The Roval is Just a Really Fast Road Course

The Charlotte Roval is being talked up as a hybrid track unlike anything NASCAR has ever run before. It’s the Reese’s Peanut Butter Cup of tracks. I have no doubt that this weekend’s races will be exciting race, but I suspect that is more because it is a new track than because it’s a Roval.

I’m not knocking the Roval. It’s a brilliant way to introduce a new track without building a whole new track. (Although Marcus Smith admits that the cost runs into the millions of dollars.) Perhaps the best thing about the Roval is that fans will be able to see the entire course. It’s the perfect road course for NASCAR.

You would think that a hybrid course would require Goodyear to create a hybrid tire that can handle the 24-degree high-speed oval turns, and the tight twists and turns of the road course. But the tire being used this weekend is a straight road course tire.

It almost didn’t turn out that way. Greg Stucker, Goodyear’s director of racing, and I went through the history of the Roval and the unique needs of road course tires to trace the path from concept to the tire you’ll see on the track this weekend. 

Tire Taxonomy

While we fans tend to divide tracks up by how they look (i.e. Superspeedways, short tracks, intermediate tracks…), Goodyear engineers look at tracks a little differently.

The essence of designing a racing tire is Grip vs. Wear.

Like most things in the world, designing a tire is all about compromise. You want a soft, grippy tire? Fine, but a slightly harder tire that doesn’t have quite as much grip will last longer.

Goodyear optimizes tires for each track. Whereas we group tracks by length, Goodyear takes a different tact. They are interested in the forces acting on the tire (in the direction the tire is traveling, (a.k.a. laterally) and perpendicular to the direction of travel); the nature of the surface (rough vs. smooth; asphalt vs. concrete) and the ranges of speed and acceleration.

Goodyear divides up their tracks into seven Venue Groups. Here’s how Goodyear divided up the tracks this year.

Goodyear venue groupings for 2018

Because Goodyear considers so many different factors, venue groupings change. For example, here are the venue groupings for 2009. 

Goodyear venue grouping for 2009

Road Course vs. Ovals

Most NASCAR fans know that tires for oval tracks have stagger. Because the car only turns left, the right-side tires are a smidge bigger than the left-side tires, which makes the car naturally turn left. And, obviously, if you’re turning left and right, it doesn’t make sense to use a multi-zone tire.

But there are some other important differences that impact tire construction for road courses vs. ovals.

  • Speed
    • Ovals have higher speed and run over a much narrower range of speeds over the course of a lap. 
    • Speeds aren’t as high on road courses, but they span a much greater range.  
  • Acceleration/Deceleration
    • Ovals don’t require much acceleration/deceleration. There isn’t any sharp braking or acceleration.
    • Road courses, on the other had, feature much higher accelerations and decelerations.
  • Forces (which are proportional to acceleration). 
    • Oval tracks produce high sustained forces.
    • Road courses feature high transient forces. Compare the force you feel jamming on the brakes to stop vs. taking an exit ramp from the expressway.
  • Turn Radius
    • All of the turns in an oval track are similar. Even the variations at a place like Darlington are minimal
    • Road courses have much sharper turns, including 90- and 180-degree turns.
  • Minimum Recommended Inflation Pressures
    • An oval-track features a left/right split to optimize turning left.
    • A road-course car features a front/back split to optimize acceleration and braking. 

Here are the differences in minimum recommended inflation pressures for the Charlotte oval (red) and roval (green).

I was iffy about whether that graph is clear, so here’s a more literal presentation of the same data:

In terms of tire construction, road course tires have much stiffer sidewalls to stand up to hard braking and acceleration, and sharp turns.

Inner Liners. Also note that inner liners (the tire-within-a-tire that allows the driver to maintain some control over steering in case of a blowout) are not used in road-course tires.

The History of the Roval Tire

Greg Stucker has been with Goodyear for 39 years. When I asked him how many brand-new tracks he’d been involved with designing tires for, he said “Not that many, really.”  He points out that a track may be new to a series, but that doesn’t mean it’s new to Goodyear.

Goodyear has been involved with racing for over a century, with their experience spanning all different types of racing. When NASCAR started going to Indianapolis, Goodyear had experience with the track from IndyCar. But the Roval is truly a new track.

