Why Losing Control At The Monster Mile Is Like Getting Cut Loose From A Rope

Dover Motor Speedway is a highly banked 1-mile concrete oval in northern Deleware known as The Monster Mile. With 24 degrees of banking in the corners and 9 degrees on the straightaways, this track truly is a monster. Constructed in 1966 by Melvin Joseph, the Monster Mile has been a mainstay on the NASCAR schedule since 1969. The racing surface was originally paved with asphalt but was replaced with concrete in 1995.

Attached directly to the Dover Downs (now Bally’s) Hotel and Casino, this NASCAR circuit features a horse racing track in the infield. The rising popularity of the dual-use facility necessitated persistent expansion. Seating capacity was added every year from 1986 to 2001, when Dover Motor Speedway topped out at a 135,000-person capacity, making it the largest sports venue in the mid-Atlantic. The speedway has since reduced capacity down to 85,000.

Steeply banked straightaways make this track into what’s colloquially referred to as a “self-cleaning” racetrack. Any driver that loses control is often sent hurtling down the banking and toward the inside wall. It’s very rare to see a driver lose control at Dover and come away unscathed. Add Dover’s narrow apron and inside retaining wall to the mix and the result is little room for other drivers to avoid a spinning car. You’re almost as likely to see a “big one” Talladega-type in Dover as you are during a superspeedway event.

Dover Motor Speedway is one of three concrete racetracks on the NASCAR schedule; the others being Bristol Motor Speedway and Nashville Superspeedway. Concrete racetracks perform differently than asphalt ones for a wide range of reasons. Let’s dive in …

Why Concrete Matters

When an asphalt racetrack is paved, the material is laid down in one continuous stream. As the surface settles and ages, it moves as a cohesive unit. As an asphalt surface ages, this movement comes in as waves and swells. When a concrete racetrack is constructed, the surface material is laid in individual slabs, like a sidewalk. As it settles, the pieces move independently from one another and create much sharper/more abrupt bumps. Think of a tree root growing underneath a sidewalk.

Even a brand-new concrete racetrack will perform significantly differently compared to an asphalt one. When new, an asphalt racetrack is buttery smooth with very few irregularities in the surface. If you’ve ever driven down a concrete interstate, I’m sure you will have noticed that you feel a bump every few seconds as you move from one concrete slab to the next. In a road car, this can be almost hypnotic. In a stiffly sprung racecar, it creates a harsh high-frequency oscillation. The concrete slabs at Dover Motor Speedway are 3m (~10 ft) long in relation to the direction of travel. When going down the straightaways at 170+ mph, drivers will be crossing 25 of these seams every second. Even at minimum mid-corner speeds of around 145 mph, drivers will still be crossing roughly 20 seams per second. In translation, the car and driver are constantly subjected to a 20-25 Hz oscillation that rattles the car as it goes around the racetrack.

Racing tires interact with a concrete surface much differently than they do an asphalt one. To understand why this is so, you must first understand the difference between adhesive friction and abrasive friction. Abrasive friction is easy; it’s the wearing-away action of sandpaper on wood we’re all familiar with. Adhesive friction is slightly more difficult to understand. As a racing tire’s surface heats up it becomes soft and sticky. The tires’s contact patch  interacts with the racing surface much like the way a piece of gum interacts with the bottom of your shoe. You can think of adhesive friction more like “stiction” than traditional friction. Concrete has less adhesive friction than a fresh asphalt surface, but more abrasive friction. It comes out as a draw when it comes to overall grip, but when a tire starts to slide the two surfaces react in distinctly different ways. Concrete’s lower adhesive friction coefficient means that when grip goes away, it goes away in a hurry. As NASCAR legend Mark Martin said, “When you lose grip on a concrete surface, you feel like you just got cut loose from a rope. It’s amazing. It’s like losing half of your grip, rather than about 20 or 30 percent that you lose on asphalt.”

