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.
 
 
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Derby Dust has just took PWD to the next level. We take an original BSA block, flip it upside down, and mill (not saw) 2 new axle slots. Because of our unique clamping system, we are able to mill axle slots perfectly sqaure to each indiviual body. And the results will show this is key to buidling a suscessful fast car.
Why does this matter? This ensure that your wheel are pointed in the best possible position, straight ahead down the track. Watch the process, see the results. Less tuning times. Straighter running cars. A must for those guys that can't have canted wheels or have to have 4 wheels touching the track at a price that will not bust the bank! Get a FULL block, not a 1/4" strip piece of wood.

Want it drilled? We can do that too. And not with some mini drill press. We do it with a precision micro mill. Why? Because it MATTERS!

Then if you would like, you can have it pre-weighted.

Thinking outside the box, Derby Dust now offers milled/ pre-weighted blocks. No need worrying about how to make the weight work. Simply make your design fit around the perfectly placed weight of our pre-weighted blocks. No additional weight will need to be purchased.

Current Block weight weight weighs around 7.2oz
Depth of weight is approx 1/4"
COG If made into a simple wedge, the center of gravity is approx 3/4-1" in front of rear axle (your design will change that)
Weight: Soft Lead (supplied and formed to weight pocket). Once car is completed, simply drill excess weight out of front weight pocket to bring to weight. You will need to glue it in place prior to race day.
Foil Tape provided to cover exposed lead for those packs that require it.

New to 2013-2014 PWD. Drilled Sots. TO make it easier to install your AXLES, we will predrill your BSA slots with #44 drill. This will elimate the need for an axle install guide. Same a few bucks. Make it easier to install your wheels. No need to worry about mis-aligned axles!

    Types Of Wheel Base
  • Standard BSA Block
  • Drilled Std BSA Distance
  • Extended Wheel Base
3 Wheel bodies also available.
 
 
Precision Measured Matched Inner Bore ***New for 2013-2014 season

We believe this option is more appropriate than mold match wheels.  Wheels are matched using precision certified pin gauges.  Accuracy of .0002".  We are the first in the industry to offer this type of service.  Let's watch the rest follow.  Rest assured that your wheels will be as near identical as we can make them.  If all your wheels have the same rotational travel, will make it easier to tune your car and reduce wheel wobble.  No need for averaging.  We will match exact diameters. 

With matched inner bores spun on same lathe, you have near identical wheels on the inside and out!  Regardless of mold, regardless of how they cooled.  

Derby Dust again challenged old thought processes!  Question EVERYTHING. Take the Red Pill.  It will only bring new questions!

Orders your now!

 
 
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Fast Pinewood Derby Speed Tricks

This is an expert build pinewood derby secret.  Everyone polishes axles.  Hardly anyone polishes wheels.  When .001 matters, this trick makes our cars  at least .01" faster every time!    Want to know why that dad always finishes first?  You can bet this is one of those tricks he does not share.
  
Nearly every once skips this step. 45 minutes of work = faster speeds as much as 0.010-0.015 seconds. So simple you cubber can do it.


Simple, no smoke and mirrors.  No inflated costs. Guaranteed results.  

Works with oil or dry lube.  If you are using oil, skip the dry-lube prep step.  

Over the 2013 summer, we did some more testing and found a way to make them a little faster.  We added a pre-polish to our previous 2 step process. 

You can hear and see the difference.  Increases speed, decreases overall time on my track around .01-.015 seconds on 30.75 feet measuring distance.  Definitely a major difference.

Included in kit:

20x micro bore no scratch buffing spears  
8x no scratch cotton swabs
1x Step 1 Polishing compound
1x Step 2 Polishing Compound
1x Inner hub Dry Lube treatment 



Instructions for application.  Takes about 45 minutes to complete a wheel set.
Enough swabs to service 1 car.  

Drill required for application

Process:

Wheels are cleaned, then polishing step 1 compound is buffed in with high speed drill and micro bore polishing spears. 

Once polish is buffed, allow buffing compound to dry, then buff clean with micro bore spear.

 Repeat above step for applying second step.  Again allowing polishing compound to dry after application and buffing clean.

Once dry, the wheel goes through a final buffing process that makes the wheel's bore pop to a nice and shiny surface.   Wheels have spun for approx 15 seconds without any lube applied.  The polish is that good!   And then I realized there was a missing step.  I spent the summer doing some research and designed a dry lube blend used to coat the surface areas of wheel and axle rub.  This lube is especially designed so that will permanently embed in the surface of the plastic wheel.  It CAN"T be blown off with compressed air once buffed in!   We don't sell gimmicks.  I know this process yields results. 

Instructions provided.  Check out the YouTube

 
 
Making BSA axles into speed axles is an art and process. You have to have very specialized tooling to do it correctly as well as efficiently.  This is the method that we followed and then tweaked to your liking.  It's a very good start, although the visuals could have been a little better.  


To start off you are going to need 3x the amount of axles that you need. If you are making one car, then we suggest a dozen axles. If you don't want to purchase 2 extra set of wheels and axles, then you can visit this store to get them by the dozen.

The reason being is that you only want to attempt to fix the ones that are the straightest. It seems that the axles just might be purposely bent...

Tools Needed

  • File--the finer the cut the better. The key is to remove the burrs and crimps without reducing the diameter of the axle. www.shopvelox.com sells the finest file we have found to date.
  • Sandpaper-wet-400 grit through the sky is the limit.... we like 2000 for dry lube. 60,000 grit for oil.
  • Derby Worx pro axle press--a must for straightening an axle
  • Metal "bucking" bar to support your sandpaper while sanding.
  • Baster of some sort to add water
  • Bowl to catch water from wet sanding
  • Clean strip of cloth material to clean each stage of sanding. YES each stage needs its own cloth. You can NOT share with another stage.
  • Your going to need a hammer
  • Proper safety equipment
  • Some sort of drill, drill press, or lathe. NO DREMEL!!!!! Spins / removed material too aggressively.
  • Metal sealant/wax of some sort to keep your new polish job from rusting. Do your research to find the DIY. Most like some kind of jewelry rouge or wax based car polish. We have our own special sealant and it's not one of those. 

Shop for Pinewood Derby Axles at www.Derbydust.com