A Year of Short-Track Tire Experiments: What We’ve Learned and What it Means for Martinsville

After a year of short-track tire experiments aimed at solving the Gen-7 car’s deficiencies at short tracks, what have we learned? And how will that knowledge affect the penultimate race of the season at Martinsville this weekend as six drivers compete for the last two spots in the Championship 4?

Why was 2024 a year of Short-Track Tire Experiments?

NASCAR’s Gen-7 (nee Next Gen) car improved racing at 1.5-mile intermediate tracks. Shorter tracks — historical venues like Bristol, Richmond and Martinsville that clock in at three-quarters of a mile or less — suffered.

Two problems contribute to the lessened racing quality.

1. The tracks in question had become single-groove tracks; that is, there is one fastest way around the track. The cost of not running that line is so high that it no will try it. If no one will get out of the preferred line, there is no passing.
2. The way the Gen-7 car loads the tires leads to less tire wear. That makes managing tires and all the strategy around same much less important than it used to be.

NASCAR tried to remedy the car’s short-track deficiencies with aerodynamic fixes. They solved the problems on paper, but it didn’t work as expected on the track. A ‘happy accident’ at the spring Bristol race, where tires wore much more rapidly than expected, pushed NASCAR’s focus from aero to tires.

That would seem to put the ball entirely in Goodyear’s court — except for an overlooked piece of physics.

What Determines Grip?

Two factors determine a race car’s grip:

1. The load on the tire
2. The coefficient of friction between the tire and the surface

Tire load is determined by the car and setup: how much the car body shifts under braking, for example. NASCAR’s rule book limits how much teams can impact this factor.

Most people interpret the second factor as the tire, but the coefficient of friction is determined by the two surfaces (rubber and track) in contact. Or, as No. 11 team Crew Chief Chris Gabehart puts it:

A tire is the black round thing and the surface you put it on.

Chris Gabehart, No. 11 Crew Chief

Solving the problem isn’t merely a matter of making a ‘better’ tire. The tire must be matched to the track surface. That introduces a slew of additional variables, many of which are not controllable.

In addition to the obvious (e.g. whether the surface is concrete or asphalt), tire designers must consider track temperature, local roughness, rubber already on the track from previous races, bumps, seams, how and whether the track has been cleaned, `whether it rained recently and how the track has been prepared.

Anyone who thinks it’s as easy as ‘let’s just use the magic tires from the spring Bristol race’ doesn’t understand the problem.

How Do You Tell Tires Apart?

Goodyear assigns each tire a code. That code is prominently displayed on each tire. Many outlets republish Goodyear’s weekly tire missive, so you should have no trouble finding that information. A tire code uniquely identifies the mold, the tread compound and the construction. Goodyear is very specific with their numbers.

This week, those codes are D-5254 on the left side and D-5256 on the right. D-5256 is the same tire as the ‘option’ tire at North Wilkesboro and the second Richmond race in terms of tread and construction. It has a different number because the lettering on this week’s tire is yellow rather then the red used to denote option tires. That’s how specific Goodyear is with its numbers.

After the fall Bristol race, when the lap-time falloff was much less than in the spring, some drivers and even some crew chiefs suggested the tires were different. While there is some variability within a batch of tires, it’s relatively small. The tires weren’t different enough to produce that big a change in the racing.

Then Why Did Fall Bristol Look So Different Than Spring Bristol?

If the tire didn’t change, it must be the track. To start with, concrete is much more temperature sensitive than asphalt. Then we have to consider the track temperature during the race. How was the track prepared? Who else’s rubber is on the track? Which one or ones of the three track prep compounds were used?

To give you an idea of how sensitive the situation is, Gabehart mentioned practice for the spring Martinsville race. The No. 54 car had a problem in the B-group practice. The track equipment, he said, blew a lot of the rubber and debris on the track into the surface. When they resumed practice, “the nature of the track had changed.”

Three Track Preps? I Thought There Were Only Two.

NASCAR forayed into track preparation in 2017 at Bristol with a compound variously known as Trackbite or PJ1 or PJ1 Trackbite. This adhesive-based resin is sticky and increases the coefficient of friction. Applying it could create a second lane to give drivers more passing opportunities.

The downside is that PJ1 Trackbite gets slippery when wet. Instead of increasing grip it actually makes the track worse than if there had been no track treatment.

That led NASCAR to a second type of track treatment they call ‘The Resin’ because that’s how VP Circle Track Resin bills itself. The media reported it as simply ‘resin’, which is misleading. PJ1 Trackbite is also a resin.

‘Resin’ covers everything from lacquer and varnish to high-tech materials used for countertops and heatproofing. Using ‘resin’ to describe a track treatment is like calling a piece of jewelry ‘metal’. It matters if the metal is tin or 24 karat gold.

I learned from Shannon Baker, project manager for advanced engineering at Goodyear, that the tracks owned by SMI (and not NASCAR) had their preferred provider develop a product comparable to ‘The Resin’.

For clarity, I’ll refer to PJ1 Trackbite as a Class I track treatment and the other two as Class II treatments.

What’s Different about the Two Classes of Track Treatments?

Class I adhesive-based resins like PJ1 Trackbite make the track surface sticky. Baker suggests thinking Class II materials more like chemical treatments: They dissolve a tiny, tiny amount of the tire surface and help it stick to the rubber already on the track. That helps the track rubber up faster.

Baker noted that Bristol is now the only track where they use PJ1 Trackbite, largely because PJ1 Trackbite doesn’t require using the Tire Dragon. The Tire Dragon can’t be used at Bristol because of the banking.

Are All These Track Treatments Just Making Things More Confusing?

Goodyear strives for consistency. The two Class II track treatments (one at SMI tracks and one at ISC tracks) behave similarly. Every track, regardless of ownership, uses the same agricultural-grade equipment to spray the material on the track. Goodyear does friction testing multiple times throughout a race weekend to measure grip.

I worried that all of this track addenda were just complicating the matter. I was concerned about adding variables like the track temperature when the treatments were applied, how long between treatments, etc. Baker assures me that this really isn’t a major issue because the track treatments are a second- order effect.

What’s Have we Learned from these Short-Track Tire Experiments?

Baker says that the most important variable for tire grip at short tracks is track temperature. With the Gen-7 car, on short tracks, temperature dependence is more pronounced that they saw with other car generations.

Let me explain with an analogy. My biscuit recipe calls for grated butter. Have you ever tried grabbing a stick of butter from the fridge and grating it? Don’t. It won’t work. You have to freeze the butter first to get it to grate properly.

The same thing happens on a cold track: it shreds away piece of tire, but those pieces don’t adhere to the track.

As your stick of butter warms, you see a transition from grating the butter to just smearing it all over the grater. That’s the analog to tires rubbering in the track when the track temperature is hot enough.

Baker says that the magic track temperature is around 90 degrees Fahrenheit. That’s track temperature, not air temperature, for those of you who went and looked up the weather conditions at various Bristol races.

What To Expect in Martinsville

Although teams have run the right-side tires before, the left-side tire is all-new. Goodyear’s goal is to produce more grip plus more lap-time fall-off over the course of a run. Teams will 45 minutes to practice on Saturday and two sets of tires due to the new setup. Race day air temperatures will be in the mid 60s.

I’ll update you more on the impact of this year of short-track tire experiments after practice on Saturday.