Concrete and asphalt also react to temperature in different ways. Anyone who has walked barefoot in the summer is familiar with the temperature difference between an asphalt street and the sidewalk. Because of its lighter color, the temperature of a concrete racetrack is much more stable over the course of a race. Changes in track temperature on an asphalt surface affect the balance of a racecar tremendously. The binding material in asphalt mixtures is a petroleum-based tar. As it heats up, oils in the tar rise to the surface and make the asphalt slick off.

As concrete heats up it “takes” rubber much easier. This means that rubber worn away from the tires settles into the surface irregularities of the racetrack. If temperatures get too low, rubber deposited onto the track will do what’s known as marbling. The rubber stripped away from the tires will stick to itself more than the racetrack and form little rubber balls, called marbles, that get flung all over the track.

Dodging The Rubber

The rubber that does get laid down does not act consistently throughout a race, however. When drivers slow down during a caution period, their hot sticky tires will act like lint rollers and pick up the rubber from the racing surface as they slowly roll over it. Take a look below at two images from the 2022 Xfinity Series race at Dover.

In the top image, you will see the dark, rubbered-up areas on the racing surface at the end of a long green flag run. Below, the cars are diving off into Turn 1 after a restart 15 laps later and you will see that the area of the racing surface where cars were driving under caution has been restored essentially to its original state.

This constant deposition and removal of rubber throughout a race makes it very difficult for teams to balance their racecar. On a restart with no rubber laid down on the racing surface, the bottom lane will be dominant. The fresh (often referred to as green) racing surface provides tons of grip in all lanes, so the shortest distance is obviously the winner. However, as rubber gets laid back down, grip in this lane will start to decrease. Typically, this loss of grip causes cars to understeer and drivers will have to move up the track and experiment with their lines in order to make lap time. You will hear the commentators refer to this lane migration as dodging the rubber.

Because of Dover Motor Speedway’s unique track profile, moving up the racetrack also causes the balance of the racecar to change. More on the physics behind this later. What’s important to know for now is that the higher up the banking a driver moves their line, in general, the more their car will understeer.

Things become even more complicated when a pit stop cycle occurs under green flag conditions, as is very common during Cup Series races, and sometimes occurs during the third stage of an Xfinity Series race. The car’s balance has been set based on fresh or “sticker” tires on a racing surface that has minimal rubber in the groove. (The stickers parlance is a reference to all the stickers and labels on the tire from the factory). During a green flag pit stop cycle, the run will begin with these fresh tires firing off on all the rubber that was laid down during the previous run. This will significantly alter the balance of the racecar. Even if the driver says their car is handling great, teams must make an adjustment to compensate for track conditions in order to make their car handle. To further add to this complication, the next time a caution comes out this adjustment will have to be un-compensated for. The track will have reverted back to its original state and this balance offset needs to be taken out of the car’s setup.

So, what have we learned? Well, for one, rubber on the racing line both reduces grip and adds understeer. Moving up the racetrack gets the grip back but also adds understeer. This combination means that the balance of the racecar will change significantly over the course of a run.

How To Balance An Unbalanced Car

A racecar at Dover will never be perfect or balanced for the entire run. Typically, drivers talk about balance using a 1 through 10 scale. Let’s walk through a couple of scenarios. If a driver’s car starts off with a 0 balance, meaning perfectly neutral, they will likely describe it as being a 6/10 understeer at the end of a run. They will put down some blazing-fast laps at the beginning of a run and then quickly fall off as they struggle to get the car to turn. If another driver’s car starts out at a 3/10 oversteer at the beginning of a run it will likely cross over neutral in the middle phases and end around a 3/10 understeer. This shifting balance is what makes racing at Dover so fascinating as different drivers will be fast at different points in every run.

