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.