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Http://www.derbydust.com

This video shows you how to install wheels and axles for your pinewood derby body without breaking chipping busting out your slots!  NO MORE HAMMERING!  Do not hammer!


Tools:
  • #44 Drill Bit
  • Pin Vise
  • Derby Worx Axle Guide
  • Clamp (optional)
  • Patience!

 
 

Pinewood Derby Speed Axles

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100,000 grit Optical Finish



Fast winning pinewood derby car designs utilize polished speed axles.  

Take a look at our pictures of our quality work of pinewood derby axle close up pictures.   They say it all!  

ALWAYS BRINGING NEW IDEAS TO THE CONCEPT.  LEXX HAS MASTERED POLISHING PINEWOOD DERBY AXLES TO THE OPTICAL LEVEL.

Lexx from Derby Dust has mastered the 100K  OPTICAL POLISH!  And man he has been setting track records since then.  

Even better!!!! LISTEN!!!!

Our prepped have been deburred, shaped, straightened and sanded down to a 2000 grit finish. From that point, each axle goes through a buffing process up to 100,000 grit OPTICAL FINISH!  We use separate buffing wheels to ensure no cross contamination. Then we seal the prepped axle with a Krytox sealing agent. Through our professional, industry leading, lubrication resources, we have found a substance that binds Krytox to metal. That's right a metal sealing agent that has one of the most friction less substances known to pinewood derby racing. This is NOT putting a drop krytox oil on it. This is binding Krytox to the surface of the metal. 

You can't even buy 2 of the tools needed to do this for under $25. Much less the files sandpaper, sealer, and buffing materials.

We are getting average speeds of 12.45+ feet per second out of these sets or 2.47's or less on a 30.75 foot metal track with DRY LUBE!

Get even FASTER speeds with lighter wheels.

 

With speeds of 15+ fps on the last 10 feet of the track.  WITH OUR GRAPHITE DRY LUBE

No reason you can't do the same. 

Axles are wrapped in tissue paper to ship to ensure that your axles are not scratched up during shipping process.  

 
 
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Pinewood derby fender flare sidewall
For those guys that want to add some flare (play on words) to their build! These are more than just for looks. They will reduce wheel drag, too!
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pinewood derby fender flare sidewall
Sidewall Fenders for BSA SLOT pinewood derby car. CNC cut.  We had to add them to the build list this year.  They cover the entire wheel with just enough clearance for all your canting and steering needs.  Again we don't hide our info, so here it is for all you guys to copy.

  • Specs:
  • Pine- White kiln dried
  • Length = 7 inch
  • Width = 1 3/4 inch
  • Thickness = 1/2 inch
  • Internal Wheel diameter 1.3 inch
  • Designed to be off-set high .05 inch (gap gage provided)
  • Weight=
These are some awesome fun flares.  You can shape them to anything that you desire.  Not just some arrow shaped piece of wood.  We took the hard work out of guessing how to do it for you. 

Every sports car has their wheels enclosed from drag to increase speed.  The same concept applies to pinewood derby.  These flares are unique that they extend all the way down to the bottom of the track.  Just remember to bevel the inner edges to keep the car from rubbing down the track.

Don't forget this comes with FREE WHEEL GAP GAUGE!

 
 

Pinewood Derby Canopy Dome Cockpit Top

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Some bodies are so thin, there is no real way of installing weight internally. This is a good solution to your problem.

Dimensions:

  • 2 inches in length
  • 1.25 inches in width
  • 1/2 inches tall
  • *Measurements are approx due to different densities of lead supply 
Method of install is GLUE on.  The bottom of this canpoy is flat.  This allows you to adjust the weight to get the perfect Center of Gravity.  

Please cover all exposed lead with paint.  DO NOT sand lead canopy without proper breathing equipment.  Lead dust can be harmful to children.  

PLEASE TAKE ALL NECESSARY PRECAUTIONS.  YOU HAVE BEEN NOTIFIED!  

