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Dr. Diandra: Changing Steering and Tire Should Help at Relentless Bristol Track

All short tracks are tough on cars and their drivers, but Bristol provides an extra dimension of difficulty. While Richmond and Martinsville are both relatively short, flat, asphalt tracks, Bristol is high-banked concrete track.

If I were to characterize Bristol in one word, it would be ‘relentless’.

A track of extremes

Let’s start with the track’s physical layout track. The official lengths of Bristol and Martinsville differ by 37 feet. The pole speed at Bristol last year was 128.382 mph while the pole speed at Martinsville was 94.780 mph.

Bristol’s progressive banking (from 24 to 28 degrees) is responsible for that 30+ mph difference in lap speed. Martinsville has 12-degree banking in the turns. The Cup Series’ next destination — Texas — is 1.5 miles long with 24-degree banking.

Centripetal force is the force that makes a car turn. Drivers experience it as a push toward the right during a left turn.

Centripetal force is proportional to speed squared divided by the track’s turn radius. Texas, with a turn radius about three times larger than Bristol, exerts one-third of the centripetal force on drivers as Bristol does at the same speed.

Turning at Bristol at 100 mph subjects the driver to about 2.6g. A 100-mph turn at Texas produces a mere 0.8g. In practical terms, a driver’s head (around 14 pounds, including helmet) acts like it weighs 36.4 pounds during a 2.6-g turn.

Today’s drivers’ seats have substantial head rests to help the driver resist those forces. Back in the day, drivers had nothing but the strength of their neck muscles.

Martinsville’s turn radius is even smaller than Bristol’s. But because Martinsville lacks significant banking — and banking helps cars turn — cars can’t get going as fast around Martinsville as they can Bristol. That makes Bristol one of the most physically demanding tracks on the circuit.

Turning well is critical because cars turn for much of each lap. Bristol’s frontstretch and backstretch are each 650 feet long. The 0.533-mile track thus has 1300 feet of straightaways and 1514 feet of turns. Drivers have almost no breathing room between turns.

And if that doesn’t make drivers dizzy enough, Bristol’s short straights means that they have not one, but two pit roads. Drivers must also remember different procedures for entering and exiting depending on whether they pit under green or yellow.

A new right-side tire: wear without weakness

Last year’s Bristol asphalt race featured 11 right-side tire blowouts. Six caused cautions, while the drivers suffering the other five failures made it to pit road.

The Next Gen car forces the right side of the vehicle to work harder to generate speed. That creates higher forces on the car and thus on the tires.

“Bristol is one of those places that can break just about anything,” Greg Stucker, Goodyear’s director of racing, said.

While other tracks also produce high loads, Bristol’s 15-second lap times mean that the tires never get a break.

After testing at Bristol last June, Goodyear brings a new right-side tire this weekend. The new tire has an updated construction and a compound that should provide higher wear with more reliability.

Construction refers to the way the tire carcass is built. The tire carcass is basically everything on a tire that isn’t the tread. That includes factors like sidewall stiffness, the specific fabrics used as reinforcements, or even the process by which the tire is made. Small changes can have significant impact on a car’s handling.

Compound is the material used for the tread — the part of the tire that contacts the track and creates grip. Tire compounds are the ultimate exercise in compromise. Softer compounds are grippier but wear more quickly. Harder compounds last but provide less grip.

Concrete, with a more uniform, smoother surface than asphalt, poses an additional challenge. Concrete doesn’t wear tires as much and it changes less with temperature.

Based on thumbs up from all three drivers at the test, Stucker expects the new right-side tire to remedy last year’s problems. It will also produce more exciting racing by requiring drivers to better manage their tires.

Steering in a better direction

Four cars failed to finish last fall’s race due to steering failure. Steering issues aren’t limited to the Next Gen car. In the fall 2020 race, before the Next Gen car debuted, two drivers DNFed due to steering system failures.

If you want to test a steering system, Bristol is the place to do it.

The Next Gen car uses a rack-and-pinion system, which translates rotary motion into linear motion. As the animation shows, turning the pinion gear (the round gear) moves the rack (the long, toothed component on the bottom.)

You can’t see the rack or the pinion in the diagram of the Next Gen steering module below because they’re enclosed. Dirt or marbles getting between the rack and the pinion would quickly disable the car.


The steering module is not rose-gold colored: I highlighted it so you could see it better.

The rack moves the rods on either end of the module. You can just see them outside the fluid seals. Those rods attach to the left front toe link and the right front toe link. The toe links, in turn, connect to the upright/hub assembly, which is where the wheel is mounted.

When the driver turns the steering wheel, the rods move left or right. That moves the toe links, which push or pull the wheels left or right to turn the car.

A hydraulic fluid system provides steering assistance or ‘power’ steering. The hydraulic steering fluid is sealed inside the steering rack.

In last year’s Bristol night race, Martin Truex Jr. told NBC Sports that the steering system “blew the seal out and pushed all the fluid out on the right-front tire.”

High tire loads make it harder to rotate the tires. If it becomes too hard to rotate the tires, the steering rack’s fluid seals become the weakest link. They leak or even fail completely.

This year, NASCAR is giving teams the option of using a larger-bored hydraulic system in the steering rack. A larger area allows more fluid to move and reduces the pressure. That decreases the likelihood of failure.

A quarter-inch-larger bore in the steering mechanism and a few tweaks to the tire may not seem like much of a change. But if everything performs as expected, last year’s problems shouldn’t plague this year’s race (6:30 p.m. ET on USA Network.)

That’s doubly important given that Bristol’s night race is also the first elimination race of the playoffs. Drivers — and fans — want those continuing onto the Round of 12 to be determined by racing, not equipment failures.

Source : NBC Sport