“Landing on the proper tire set-up for the Charlotte road course has proven to be a challenge,” Stucker said. In talking with him, it was clear it was a challenge he and his team enjoyed meeting.

Timeline

Marcus Smith said on Nate Ryan’s NASCAR on NBC podcast that he came up with the idea of running a hybrid course three years ago. His initial proposal included three variations on a potential road course/oval circuit. He was pushing for a Roval race in Fall 2017, but the decision was made to push the date to this fall to allow adequate preparation time.

Stucker told me that Goodyear first heard about Roval plans toward the end of 2016, which meant they needed to plan a strategy for developing a brand-new tire.

In January 2017, A.J. Allmendinger ran laps using Watkins Glen tires on the 2.4 mile Charlotte road course/oval. Although Goodyear had experience with sports cars on the Charlotte road course, this was their first chance to look at a stock car on the course and gather some preliminary data on the ranges of speed, accelerations and forces the tire would be required to handle.

A lot of work happens behind the scenes before the first tire test. Goodyear works closely with teams and the manufacturers on simulations. Goodyear knows tires, but they don’t have the experience of the teams in terms of set ups. Goodyear provides tire parameters and the teams run those parameters through their simulation programs, then report back to Goodyear what kinds of setups they might choose for those tires. Goodyear feeds that information back into their development. It’s an iterative process: as Goodyear refines the range of tire parameters, the teams refine their setups. 

There are two parts to a tire: the tread package and the carcass. Goodyear compounders — the people who develop the tread compound, can mix up a range of compounds and study their properties on the small scale. The carcass for a new tire starts with an existing tire and is modified as data is acquired.

Once the parameters for an actual test tire are determined, Goodyear will test the tires in-house on a tire-testing rig. The rig shown below isn’t the Goodyear rig: It’s a similar system at the National Tire Research Center in Alton, VA. The tire is spun against a belt and rotated to simulate the angles the tire would make on an actual track.

Like an engine dyno or a seven-post rig, you can program the tire’s movements, so you can test a tire against data from a specific track, for example. The wheel is outfitted with sensors to record tire forces and moments. That data is also fed into simulations and models.

The first tire test was in October 2017. Kurt Busch, Martin Truex, Jr., Jamie McMurray and Daniel Hemric drove the 2.42 mile road course, reaching top speeds of about 175 mph

They started out with Watkins Glen tires, but those were a little too hard for the slow corners in the infield. They worked their way through alternate tires with softer compounds, looking for the ‘just right’ tires that would balance durability and grip. Goodyear came out of that test feeling “pretty good” about the tire that emerged as the leading contender.

But, as the great philosopher Heraclitus tells us…

All is change

Heraclitus

The drivers (Busch in particular) felt that the twisty, windy part (that would be the section from turn 6 to turn 10 in the diagram above) presented a problem: The cars were very slow through that area. So those turns were removed to yield the course we’re using this weekend. 

This diagram was from back when the race was to have been 500 kilometers. The length was subsequently shortened to 400 km, which is about 250 miles.

Looking at the course, you’ll notice that they run almost the entire 1.5 miles of the oval, which means there’s about a eight or nine-tenth of a mile of road course. So why use a road course tire when the majority of the track is a mile-and-a-half oval?

It’s because drivers won’t be driving the oval part of the track the way they’d be driving it if they were just driving the oval. Remember that Goodyear designs tires based on speed, wear and loads. Coming out of the new turn 8, cars will be going very slowly. It will take some time to accelerate to speed. It looks like most cars are maxing out at about 170 mph on the backstretch.

If the only change had been eliminating the turns, the cars would’ve been running all out from turn 2 all the way down the backstretch and back to the entrance to the road-course portion of the turn.

Two chicanes were added, one on the backstretch (11-12) and one on the frontstretch (15-17). Those will slow down the cars a lot. Brendan Gaughan said this morning that the cars will go from maybe 150 mph to 50 mph going through that frontstrech chicane.

Stucker said that those changes made a huge difference to their development efforts because the narrowed the window of speeds the tire had to handle.

