Brief Thoughts on the Nationwide Accident at Daytona

We’ve been painting the new house.  I was straining to hear EPSN’s commentary over the swoosh-swish of the paint roller as the race came to a close – but it was all too easy to hear the change the tone of Allen Bestwick’s voice.  We heard it in Marty Reid’s voice in Vegas not too long ago.   I remember the first-hand feeling sitting about 50 yards from Michael McDowell’s wreck during qualifying at Texas.  A track full of race fans – all quiet – is one of the worst sounds in all of sports.

The first reaction to things like this is often blame.  Blame NASCAR for blocking videos, blame ESPN for showing too many replays — or not showing enough replays.  Blame reporters for not having information fast enough.  Blame reporters for information reported in good faith that turns out to be incorrect.  Blame drivers for blocking.  Blame drivers for trying to pass.  Blame NASCAR for letting the cars go too fast.

I was at the NASCAR R&D Center a couple of weeks ago talking with the head of NASCAR’s safety effort.  There is no one more committed to safety or doing more to make racing safe — for fans and for drivers.  There is no one at NASCAR who thinks the show is more important than safety.

In talking to folks at NASCAR and people like Dean Sicking, inventor of the SAFER barriers and one of the foremost motorsports safety experts in the world, the same themes emerge.  We have solved 99% of the safety issues.  The fact that Kyle Larson emerged from what was left of his car uninjured is a miracle.  The fact that the engine did, in fact, get stopped by the fence, saved lives.

The safety issues that remain are the ones that are hardest to solve:  The ends and the breaks in pit road walls.  SAFER barriers for inner walls that can still open quickly — even when damaged — to let emergency vehicles onto the track.  Gates in catchfences that open, but retain the same strength as a solid piece of catchfence.

I’ve got some general information about catchfences that was written after the Dan Wheldon accident, and I expect I will reiterate my thoughts that there needs to be a concerted effort to figure out how to fund the very expensive research necessary for preventing what happened Saturday night from happening again.

Right now, my thoughts are with the people who were injured and my best wishes go to them for speedy, complete recoveries.

Did Danica Get the Daytona 500 Pole Because of Her Weight Advantage?

Note – this was revised 2/20/13 because new information became available.  It is amazing how hard it is to get a straight answer to things sometimes!

Did Danica Patrick win the Daytona 500 pole because she has a weight advantage?

Chuck Tolsma asked via Facebook:

Evidently weight is added for lighter drivers. How is it distributed in the car? Did Danica win the pole because she has a weight advantage? What is the effect of weight on downforce and is it really as significant as alleged by a couple of media people?

Minimum Weight Rule

Let’s start with the facts: NASCAR requires all cars meet a minimum weight requirement. (Car weight is measured with all the fluids and a full tank of fuel. The way the rule is phrased in the NASCAR rulebook is sort of confusing because they specify the minimum car weight without driver, but then the minimum car weight changes depending on the weight of the driver. So if the driver is 180 lbs and above, the car must weigh at least 3300 lbs. If the driver is 170-179 pounds, the car must weight at least 3310 lbs. The list keeps going, in increments of 10 pounds, all the way down to 140-149 lbs.

From That’s Racin’, the NASCAR rulebook says:

DRIVER WEIGHT MINIMUM OVERALL CAR WEIGHT
180 lbs. – Above 3,300 lbs.
170 lbs. – 179 lbs. 3,310 lbs.
160 lbs. – 169 lbs. 3,320 lbs.
150 lbs. – 159 lbs. 3,330 lbs.
1400 lbs. – 149 lbs. 3,340 lbs.

@bobpockrass clarified this rule earlier today on twitter:  The max ballast anyone is allowed to put on their car, regardless of weight, is 40 lbs.

Drivers are weighed with all their gear on — helmet, firesuit, gloves, sunglasses, sharpies… This can add another 15-20 lbs of weight to a driver.  So although Danica weighs about 100 lbs, with her gear, we’re actually talking 115-120 lbs.  Same goes for the other drivers as well.

This would imply that Danica’s car is 3340 lbs.  Add in her and her gear and the total weight is 3340+120 = 3460 lbs, which is 20 lbs below the 3480 lb absolute minimum weight that any other drivers could get down to.

