Pinewood Derby Stories and Photos from Maximum Velocity
Wheel Alignment: Make it Straight!
I overheard a conversation the other day, between two young men (young from my perspective). One of them said, "My car is pulling to the left, and I have to constantly adjust to keep it going straight. I think something is seriously wrong, but the shop says I just need an alignment. An alignment!? I paid a lot of money for the car; it shouldn’t need to be aligned? It’s supposed to be a precision car!"
Maybe this is a common misconception of younger drivers. I have driven a number of older cars, and alignment adjustments were needed on a regular basis. Newer cars seem to have fewer alignment issues, but it is still a recommended maintenance procedure. Why is that?
All cars (regardless of price or quality) are designed with the ability to make adjustments to the alignment. Why? When the car was originally assembled, the alignment was set properly. But over time, rough roads, tire wear, and generally wear and tear of the steering components affect the alignment. If the alignment is not adjusted regularly, excessive stress is placed on the steering components, and the tires wear unevenly (and more quickly).
How does this relate to pinewood derby cars? In an automobile, a minor alignment issue can be readily corrected by the driver, so the car goes straight. But with a pinewood derby car, the only ‘driver’ is the guide rail(s). Thus, any alignment issue will result in excessive collisions with the guide rail. Since every collision reduces the speed of the car, the desire is to minimize or eliminate guide rail collision. How? By setting the alignment to be as accurate as possible.
MINIMIZING ALIGNMENT ISSUES
Using precision components and tools(1) will minimize the amount of required alignment. Some options include:
- Pine block with precision drilled axle holes, or precision cut slots - Start with an accurate platform
- Pro-Body Tool - To create accurate holes, or pilot holes in axle slots
- Pro-Axle Press - Straightens nail-type axles
- Pro-Wheel Shaver XT - Trues the wheels
- Pro-Axle Guide - Ensures accurate axle installation
These products (and others) will minimize the amount of alignment needed. But just like an automobile, regardless of the level of precision or cost, wheel alignment is still necessary.
In order to adjust the alignment of a car, you must first have a way to measure the amount and type of misalignment. I have found that this is most readily accomplished with a test track. Don’t let the words ‘test track’ scare you. This is simply a hard, flat, pitched surface, down which the car is rolled. In Volume 3, Issue 13 (March 17, 2004) there are plans for a nice test track. But here is a simple solution:
- Get a sheet of MDF (medium density fiberboard) which is a material available at any home store. Have the store cut off a piece 8 feet long by 2 feet wide (you might be able to buy a piece already cut for shelving).
- Down the very center of the board, draw a straight line with a permanent marker.
- Lay the board on a flat surface. Test the surface first with a level, and orient the board so that it is running in the downhill direction (patios, garages, driveways, etc. tend to have a slight pitch).
- Prop up one end of the board about 4 inches, and place a pillow at the low end.
- Use a ‘level’ to make sure the board is level at all points. Use small pieces of wood or other material (I use business cards) to shim the board as needed.
To test the car, place it at the uphill end and align the edge of the car with the straight line drawn on the board. Make sure to place it the same way on each test - a slight difference in placement will make a big difference in the measurement. After you are satisfied with the placement release the car and observe the direction and amount of drift. The goal is to get the car to deviate less than ½ inch over the 8 foot run. Test the car a few times until you have a good idea of the amount and direction of drift.
There are two primary methods for adjusting wheel alignment: the axle bend method, and the axle shimming method. A third method (if the car has axle slots), angling the axles, is not recommended as it can cause binding between the axle and wheel bore.
Axle Bend Method
The axle bend method is cruder than the shim method, but is the method of choice if time is short. It is most easily done on a car with a raised front wheel. The method is quite simple:
1. Remove the front wheel/axle which is on the ground,
2. Make a ‘slight’ bend in the axle, and then reinstall the wheel/axle (see Figure 1),
3. Test roll the car, and then slightly rotate the axle by grasping the head of the axle with a pair of pliers,
4. Repeat until the car goes straight, then make sure to glue the axle in place.
Figure 1 - Axle Bend Method
Wheel Shimming Method
The axle bend method corrects alignment by imparting some toe-in, toe-out, or some cant. Although it works, there is some energy loss in the front wheel due to this correction. A better way is to set all four axles such that each is parallel to the ground (no cant), and pointed in the same direction (no toe-in or out). This can be accomplished by placing thin (2 to 3 thousandths inch thick) shims between the axles and the car body such that the desired alignment is accomplished.
The shim method was developed by Stan Pope, and is documented on his web site. Due to the length of the procedure, I won’t include it in this article, but here are some considerations.
- To fully implement the method is somewhat tedious and time consuming. Plan on several hours to complete the process.
- If you don’t have the time (or patience) for the full procedure, you can apply the method to the front wheels alone (or to the front ‘steering’ wheel if one front wheel is lifted). In this case, the shim method generally gives better results than the axle bend method.
Wheel alignment is a critical procedure for ensuring top speed. Whichever method you choose to implement, make sure to allocate time for alignment. Then as long as the car is accurately placed on the track (see the tip below), whatever time you spend aligning the car will pay off at the track.
(1) Precision blocks can be found Here,
and specialty tools can be found Here.