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

Every week we hear at least one driver say that they are bringing back “the same car we raced at…”.  This is a little misleading because — unlike Indy or ALMS racing — each shop builds multiple cars, each specialized for a specific track.

NASCAR Chassis

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.  Since the design was developed to optimize safety, teams aren’t allowed to modify the chassis at all.

How faithful teams were to the original blueprint is determined using  coordinate-measuring machines (CMM). CMMs consist of a probe (which may be mechanical, optical or other) and a reading device that transmits data back to a computer that processes and stores the information.  Mechanical CMM devices include the Romer and Faro arms, which are brand names of popular CMMs.  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.) To measure something, the arm is touched to the car in specific spots. The probe transmits its three-dimensional coordinates to the computer.  The pictures below shows a Faro arm.

NASCAR uses a Romer arm to certify the chassis (testing over 100 distinct points), and for measuring the body (as I’ll explain in a moment). One of the challenges 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. To improve the measuring accuracy, 5/8″ diameter touchpoints are mounted in the plate every three feet. The placement of the touchpoints is verified during surface plate installation using laser triangulation. Before measuring the car, the CMM is touched to any three of the points to ensure that the probe uses the same origin every time and 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 of your triangle (which you do using your reference points on the plate), you can calculate the lengths of all sides and all angles.

After verifying the chassis, NASCAR attaches RFID (Radio Frequency IDentification) tags to strategic points.  Those tags are scanned at the track to make sure that the chassis hasn’t been changed.  For example, if a car was in an accident, these measurements tell the team whether the chassis has been even slightly bent or twisted.  Very small changes can compromise safety, so accuracy is very important.

The Body

The roof, hood and decklid (a.k.a. trunk) are supplied by the manufacturer.  The remainder of the body is fabricated by scratch from flat sheets of steel.  The steel that makes up the body is surprisingly thin – in the the range of 25-30 thousandths of an inch thick.  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 accidentally dent the hood of a car during a fight discussion.)  The only parts on the body that aren’t metal are the front and rear fascia, which are made 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 over to the R&D shop anytime to have them checked with the ‘official’ equipment, although most have one or more Romer arm systems in their own fabrication shops.  It’s not a small investment:  A Romer system costs about $60,000.  That’s not including installing a surface plate, which has to have no more than a few thousandths of an inch variation in height across a distance of 12 x 20 feet.

It is impractical to bring a Romer arm and surface plate to the track.  At the track, NASCAR uses a template structure – similar to the one shown here (from the Super Chevy website) to check that each car conforms to the rulebook. The template grid is not the most sensitive measuring device. I have watched inspectors tap the template to “make” it fit more than once. The template makes it easy to see gross violations, but racing these days comes down to thousandths of an inch and that is why the cars have to be brought back to the R&D center for measurement.

The video below shows the template grid system and the body.  After the templates are lifted off, the body rises to reveal the chassis underneath.  (In reality, of course, the body doesn’t just lift off the car – it’s attached with rivets and welds.) I think this demonstration (from the Hendrick museum and video courtesy of Santa Fe Productions) illustrates well the difference between the chassis and the body.

The “parts” as I call them are all the pieces that are bolted to the car:  suspension component, transmission, engine, windows, etc.  Because they aren’t welded to the car, these pieces can be changed during the course of a practice or even a race.

What Does “Same Car” Mean?

When a driver or a crew chief talk about ‘bringing back the same car’, they are almost always talking about the chassis.  When you give “a car” a name, you’re naming the chassis, not the bodywork and certainly not the A-arms or the engine.  When a car comes back to the shop after a race, the engine is removed, most (if not all) of the bolt-on parts are removed and more often than not, the body is removed.  The engine is stripped down and entirely re-built before being used again.  All of the bolt-on parts are  inspected for wear and possible damage.   In theory, the body could be left on and all the parts re-used.

It is rare, however, for a team to be satisfied with how a car ran — even if the car won the race.  Teams are always looking for advantages, so there may be different bolt-on parts used for the next race, or the crew chief may want to modify the body slightly (within the rules, of course) to make it more aerodynamic.  When a team talks about “a car”, they’re almost always talking about the chassis — which is changed only when it has been damaged.

Can You Bring Back “The Same Car”?

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

A graphic showing how laser scanning works

The key is laser scanning.

Mechanical arms are really nifty pieces of technology; however, they measure specific points.  The more complex a curve (or the more subtle its departure from the specification), 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 exactly how fast light travels (300 million miles meters every second), so measuring how long it takes for a beam of light to travel to and from a surface lets us calculate the distance from where the beam is emitted to the object.

A slightly more complex setup is used for 3D scanning.  A laser stripe is projected on the car.  If the surface onto which the line is projected is flat, the line will appear 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 was able to produce laser scans of each of their speedway cars for the last year and show how the C-posts on those cars compared to the C-posts on the car that was deemed illegal.  I can’t say anything about the decisions that were made on the basis of those measurements, but the routine laser scanning of cars provides a pretty solid documentation of everything about a car.

Putting Bristol “Back”

Cars aren’t the only thing laser scanners measure.  Laser scanning is also used (in a slightly different form) to scan tracks.’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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About Diandra 455 Articles
I'm a recovering academic who writes about the intersection of science and life. I'm interested in AI, advanced prosthetics, robots and anything that goes fast. Author, THE PHYSICS OF NASCAR and Editor, BIOMEDICAL APPLICATIONS OF NANOTECHNOLOGY

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