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This stuff is so good, soon you will be asking for it by name! People can't tell us our lube doesn't work because we use our dry lube for every build. Our faster builds are reaching average speeds of 12.35+ with just sanded BSA wheels and axles  (100% legal)! 

Contains proprietary blend of the industry best dry lubes. It's more than just "graphite."  Believe it or not, our product costs more than the packaging.

Derby Dust ™ Dry Lube Feedback

  • Author: Fred-PA
    Tried the comp sample. Thanks. We won the local division! Onto districts. Now supporting you! :)
  • Author: Member id trekkie527
    Hi. I bought this item recently and used it on my son's derby car. Thanks to this stuff, it clinched the pack victory in a really, really close championship race. My son is now pack champion and he's thrilled. Was wondering if it's possible to purchase more ... and to save it for next year? Would it keep and be as effective if I save it at home for next year as opposed to purchasing it next year before his pack derby? Please let me know. Amazing stuff. Thanks so much! Now he's just eager to get his trophy!
    - trekkie527
  • Author: Gary O.
    5/5: "Well satisfied with Derby Dust , Won fastest in Pack."
    January 30, 2012
  • Author: Member id thomas13103
    Good Times!!!!! We Won!! Buyer: Member id thomas13103
    Mar-16-12 15:07
  • Author: Member id call6573
    awsome stuff Buyer: Member id call6573
    Mar-07-12 19:33
  • Author: Member id byhisname
    Great product--derby dust--we used it & we won. Thanks!!!!!!!
    Feb-19-12 20:37
  • Author: Member id wreckem72
    Fast shipping! Awesome product! 100% Satisfied!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    Jan-31-12 19:30
  • Author: Member id c-1
    Premium product, professionally packaged with quick shipping! A+++
    Jan-26-12 08:52
  • Author: Member id iraqivetgijoe
    WOW! This stuff really works. Product is highly recommended. A+ seller Buyer:
    Dec-02-11 16:27
  • Author: C. Volk
    Hi, I just wanted to let you know that my sons car use durby dust and took 1 place at the pack races. Then took 1 place at distric and set new track record of 3.106 at a speed of 159.7 scale miles per hour and now he gets to go to council races May 5th in Wichita Kansas. thanks Durby Dust!!!!! P.S. I will be ordering more soon!!!
  • Author: bryan 3/5/12
    Hello,

    Thank you for getting me the derby dust last week when another vendors highly rated product just did not cut it.

    I just wanted to take a moment to thank you for sharing your products with me. The experience has been really positive.

    For the derby the combination I ended up running on my sons car and three other kids car (single moms) was

    bsa certified wheels and axles rules
    The polished nail (1000 grit) with creme toothpaste polish Light initial dusting of BP2000 dry lube gently hand rubbed into the axle Pre fill the wheel and axle with another dry lube and spin 5 by hand at slow speeds with a slight shake to distribute, This could take 5-6 times Once I have 20+ spins the wheel is mounted Once the car runs straight the final dry lube is added by a needle fill to both side of the wheel and spin for maximum speed and duration.

    Progression: based on processing 20 nails, fastest 16 running on a car Straight wheel and axles nothing done 10-12 spins of time (seconds) Sand and polish (tooth paste and rinsed) 15-16 seconds of revolutions before stopping

    Light dusting and burnish maybe 1 more second of spin

    If I use bP2000 as the final lube and break in the maximum wheel spin is
    23 to 24 seconds, good for most races but not going to districts.

    With derby dust dry lube added at this level of prep the spin count averaged 31 seconds of spin before stopping.

    Based on running on the test track at the house (25 feet) with a pace car
    20 spins/seconds loses to the pace car by 1 car length (7)
    24-25 seconds of spin loses by 3 inches at the finish
    31 seconds of spin beats the pace car by 2 inches based on 5 runs with lane swapping

    In real time comparisons:
    Track 32 feet, wood with high tech finish electronic time and start gate

    5 Oz car, running 4 wheels down, 7 inches long ran the track in 2.49 seconds, which Grand Prix software calculated as 216 mhp estimated.

