Next-Gen Tires: Chewy on the Outside, Crunchy on the Inside

Listen to SiriusXM NASCAR radio, or peruse any of the racing websites and you will find a lot of theories about how races should be changed to make them ‘more exciting’.  To try to amp up the All-Star Race, NASCAR went with four 20-lap segments, followed by a realignment (the cars were ordered in rank of average finish over the first four segments) and a 10-lap shootout.  With no series points on the line, that should have made for an exciting evening of hard driving and competitive racing.

Or not.

First, let’s acknowledge a fundamental sports fact.  Sometimes, competitions just aren’t exciting.  The blowout between two unmatched football teams, for example, isn’t going to be interesting unless you introduce profoundly contrived gimmicks like loosing live lions on the field during timeouts.  So let’s just accept that sometimes we’re going to see races that just aren’t very exciting.

That doesn’t mean there’s nothing to be done.

We want side-by-side racing with lots of passing.  We’re frustrated by long green-flag runs in which the car that starts out leading is never challenged for the lead.  The only chance to get track position is to take two tires, or no tires during a pitstop and hope that your lack of new rubber doesn’t hurt you too much when the cars that did take tires catch up to you.

We want to see changes in the running order during green flag runs.  So what naturally changes on the cars over that time?  The two most significant factors are:

• The tires heat up and wear down.
• The fuel burns off, making the car lighter.

A NASCAR car holds about 120 lbs of fuel, so as a green-flag run progresses, a car ought to get faster because it’s getting lighter.  But that’s not what happens.  Lap times increase over the course of a green-flag run because the tires wear down (which we call “tire fall-off”).

Grip is just another word for friction.  When tires run against a track, two types of friction are in play.  The first is abrasive friction, which is the same type of friction as a wood block rubbing against sandpaper.  This wears down the tread.  The second type of friction (which they never seem to teach in school) is called adhesive friction.  Imagine you have a piece of chewing gum on your shoe.  It’s a hot day and you’re walking down the sidewalk.  You walk over another piece of chewing gum.  The two pieces glom onto each other – that’s another type of friction.  As tires run on a track, they heat up and the first few atomic layers become very soft.  Those layers interact with the layers of rubber already on the track and increase adhesive friction.

The more friction, the faster the tires break down.  Those top layers of rubber are worn off – they get hot.  Tires can easily reach 250-325 degrees Fahrenheit.  The “marbles” — clumps of rubber, track dirt and dust show you how much rubber used to be on the tires.  The tires lose their tread, get warmer and thus lose their grip.

Consider a track like Atlanta Motor Speedway.  Tires last for about 40 laps and a typical lap time is around 30 seconds. At a 1.5 mile track like Atlanta, the typical lap time will be one second longer after the first 10-15 laps.  By the time you’ve completed 40 laps, you’ve added another second to your lap time.  That corresponds to decreasing your average speed by 10 mph over the course of the green flag run.

The problem is that tires wear pretty much the same for everyone.  If we all start with fresh tires, and we all run 20 laps, then (barring accidents and acts of stupidity), we all experience the same tire fall off and we’ll stay pretty much in the order we started in.  In cases where the tires really don’t fall off much, you’ll see teams stopping for fuel and not taking new tires because it doesn’t get them anything.

Back in the day, tires were a heck of a lot softer than they are now.  You might see lap times increase by a couple of seconds per lap.  That’s a situation in which strategy starts to become important.  It might make sense for me to pit and get new tires because the time I lose pitting could be made up on the track since my new tires make me significantly faster than the cars that didn’t pit.  A few extra laps on the tires made a huge difference in speed.

The problem is that very soft tires wear quickly (especially if teams use very aggressive setups) and can lead to tire failures.  Then you have, for example, Tony Stewart very publicly excoriating Goodyear for making “the worst tire I’ve ever been on”.  Goodyear has some pretty stiff challenges:  tracks are constantly being repaved and reconfigured, and there’s an entirely new car this year with different characteristics.

When a Goodyear tire fails, it damages the company’s reputation.  Goodyear is in the sport to get business.  When a driver announces that he or she doesn’t trust the tire, or that Goodyear is incompetent, it’s a major blow.  So Goodyear stays on the conservative side, producing harder tires that will withstand some level of abuse from overly aggressive setups and overly aggressive drivers.  Harder tires don’t fall off.  They also cause fewer accidents and less negative publicity.

If I ran Goodyear…

OK, scratch that.  If I ran Goodyear and had all the money in the world, here’s what I would develop:  Multilayered tires.

In the nano world, we make things like coatings using multiple layers of different materials.  In making a coating for, say, a drill bit, we may start with a material that sticks really well to steel, but isn’t superhard, and then follow that layer with a layer of a material that is superhard, but wouldn’t stick well to the steel.  The two layers together give you superior properties to either one.

You could do the same thing for tires, right?  Make the outer layer of the tread a soft, grippy, really fast rubber that wears down within the first quarter to third of a fuel run.   The tread layer below could be a harder layer that still gives reasonable grip, but is nowhere near as fast as the upper layer.  This would give the crew chiefs some serious options for strategy while still keeping the tires from being unsafe.  The disadvantages, of course, are that the tires would be more expensive and take a lot more time to develop.

Goodyear has a neat video up on how the NASCAR tires are made.  The video could stand to have some titles to tell you what’s happening at different spots – and it doesn’t really do justice to the fact that a significant portion of the work is done by hand.  Different tires are made for different tracks and Goodyear is constantly tweaking the recipe.  There’s also a nice article up on Autoweek talking about the NASCAR tire factory in Akron.

And here’s a re-run of a video in which some of the top crew chiefs and engineers from NASCAR argue for more tire fall off.