Pinewood Derby Stories and Photos from Maximum Velocity
FEATURE ARTICLE Wheel Preparation: Where the Plastic Meets the Road
As I was driving down I-17 the other day, I passed a truck pulling a trailer loaded with a race (stock) car. What caught my attention was the rack of tires at the front of the trailer. There wasn't just one tire, or even four tires. No, the tire rack held at least ten tires. That trailer load drove home to me the point that tires are highly important racing equipment.
In pinewood derby racing, the wheels (not tires, as the term 'tire' implies a rubber-type product) are even more important than they are in stock car racing. The number one force working against a pinewood derby car is friction, and all of the frictional loss will come from the wheels (wheel to track, wheel to axle, wheel to body). Many pinewood derby car builders spend most of their time working on the car body. The wheels and axles are then given little time in the rush to complete the car. This tactic is appropriate if the builder is mostly concerned about the appearance of the car, or is looking for a design award. But if the builder desires a fast car, a significant amount of time must be allocated for working on the wheels and axles.
Axle preparation was thoroughly covered in a previous newsletter (Volume 1, Issue 8), so this article will focus on wheel preparation - specifically the required steps. For those car builders with more flexible rules (and with a non-risk-averse personality!), extra steps can be performed. Those steps will be more thoroughly covered in a future article.
To make sure your wheels are ready to race, you will need the following tools:
- Drill - Clamp, vise, etc. to hold the drill in place - Wheel Mandrel - 600 grit sandpaper cut into 1 inch by 4 inch strips (1 or 2 strips per wheel) - Cup of water - Graphite or automobile polish - Pipe cleaner - Pro-Hub Tool (optional) - Sharp knife (optional)
I also suggest that you acquire an extra set of wheels. This not only provides a spare if a wheel is damaged, but also allows you to select the best four wheels for racing.
First, make a careful inspection of each wheel.
- Are there any obvious flaws? - Compare each wheel. Do they all appear the same? - Roll each wheel on a hard flat surface. Does each wheel roll nicely, or does one appear to be more oval than round? - Look through the wheel hub. Does it appear to be clear, or is there some debris inside?
After inspection, replace any problem wheels. There is no reason to start with a bad wheel.
The next step is to remove any excess molding material with a sharp knife. This is essential on Awana wheels that usually have a molding spike.
Oftentimes, the inside wheel hub is not molded square with the wheel bore. This causes the wheel to mount improperly on the wheel mandrel. To correct this problem, use the Pro-Hub tool to square the wheel hub.
Now its time to smooth the tread and inside edge of the wheel surface. First, clamp the drill firmly to the work surface. Then insert the wheel mandrel into the drill. Test run the drill to make sure the mandrel spins smoothing. If the mandrel 'wobbles', then the shaft of the mandrel is either not centered in the drill chuck, or the shaft is bent. Try inserting the mandrel further into the chuck and tighten down on the wider portion of the mandrel.
Once the mandrel is secure, mount a wheel on the mandrel and tighten the screw firmly. Don't over tighten as that could deform the wheel.
Now start the drill, dip a strip of the 600 grit sandpaper into a cup of water, and apply the sandpaper to the tread surface. Apply light pressure, and move the paper so that most of the surface of the strip of paper is used. Keep the paper wet by dipping it into the water as needed.
After sanding the tread surface for about 20 seconds, sand the inside edge of the wheel (where the wheel will touch the center guide rail). If your car will run on a track with two outside wheel guides, then sand the outside edge instead.
Finally apply the paper to the 'corners' of the wheel. This removes any ridge on the edge of the wheel that could cause the wheel to roll poorly.
The wheels should now be evenly sanded and very smooth. To make the wheels even slicker, some polish can be applied. But before applying the polish, place a small amount on the inside of a wheel - or on a bad wheel - to make sure that the polish leaves the wheel very slick, and not sticky.
Place a small amount of polish onto a rag, and apply it to the spinning wheel. Make sure to buff off all excess polish with a clean dry rag.
As an alternate to car polish, use your index finger to rub some graphite onto the tread surface and the inside edge of the wheel. Wipe off any excess.
The inside of the wheel hub can be polished with a pipe cleaner and a drill. I recommend using real 'pipe cleaners' instead of the craft type, as they are made of a softer material.
Cut off a 3 inch piece of pipe cleaner and insert it into the drill chuck. Apply some graphite to the pipe cleaner, slide the wheel onto the pipe cleaner, hold the wheel and start the drill. Move the wheel back and forth for a few seconds, stop the drill, add some more graphite, and repeat.
Instead of graphite, some people use toothpaste (a brand that is advertised to whiten your teeth - it has a fine abrasive) to polish the inside of the wheel hub. If you try this, use water and a pipe cleaner to remove all of the toothpaste from the wheel hub, and dry thoroughly.
If allowed by the local rules, removing wheel material can result in additional speed. A common operation is to 'cone' the wheel hubs. This removes material from the inside wheel hubs, thus reducing car body to wheel hub contact. The Pro-Hub tool makes this operation very easy to perform.
Other wheel cutting options include removing tread material while keeping the wheel width intact, removing one-half of the tread (resulting wheel is one-half the width), and removing material from the side-walls (on wheels with solid side-walls). All of these steps require careful work and strict adult supervision.
Preparing the wheels can be a bit tedious and time consuming. But this type of preparation pays off in the form of extra speed on the track.