    At the race on Saturday, my sons car won the grand prize for best average time over 4 runs and set the track record for speed. The attached picture is his car.

    How do I know the extra revolution of spin made a difference as the number two car, lost by 500th of a second. Less time than it takes for a hummingbird to flap his wings 3 times in hoover flight.

    If you have any question please feel free to call and I'd be glad to try it. My wife this morning said she had still not sent the extra $6 for speed shipping I will make sure it out tonight. The only thing better than your product, was the teams attention to detail, in getting the product out to me quickly, to make the race day event. The three kids cars, who I used it on also did well making the day special for them.

    Thanks so much for your time and help.

    Bryan
  • Author: L. Cappelli
    We won this weekend! First try after 47 years. Thanks for all your help, great product & we would not of done so without you. 3 generations are very proud. Humble lessons are on tap.

  • Author: @403woodcrafts
    So the weekend before our Pack race, I gave a sample of Derby Dust to some friends that are in another pack. They generally have good cars and have been very helpful to us in our first year. So they watch the treadmill turn in video and used the Derby Dust on his car. Well, he won Webelows II Den and his Overall pack. He had a top speed of 195mph!!

    My sons are in the Tigers and the Wolves. Our Pack has a wooden 3 lane 28 foot track and each car runs each lane twice, then after the slowest time is thrown out they place the top 3 by average time. My Tiger won his den by having an average of 0.018 seconds faster than second and finished 4th in the Overall. My Wolf won his den by having an average of 0.086 seconds faster!!! The Cub master walked over to me after the first run and mumbled.... damn that was fast! An average car on our track runs about 2.65 seconds (180 mph) My Tiger was running 2.63's and .64's (his is the car with the fishtail problem) and my Wolf was the only Scout to run under 2.6 4 of his six runs were 2.58's and .59's!!
  • Author: Member id smb9495
    Great product, won our first derby!
  • Author: Member id mitchell_99
    Great product, love the derby dust!
  • Author: Member id phyedguy1269
    A+++ First Place with Lube
  • Author: Member id tater67_99
    ausome product. Race was friday my boy took 1st place
    Apr-15-13 13:44
 
 
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Fast winning pinewood derby car designs utilize proper pinewood derby tools and jigs. 

Pitstop™ is your first stop for pinewood derby wheel installation and building.  This is our unique, never before seen jig brought to the PWD industry.  Out of box thinking done at Derby Dust!  Let's watch them copy another one of our designs!   Designed for all shapes, profiles, wheel bases.

Pitstop™ also holds all the necessary tools for building and repairs!

Every den should have one of these at the pits to make all the necessary adjustments.

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No more busted wheels. Pitstop attaches easily to any base with provided mounting screw holes. Great for build or repairs.

No more hammering in the under wheel installing the other side!  Watch my son use it with ease!

Available with or without tooling.  

Every Pack needs one at the Repair Station.


 
 
Wheel Modifications

There are many ways to turn that $0.02 wheel into a proven winner.  We will discuss the steps in depth.  Just a brief description of how PWD BSA wheels are made.  Although thermoplastic vacuum is not a complicated process, understanding why wheels that come out of the same mold can vary from piece to piece is even more complicated process with variables that most don’t care to understand.   The mold can be too hot, too cold, the plastic can be slightly thicker than specs or too thin.  The plastic can warm for too long or not long enough.  You could have a top sheet of plastic that has more water vapor than the sheet below it, etc, etc, etc.  Since these wheels are massed produced, quality control is not German engineering quality.   At 600,000 cub scouters per year with 4 wheels per scout you have at least 2.4 Million wheels produced each year.  With 16 molds, it takes about 150,000 sheets of plastic if you did it perfectly every time.  150,000 sheets at 260 work days a year = 578 sheets a day.  On a 12 hour work day it is approximately 49 sheets an hour or roughly a sheet every 75 seconds without a break!  Its about numbers!  Not quality!

