Whose Fault Is It? Tires or Track?

There were 15 cautions last week at Kansas Speedway and at least 15 drivers complaining that driving on the repaved track surface was like driving on ‘razor blades’.  “The worst racetrack I’ve ever driven on.” said race winner Kevin Harvick.

Normally when you have a lot of cautions, the drivers’ first target is Goodyear.  Goodyear even brought a special tire (a multizone tire I analyzed last week) to deal with the specific challenges of repaved tracks.

Surprisingly, the drivers turned their attention this week to the tracks.  Jeff Gordon suggested that the lack of abrasiveness being the origin of the lack of grip.

“To me, it’s really the surface. We’re paving the racetracks with what we pave new highways with, and it’s not a highway.  We had the same issue in Phoenix, at Darlington. We have had the same issue at every repave that we’ve had the last six or seven years.”  (via the Las Vegas Sun)

Friction (the scientific word for ‘grip’) has to do with the rubbing and sticking of two materials against each other.  When you talk about the coefficient of friction for a tire, you are actually talking about the coefficient of friction for a tire on a specific surface.  The coefficient of friction (how ‘sticky’ the tire is) is different on asphalt vs. concrete.  (Also on wet vs. dry surfaces.)

Asphalt is a combination of aggregate (rocks or sometimes metal slag) held together with a binder.  The binder historically has been bitumen, a sticky tarlike substance that comes out of petroleum refining.

The American Chemical Society recently had their annual meeting in Indianapolis and they had some of the folks who developed the Indy race surface speak.  The Heritage Research Group was charged with researching asphalt for the 2004 repave.  They actually worked with Firestone Polymers to develop a superior binder, one that would make a smoother race track without losing any grip.  I also found a really cool presentation on the paving history of Indy.  Nowhere in any of those materials does anyone discuss the 2008 fiasco that was the Brickyard that year.

Gordon’s assertion that there must be roughness may not be true anymore because of all the games we can play with chemicals and making surfaces smooth but still sticky.  There are, however, a ton of variables that come into play.

Kansas was cold.  Very cold, even for Kansas this time of year.  Try this experiment.  Get two sticks of butter.  Put one in the freezer for a couple hours and one in the fridge.  Now get a cheese grater – one of those raspy things would be perfect – and try grating each one of the sticks of the butter.

What you will find is that the frozen butter gives you small powdery stuff and the fridge butter melts and leaves you with a layer of butter stuck on the grater.

That’s exactly what happens with laying down rubber on a race track.  At higher temperatures, you get a nice layer of rubber that comes off the tires.  When it’s cold – like Kansas was – you get powder.  In fact, that’s what drivers and crew chiefs were complaining about – the tires were powdering.

That had little to do with the track or the tires – it had to do with the unexpected temperatures.  Remember that the same tires were used in Atlanta and the drivers were raving about how good they were.

It’s a moving target.  You can’t predict the weather months in advance – the time you need to settle on a particular tire and start making it.  You can’t pave a track such that it will have grip in all possible weather situations.  And you can’t control the weather.

One of the issues, though, is that there are a good number of very smart scientists at Goodyear who know a lot about rubber for race tires.  The folks who research asphalt have their eyes firmly on the millions of miles of roads that you and I travel each day.  The ACS article mentioned that roughness in the asphalt we travel is responsible for 555 million gallons of fuel wasted each year on interstate highways.

If the asphalt isn’t stiff enough, the cars leave dings and dents.  That also takes energy, energy that could be used to move the cars.  They cite a figure of about 200 million gallons of fuel wasted due to destroying the road on interstate highways.

And interstate highways only make up two percent of the road surfaces in the country.

The point is that there aren’t really people who are researching asphalt for racetracks.  All of that research would have to be funded by racetracks.  As roads have gotten better for our cars, the technology that’s been developed might actually be less good for racetracks.