Pinewood Derby Wheels Wobble – How to Check

Pinewood Derby Wheels Wobble are a very common issue.  Derby wheels are made with an injection molding process.  Because they are not machined from raw material, flaws such as concentricity (wobble) will cause a wheel to wobble because the bore is not aligned with the outer diameter.  other manufacturing issues are present as such the plastic can blister due to heat of the mold or moisture content in the plastic chips. Those blisters cause imperfections in the wheel. Imperfections increase friction.

In 2009 BSA produced a new wheel mold. With the improvements to previous designs, today’s Pinewood Derby® wheels require little preparation to be race ready when compared to previous molds.  Unfortunately, most of your competitors will have the exact same wheels that are equally fast. After 12 years of production the molds are showing signs of wear. Thus, it is important to inspect your wheels prior to racing. No wheel mold is safe from flaws. Having good wheels helps a lot to get you to the finish line quicker.

We can do some rough math: 600,000 cub scouts annually, 600,000 car kits x 4 wheels, plus some extra wheels to sell, we can see that 4-5 million wheels are made annually. Divided by 365 = 11,000 wheels a day without any down time. When you are making this many wheels, you must understand that not every wheel is perfect, and every wheel cannot be made perfect even with $250,000 Haas lathes. Making a better product is doable, making each part perfect is not mathematically possible. With that understanding, we will dive into what can be done to make a part better than stock to give you an advantage in both reduction in friction and the next racer.

How to check for pinewood wheel wobble – Concentricity

I have been asked to show Pinewood Derby Wheels Wobble – How to Check.  This is the easiest done with a solid axle.  Simply place a wheel on the axle and spin.  Please add lube to axle / bore prior to ensure friction is not the reason why the wobble is present

Derby Dust offers an inexpensive 3D printed a 4 tool that incorporates an over sized axle 0.094″  Be sure to lube each wheel prior to spinning to ensure that the spin is not skewed because of friction   I suggest get 3x the amount of wheels that you need since there is a 40% failure rate for each set.  If you have 12 wheels, math says you’ll have at least 1 good set.  Yes winning does cost money.  And winning does require extra effort.

Once you have your 12 wheels.  Time to Spin them.  Find out which wheels get to move on to the next phase of making pinewood derby speed wheels.

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Here’s a short little lesson.  Watch the wheels spin.

After you sort those wheels, lets see what we need to do next.