Because of this, you could have 4 “Mold Match” wheels that roll different ways.  This simple reason you could rob yourself out of a win.  SMOKE AND MIRRORS: Just because you bought 4 match wheels doesn’t mean they are exactly the same.

With that said, one has to understand that no matter how many modifications are done to the wheel, it will never be perfect.  It was never designed to be perfect.   It is not manufactured to be perfect.  IT WILL NEVER BE PERFECT.  What we try to do is make the best lemonade that we can.  Before reading further, take a break.  Think about this paragraph. 

To increase the performance out of your wheel the following steps are how we bring performance to those factory wheels. 

 Step 1-is to inspect each wheel for true center.  The #4 mold is the worst wheel out of the current mold.  Simple visual inspection with the naked eye one can see it is off center.   The wheel basically travels in an elliptical rotation.  A customer made us aware of this flaw in manufacturing in Jan ’12.  Since this information was brought to our attention, we no longer provide wheel sets with this mold.  We simply throw it away.  NO #4 molds from us.  Occasionally a few other wheels are off center for unknown reasons, we simply throw them away, as well

Step #2-Ream (or simpler terms drill) the inner diameter to a consistent diameter.  A reamer is a type fancy drill bit used to make exact dimensions out of pre-drilled holes.  There are multiple cutting sides to a reamer so that it will leave a consistent smooth finish.   At www.derbydust.com we have determined that the best possible inner diameter is, of course, what the BSA engineers designed it to be.  That is the reamer size we use.   This is the first modification that we do.  This is to ensure that there is no binding or friction caused by smaller than designed inner wheel diameters.  This is the key to ensure you are getting the best possible speed out of your wheels.   With most molds, there is no material removed with this ream, however there are a few that need it done. 

Step#3 -(optional)  Removing material from the inner portion of the wheel.  If allowed by your pack, you can choose this modification that will lighten the wheel.  Using a dedicated computer controlled lathe, we take away a small portion of inner wall thickness to lighten the wheel.  This modification decreases the overall mass of the wheel, thus allowing for quicker starts. The scientific theory behind this has to do with rotational coefficient of friction.  We leave the outer edge thickness as is, so that this modification only be seen to the experienced inspector.    This process reduces the weight of each wheel by xxxx.  Increase in speed is usually about xxxx on our test tracks when compared to factory wheels.

Step #4-The next step(optional) if chosen by you, would be to remove the outer step of the wheel hub.  Once the outer step is removed, the head of it is shaped similar to a dome.  By decreasing the surface area where the axle and wheel touch, you decrease friction.  This modification instantly increases speeds.  The tapered head of the speed axle rides on the smooth surface of domed head of the wheel.  Our data shows this decreases overall times usually between .01-.015 seconds when paired with our speed axles.  Most packs allow this modification.  PLEASE read your rules.  YOU be the judge.  It is your child’s race. 

Step #5- Once the head is shaped, then the wheel is chucked into a mandrel. The outer surface of the wheel is made to a consistent shape using another dedicated computer controlled lathe (we have many of these).  Our dedicated machine does not change in the z axis, so our wheels theoretically should always be the same diameter.    Approximately 0.005” is removed from the outer diameter of the wheel.  We find this to be the necessary depth to remove not only the high spots on the wheel, but also the low spots.  With the computer controlled lathe, we are able to control the rate at which the machine removes material.  Because of this we can produce a wheel that is appears to be completely smooth at first inspection.  It will feel smooth to finger nail test. No noticeable ridges unless you use a magnify glass.  Then if you choose, we will wet sand the wheel to 1200grit smooth finish.  If you pack does not allow “lathed wheels” these are the wheel set that will be “under the radar.” 

We do not do any work at this time to the inner hub facing.  At this time we have not found that there is much benefit to machine work at this location.  Removing material at this location will also require removing material on the width of the wheel.   This violates most pack rules.     We offer wheels from Derby Worx that have these modifications.   There is no need to “re-invent the wheel”. 