Even if Dover Motor Speedway was repaved with traditional asphalt, it would still behave differently than most any other oval on the schedule. Dover is often described by drivers as being like a high-speed roller coaster. Why is that? Well, because of the 9-degree banked straightaways, the bottom groove of the corners is significantly lower than where drivers run on the straights.

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On corner entry drivers will drop roughly 9 ft (2.7 m) down into the banking of the corner, and they will have to climb back out of it on corner exit. We can plot out the vertical load over distance and see how strange the drop-in and climb-out nature of Dover’s corners truly is.

The X-axis on this graph represents vertical loading as the car is going down the straightaway with zero representing baseline, steady-state straightaway load. Below the X-axis the car is less loaded than the baseline, and above it is more loaded. The numbered points on the graph can be correlated to the numbered points on the Google Earth view of Turns 1 and 2 at Dover Motor Speedway.

1. Straightaway – This will be our baseline load as the car is in steady state
2. Corner Entry – When cresting the banking and “diving” into the bowl, the car initially gets very light as the racing surface falls away
3. Landing – Maximum load point as the car reaches the bottom of the banking
4. Mid Corner – Drivers get to their minimum cornering speed here and the load falls off slightly
5. Corner Exit – Vertical load starts to increase again as drivers apply throttle and accelerate around the turn. Increased velocity causes the car to compress more into the banking
6. Takeoff – On late corner exit as the car crests the hill onto the straightaway it has another brief moment where it gets light again. The sensation can be compared to going a little too fast over the top of a hill when driving down a back road
7. Straightaway – Back to baseline load

The transition from Points 1 to 3 and Points 5 to 7 are where you will see most drivers get themselves into trouble. These two regions have a tendency to make the corner feel very disconnected for drivers. Let’s break them down:

At Point 1 the driver is wide open, against the outside wall on the straightaway getting ready to enter the corner. Approaching Point 2, they are diving off into the corner as the racetrack falls out from beneath them while they are simultaneously trying to decelerate their car. This effectively kicks the tail up and magnifies the deceleration pitch as the car enters the corner.

The timing of the deceleration acts like the motorcycle in the GIF above, decompressing and pitching the rear of the car toward the sky. This overloads the front tires, which are doing the turning, and underloads the rear tires, which are trying to keep up. Essentially, the unloading and deceleration moment creates corner entry oversteer.

Approaching Point 6, drivers are wide open in the throttle, with significant steering angle being applied. As we all know, acceleration shifts weight off of the front tires and onto the rear. As the driver crests out of the banking onto the straightaway it acts like a ramp with the front tires becoming unloaded a split second before the rears. This will create a moment of understeer late in the exit of the corner.

Normally, this is a simple fix for drivers: Counter-steer slightly to account for the entry oversteer, then apply a bit more steering angle on exit to correct the understeer. On a “normal” track, that’s all it takes. But at Dover, not so much.

I’m sure at some point or another as kids, we all launched our bikes off plywood ramps, much to our parent’s dismay. If you landed with the handlebars (and thus, the front wheel) straight, you rode away like a hero. But if you touched down with any steering angle other than dead ahead, the bike would take off in that direction and slam you into the ground.

Keeping the bike analogy in mind, any countersteer still applied when the driver reaches Point 3 and the tires are subjected to maximum load will cause the car’s trajectory to change, shooting it up the track. This will need to be corrected with more mid-corner steering angle. Drivers often mistakenly refer to this condition as being “tight on landing” when in reality they are free on entry and don’t have the wheels pointed in the correct direction when the car loads back up. The same thing applies at Point 7. If the driver has increased steering angle to compensate for understeer, The car will dart to the left when it settles, creating snap oversteer. This can again lead to driver confusion when they ask for an adjustment to be made. What they’re struggling with is snap oversteer on exit, but what’s causing it is understeer from center-off. The disconnect that drivers talk about is this shifting balance between entry oversteer, understeer in the middle, and back to oversteer on exit. It makes them feel like they’re always one step behind the racecar and just fighting to keep up with it.

