PHOTO: Brian Hoar (#37) won the pole for last year’s TD Bank 250 at Oxford. This year he wants to take on ‘dingbat’ Kyle Busch for the win. (Leif Tillotson photo)
–by T.J. Ingerson
VMM Correspondent
“I can’t freaking wait.”
That is all that needs to be said about the TD Bank 250 at the Oxford Plains Speedway. That was said by Brian Hoar after his win at Twin State Speedway for the Jim’s Captown 100.
“To me, the Oxford 250 is the ultimate race,” Hoar said. “The racing at Oxford is second to none now. It’s just fantastic. If you’re a race fan and you’re not planning at being at Oxford, you’re nuts. Three wide racing all around the track.”
“Rumor has it some little dingbat named Kyle Busch is coming. I can’t wait to get my piece of him,” Hoar said with a smile. “It’s gonna be fun.”
Now do you see why I’m excited?
***
This week’s tech section requires a little backstory: Some racers believe that if they purposely “tweak” a chassis, it can help their race car. The theory is that if you bend the right front and left rear corners of the chassis downward, you can add cross weight to a car, thereby making it handle better.
Now, a question this week came in from Al, who works on a race car at a local track. His team has measured the car and came to the conclusion their car was “tweaked” the other way, with the left front and right rear being the low corners. Al asked if the car is that way, are the adjustments opposite?
The big thing I worry about when this is true is if the car will react to changes. This may be funny, but race cars are very temperamental. If they think something is wrong, they won’t do anything. But, in reality, the suspension may not react to change if something is wrong.
In regards to the adjustments being opposite, in theory, the adjustments should be the same. The best way to explain an adjustment sometimes is using extreme means. If you put 10 psi of air in the left rear tire and 40 psi of air in the right rear tire, the car should be extremely loose and you’d hardly be able to hang on. If you use the same air pressures for the front, the car should be massively tight. So, if your car is tight, and you apply the rear tire pressures, and your car is still tight, your car is not reacting to changes.
Should you cut the car up? No. Every race car is different; even two identical cars that are built using the same parts in the same way will be different and react different. You could make a slight air pressure adjustment on identical cars that are handling the same, and that adjustment will make both cars react differently. One car may not change at all, and the other car may become unbearable to drive.
The best thing is to keep experimenting and find out what works for your car. While the adjustments may not be backwards, they could have a cliff effect. Your car may not react through multiple changes, and then it will be “over-adjusted” after one more adjustment.
Keep working hard though.
For this week, I’m taking everyone back to high school. Welcome to Introduction to Geometry. And unless you’re a nerd like myself, you can begin to roll your eyes and sneer. But, the reality is, geometry keeps teams in the race shops night after night, week after week, as they try to perfect it, particularly front end geometry.
Aside from steering, which will be covered in a later edition (including bump steer), there are three main measurements that teams will try to optimize every week: caster, camber, and toe.
We will start with the easiest one: Toe. While it is ideal to have your street car’s tires exactly parallel to each other, this is not true for a race car. In most racing applications, if the left front tire is perfectly straight (as in, pointing straight ahead), you would want the right front tire pointed just slightly to the right (known as “toe” or “toe out”).
How much? On average, most teams won’t run any more than a quarter (1/4) of an inch, and probably even closer to an eighth (1/8) of an inch. But, that incremental amount can make all the difference in the world.
Why is it ideal for your street car to be straight, but not for a race car? Well, on your street car, any minor alignment issue will cause excessive tire wear, and can cause instability in a straight line. But on a race car, the tire wear isn’t that huge, plus racers are willing to give up a little stability for what they can gain.
Adding toe to a race car allows the driver to turn the car into the corner sharper. When the right front tire is pointing straight, the left tire is starting to turn left. Thus, as the driver turns the steering wheel, the right front tire will always be fractionally behind. This allows the left side tire to turn at a sharper radius than the outside tire, which makes perfect sense. On an oval track car, the left side is always making a sharper radius than the right side.
Measuring toe is extremely simple. Many teams use toe plates — flat pieces of aluminum, steel, wood, or whatever leaning flush up against the tire — using tape measures that are put in slots and measuring the front to the rear. The measurement of a quarter-inch comes from how much greater the distance between the front of the tires is compared to the rear of the tires.
Camber is visually easy to see. Camber is the vertical angle of the wheel compared to the ground. When a tire has camber, the wheel is leaning. Usually, the right front, which normally has the largest amount, has negative camber, or where the top of the tire leans in. The left front tire normally has positive camber, where the top of the tire leans out.
In most oval track applications, the ideal amount of camber is told by the tire temperatures. As the car goes through the corner, you want the car to have the largest contact patch as possible. As the car compresses when entering the corner, the bottom of the tire pulls. Hence, it is not ideal to run no camber.
When teams take tire temperatures when the race car comes off the track, they are looking for even tire temps across the tire. They take the temps in three places, on the outside of the tread, in the middle of the tread, and on the inside. If all three temperatures are equal, you have the perfect amount of camber. If the tire is hottest on the outside of the tire, you may have too little camber. If the tire is the hottest on the inside of the tire, you may have too much camber.
Caster is impossible to visually see when looking at a race car, and may be just as hard to understand. Imagine a line going vertically straight through the center of the tire. Now, if you could view the line that runs from the upper ball joint to the lower ball joint, you could measure angle between these two lines. This is known as caster, or the angle of spindle. Most race cars have positive caster in both front tires. Positive caster is when the upper ball joint is closer to the rear of the car than the lower ball joint.
What is the advantage of this? Having caster gives the car directional feel and directional stability. But, racers are clever folks. They found out that if you have more positive caster in the right front corner, giving the car a positive caster split (more in the right front than the left front), it helps the car turn on an oval track.
The advantages of this are huge. The car wants to turn left, thus the driver doesn’t have to turn the wheel as much to turn the car. If the driver doesn’t have to turn the wheel as much, he has more control over the car. Seems simple, doesn’t it? Yet, like I said, it’s something teams will fight with for many hours trying to find the perfect geometry setup.
As always, email me at with your questions, ideas, or comments.