We continue to gather data and with hundreds of completed cars each season, we are able to compile information that improves our process and our results.  

 
 

Free Pinewood Derby Tips curtosy of Derby Dust

This is a 10 minute read.  Sorry about this, but a lot of words.

Don't waste cash on packaged tips and tricks until you read all of ours for free!  Video of this is posted on YouTube.  Its posted at the very end of this article.  Long process by words.  Not so bad watching the video.

Without getting into all the fancy scientific answers, the plain and simple reason to tune a pinewood derby car is for speed!  There are many different ways and theories out there.  From wax paper to set screws.  We like our method the best which shows your car traveling at its near top speed in a static setting.  Utilizing a treadmill, you can see your car at its top speed while making all the necessary real-time adjustments.  NO NEED for a PLASTIC test track! 

Don't own a treadmill?  I bet you know someone that does.  Buy them dinner, use it for an hour or two.  Beg, Borrow, Barter.  Do what it takes to get your win! 

Because a pinewood derby car is only powered by its stored gravity at the top of the track, you must tune your car so that it will use that stored energy to get the car to move down the track.  If this is your first derby, or your last derby, take a few minutes to educate your self about TUNING a pinewood derby car.

Tuning your car keeps the car moving forward.  That is the ideal direction.  A car that travels side to side, bumping each side of the car will not get you in the winner's circle.  A car that fish tails will not get you in the winners circle.  Grandpa's car wins because he puts the time in making sure the car does not do this.  There is NO aftermarket part that will replace this step in building a car.

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When you bent your axles. Did you gap your axle prior to bending? Otherwise your bend will begin somewhere inside your wheel hub which will cause all sorts of chattering and aligning issues.


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TUNING YOUR PINEWOOD DERBY for the WIN! 

Builder's Note:  It is near impossible to tune 4 bent axles without a treadmill in a fair amount of time. You’ll drive yourself crazy. Find you a treadmill. Take it to 10 MPH and watch what is happening. http://youtu.be/OyC_PTMHNe8 if you have to have 4 wheels touching- then I would bend only 1 wheel and it will be a steering wheel. Watch this too: http://youtu.be/IoQNVwTeJAA

1.5 or 2.5 degree bends? A problem is with a 2.5 degree bend you have basically 30 degrees of rotation or less to get it to ride on the axle heads. It’s just a really sharp bend. If you want to bend 4 axles, I like doing 3x 1.5 degree bends. If you need a 2.5 degree bend, make it your front steering wheel. 2.5 degrees in the rear is not really necessary. We even do straight axles and just angle them in the BSA slots. 
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Setup: Install the wheels and axles on the car, use the gap gauge to properly gap wheels. Mark the 12 o'clock position on all wheels with sharpie, depending on setup. 

Tape the string on the center of forward kick plate of your treadmill, and tape it to center on the front of the car. 

Dust the wheels and axles with Derby Dust Dry Lube.
Tuning:
Turn the treadmill on. 1-2mph at first. If incline is available, 1 degree would be great.
Note the characteristics of the car. If it is swerving all over the place, there is a lot of work to be done. If it pulls to one direction or the other, directional tuning needs to be done to get to a slight deviation off center for a center rail rider (3 wheels) or center (4 wheels).

The goal is to get your car to deviate just slight off center to make a center rail rider or straight down the middle if you have one of those type of races.

Using pinewood derby tuning pliers, make an adjustment on a single axle turning 1/8th of a turn or less until you have made up to one complete rotation. If no change in deviation, then move to another axle on the car, and repeat process. Continue this process until you get the car to be off center or straight down the middle, depending on your car and race scenario.

