In the Zone: Goodyear’s New Tire Design

Kansas marks the second appearance of Goodyear’s “Multi-Zone Tread Tire”, which was first used at Atlanta Motor Speedway over Labor Day weekend.

Stop for a moment to appreciate the challenge Goodyear has to face each race.  They must design a fast, durable and safe tire for each track on the circuit – tracks with individual characters that change from year to year due to weathering and re-paving.

The new  Gen-6 car, which  is lighter and faster, adds an additional complication.  NASCAR really hoped that the Gen-6 car would help address the challenge of one-and-a-half mile tracks.  The importance of aerodynamics at these tracks makes it very difficult to pass and has led to a lot of criticism about ‘cookie cutter track’ racing.

Anatomy of a Tire

Race tires are surprisingly similar to  production car tires.  They’re built to be much sturdier because they have to handle much higher forces.  They’re wider to give them better bite.   The most noticeable difference to the eye, however, is the tread.

Most people think ‘tread’ means the grooves.  That’s the tread pattern and it’s there to make tires safe to use in the rain.  NASCAR tires don’t have a tread pattern – we have the good sense to go inside when it rains and wait for it to stop.   (Yes, I’m still bitter about standing outside for eight hours during the Petit Le Mans one year where floods filled the track so deep with water than Porsches could be drowned.)

The tread is simply the outer layer of the tire – the part that comes into contract with the track.  On a NASCAR tire, it’s smooth and only about an eighth of an inch thick.

The tread is made from a tire compound, which is a mysterious (read: proprietary) mixture of rubber, small particles of carbon and other alloys and a laundry list of other chemicals. The particular make-up of a compound is the secret to its durability and grip.

Tire compounding is a complex engineering task because you have to balance two competing behaviors:  soft and grippy vs. hard and durable.

A soft tire compound gives you a lot of grip.  It gets sticky when it heats up, allowing the tire to grab the track and letting you turn a lot faster.  The downside is that softer compounds wear faster.

Underneath the tread are the belts, which are made of woven metal threads, often with a superstrong polymer like Kevlar added for durability.  Belts are made for strength, not generating grip.

When tires wear, they become weak and as soon as one spot becomes weak enough, they blow out.  You can make a really, really grippy tire — but that means you’re going to have to change it very frequently.

The other extreme is a harder compound, which won’t give you as much grip, but also won’t wear as quickly.  Hard tires don’t blow out as easily, but they also don’t let you race as hard.

Goodyear has a constant balancing act:  how to create a tire that’s grippy enough, but also durable enough.

Multi-Zone Tires: A Technology from the Street.

Anyone old enough and from a cold enough climate to remember when we had two sets of tires?  I remember having to walk around a set of ‘snow tires’ as a kid growing up in Wisconsin.  We didn’t mark the change of seasons on a calendar – we knew it was winter when the car slid around the road and Dad had to make an appointment to get the snow tires put on the car.The question of how you balance different qualities in a product is an essential feature of engineering.  Consumers want tires to behave at peak performance in all different conditions, whether they be dry, wet or icy.  The problem is that a tire that performs best in dry conditions rarely also performs best in wet or icy conditions.

You can change the tread pattern to optimize the tire behavior in different conditions.  The  Goodyear Assurance TripleTred All-Season passenger tire combined three distinct types of tread patterns.  According to Goodyear:

• The water zone has a sweeping tread pattern that helps move water our from under the tire for better wet traction.  (Those grooves direct  water from the inside of the tire to the outside, getting it out from under the tire and giving the tire more contact with the road.)
• The “ice zone” has lots of biting edges, which offer enhanced gripping traction on icy and slick roads.
• The “dry zones” are the large tread blocks along the outer edges, which give you the best behavior when you don’t have to worry about ice or rain.

A tire like this won’t behave perfectly in any one of the three conditions, but it will behave well in all three.  That’s an example of the compromises you make in engineering.

Bringing Multi-Zone Technology to NASCAR

NASCAR tires don’t have tread patterns, but you can apply the same idea to the tire compound.  That’s what Goodyear did in the tires used at Atlanta and at Kansas this week.

The left-side tires this week are the ‘regular’ single-compound tires and are a little grippier than before.

The right-side tires, however, feature two different compounds, as shown in the diagram at left (from Goodyear).  The inside three inches (meaning the three inches closest to the car body) are made from a harder compound that is more durable and wears more slowly.  The outer nine inches (roughly) are made from a grippier compound that will provide additional traction.

When tire fail, Goodyear studies the specific location of the failure because it teaches them about how to build a better tire.  We’ve talked before about the fact that sometimes you don’t learn things except when an experiment fails.  Well, at 1.5-mile tracks, the inside shoulder of the right-side tire gets a lot of stress.

The old solution would have been to use a harder tire compound throughout the entire tire – but that makes for a less grippy tire.  Less grippy tires tend to lead to more grumpy drivers.  Goodyear came up with a solution that uses a harder compound on the part of the tire that needs to withstand the most stress, but still gives a grippier compound in the area that should be able to handle it.  You get the best of both worlds.

Let me remind you, however, that every step forward Goodyear takes is matched by the advances of the race teams.  It’s the teams’ job to push the limits of the equipment.   The older, single-compound tire limited how aggressive their setups could be.  Too much load on the tire would result in an early blowout, so teams had to back off their setup to preserve tires.

The new tires will take additional stress and I guarantee that at the testing session today, the teams will be experimenting with new setups, trying to eke out that last extra tenth of a second or hundredth of a second.

There is no such thing as “the perfect tire”.  There is always a tradeoff between grip and wear.  This new tire is a great example of the type of compromise engineering is designed to address.

Other tire stories:

• Racing in the Rain
• Another multi-zone tire idea – but this time, from the inside-out
• My video on tire fall-off