Wheels & run out, Info, Q/A, information for new builders

[sporty]

its been several years and I thought id do a bit of a refresher for newer members here.

Lets start off with a over view of information. The Question and Answers here, are what I have found to be many of the most common questions from a newer pinewood derby builder.

I have left many things out, because I would be writing a book if I got super detailed. But I wanted to get a refresher out there for newer member and viewers of the forum.


Question-

What is wheel run out..

Answer:

The plastic pinewood derby wheels are made from a die cavity/mold, that is placed in a mold machine. Hot melted liquid plastic is squeezed into the die and fills the cavity to make the wheels.

The die is in two parts. and opens up and ejects the wheels from the mold.

While the die/mold is made very accurate. The heating and cooling of the plastic and the time cycle (how long the whole process takes). and what is called a ejector pin. Pushes out the plastic wheels. All these combined process's can create warp age and differences in the plastic.

The roundness of the wheel. Is more or less called the run out. the roundness may not be as round or as true as one would like.

Question-

So what does it really mean ?

Answer- People wanting to go faster or have there car perform better. Reduce the run out. Either buy buying wheels already trued or they attempt to do it.

Question-

If I reduce wheel run out, Is it really worth doing ?

Answer-

If you are really wanting to win or try and win, Go faster.

Then wheel run out reduction is one factor in going faster.

Question-

I don't have tools to check wheel run out and I can't afford to do it. Is it a must do ?


Answer-

No, its not a must do, But if you or your child who is racing against someone else who has better wheels and have a good car. The odds are that they will be faster then you.

Question-

How much faster will it be ?


Answer-

This depends on a lot of different things. car build, weight, axles, prep. ect.

However, If we took two cars that were the same in every way. The car with the better wheels would win, or should win.

The difference could be as much as the other car being ahead by 1/2 a car length. To as little as 1/8th of a inch difference.


Question-

I have heard also, that trueing up the wheel with less run out over a wheel that has not had it done, Is faster because it is also a little lighter then the wheel that has not had it done.

Answer-

True, naturally, when removing some material to true the wheels up, the wheels tend to be a little lighter. Sometimes a lot lighter. Depending how bad the run out is, or how much someone takes off the outside of the wheel.


Question-

I have heard people talk about inertia of the wheel, what is that ?

Answer-

Inertia of the wheel, is how easy it will move / roll and how fast it will start to roll or spin.

So some people also true there wheels to also reduce the moment of inertia on the wheels.

To get up to speed quicker, start off the line faster. and it spins faster and easier. less weight.

Question, what is Grams ? (scale)


Answer-

many people buy a pocket scale, that measures in grams. and also to weigh there car.

grams is a fine measure of weight. Think of something light, Like table salt. Its' so small and light, 1 piece is hard to weigh. So grams is a standard for measuring things small and light.


Question-

I have heard most stock wheels weigh from 2.6 grams to 2.4 grams. Why is there a difference ?


Answer.

While 2.6 to 2.4 grams does not seem like a lot of difference, It can be a factor as I mentioned. because the one is already lighter then the other.

The difference comes from the mold machine process, different heat temperature of the plastic and cycle time of the whole process and as time goes on, the molds/dies cavities start to wear a little and get a little thinner or deeper in spots.

Mostly, its due to polishing them all the time, to keep the parts from sticking to the mold / die. So that the ejector pins that push out the wheels from the mold / die.

If the part sticks, it can warp, jam up the machine. Most of these machines are automatic and keep running on there own.


Question-

So people check there wheels, they buy extra sets of wheels to check the weight ?


Answer-

People buy extra sets of wheels for a few reasons, To get the best set of wheels for there car. Lighter in weight and smaller size wheel bore.

Question-

What is the wheel bore ?


Answer-

The wheel bore is the hole in the middle of the wheel. The axle goes thru this hole and holds the wheel onto the axle and onto the pinewood derby car.

Question- Does the wheel bore matter ?


Answer-

The wheel bore, can very in different sizes. Many people who want a good performing wheel and as fast as possible car, want a smaller size wheel bore.

Question-

Why do people want a smaller size wheel bore ?


Answer- Many people have to use the stock axles. The stock axles are much smaller then the wheel bore size, opening in the plastic.

its sloppy and can cause the wheel to wobble and bounce and not spin well.

A wheel should not be too tight or too loose on your axle.

Question-

How does one check the size of the wheel bores.


Answer-

Some people buy pin gages or use different size drill bits to check the size of the wheel bore.


Question-

What is a pin gage ?


Answer-

A pin gage is a round small piece of steel that is accurate in size of how big the round piece of steel is. Just like a drill bit. It has a size on it, On how big of a hole it will cut. that's the size of the drill bit. It's also the size of what will fit into the hole or something smaller.


Question-

I see people talk about the hub, What is a hub ?

Answer-

The hub, inner and outter, or front and back. is the plastic around the hole in the center of the wheel. Where the axle goes thru.

On the front or outside of the wheel bore area, is the hub. many people prep buy sanding and polishing and rubbing in graphite here, to reduce friction, where the axle head of the axle will touch the wheel hub area.

The inner hub, back side hub, Some people call it the cone area. the cone.

This often gets sanded and polished and graphite rubbed into it. So that if it comes to touch the wood on the side of the body, it will be slick and not slow the car as much due to friction.



I have tried to think of the many common questions that I get asked or see asked. And I hope this Q/A has helped you newer builders with answering some of the more common questions.

I have left out a few things and tried not to get super advanced and in-depth to the point, that you may not understand. I was trying to reach the middle ground and average newer builder.

I hope you find this post helpful.

I will try and get some photos up also.

Sporty

[ngyoung]

Some good info. Should pin it to the top

[Noskills]

I was very confused about the wheel hub "step" before doing lots of reading on this site. Nice review. Thanks Sporty. Write that book anyway.
Noskills