The 2019 Rules Package: The Tapered Spacer

NASCAR announced the 2019 rules package last week. Reactions from fans ranged from wait-and-see to despair to a surprising amount of anger.

The 2019 package is similar to the package was tested at the 2018 All-Star Race, but different in some very important ways. It further specializes the standard set up for different types of tracks. The larger spoiler and splitter and the underbody changes will be required at all tracks. Other changes (the tapered spacers and the aeroducts) will be different at different tracks.

So how much is really changing?

Tapered Spacers Aren’t New

A 1.170″ tapered spacer was introduced in 2015, reducing engine horsepower from about 850 hp to 725 hp. (Note that teams did quickly find ways to increase the horsepower a little, despite the new rules.)

That same spacer that was introduced in 2015 remains one of two spacers that will be used in 2019.  You’ll also note that the spoiler goes back to its 2014 height and the driver-adjustable track bar that was introduced in 2015 is being taken away.

Which Rules at Which Race?

  • The Daytona 500 will be the only race that will use a restrictor plate.
  • A 1.170″ tapered spacer will be used at all tracks less than 1.33 miles and will (still) result in about 725 hp* overall engine power.
  • A 0.922″ tapered spacer will be used at all oval tracks 1.33 miles and above. which will decrease engine horsepower to about 550 hp*.
    • At five of those larger tracks (both Pocono races, Darlington, Atlanta and Homestead), the aero ducts won’t be used.
    • Aero ducts will be used at the rest of them.

*Note: NASCAR regulates the spacer/restrictor plate, not the horsepower. 

Since different horsepower means different mileage, NASCAR will require teams to block part of the fuel cell so that the number of laps run between full fuel runs should be the same.

Let’s see if we can’t make this clearer with a graphic.

You may wonder about my choice in how I listed the tracks. They’re listed in order of most recent pole speeds for each track. Most pole speeds came from 2018, but some qualifying sessions were rained out, so I went to 2017 and, in one case, 2016.

I put Sonoma at 2.52 miles because they’re changing it for next year, even though the pole speed was for the shorter track.
  • Tracks with the 1.170″ tapered spacer and no aero ducts have pole speeds ~160 mph and below
  • Track with the 0.922 tapered spacer and no aero ducts have pole speeds 173-184 mph
  • Tracks with the 0.922 tapered spacer and aero ducts have pole speeds 185 mph and up.
  • Chicagoland looks like an exception, but the pole speed there this year was anomalously low, so I understand why they put it with the last group of tracks.

Lemma: Doesn’t Pole Speed Scale with Track Size?

Sort of. In the graph below, the three configurations are represented by the same colors as I gave them in the table above. You could make an argument that speed is somewhat linear for the short tracks. (I did use five or six speeds for each track and they’re pretty consistent.)

But our 1.5-mile tracks range from 173 mph to 201 mph, and the superspeedways are already artificially restricted.

Tapered Spacer vs. Restrictor Plate

The All-Star Race package used restrictor plates to throttle the engine back to around 400 horsepower. Most fans liked the All-Star Race, but a few drivers (notably Brad Keselowski) objected, saying that the pack racing that resulted put less control in the drivers’ hands. 

It’s hard to compare All-Star Race data because they change the rules every year. Some years require a pit stop during qualifying. However, in 2013, 2014, 2015 and 2017 (2016 was rained out), the pole speed was between 144 mph and 147 mph. The pole speed for last year’s All-Star race was 127.644 mph.

How Plates/Spacers Work

A restrictor plate (or the tapered spacer) slows cars down by preventing them from bring air into the engine as quickly as without the plate or spacer. Remember that aerodynamic forces go like the square of the speed: double the speed and you quadruple the force. 

When cars are so dependent on aerodynamics, however, it’s hard to pass. Lower speeds, along with the aero ducts creating bigger wakes behind the car is theorized to improve passing. 

The Chemistry of Fast

Combustion is the chemical reaction between fuel and oxygen that releases energy. It’s very similar to another chemical process called respiration, which is how your body converts food to energy.

For example, to combust two octane molecules, you need 25 oxygen molecules. Not 24, not 26, but exactly 25.


So if reduce how many air molecules you have in the cylinder, you have to reduce how much gas you put in the cylinder. Otherwise, you’re just wasting gas.

But tapered spacers and restrictor plates work differently when you get down to the details. Below, on the left is a restrictor plate. It is 1/8″ thick and really nothing more than a plate with four holes on it. On the right is a tapered spacer, which is on the order of an inch thick. It also has four holes, but the holes are conical.

In fluid or aero-dynamics terms, the restrictor plate is a set of orifices, while the tapered spacer is a set of nozzles.

Both fit over the spot where the carburetor used to be.

Some Differences

There are a couple minor differences between these two parts. Restrictor plates are stamped: A big die comes down and punches out the hole, leaving a bit of a chamfer on the side the air enters and a bit of a burr on the side the air leaves. This significantly affects the way the air travels into the engine. One engine builder told me that the four outer cylinders get about ten times less air than the central four cylinders with restrictor plates. Tapered spacers, on the other hand, are machined parts and provide for much more even distribution of air.

