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Dr. Diandra: All-Star Race a proving ground for softer tire

Tire specialists will work double duty at this weekend's All-Star Race as Goodyear provides two different tires for the first time since 2017. In addition to the standard, yellow-branded tire, Goodyear will also offer an 'option' tire. The new tire, identifiable by its red lettering, has more grip but also wears faster.

Allowing crew chiefs to chose between two tires injects an additional element of strategy into the exhibition race. It also offers NASCAR the opportunity to test a softer tire under race conditions.

Drivers reacted favorably to the much softer wet-weather tires used the heat races for last year’s All-Star Race and again this year at Richmond. Tires with higher grip, faster wear reward drivers who manage their tires well, and allow teams to pursue different strategies. Driver and fan reaction to the abnormally rapid tire wear at the spring Bristol race suggested that pursuing a much softer tire might be the key to restoring short track racing.

But making such a tire isn’t as easy as cranking up a ‘softer’ knob on the tire production line.

Tires are like ... chocolate chip cookies?

Anyone who has experimented to create the perfect chocolate chip cookie recipe knows that the final product is sensitive to many factors: how much and what type of flour and sugar; softening, melting or browning the butter; the ratio of baking soda to baking powder and many more possibilities.

Tires are like chocolate chip cookies, only much more complicated. The photo below shows the different components that make up a Goodyear tire. The ingredients include waxes, oils, resins, natural and synthetic rubber, carbon black, silica, and textiles.

GOODYEAR Tire Components
GOODYEAR Tire Components

The precise nature of these components is top secret. When you get the perfect recipe, you don’t give it away to your competitors.

Not only do tires have more ingredients than cookies, each one of those ingredients has multiple options. And just like cookies, tire designers have to consider time and temperature profiles for the tire’s final curing.

Nature limits possibilities

The chemistry by which baking turns ingredients into cookies limits the final outcome. There is a tradeoff between taste, texture and color. Using only white sugar in the recipe creates a pale, flatter, crisper cookie.

If you use all brown sugar, however, the cookie comes out more cake-like: thicker, darker and with a hint of molasses.

Tires have the same kinds of constraints. Instead of taste and texture, the tradeoffs are grip and wear. Softer tires have more grip, but the same factors that produce grip also cause the tire to wear faster.

I think about this relationship like a seesaw.

DRD_tire_seesaw
DRD_tire_seesaw

The yellow see-saw plank represents a harder tire that doesn't wear very quickly. This tire won’t have much grip. The red plank represents a softer tire with a lot of grip, but that tire wears more quickly.

It is impossible to make a tire with high grip and low wear.

Tire fall off

‘Tire falloff’ doesn’t sound like a good thing. It is, though, because when people talk about tire falloff, they actually mean lap time falloff.

The graph below shows an idealized plot of lap time versus the number of laps run for a pretty soft tire. Lap times increase rapidly over the first five to 10 laps. After that, the tire continues to degrade, but not as quickly.

DRD_Tires_conceptual_tirefalloff_graph
DRD_Tires_conceptual_tirefalloff_graph

I didn't include specific lap times on the graph because the amount of falloff differs from track to track. At Darlington last week, lap times increased by about three seconds after 30 laps. The tires used at Kansas had only a second-and-a-half increase in time over 30 laps.

Those numbers depend on the track surface, but also vary according to track temperature and how hard a driver pushes the tires.

The red tire or the yellow tire?

NASCAR requires all cars to start the All-Star Race on the softer red tires. Barring accidents, that edict allows them to gather data over a green-flag run with all teams on the same tires.

After that, crew chiefs can chose which tire they want on their car. The graph below shows what we expect to happen.

Tires_laptime_falloff_compare_two_tres.png
Tires_laptime_falloff_compare_two_tres.png

This graph shows lap time falloff for two different tires. The red line shows the behavior of the softer red tire and the yellow line represents the regular tire. Remember that, on this graph, down means faster.

On the first lap of a run, the red tire will be faster than the yellow because the red tire has more innate grip. But the red tire wears faster, so the advantage over the yellow tire is much smaller after five to 10 laps.

I’ve drawn the graph so that the two tires produce roughly equal lap times somewhere around 15-20 laps. Beyond that, the red tire has worn so much that it is now slower than the yellow tire.

Crew chiefs will have to decide whether they want speed early in a run or late in a run. That decision will depend some on many factors, including how well their driver manages tires and where they are in the field.

A crew chief who chooses the red tire gets an immediate advantage, then hopes that their driver can get enough of a lead in the first part of the run that he’s far ahead of the pack by the time his tires start to fade.

A two-tire approach may make for a much more interesting All-Star Race, but the trophy isn't all that's on the line. How well these tire perform may determine the future direction for short track racing.