If no change is noted after adjusting all axles, then you will need to bend one axle. 1.5 degree would be best. I would install that axle on the front. Repeat tuning process until deviation is obtained. If no change, make sure the bent axle is touching the ground. If so, then the bent axle needs to be moved to the rear side of the direction of deviation and then tuned. If no change is noted, move axle to opposite side of car. Bending more than one axle is counterproductive. If you car does not respond to tuning with just the bend of one axle, think about making a new car.

Point being, if your inspections requires pulling of axles, and you have more than one axle that has to be bent, there is a greater chance that all of the tuning work will be ruined.

Break in:
Once tuning is complete, turn the treadmill up to as fast as it will go. Your wheels are not going to burn up! Now observe characteristics. Note if wheels are running the way you want them to i.e. rubbing on the outer wheel hub, running in the middle of your axle, rubbing against the body. Adjustments will need to be made if not satisfied. A wheel that rubs on the body needs to be bent upward. A wheel that rubs on the axle head, needs to be bent downward. At top speed on treadmill, you will be able to visualize the performance of the car. This method is better than any "tuning board" every day of the week.

Once you are happy with the wheel play, then it is time to start building up layers of dry lube.

Add a LIBERAL amount of dry lube to all running wheels as it is traveling every 45-60 seconds. Continue this process for 10 minutes. 10 minutes at top speed should yield the equivalent of approximately 400-500 races.

This process will also yield the 20-30 second spin benchmark theory! If you have a wheel that is not performing this well, it could possibly be that it is out of balance or has a warped inner hub due to cooling during manufacturing. Replace it and start process over from beginning (SORRY!)

Using rubbing alcohol applied to a rag, remove the marks on axles without getting alcohol into the hub, then reapply new marks back in the 12 o'clock position. If you had to bend an axle, then be sure to make a mental note which one it was or mark it on the bottom of the car, and BEG your inspectors not to pull it.

After the 10 minutes and the final marking. PACK your car up, and do nothing with it until race day. If you have to pull an axle, be sure to return it to the exact spot.

No other lubing is necessary. We have not seen any data that shows any additional lube after this point helps.

What you have done by doing this process is used the cars weight under load to "roll" multiple layers of lube on the axle and wheel. You have also tuned your car to eliminate fish-tailing and gain greater speeds for your derby car way beyond a simple dust/ finger roll job. We have decided to share our research with you. This technique does not require a "drift" board, it does not require a test track, and it does not require a great knowledge regarding polishing techniques. It does build layers of near frictionless surface on both the axles and inner wheel hubs that is good for many races.

This process is very hard to describe with words, and our video will show you how simple it really is.
 
 

Center of Mass / Gravity Pinewood Derby Car

Free Pinewood Derby Tips Courtesy of Derby Dust

Placing Weights in a Pinewood Derby CarBecause there are MANY more factors involved making a pinewood derby car, there are many more articles to read.  This article is only going to address WEIGHT.

  • ITEMS NEEDED:
  • Completed Painted car with wheels and axles to a weight of about 4.3oz
  • Tungsten Putty (1oz)
  • Ruler (attached to a base so that it is standing on its edge)
  • Digital scale measuring in .001 oz (these are rather inexpensive these days.  Less than $10 shipped from Ebay)
This is no secret to seasoned builders.  Weight placement plays an important role in how well a PWD car will perform.  There are numerous scientific equations that will explain the science behind this.   Simply put the more weight you can shit towards the rear of the car, the more "potential" energy it will have.  The key important term his is POTENTIAL.   It is believed that the more stored energy you have, the faster your car can travel.   However, the PWD world has been proven that COG (center of gravity) is the more important than shoving all the weight in the rear of the car. 

What is COG?  It is an important function in building a pinewood derby car.  COG is the balance point of your car.  This will be measured by using the ruler.  There is a COG tool on the market for those that like to spend a few extra $$$.  I'll update this once I find it again.  WHY is COG important? Putting weight randomly on your PWD car is not the key to getting the most out of your build.  Center of gravity placement should be between 1/2-1" IN FRONT of REAR axle.  This is true for all wheel base types.  Whether you are using a standard wheel base or an extended wheel base.  This has been determined not by mathematical formula, but by the PWD junkies with thousands of builds underneath their belts. I have tried to prove them different, and just came to the same conclusions as they have.

