The Best Pinewood Derby Racing Techniques, as Told by an Engineer and Toy Designer

Dr. Jess’s Best Pinewood Derby Tips & Secrets

PWP: I'm wondering if we can talk a little bit about Pinewood Derby car design, like specific tricks of the trade, or how you might design a Pinewood Derby car based on your experience as a professor. The first question: If you got a Pinewood Derby kit, what's the first thing you would do before touching any tools?

Dr. Jess: The first thing I would do is really inspect the provided materials, and namely, ensure that the piece of wood that you have is solid. Whatever piece of wood you're using for the car body, let's say if you're starting with a stock material piece of wood, make sure that it's straight, that there's no wobble, there's no curves to it, it's not bent in any way. If there's knots in the wood, make note of those; sometimes knots can indicate there's a hollowness inside, and that will mess with the density of the wood.

PWP: Right, where the center weight is.

Dr. Jess: Right. So definitely checking the material and making sure everything seems high quality, seems like it's good, and if it's not, returning it or getting something else that might be a little bit better, I think would be my first step.

PWP: Yeah, that's good advice. I feel like it's so easy to just pick something up and start drilling.

So once you've, you've inspected everything, you've maybe started to assemble some parts of your car. I'm wondering about test runs. How many test runs would you say you need to do before race day to make sure you're working out all the kinks and are able to improve your design?

Dr. Jess: As a scientist, it's infinite, right? The limit doesn't exist, you could never run enough test runs to really understand how things are working. In the reality of having to race this car,

Once you hit between five and ten, and it's not necessarily a number, it's when you start to get three, four in a row, consistent runs with consistent times and there's no real wobbles and nothing looks different every time you're running it. You should look for consistent runs each time independent of the lane that you're on or things like that.

PWP: That's a way better way to think about it. When you get consistent runs, then you kind of know this is a three second car versus a two second car, etc. And it feels like you can start experimenting with changes and tweaks and rolling to get a steady number that consistently beats your last time.

Dr. Jess: Yeah, I think if you're only running one version of the car once and then tweaking things, you really don't have a good understanding of what other variables might be affecting it outside of the car design. Running it a few times and then trying to see when it's consistent would be a good idea.

PWP: That makes a ton of sense. As a person who strongly relates to the artistic design side of these things, what are some creative ways you would add some of your personality to the car, but without impacting the weight in a way that would detract from performance?

Dr. Jess: Stickers are always good.

You can add a high gloss finish, anything like that. You do want to be aware of how many layers of a gloss you put. Any of that stuff, once you get to a high amount, might start messing with the fit of the wheels and the axles, etc. But I think decal stickers, high gloss finishes, a little bit of paint, not bad to put on.

PWP: It sounds like if it's a decoration that spans the whole car, you're not going to accidentally overweight some end of it, versus, if you have a specific car design in mind that's lopsided, that may contribute to performance change.

Dr. Jess: You just need to understand the sensitivity. It's called a sensitivity analysis in engineering. Most of the time when we're talking about decals or high gloss finishes, that's not going to change most of the way your car is running. It's not going to be measurable, so have fun there.

PWP: What would you say is the biggest mistake people make when choosing where to put their weights?

Dr. Jess: I think especially if you're really a creative person, you might have a particular idea of what you want the car to look like. A lot of times when you’re like, “I want it to look aesthetically like this,” that may not map up with where the best placement of the weight is. We'll see a huge mistake in either putting the bulk of the weight of the car in the front, so too far forward, or spreading out the weight evenly across the car.

When you put it too far in front, you're going to get some kind of tail flipping, right? It’s not going to go as fast if it's too far forward. You'd want your weight in the back. You don't want it too far back, but you do want to be towards the back of the car.

PWP: What would happen if it's too far back? How do you know?

Dr. Jess: Generally, what we have found at Pinewood Pro is, the best place for a majority of your weight is going to be about three quarters of an inch in front of the rear axle. That's going to shift dependent upon the design of your car, dependent upon the weights that you're putting on.

The reason you don't want your center of mass all the way in the back is because you could get this kind of flip up, this wheely situation where your car's really unstable, it's fishtailing when you're going down the track, which would mess with the speed.

We advise putting your center of mass towards the back of the car because it’s a really simple potential energy problem. If we talk about sledding, and you start at the top of the hill, and your friend starts halfway down the hill, which one of you is going to go faster? The person at the top is going to pick up a ton more speed because they have a lot more of what we call “potential energy.”

Very similarly with your center of mass in the car, if you put your center of mass towards the back of the car, the back of the car sits higher up on the track. It's just like you being at the top of the hill. Let's say the front of the car is your friend who's midway down the hill. If most of your mass is in the back of the car, your car's going to go faster than if most of your mass is in the front of the car because in the back of the car, the car as a total has a higher potential energy, which gets converted to kinetic energy, which is your speed.

