Bench Racing with NASCAR Tech Patrick Reynolds: Wedge Explained

“Martin Truex Jr. brings the Bass Pro Shops Chevy to the attention of his crew. He slides into his pit stall. Right side is up and the tires are being changed. The first can of Sunoco fuel is being dumped in. Jack is dropped and the crew jumps to the left side. Four Goodyear Eagles are on, fuel is in, a round of wedge into the left rear and he is on his way in thirteen point one seconds.”

How often have we heard a call like this from a TV or radio pit reporter? Longtime race fans can answer that question with the words “a lot.” It is seen all the time. It is heard all the time. But what really just happened there? Changing four tires are fairly evident. Pouring in two cans of fuel is also easily understood. Over the wall crew members sometimes take tools and make chassis adjustments through holes and extensions in the rear glass of a Sprint Cup machine. Wedge adjustments are made. But what is really technically happening when turns are made one way or another? This question is asked often.

Here is the answer.

First we will start with some basic background. Before a car is loaded to head to the racetrack from the shop, it is set up on the surface plate. It is an involved chassis process that takes several hours, depending on what exactly is being done. One of the final stages of preparation is scaling. That is the portion of the setup that we will address here.

Most professional NASCAR teams have electronic scales. A scale pad is placed under each tire as the car sits, after many alignment checks have been previously completed. Each pad is not unlike a bathroom scale. A readout screen is placed at the front of the car so each corner’s value can be seen from that viewpoint.

There are four pieces of information that are the primary concerns: the car’s total weight, right side weight, nose weight, and the wedge. What are these terms? All will be explained.

For examples- we will use 2008 NASCAR Nationwide Series requirements. I have to thank Dan Brown, a fellow northeastern transplant to the south, who taught me quite a bit at Germain Racing while we worked on the setup plate together.

The total weight is how much a car weighs ready to compete without the driver. With all fuel, water, and oil included, the machine must weigh a minimum of 3400 lbs. per NASCAR’s rulebook. There is no maximum rule. All racers try to make their cars as light as possible. As long as a car does not weigh less than 3400 lbs., inspection officials will approve the total weight check. Each car is checked at the racetrack on NASCAR’s scale pads before the weekend’s first practice session, before qualifying, and once more before the race if the cars have not been impounded after the time trial run.

A right side rule states the total for the right front and right rear weights must be at least 1625 lbs. Since oval events have all left turns, it benefits each car to have the most weight possible on the left side. With NASCAR’s minimum right side rule it keeps the left side weight from getting to what the sanctioning body may feel is excessive.

Nose weight is the total of both front wheel weights expressed in a percentage. If all four wheels weighed equally at 850 lbs. giving us a total of 3400 lbs. the nose weight would be expressed as 50%. Our right side would also weigh 1700 lbs. which meets our minimum requirements and is acceptable for this instance.

Now comes our wedge. Also known as cross weight or bite. The wedge is the total of the right front and left rear weights expressed in a percentage of the total.

For an example, if we kept our corner weights from before and the right front corner weighs 850 lbs. and the left rear weighs 850 lbs. the wedge would be expressed as 50%. Mathematically speaking 850 + 850 = 1700. This is 50% of our 3400 lb. total. In reality the numbers do not come out nice and even but our shop scale readout is already programmed to automatically show the percentage.

On oval track races, more wedge will tighten a car in the corners, or have it turn less. Less wedge will loosen a car up or make it turn more. How do we take wedge in and out of a car? That is where the adjusters built into the rear windows come into play.

All four corners contain a coil spring supporting the chassis on the suspension. The top of each spring is seated into a cup attached to a threaded rod, called a jacking bolt. These are the items seen on TV that are being turned by the crew members. There is an extension from the jacking bolt up to the inside of the rear glass. Holes are cut into the lexan so a tool can be inserted to turn the jacking bolt one way or another. Perhaps you have noticed small orange circular decals on the rear windshields. This is exactly what they are for: to help that crew member locate his target. Remember this process occurs during a pit stop so speed if of the essence.

When a jacking bolt is turned clockwise that corner of the car is raised. Turning the bolt counter clockwise will lower that particular corner. The higher a corner is the more it will weigh. On our scales, weight will read from the diagonal corner across, to the one we just turned. The other two corners share some of that weight as well, but to a lesser extent.

For instance one turn into the left rear jacking bolt during a pit stop would increase that corner’s height and our wedge, and tighten the chassis. A turn out of the left rear would lower that corner, decrease our wedge, and loosen our chassis. The right rear had the opposite wedge reaction. Turns in decrease wedge and loosen a car. Turns out increase wedge and will tighten a car.

It is important to keep in mind our total weight and nose weight are not affected by these adjustments. There is no magical moving of actual steel, lead, or bolted components. We are merely raising and lowering frame heights. So a 3400 lb car is still a 3400 lb. car. Our wedge percentage can increase or decrease, but weights for the total and nose remain the same. No pieces are physically moved from one part of the car to another.

So when a crewman jumps over the wall in his colorful nomex suit and starts turning a tool through the rear window, here is a nice television cheat sheet. Turning into the left rear puts wedge into a car, tightening the chassis, which means the car was loose. Turns out of the left rear takes wedge out of the car, loosening the chassis, meaning the car was tight. The right rear is exactly the opposite. Turns in decreases wedge which loosens the car, and turns out increases wedge which will tighten the car.

It is possible for a sharp eye watching pit stop replays to tell how a car was feeling to a driver, right from the comfort of a living room couch.

Bump Drafts contributor Patrick Reynolds most recently served as a mechanic for Germain Racing on the Nationwide Series team of Mike Wallace- driver of the #7 Geico Toyota. Reynolds also contributes for Race Talk Radio.com and Spin Out Zone.com.

PHOTO CREDITS- Photos by Walter G. Arce. More of his work may be found at flickr.com.