Because the restrictor plate is so thin, any imperfection makes a big difference. A scratch can mean more horsepower. Tapered spacers are much less sensitive.

The Big Difference

While the distinction between the two seems minuscule, air molecules see two very different things. The next two graphics show the airflow through an orifice and a nozzle. The air comes in from the left.

The animation I took these clips from shows the motion, but you can still see that there’s much more turbulence with an orifice than a nozzle. Some of the arrows to the right of the orifice point away from the orifice, while others point toward the orifice. The flow lines are messier, also.

Compare that to the nozzle (below). See how much cleaner the flow lines are? And all the arrows point away from the nozzle. There is much less turbulence with a nozzle than with an orifice — meaning that the tapered spacer provides air to the engine in a very different way than a restrictor plate does.

When an air molecule passes through an orifice, it essentially has to take a right-angle turn. The flow of the air makes the effective diameter of the orifice smaller than the actual hole diameter.

The walls of the tapered spacer NASCAR uses are machined to be at a 7 degree angle. That’s the maximum angle at which air can travel without separating from the surface. This minimizes turbulence.

Simulations are useful, but there is nothing like being able to see fluid flow. Luckily for us, air and water are both fluids and a five-gallon water bottle provides the perfect illustration of the differences between a tapered spacer and a restrictor plate. 

A hole — the same size as the hole at the top — is cut into the bottom of the five-gallon jug. The hole in the bottom is like a restrictor plate and the top is like a tapered spacer. 

Now watch how the water empties differently.

Why is NASCAR Reducing Horsepower?

NASCAR is all about speed, but high speeds mean high dependence on aerodynamics (difficulty passing) and requires harder, stiffer tires (less opportunity to engineer fall-off into the tire).

More Tire Falloff.

When I talked with Goodyear’s Greg Stucker, he noted that race length doesn’t really factor into tire design because a tire only has to last for a fuel run. That forces teams to change tires (or chance not changing tires).

Corner entry speeds have become so high that Goodyear has to make relatively hard tires — which means they don’t wear as quickly. Lower corner entry speeds will allow Goodyear to go to softer compounds and different constructions. That will allow for more strategy.

The Future of the NASCAR Engine

Formula E, in its sixth season, has eleven manufacturers. The overwhelming interest in what is currently a niche series can be attributes to manufacturers looking to remain relevant in the future.

NASCAR’s been very clear that the eight-cylinder eight-hundred+ horsepower engine is a barrier to entrance for other manufacturers because it’s so far removed from current production cars. 

“it gives us the option to be more relevant. It gives us that option to look at new technology in the future and our current package doesn’t do that.

Steve O’Donnell (via NBC Sport)

So why not just mandate a new engine and not worry about tapered spacers? Change costs money and takes time. There are parts inventories to be considered, especially as teams struggle for sponsorship. There’s an additional issue for engine companies because NASCAR is requiring engines to be used for multiple races. That means fewer engines built.

NASCAR is the proverbial aircraft carrier trying to turn. The inertia is huge.

Aerodynamics and Passing 

Every engineer I’ve consulted says that their simulations tell us to expect pack racing at most of the 1.5 mile tracks next year. They expect drivers will need to be full-on the throttle around the track, although that may not be the case with less-banked corners and/or if tires have a lot of fall off. 

Pack racing gives you passing, but it’s a different kind of passing. If the inside line passes the outside line on the frontstretch, then the outside line passes the inside line on the backstretch, that seems to me to be a wash. 

So Will It Work?

Most drivers are taking a wait-and-see approach to the new package. Even Kyle Busch has been restrained in his remarks after the new package was announced. Everyone agrees that NASCAR is trying to improve the racing, even if they don’t agree with the precise way they’re doing it. 

The aerodynamic changes and the horsepower changes together are a pretty big change. There’s a test with the new package at Charlotte on October 23rd. We’ll see what happens, both on the track, and with driver reactions.

And there’s still time for changes. Goodyear can tweak tires and teams have time to experiment with different set ups. It’s all part of progress. You try things and you see if they work. This is the nature of research.

I’m along with Joey Logano on the change for the moment:

“You make change, and not every change is good, but you learn from every change. If you just sit still, you never make any progress forward. You don’t learn what’s wrong, you don’t learn what’s right, you’re just there… 

we will learn from this decision one way or the other, and I think as a society we need to be open to do that, not just in our sport, but in life. It’s a good thing for us. It’s healthy.”

Joey Logano (via NBC Sports)

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1 Comment

  1. The point of racing is to stay away from the other racers by passing them instead of artificial restrictions which bunch the cars together causing these “big wrecks”. faster means safer because the fast guys get away from everybody else. NASCAR is acting like any government body … they are the cause instead of the cure…

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