Sprint Car Safety

NASCAR fans are used to having our drivers walk away from spectacular crashes.  Unfortunately, we are reminded all too often — like last night — that racing, regardless of all the technical improvements we’ve made, remains a dangerous sport.  As you move from the top-level Indy and NASCAR series, the number of driver deaths increases.  Some of the higher risk level is because of the funding – racers running on much smaller budgets tend to want to put their money into making the car go faster rather than buying more/higher-quality safety equipment.  Sanctioning body requirements are also not as rigid

Sprint Cars (like the one shown at right) are tiny, very powerful racecars.  The 410-series uses a 410-cubic-inch V-8 engine that generates 800-900 hp.  For comparison, NASCAR Sprint Cup engines are 358 cubic inches and generate around 900 hp; however Sprint Cars are about half the weight of a NASCAR car.

You’ll often hear people talk about power-to-weight ratio.  For a NASCAR Sprint Cup car, the power-to-weight ratio is 900 hp/3480 lbs = 0.26 hp/lb.  (I know, those aren’t standard units, but they’re more accessible than W/kg.)   Taking a weight of 1575 lb (including driver) for a Sprint Car (I’m finding all kinds of numbers on the web for required weight), the power-to-weight ratio for a Sprint Car is 850 hp/1575 lb is 0.54 hp/lb.  Just for reference, Wikipedia lists the power-to-weight ratio for a Funny Car Drag Racer at about 3.3 hp/lb.  A street Corvette Z06 is about 0.16 hp/lb.

That’s an awful lot of power for a very light car and Sprint Cars need aerodynamic help to stay planted on the ground.  That’s the purpose of the giant wings on the top and front.  The wing at top is about 5 foot x 5 foot and the wing  over the front wheels is about 2 foot x 3 foot.  Those giant areas give air molecules plenty of places to hit and push the car into the ground, thus generating a lot of downforce.

Sprint cars are smaller (they have a 84″ wheelbase, while the NASCAR Sprint Cup cars have a 110″ wheel base), but they have the same type of tube frame construction as stock cars.  They also have a relatively high center of gravity, which makes them much more prone to tip over than other types of cars.  For the gearheads among you, Circle Track does an absolutely great job with tech details.   NOTE:  Although the wing does raise the Center of Gravity, the issue is not just with the wing:  wingless Sprint cars have the same issue with a high CG.

Sprint Cars reach a maximum of about 140 mph, which is a combination of the very powerful engine, the light weight, and the huge amount of drag that the wings create.  Using the max speed of 140 mph, a Sprint Car has the same kinetic energy (aka energy of motion) as contained in a third of a pound of TNT.  Energy is critical because (as you no doubt have had pounded into your head), energy cannot be created or destroyed – it can only change forms.

There are two critical factors in crashes:  How much energy you’re carrying when you crash (your kinetic energy) and how that energy is transformed into other kinds of energy.  For example, when a car pulls into the pits on a green-flag pit stop, its kinetic energy is slowly transformed into other forms of energy:  heat (brakes, the tires if you skid them), light (brake rotors glowing), and even sound (squealing).  It’s a slow, controlled transformation of energy from kinetic to other forms.

When you crash, energy is transformed into different forms.  Energy may be transformed into spinning or skidding motions of the car, the noise of tires squealing — or sheet metal crushing.  The one place you do not want to dissipate energy is through your driver.

The amount of energy is important, but so is the time over which the energy transformation happens.  The force you experience when you change speed is proportional to the change in speed divided by the time it takes for you to change speed.  I like to say that it’s not how fast you go… it’s how fast you stop.

The airbag in your car works on the principle of slowing down how fast your head comes to a stop.  If you extend the time it takes for your head to stop from a tenth of a second to a second, you experience ten times less force.  This is the principle behind how SAFER barriers work:  They flex when hit slowing down the car in a much gentler way than a concrete wall.

It took four deaths between 2000 and 2001 for NASCAR to put their considerable brain power to making revolutionary changes in safety.  The folks at the NASCAR R&D Center are concerned about racers at all levels of stock car racing, from the Sprint Cup down to the local tracks.  Some of their research – like the development of strong tube-frame chassis and solid construction methods – are transferable to open-wheel racing; however, there are some unique challenges to improving safety for this type of racing.  There are also people like Randy LaJoie, who work with racers in many of the lower series and are just as concerned about short track racers as they are NASCAR drivers at the top level.

Sprint Cars race at a lot of tracks that do not have SAFER barriers.  Installing SAFER barriers is very expensive and many smaller tracks are struggling to stay open during the economic challenges of the current era.  Maybe this is a place for someone to design a lower-cost SAFER barrier that doesn’t need to meet the requirements of a Daytona or Indy.  Sprint Cars race at many highly banked tracks — when you combine an incline with a car having a high center of gravity, you get cars flipping over.  Lowering the CG of the car would go a long way to keeping them on the ground.  An additional complication is that there are a slew of sanctioning bodies for Sprint Car racing, which complicates any type of unified action.  It was easy for NASCAR to put their considerable economic heft behind an edict that all tracks they race at must have SAFER barriers.  It will be much harder for a similar effort at smaller tracks and multiple sanctioning bodies.

Perhaps the tragic loss of Jason Leffler will be the catalytic incident that spurs a safety initiative for Sprint Car racing similar to the one NASCAR initiated in 2001.  I can think of no greater tribute to a driver than that his very untimely death ends up saving more lives.  Thirty-seven is just too, too young to go.

NOTE added:  As I noted above, the win provides a LOT of aerodynamic downforce and drag.  This does help the car be more stable; however, it does not address the problem that, in high banked turns, a high center of gravity make a car more probable to tip over.