Late-corner snap oversteer is what caused Jimmie Johnson to lose control during qualifying for the 2006 Neighborhood 400. He managed to keep the car off of the inside retaining wall in a now famous save that is shown during just about every race broadcast from Dover. In the video, you can hear him describe how he kept adding steering wheel angle on corner exit and then the car just suddenly snapped on him.

Making adjustments to a racecar can be very counterintuitive for teams when trying to help their driver get around Dover Motor Speedway. You hear the driver complain about understeer on landing and the solution is actually to shift the balance more towards understeer so that they can get into the middle of the corner without counter-steering. The same thing applies in reverse on corner exit. The driver relays that they’re struggling with oversteer late exit and the answer is actually more oversteer in the center of the corner to reduce their steering angle on exit.

One of the most crucial aspects of a vehicle’s setup at Dover is the damper package. If you’ve never seen a shock graph, here is a generic Roehrig graph that I grabbed from Performance Trends for an example:

The Y-axis of a shock graph denotes force and X-axis denotes shock shaft velocity. Above the Y axis is the compression region, or how much the damper resists being shortened in length. Below the Y axis is the rebound region, or how much the damper resists being pulled apart. Damper tuners traditionally separate the X-axis into two regions, low speed (below 5 in/sec) and high speed (above 5 in/sec). Using these parameters, we can divide the graph into four quadrants: low-speed compression, high-speed compression, low-speed rebound, and high-speed rebound. The low-speed regions typically control things like body pitch and roll while the high-speed regions take care of responding to road surface irregularities.

At a typical banked oval, cars will undergo low-speed compression on corner entry, achieve semi-steady state mid-corner, and then undergo low-speed rebound on corner exit. If you haven’t guessed it already, this is not the case at Dover. Using the same numerical markers around the corner from our discussion of vertical loads, let’s look at what happens to the dampers between these points.

1. Points 1 to 2: High-speed rebound
2. Points 2 to 3: High-speed compression
3. Points 3 to 4: Low-speed rebound
4. Points 4 to 5: Low-speed compression
5. Points 5 to 6: High-speed rebound
6. Points 6 to 7: Low-speed compression

The chassis never fully settles in the corner and the varying loads cause the dampers to constantly flip back and forth from compression to rebound at varying velocities. Add into this the constant 20-25 Hz surface undulations from the concrete seams and you quickly begin to realize how complex damper selection can be for this racetrack.

As I mentioned earlier, when drivers start moving their line up the racetrack the balance shifts more towards understeer. Referring back to the picture from earlier you will notice that the upper lanes are higher than the straightaways. When running the upper groove, instead of diving in and climbing out, drivers will rise up to the apex and fall back down to the straightaway. As drivers apply throttle past the apex, weight will obviously shift from the front tires to the rear tires. When this combines with the racing surface falling out from underneath the car it creates understeer by underloading the front tires and overloading the rear tires.

When a driver is struggling with their balance around Dover Motor Speedway, the diamond line is their best friend. If you don’t remember the discussion of this line from our deep dive into Martinsville Speedway, here is a quick reference from the Driver61 Youtube channel describing a right-handed corner.

This line accomplishes several things that help drivers make lap time, but it is most effective at correcting corner exit handling issues. By running up the racetrack and taking a higher apex, drivers will straighten out their exit and have to apply less steering angle on corner exit. When running a lower lane this will help alleviate the late snap oversteer condition. When running a higher lane this will reduce the center-to-exit understeer. An additional benefit is that literally running down the banking while on throttle helps generate momentum and accelerate the car out of the corner.