It's not necessarily further forward back on the car, but just think about it higher up on the track and just like that sledding analogy, you're going to go faster.

PWP: That's a golden insight right there. Another key component to Pinewood Derby racing is this idea of friction. And one of the ways to manage this is adding graphite to the wheels and to the inside of the wheel on the axles. It’s easy to make a terrible mess with even the smallest amount of graphite. Do you have some tricks for managing a little bit of a mess, but without sacrificing performance?

Dr. Jess: Yes. But first, why do we care about friction? I said earlier, you want to increase potential energy because potential energy gets converted to kinetic energy. Let's say potential energy is like your bank of money. If you want to take out $30, there's this really sneaky bank thief called friction that would be like, okay, you can take $20, but I'm taking 10, right? So you don't get the full $30, and that's really frustrating.

Similarly with potential energy, we want it all to be converted to kinetic energy so you have a super fast derby car, but friction steals from that kinetic energy, so you don't get the full speed. To reduce the friction, you can put graphite onto your wheels! There are lots of ways to do it without making a mess. One is to get graphite that has an applicator, sometimes that helps a lot. We have some on our website with applicator tips already ready to go. If you don't have one of those, you can also take a small sandwich bag, put some graphite inside it, insert your wheel and axle, and shake it all up. It'll coat everything and you're ready to go.

PWP: That sounds like a much better way to not sacrifice performance, but also not get graphite everywhere.

When you were talking about the first steps of getting your Pinewood car set up and inspecting all the components, most of the holes that come pre-drilled in Derby kit blocks are garbage. If you just use them directly, they're not always perfectly aligned. There's so many things you can do, but I'm curious—how does wheel alignment affect speed, and do you have any tricks for getting it right?

Dr. Jess: Yeah! Wheel alignment has a pretty big effect on speed. If everything else is correct and wheel alignment is off, it will slow your car down. When the wheels are misaligned, you might again be introducing some areas for friction. You're going to have a frictional loss, and you want your wheels to be perfectly aligned. Again, you're reducing this friction.

One way to see if your car’s wheels are aligned is to do a roll test. Basically, put them on a flat surface, give them a slight nudge. They should roll freely for four to six feet in a straight line. Mostly. These are kind of toys, so they might not be perfectly straight, but they might be mostly straight. If you see some very significant bending or turning or things like that, then your alignment is off. You're probably going to need to adjust the axle slightly. You can mend them, you can rotate them, kind of figure them out how to work.

This helps to reduce the friction and keeps the wheel a little bit off the body. So that's another thing that can greatly improve. I believe that Pinewood Pro has a tool to help with this.

PWP: We do! And we think it's pretty great. It drills pretty straight. So as long as you have something to help you drill straight holes, that should immediately improve performance.

Dr. Jess: It does improve by a ton through real alignment. I'm definitely one of those people that's like, how hard can it be to drill straight holes? But it's better to buy the holder, buy the tool, or set up a system to hold the block steadily in place to ensure you're getting a straight-through drill every time. You want to plan out the process so you could repeat it with a hundred percent accuracy every time. This is one of those times you really want to get good alignment.

PWP: For kids who are considering a career in engineering or in STEM, what's something you're optimistic about right now for the future of STEM careers? What's something that you think is super fun that is about to happen to them?

Dr. Jess: What is really exciting right now for anyone looking to get into engineering is how accessible it is and the democratization of design. It is so easy right now to get some engineering tools and start tinkering around. If you're not familiar, there's a software called Tinkercad that AutoCAD came out with. It is a free online software that you can go into and build your own 3D models. If you have access to a 3D printer, you can start printing stuff. You can start your own toys. And that is so cool! You've got things like Tinkercad where you can design your own products.

You've also got things like Arduino and all sorts of other micro-electronics that have come out onto the market that make it really, really easy for you to start getting into electronics, which is honestly a really terrifying area. But with Arduino, you can start building! It's super easy and super fun, and you don't need a million bucks to do it. It's very accessible.

And I think the other really exciting thing is, there are so many online platforms now for how to build stuff. Like Thingaverse, which is a really great community for 3D printing. There's also Instructables, which is a phenomenal community for crafting, and robots, and 3D printing, and electronics projects. Somebody has tried just about everything and built it and put up a how-to on how to do it. I think leveraging all of this to just start building some stuff and testing around, you're going to pass our classes here at Penn State with no problems.

PWP: Dr. Jess, thank you so much for spending time with me and all of our readers. You're an inspiration and we all look up to you very much at Pinewood Pro. You're the best.

Ready to put your newfound knowledge to the track? Check out these car design ideas to get inspired for your next race, and brush up on these proven Winning Secrets for the ultimate edge.