Take notice on one particular detail.  TYPE of WEIGHT.  It will not matter if your weight is lead or tungsten to achieve a fast car. Do not listen to the hype.  Tungsten does not make a car faster.  Weight is Weight.  The maximum weight is 5oz.  COG does not care whether it is wood, steel, lead, or tungsten.  Before spending all your available funds on just weight, please understand this statement.   FOR all my builds, I use lead as primary weight.   Weight pocket (meaning how big a hole is drilled for lead) depends on car design.  Small profiles will need larger pockets to offset their reduction in wood weight.   For final weight,  I drill a single 3/4" forstner hole about 3/16 " deep just in front of the rear axle.  I add the remaining tungsten putty throughout this hole to properly distribute the weight according to its balance point. 

This balancing point (COG) will differ from car to car due to design, type of weight, type of wood, etc.   The first thought that comes to mind is that the most potential energy would be a weighted rear bumper.  This will not give you the fastest car.  (Actually this type of weight placement will give the car too much "push" and will cause your car to fishtail don the flat of  the track. )  Putting the weight on the front, although gets you a slightly quicker start down the curve, does not prove to be the best weight placement for the remaining flat portion of the track. The closer to a 1/2" COG (in front of rear axle), the more potential for a faster car.  From my experience, the closer the COG to the rear of the car, the more time it will take to tune it to its fastest speeds

For your first build, I suggest a 1" COG.  It will be the easiest to obtain.  It will give you a more stable ride, will require less tuning time.   Unless you have built the same design over and over, it might take some time tuning the COG.  For a preliminary run at things, cut out your body.  Sand it to near final sanding.  Drill out the holes for you weight.  If you are using the solid "plate" lead weights, it will be more difficult to distribute weight to obtain the proper COG.  I'm not a real fan of these as they have a lot of ZINC in them to make things shiny and it takes up a lot of surface area to use.  I am a big fan of 1x 3/8" hole drilled behind the rear axle, with 2x 3/8" holes in front of the rear axle as close as you can get them.  Then adding 1/4" weights.  If your build can accommodate 5/8" holes, that would only require a hole in front of and behind the rear axle using 1/2" weights.   Once you have the balancing act close, then finish the car, add the wheels, and then fine tune your COG with tungsten putty.

I suggest to bring you car (painted with wheels and axles) to a total weight of 4.3oz.  I suggest using tungsten putty for the remaing last ounce of weight.  It will be a trail and error prcoess.  Take a ruler, attach it to some sort of base so that it can rest on edge side up.  Mark the range of 1/2-1" in front of rear axle of your completed car, then start the balancing game.   Depending on your design, most builders drill holes on the bottom of the car to pocket the putty.  Use your best judgement.  You will use nearly all of the of the putty to bring it to proper weight.  By leaving the extra ounce of "ballast" you can easily move the COG to the proper location.  If you bring your car up to a higher weight, the less ballast material you have to adjust your COG.  The extra few dollars for the tungsten putty is worth the win. 

Once your COG is obtained, then the next step would be tuning your car.  Click here for the NEWEST method that is making winners out of first time builders.   Simple to see, simple to understand.  No track needed.  

 
 

Inner Bore Dimensions

There are 16 different molds in the NEW BSA Wheel set.  Below is our data regarding this info.  Measured with precision pin gauges with 0.0002" accuracy.  Our mathematical calculations are based upon our best attempts at measuring data.  We measured 50 wheels of each mold (800x wheels) and complied the data below.  Wheels are coming along very well.  Most molds are dead spot on.  

Best results are wheels with the smallest average deviation and smallest bore size.  View Excel Spreadsheet

MODE:  The most common value in a data set.  

Typical measured diameter of all wheels (TMD):  0.0970

Our favorite wheels are the #9 and #11 molds.