Why doesn’t NASCAR do things the way many other series do?  Just weight the driver and the car together and it has to meet a minimum weight.  My guess is that NASCAR drivers spend so much time doing publicity for their sponsors and fans that it would be tough to schedule.  This way, you only need the driver once (or twice) a year.

The question that remains (now that we actually have a reliable answer to the weight question) is:  Does that 20 lbs make a difference?

Weight Distribution

Total weight is not as important as where the weight is located.  NASCAR has a bunch of rules on where ballast (additional weight used to bring the car to minimum weight) can be located.  They also mandate a right-side weight of (I believe) 1,620 lbs minimum.

Why does NASCAR mandate how much weight is on the different sides of the car? Because weight distribution determines mechanical grip. The mechanical downforce on each tire — the grip — depends on much weight is pushing down on that tire. More weight on the tire means more grip.

When you turn left, the body leans from the left side of the car to the right side of the car. So when you turn left, you decrease the force pushing down on the left wheels and thus you lose grip (i.e. mechanical downforce) on the left side of the car.

How much weight shifts depends on the center of gravity of the car. The higher up the weight is, the higher the center of gravity of the car becomes. The higher the center of gravity of the car, the more weight shifts when you turn. Think about taking a corner in an SUV with a high center of gravity vs. a sports car with a low center of gravity. The higher center of gravity makes the car lean more in the turn.

For these two reasons, anytime you have a choice where to put weight, you choose left and low. Left because you want to keep as much grip on those left tires while turning and low because it decreases the center of gravity. The center of gravity is why teams have been making carbon fiber dashboards – it decreases weight relatively high in the car and allows them to compensate by putting the weight where it will decrease the center of gravity.

It’s pretty straightforward to compare the CG of a car given the driver weight, the ballast weight and the car weight. So my friend Josh Browne (one of Elliott Sadler’s former crew chiefs and now a Ph.D. student at Columbia) and I plugged some numbers to see if this made much of a difference.  I went through a bunch of possible scenarios this morning once I got confirmation on the weight.

Based on these estimates — which don’t take into account a lot of other factors — if their put the entire 40 pounds on the left hand side, Danica’s car might have a lower CG by maybe a tenth of an inch — or two.  That’s simply not enough advantage to matter, especially since you have (as pointed out by @keselowski) other factors.  The one Brad pointed out was that the car height is measured with the driver in the car – a lighter driver doesn’t bring the car down as much.  I’m still trying to find how much lattitude teams have with rear springs at Daytona to figure out whether the set up could compensate for that.

Regardless, remember that the center of gravity and the overall weight is one of a bunch of factors, all of which could be a plus or a minus.

The calculations also explain why you don’t keep letting them add ballast — at some point, you get too big of an advantage if the ballast amount gets large enough and that more than overcomes having the weights equal.  Weight distribution is way, way more important than total weight.

But Wait! Don’t Women Have a Lower CG than Men?

Yeah. About an inch lower. Even taking that into account, the numbers don’t change much. The advantage she’d have is in the noise because you have so many other variables, like seat weights and placements, dashboard weight, etc. that could change. Women have a lower of center of gravity because (in general) we have wider hips and narrower waists, whereas men are more uniform.

Remember — we’re talking about 3300 pounds+ of car and 100-200 lbs of driver and ballast.  The driver and ballast is such a small part of the center of gravity, that you’d have a really hard time significantly manipulating the CG that way.

Conclusion

In talking to engineers on race teams, I’ve heard the same thing over and over: she won because Hendrik gave her good equipment and the fastest engine. They had nothing to lose. Being on the pole at Daytona doesn’t mean very much in terms of winning the race, but look at the huge publicity boost. It was on the nightly network news. How often do we get on the mainstream news for anything other than crashes and fights?

The folks in the garage are pretty quick to raise a ruckus if they think something sneaky or unfair is going on.  Have you heard scores of drivers complaining about the 10 having an unfair advantage?  If none of them think there’s anything suspicious about Danica’s pole, why do we?

