Every wheel bore in a molded pinewood derby car wheel has taper, it has to to make the part release from the mold. Some mold pocket numbers have more and some have less but all have some. This taper causes the bore to have a smaller diameter or surface area on one end and a larger diameter or greater surface area on the other. These two points will have different levels of friction due to the slightly different amounts of material passing the axle per revolution and there for not allow the very best alignment on that axle.
All Derby Worx Pro Wheels ( Ultra Lite, Inertia Lite & Precision Stocks) are C.N.C. machined using ONLY Official B.S.A. wheels that are hand checked for imperfections and mold number matched. These wheels feature our exclusive reamed (straightened) and burnished hub bores, this process makes for a perfectly round and parallel bore for the axle to ride, helps reduce friction and aids in alignment. While no further work is required, additionally polishing the hub bore to a slick and shinny finish will further enhance the wheels performance.
A fluffy pipe cleaner and a fine polish like Derby Worx Micro-Polish in a drill will produce excellent results. Be sure to finish wash your wheels in warm water and a mild liquid soap and dry well before assembling your racer.
When using a Racing Oil like Krytox 100, Derby Worx recommends finish waxing your wheel bore for the ultimate performance. Waxing has proven to reduce “stiction” or the initial starting friction producing quicker starts and faster runs.
Every molded Pinewood Derby Car Wheel has a number inside of it, this tells us which pocket it came out of in the mold cavity. While all wheels look similar, each mold pocket has its own unique characteristics and by mold matching your wheels you are one step closer to all 4 or 3 corners of your car being equal.
Tread Surface Finish
It is a common practice for some to “Polish the Tread” as some believe this is a speed tip and go as far as trying to sell graphite coated wheels. There is no rolling friction at the point of contact of the track, a smooth, uniform finish is more than sufficient and in many tests we have seen that a car looses stability with a polished or coated tread face as it promotes car wiggle. At Derby Worx we recommend a finish on your wheels of no more than 600 to 800 grit wet and all of our CNC machined wheels have a finish close to untouched wheels.
Overall wheel weight can greatly effect the performance of a properly built Pinewood Derby Car. Lighter wheels are quicker off the start because of less mass to put into motion and they allow more weight to be added to the rear of the car for additional potential energy. A standard B.S.A. Pinewood Derby Wheel weighs 2.6 grams, a trued or corrected wheel like our Precision Stocks or Mold Matched & Machined wheels will weigh slightly less, 2.4 grams but significant performance gains are made by correcting the flaws for a smoother, better aligned wheel. Where rules allow Derby Worx has 2 lightened versions, the Pro Inertia Lite which retains all lettering and numbering on the inside and out to meet many rules and weighs only 1.5 grams or a 43% weight reduction. The lightest of our wheels are the Pro Ultra Lite which retain all of the markings and lettering on the exterior but are completely CNC machined out on the inside to reduce the overall weight to 1 gram or a 62% weight reduction.
As for overall performance, with all things being equal, lightening wheels will equal aprox .035+ sec gain per gram of wheel weight reduction. While this does not sound like a significant reduction in time, what will be realized is about 1 car length per .03 sec gained at the finish line.