Dover falls squarely into the category of high-speed racetracks with mid-corner speeds hovering around 145-150 mph (230-240 kmh). The high cornering speeds combined with the already unstable nature of the racecar makes downforce and aero racing crucially important. Please see the piece on Texas Motor Speedway for more on this, but here’s a key passage:

At Texas Motor Speedway, the vertical loads in the faster, steeper banked Turns 3&4 are about 20% greater than they are in the slower, flatter Turns 1&2. This causes the suspension to compress, aka travel, significantly further at one end of the track than the other. If the aero platform is set correctly in Turns 3&4, the vehicle will be too high in Turns 1&2 to make optimum downforce. On the contrary, if the aero platform is set correctly for Turns 1&2 where there is less banking and drivers are struggling for grip, the vehicle will bottom out in Turns 3&4 and be undriveable. The catch-22 of Texas Motor Speedway is that in the corner where you need to generate the most grip the car will be the least optimized for generating it.

So, what exactly does it mean when someone talks about “aero platform”? Put simply, every vehicle of any kind has an optimum pitch (combination of front and rear ride heights) and yaw at which it will make the most efficient downforce. By efficient we mean most downforce to least drag or the optimized point of that ratio.

The load variation throughout the corners at Dover Motor Speedway act like a combination of both ends of the racetrack at Texas Motor Speedway. Referring back to our numbered corner points, we call Point 3 the overshoot point. This brief load spike is the point of max suspension travel when the car is compressed most into the racing surface. The static ride heights of the car are determined by this one small point of the lap. Teams want to get their vehicle as low as possible without bottoming out during this landing moment. This is the point that acts like Turns 3&4 from Texas. As we transition around towards Point 4 where the load bleeds off and the car rises, it can ride above the preferred aero platform window. This section in the middle of the corner tends acts like Turns 1&2 from Texas.

To make a pass by packing air, the overtaking driver will attempt to turn under the defending drive in the middle to exit of the corner and placing their right front nose alongside the defending driver’s left rear quarter panel. The wake off the overtaking driver’s nose will push against the left rear of the defending driver’s car which counteracts their side force and causes the car to oversteer. When done properly the defending driver will have to lift out of the throttle and counter steer slightly to recover their vehicle, breaking their momentum and allowing the overtaking driver to pull ahead of them on the straightaway. If the overtaking driver gets a bit too aggressive, or if the defending driver is already struggling with oversteer, packing air can cause a crash even without contact between the vehicles.

You will sometimes hear the commentators refer to one driver as having “put it on their door” in reference to another driver and this is an important defensive technique at aero racetracks. In this scenario the overtaking driver has positioned their vehicle inside of the defending driver and attempts to go through the corner side by side with them. The defending driver will try to get as close as possible to the inside car which is where the term putting it on their door comes from. In this scenario, the wake flowing off the right front of the inside vehicle and the left front of the outside vehicle is squeezed into the small area between them. Sticking with Bernoulli’s Principles from earlier, as a continuous fluid flow is squeezed into a smaller area, its velocity will increase, and its pressure will decrease.

Therefore, the air flow will create a low-pressure region on the left side of the defending vehicle and on the right side of the overtaking vehicle. More importantly, it will pull the defending car towards the center of the corner creating slight understeer and more stability. For the overtaking car, it will negate most of their side force and want to pull the car towards the outside of the corner, creating oversteer. Drivers who crash from this position often describe the outside car as having sucked them around.

The effects of aero racing, or the interference of one car’s aerodynamics with that of another, is greatly exaggerated at Dover due to the inherent instability of the cars throughout the corner. You can see both of these maneuvers come into play in this famous clip from the 2011 Xfinity Series race. Joey Logano (Black and red #20) and Carl Edwards (White and blue #60) are battling for the lead of the race coming to start the final lap. Joey puts his car right on Carl’s door getting into Turn 3 and causes Carl to oversteer and have to correct up the track to save his car. By moving up the track, Carl inadvertently packs air on the left rear of Joey’s car, causing him to oversteer and crash, triggering a massive pileup.

At the end of the day, the driver and team who can successfully battle through all of these challenges will emerge victorious and take home their own miniature Miles the Monster.