Want to know stuff about the Gen-6 Car? Tweet your questions to @drdiandra or find me on facebook. I’ll find the answers for you.  And hopefully they won’t be as hard to figure out as this one was!

Other Relevant Posts

Gen 6 Car

Superspeedway Science

Buy my book! The Physics of NASCAR

Reader Questions: Gen-6 Windshields on Passenger Cars?

PittCaleb asks:

If we used Lexan in passenger cars, would there be any benefit such as reason repelling our ice buildup? Scratching or other potential downsides? What would the price diff be?

The implementation of superstrength laminated polycarbonate (Lexan) in NASCAR windshields raises the obvious question:   “If it’s so good for NASCAR, why isn’t it in my car?”

A couple considerations:

  • Weight:  The less a car weighs, the less fuel it takes to run, so decreasing weight is not just good for going fast:  it’s good for saving gas as well.  That said, the weight differential replacing a windshield with Lexan is pretty small compared to other places on a car.  the Department of Transportation (DOT) must approve all windshields for use in passenger cars and they require 1/4″ hard-coated Lexan.  Since the density of Lexan is roughly half the density of glass, assuming equal thickness, a Lexan windshield would weigh about half of a laminated glass windshield.   Comparing that to a 3500-lb overall car weight of, you’re not saving much in terms of fuel.
  • Cost:  You can buy a sheet of 1/4″ thick Lexan big enough for a windshield for about a hundred bucks.  BUT:  Lexan (polycarb in general) is extremely susceptible to scratches.  A cheap piece of basic polycarb will be scratched the first time a bit of sand or dirt gets under your windshield wiper.  Manufacturers get around this by putting hard coatings over the polycarb that make it more scratch resistant – but those coatings are expensive and ramp up the cost pretty rapidly.  You’re probably talking 2-3 times the cost of polycarb vs. glass, which is probably a couple hundred dollars for a windshield.  Does that offset the lighter weight?  Depends on the person buying the car.  Polycarb is becoming more common for things like headlight covers, but the only cars using a lot of Lexan are in the class of the Bugatti Veyron – which costs more than most of us make in a decade.
  • Maintenance:  Americans are not very good at taking care of their cars.  Most people don’t check their tire pressure, change the oil regularly, or even pay heed when the engine warning light comes on.  Manufacturers won’t implement  Lexan windshields until they require absolutely no additional TLC relative to glass.
  • Icing:  Interesting point.  The thermal conductivity (how well a material transmits heat) of Lexan is about a quarter that of glass.  That means Lexan is a much better insulator than glass – one attractive point for Lexan from the perspective of environmental aspects is that Lexan would enable you to use less heating and air conditioning.  The thermal conductivity of polycarb can be changed by using glass fillers – but that also changes the strength.  We argued a bit about  this one.  It would take a longer time for the inside of the car to get cold, but since Lexan is a bad thermal conductor, that might not impact the outside of the windshield very much.  If you were using the defroster, it would take a long time for heat on one side of the Lexan to get to the other side, and thus longer to defrost.

The thing might make Lexan a feature of road cars is (in my opinion), if electric vehicles really take off.  Saving ten or twenty pounds on a race car is huge; but it won’t make much of a difference on an internal combustion engine-driven vehicle.  For an electric vehicle, however, every pound counts in terms of extending the car’s range.  Since range limitations are one of the big barriers for EV acceptance, using Lexan to reduce the weight without compromising safety could make a real difference.

 

Secrets of the Gen-6 Car: Superstrength Windshields

A number of drivers have sounded a common refrain:  the CoT was engineered to be safe … and that’s why it was… well… sort of ugly and not very racy.  The Gen-6 car is a much better looking vehicle and (once the teams get a handle on the engineering) it should also give us a better show.  But don’t let its looks fool you:  NASCAR did not forgot safety in the Gen-6 car.

During a recent visit to the NASCAR R&D Center, Tom Gideon — NASCAR’s Safety Czar — gave me a tour through some of the changes you might not notice… unless something bad happens.  The drivers were briefed on these changes during Daytona testing last month and the reactions have been uniformly positive.

