Can You Really Bring Back the Same Car? (Or the Same Track?)

Every week at least one driver says they are bringing back “the same car we raced at…”.  But unlike Indy or ALMS racing, each shop builds multiple cars, each specialized for a specific track.

Let’s start by examining the anatomy of the stock car.  I think of the car in three major components:  The chassis, the body and the bolt-on parts.

The Chassis

The skeleton of the car is the chassis, a purpose-driven structure welded together from very strong round and square steel tubing.  Shown at right, the structure consists of a front clip (to the left), a rear clip (where the fuel cell sits) and the roll cage (located in the center).

The plans were provided to teams via an AutoCAD file – which should give you some idea of how precise NASCAR expects the teams to be in implementing the chassis plan.  The design optimizes safety, which is why NASCAR prohibits any chassis modifications.

Measuring Machines

Coordinate-measuring machines (CMM) determine how well teams followed the blueprints. CMMs are a probe (mechanical, optical or other) and a reading device to transmit data back to a computer. Mechanical CMMs include Romer and Faro arms, which are brand names.

These devices really do look like arms, with joints that mimic the elbow, wrist and fingers. Those joints allow motion along all three axes (up/down, left/right and back/forth), plus the ability to rotate about each of these axes. (Check out this interview with the inventor, Homer Eaton.) The user touches the arm to the car in specific spots to make measurements. The probe transmits its three-dimensional coordinates to the computer.  The picture shows a Romer arm.

How Measuring Arms Work

NASCAR uses a Romer (or similar) arm to certify the chassis, testing over 100 distinct points. They are also used for measuring the body. One challenge using mechanical CMMs is that they have to be accurate over a very large volume. The NASCAR system measures over a 13′ x 20′ area defined by a set-up plate. 5/8″ diameter touchpoints mounted in the plate every three feet improve the accuracy. The touchpoint placement is verified during surface plate installation using laser triangulation. The user starts by touching the CMM to any three touchpoints. That ensures the probe uses the same origin every time, which means measurements are consistent from car to car.

Triangulation is also the basis for the CMM.  The distance from the origin to the arm’s pointer is the unknown length of one leg in a triangle. If you know the length of one side and two angles, you can calculate the lengths of all sides.

After verifying the chassis, NASCAR attaches RFID (Radio Frequency IDentification) tags to strategic points.  NASCAR scans those tags at the track to make sure that the chassis hasn’t changed. These measurements tell the team if a chassis is even slightly bent or twisted.  Very small changes can compromise safety, so accuracy is very important.

The Body

The manufacturer supplies the roof, hood and decklid (a.k.a. trunk).  Fabricators create the remainder of the body by scratch from flat sheets of steel.  The steel that makes up the body is surprisingly thin — just 25-30 thousandths of an inch.  Most people who see a stock car up close are surprised at just how flimsy the metal is. (Ask Kevin Harvick and Carl Edwards how easy it is to dent a car hood during a fight discussion.)  Only the front and rear fascia aren’t metal, but from a carbon-fiber/Kevlar composite.

NASCAR uses Romer arms to measure  body position and sheet metal thicknesses, as shown at right.  We’re talking accuracy to the thousandths of inches level.  Teams can take cars to the R&D Center anytime to have them checked with the ‘official’ equipment. Most teams have one or more Romer arms in their own shops. It’s not a small investment:  A Romer system costs about $60,000.  That’s not including installing a surface plate, which must have no more than a few thousandths of an inch variation in height across a 12 x 20-foot area.

It is impractical to bring a Romer arm and surface plate to the track.  There, NASCAR uses templates similar to those shown here to check each car. The template grid is not the most sensitive measuring device. I have watched inspectors tap the template to “make” it fit more than once. Template show gross violations, but racing now comes down to thousandths of an inch. That’s why cars have to be brought back to the R&D center.

Can You Bring Back “The Same Car”?

When a driver talks about ‘bringing back the same car’, they are almost always talking about the chassis.  When name a car, you’re naming the chassis, not the bodywork and certainly not the A-arms or the engine. 

In their recent appeal, the 48 team claimed that the illegal car was the ‘same car they used” for all plate races in 2011.  How is that possible if so much changes from race to race?  I guarantee you there wasn’t a speedway car sitting in a corner in the Hendrick shop under a cover waiting to be brought back out for the next plate race.

The key is laser scanning.

Mechanical arms are really nifty pieces of technology; however, they measure specific points.  The more complex a curve, the more points you have to measure.  Laser scanning takes accuracy one step further.

We can make measurements similar to those made with a Romer arm using a laser.  We know how fast light travels: (300 million meters every second. If we measure how long it takes a beam of light to travel to and from a surface, we can calculate the distance between the source and the object.

How 3D Scanning Works

In 3D scanning, the user projects a laser stripe on the car.  If the surface is flat, the projected line appears straight.  A curved surface distorts the line, with the distortion proportional to the amount of curvature.  A sensor looks at the line and back-calculates what surface shape would cause the observed line to appear as it does.  Most of the big teams have their own laser scanning system and scan every car before and after it goes on track.  Subtle differences in curvature could mean a few hundredths of a second improvement per lap.  Everyone knows that the days of finding a half second per lap are over.  A few hundredths can make a huge difference.

I suspect that the 48 team produced laser scans of each speedway car for the last year. They could show how the C-posts on those cars compared to the C-posts on the ‘illegal’ car. I can’t say anything about the decisions made on the basis of those measurements, but routine laser scanning of cars provides pretty solid documentation.

Putting Bristol “Back”

Cars aren’t the only thing laser scanners measure.  Tracks are also scanned with lasers, although in a slightly different form. NASCAR.com’s Raceview and iRacing provide amazingly accurate pictures of the tracks.  Those graphics are due to 3D laser scanning that allows them to measure every dip and every oil spot on a track.  See how iRacing does it.

Bruton Smith definitely has access to very detailed measurements of the pre-2007 Bristol from a variety of sources.  Does that mean he can put it “back” the way it was?  If he can, does that mean racing will go back to the way it was?

No.  Definitely not.

Our ability to measure accurately far exceeds our ability to replicate accurately.  There is a huge human element, whether it be making a car or re-surfacing a track.  Sure – you can replicate the track dimensions pretty accurately — but how do you duplicate exactly a concrete surface that has been weathered by decades of weather and use?  Bruton hasn’t announced exactly what he’s going to change, but we’ll analyze it when he does.

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