A Little Lemma* on Chicanes

*A lemma is a sidenote in a proof, not a small furry animal that has gotten an undeserved reputation for blindly running over cliffs.

A chicane is an S-shaped curve in a road added strictly for the purpose of slowing down traffic. They are used on public roads and racetracks to enhance safety and (on the racetrack, at least) are ideal places for passing.

A Bus stop is just a type of chicane. 

The interesting part of the story is how the Bus Stop chicane got its name. It apparently comes from the Spa-Francorchamps circuit in Belgium. The location of the chicane, which was added to slow down cars on the back straightaway, was an actual bus stop back when the track was a public road.

Back to the Story

The next tire test was in March 2018, and it was the first on the new configuration. Bad weather cut the test short and it had to be completed in May. Stucker says that the base tire they started with (the ‘control tire’ against which the other tires are compared) was good, but that they thought they might try a slightly softer compound to give drivers a little more grip.

Chaos and Chunking

That slightly grippier tire was the one they used for the first open test in July. Half the teams ran on the 10th and the other half a week later. That first test was the one that generated lots of stories with the words ‘chaos’ and ‘chunking’ in the headlines.  A number of drivers had issues in Turn 3. Additional rumble strips and barriers were added.

The description of tires ‘chunking’ was new to me. We’re familiar with things like excessive wear (cording) and excessive heat in the tread (blistering). Chunking sounds like whole pieces of the tire are coming off, but it’s actually just pieces of tread coming off due to failure at the interface between the tread and the rest of the tire.

Stucker attributed the chunking to two things and one of those two things might also have contributed to the ‘chaos’ issue: 

  • Goodyear wanted to try to give the drivers a little more grip and offered them a softer tire. Softer tires build up more heat.
  • Speed also creates more heat. Stucker notes that the drivers were also getting more comfortable with the course, which meant they were driving harder and faster as they gained confidence. So what worked ideally back in March/May turned out to be a problem in July.

The solution was simple: go back to the slightly harder tire, which was what some teams used during the July 17th test and is what everyone is using this weekend. So the tires that you heard about failing during the tests aren’t the tires they’re actually using.

Building the Tires

When I visited the Goodyear racing tire factory last month after the Michigan race, they were making the tires for this weekend. About 250 Goodyear employees hand-make 700-800 racing tires a day. One of the workers assembled a tire before our eyes. It took him about 10-15 minutes, but I bet it goes a lot faster when he doesn’t have to explain what he’s doing to a group of people who ask a lot of questions.

In case you’re thinking of blaming me if there’s a tire incident this weekend, don’t. We went through each step of Goodyear’s extensive quality control process. Every tire is thoroughly inspected visually, with light, and with x-rays. Anything that doesn’t look perfect gets pulled. The people who make these tires prides themselves on a quality product and know how much is (literally and figuratively) riding on their tires. 

Goodyear tire building Rob Ford performs a visual inspection of a cured race tire before the tire is stenciled with ‘Goodyear Eagle’.

NBC has a nice video segment from 2016 that shows much of the process.

The Day Arrives

I have a lot of friends whose research involves launching satellites and rockets. They said the worst part of the job was after the rocket launched because everything was out of their hands. They had done the best they could and now they had to wait.

Each weekend, Goodyear has teams of engineers systematically monitoring Pit Road. They collect information about wear, pressures, and temperatures from the teams and look for anything unusual. I asked Stucker if they would do anything differently this weekend given the brand-new tire. He laughed and said “We’re not planning on it.” But, he said, they were going to keep their “eyes wide open”. 

So much of the use of the tires is out of Goodyear’s hands. The teams have a lot of leeway in terms of setting the car up. An aggressive set up that wears tires unevenly can lead to failures. One of the other things Goodyear is keeping an eye on right now is cuts and nicks that come from tires hitting the sharp edges of some of the curbing. 

The Goodyear executives alternate travel weeks. Stu Grant, the General Manage of Global Race Tires will be the on-site lead at Charlotte, which means Stucker will be watching the race from home. But, he said, his phone will be in his hand the whole time. 

Thanks to Greg Stucker for the interview and to Mike Siberini for setting everything up.

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