ever use lead fishing weights or lead shot. Besides, it's almost a sure thing that the child handled the lead while assembling the car. Finally, other than destructive testing it can be difficult to tell the difference between lead and many other metals used for weighting a car.))

D. Height - Not to exceed 3 inches

E. Clearances:

 Center Rail Width: Must clear center guide rails, typically no less than 1-3/4 inches minimum.

 Bottom: No less than 3/8 inches from track surface between center rails. (These last two are to insure that the car doesn't drag on the track.)

F. Wheelbase –Any wheelbase is allowed as long as it does not create an unstable car that could cause it to leave its lane and interfere with other cars. (Permitting wider wheel bases allows for greater creativity of design.)

G. The front end must be at least 3/4-inch inches wide in the middle so that it can trigger the end-of-race timer.

H. No part of the car body, wheels or attachments may protrude in front of the starting peg.

I. The car design may be enhanced by the addition of other stable materials such as plastic or metal. Any additions must be firmly attached and meet Car Size Requirements.

J. No part of the car or any attachment to the car may be capable of coming into contact with the track other than the wheels.

 
PROHIBITED Items:

A. Springs

B. Starting devices or propellants

C. Electronic or lighting devices that interfere with the race electronics.

D. Liquids, wet paint, oil, sticky substance, or powders of any kind (other than axle lubrication)

E. Glass or excessively fragile parts

F. Bearings, bushings, washers, sleeves, hubcaps or inserts attached to or in contact with the axle, body or wheels.

G. Loose objects on car

H. Magnets

I. Sharp protrusions that could injure someone.

 

WHEELS:

A. Use only Official Scout Grand Prix wheels. All lettering/numbering, both inside and outside, must remain complete and be visible. The fluting and other BSA markings on the outside wheel area must remain visible. The outer wheel surface that touches the track may be sanded, shaved, lathed or polished to remove surface imperfections, mold casting burrs and correct off center wheel bores. The outside wheel diameter may not be reduced to the point where the outer ring of decorative bumps (tread marks) is touched. (For AWANA cars the wheel tread may not be reduced to the point where it touches the bulge of the wheel face.) The inside wheel diameter may not be sanded or machined in any way that increases its diameter. The outer wheel surface must not be reshaped in any way in an attempt to minimize tread contact or alter aerodynamics. Tread surface must be flat and parallel to the wheel bore. Coning the hubs and truing the inside tread edge is allowed. Tread width may not be reduced. You may add material such as glue, fingernail polish, or tape to the inside of the wheel to aid in balancing of the wheel, but no material may be removed from the inside surfaces.

B. Wheel Bore treatment is allowed including polishing and/or tapping. Wheel bores may not be filled and re-drilled to alter bore diameter or to achieve better fit with the axle.

C. Any and all work done on the wheels must be done by the racer with minimal adult guidance.

D. There must be at least four wheels on the car, however, it is not required that all four wheels make contact with the track surface. Each wheel must be mounted on an axle, on the outside of the car, in the vertical position. Each wheel must be attached directly to the wood car body by an axle and spin freely.

 

The following wheel modifications are PROHIBITED:

A. Rounding of tread surface/wheel edges

B. Grooving, H-cutting or V-cutting

C. Altering of wheel profile

D. Narrowing the tread surface, other than truing inside tread edge

E. Drilling sidewalls

F. Hollowing, sanding, or otherwise removing or modifying material from inside the wheel

G. Filling of any wheel surface with any type of material

H. There are after-market modified wheels that are LIGHTENED. This is usually done by turning the wheels on a lathe and removing material from the inside of the wheel. These wheels are NOT allowed and EASILY RECOGNIZED at inspection. Cars with these wheels will not be permitted to race. (The purpose of this rule is to avoid a racer "buying" a race by purchasing a set of these wheels, which provide an unfair advantage over racers who do not have the economic resources to purchase such wheels. Additionally, using professionally lightened of lathed wheels violates rules related to third party work and undermines the idea of the child doing most of the work himself.)

I. Coating the outside surfaces of the wheels with lubricant is prohibited because it can foul the track.

J. Using a guide vane or pin in place of one of the front wheels.

 

AXLES:

A. Only BSA approved nail type axles may be used. Filing, sanding and polishing to removed burs is permitted.

B. Grooves are allowed.

C. Axles must not be connected to any device that mechanically alters rotation or spin. Axles must be mounted into the wood sections of car. Drilled holes or slots can be used.

D. Approved lubricants include (but are not limited to) graphite, Teflon, Nyoil, and Krytox.

E. Over-application of lubricant which results in shedding onto the track is not allowed.

 

INSPECTION:

Each car must pass inspection by the Official Inspection Committee before it may compete. The Inspectors will disqualify any car not meeting the rules. Any adult or scout may appeal the findings of the Inspectors to the Race Committee Chair-person, whose decision is final. After acceptance only race officials will handle the cars.

Cars may be reclassified or disqualified at any time if they are determined by the race officials to not meet requirements.

 

WEIGHTS:

The drilling/removal of lead(Pb) will NOT be allowed at the race venues or at check-in time due to the toxicity of the material.

 

REPAIRS:

Race officials may authorize repairs, usually when damage is caused by collision with another vehicle or object or dropped by an official. The Cub Scout is in charge of all car repairs. Adult guidance is allowed and encouraged. Repairs must be done before the next heat for which the car is scheduled starts. Officials may delay the start of the heat depending on the circumstances.

 

BEHAVIOR:

GOOD SPORTSMANSHIP AND BEHAVIOR IS EXPECTED. Race Officials may ask anyone not following this rule to leave.

 

Conclusion:

The goal of the BSA Pinewood Derby Program is to promote adult-youth bonding, building skills, tool working, creativity, positive competition and above to all have fun. A good set of rules is necessary to encourage all of these. I sincerely hope anyone visiting this page found it helpful.

 

 

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