There is a line of Diet Coke cans sitting on the front edge of Tom’s desk.  They aren’t for drinking:  they’re there to become high-speed projectiles.

Why Diet Coke?

Because, Tom explained, if you splat regular Coke onto a car, you’ll spend the rest of the afternoon cleaning up the gooey, nasty mess produced by all that high-sucrose corn syrup.

The soda cans (actually, their less-fortunate cousins) were projected at car windshields.  NASCAR windshield are, of course, not made of glass.  They are made of a plastic called polycarbonate, which is better known by the trade name Lexan.   Lexan is clear, like glass, but it gives more easily and thus can take higher impacts without breaking.  In fact, the shark fins on the Gen-6 cars are made of Lexan, which makes them virtually invisible when the cars are on the track.

Lexan is also more expensive than glass, which is why most passenger cars still use glass in their windshields and windows.  Windshields are made from laminated safety glass.  Laminated means stacking up a bunch of layers of something and compressing them to make a single unit.   Plywood is a laminate of wood, which you can see if you look at the end grain.

Laminated autoglass sandwiches a very thin polymer film (polyvinyl butyral, a.k.a.  PVB) between two layers of glass. The layers are heated under pressure, chemically bonding the glass and the film.  The polymer film (in contrast to glass) is elastic – that’s the layer that allows the glass to absorb energy when something hits it.  This is the same idea as padding your dashboard – the padding extends the time of your collision and thus decreases the overall force.  The polymer film insert in your car’s windshield also absorbs UV rays from the sun, protecting the fabric, leather and plastic inside the car.  Most importantly, if laminated glass breaks, the polymer film holds the pieces together.  The side windows in your car are made from  a different kind of glass that is designed to shatter into a zillion tiny — and rounded — pieces if it breaks.  This allows a person to climb out a broken side window without restriction (or cuts).

NASCAR_brokenThe Diet Coke cans on Tom Gideon’s desk were representative of the types of projectiles that might land on a track.  If you think something as seemingly innocent as a soda can  can’t do any real damage, look at this blog I wrote awhile back when a Dallas TV station contacted me to verify the story of a woman who claimed a styrofoam drink cup thrown from a passing car had punched a hole through her windshield.  The hole is shown at right and, yes, a styrofoam drink cup traveling at high speed can break a windshield.

A Lexan windshield wouldn’t have broken, but the windshields in NASCAR racecars have to stand up to much more than soda cans.  They have to survive impacts of things like like wayward car parts.  Last year in Charlotte, a piece of brake rotor hit Greg Biffle’s windshield.  The brake rotor didn’t go through the windshield, but the impact did blow out the interior window braces so that they were hanging over the steering wheel and impeding Biffle’s ability to steer.

Five years ago, NASCAR was in reactive mode when it came to safety.  They weren’t anticipating problems, they were rushing to develop solutions when something happened on the track.  Things have changed:  NASCAR is sufficiently ahead of the game that they aren’t waiting for a catastrophe to happen before they start innovating.

One of the R&D Center’s new toys pieces of scientific equipment is a pneumatic cannon.  It uses compressed gas (just like a potato gun) to propel a projectile toward a windshield at about 50 mph.  In addition to the soda cans, NASCAR used solid metal cylinders to test the Gen-5 windshield using the new pneumatic cannon.  The old windshield wasn’t unsafe, but the R&D Center realized they could do better.

NASCAR_Gen6WindshieldLamination improves the strength and energy-absorbing ability of glass, and it does the same thing for Lexan. The Gen-5 windshield (shown at top left) was a little less than a quarter-inch thick.

The new window uses two pieces of Lexan, each half the thickness of the old window, with a 30 mil (that’s 30 one-thousandths of an inch) polymer film between them.  A really good-quality heavy duty trash bag is 4 mil thick, so the film in the new windshield is about seven or eight trash bags thick.  After heating and pressure treatment, you have a perfectly clear, superstrong windshield that is only thirty thousandths of an inch thicker than the old window.  Robin Pemberton told the media that the new windshield could withstand the equivalent of a connecting rod going 200 mph without breaking.

The pneumatic cannon resulted in some additional developments that I’ll detail in my next post.  Questions and comments are always welcome.