Jun 132013
 

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.

SprintCarChassisSprint 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.

ForceMomentumTime

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.

 

  11 Responses to “Sprint Car Safety”

  1. In dirt racing you often have to raise the CG to get the car to transfer the weight to the right side of the car. The wing actually drives the left side of the chassis down if you ever would take the time to go to a sprint car race. Like Tim said the reason a lot of flips happen is because of the open wheels.

  2. A part broke and he hit the wall in an angle that cause a hard neck impact. You could have 5000 more crashes and not recreate all the variables that came into play in this crash. It is also unlikely that ANY changes could have been made to change the variables in this crash. .Sadly there are things that happen which we have no control over and will never have control over. No matter how much we think we can.

  3. You think the sprint cars are bad look at the quarter midgets these kids hang all the way out of the car head and sometimes both shoulders talk about needing a new design.

  4. This is a very informative video of a Sprint car during a crash test. https://www.youtube.com/watch?v=WOsoNGwDTcg

  5. Thank you Jimmy! You are right about power-to-weight. When you use metric units, you use Watts per kilogram. In British units, if you do horsepower over pounds, you get numbers smaller than one, so in British units, you use (as you point out) pounds per horsepower. I debated about whether calling it power-to-weight ratio and then giving weight-to-power ratio was more confusing than decimals. To covert between the two, just take the inverse (1 divided by the number) and you’ll get the numbers in the units you’ve used. Thank you for taking the time to comment!

  6. Tim: Thanks for the comment. You are right – there is an inherent safety issue with open wheel cars and the launching problem when they touch. The only way the problem will be solved in Sprints and variants on Sprints is for there to be a concerted effort to redesign the car. It always seems to take a tragedy to spur action on these things. I hope it doesn’t take any more tragedies for us to see some major action. Thank you for taking the time to comment.

  7. Another great article from one of the best racing sites on the web! One question/comment…You use hp/lb vs. lbs/hp for your power to weight units. I think lbs/hp (weight/power) is a more common unit for the auto and racing industry plus I think it’s easier to understand and compare for most people. My American Iron Road Racing series limits power to 9.0 lbs/hp (roughly 3375 lbs/375 RWHP), for example. This puts a 2013 Cup car at 3.6 lbs/hp (3300 lbs this year) which is nearly three times my weight/power and the Sprint car at 1.8 lbs/hp (nearly six times as much!).

  8. Nice to hear from you again. As always, inciteful and educational.

  9. All the above considered, the biggest reason these cars flip is the open wheel nature of the car. Get any part of your car in contact with the open wheel of the car closest – especially the trailing car’s front wheels in contact with the massive powered rear wheels of the car in fromt and the sling-shot effect launches these cars. Same problem was present with the Indycars as illustrated at LasVegas in the Wheldon accident when 4 cars were simultaneously airborne and resulted in DW’s demise. Indycars solved the problem in their latest generation cars with farings to surround the rear wheels making tire-to-tire contact almost impossible. Autosports will always be dangerous, but racing open wheels is especially dangerous. Go to any short track around the country on any given weekend and watch 10-20 year old beginner racers in micro-sprints or even Legends cars. No one that goes regularily hasn’t seen one of those flip either.

  10. One thing more dangerous than a 410 on dirt is a 410 on asphalt. I’ve seen them at Mansfield, Ohio on the “just less than 1/2 mile” paved track. They are lethal!! Hopefully, Jason’s untimely death will cause more assets and effort to be directed to increasing safety than speed.

 Leave a Reply

(required)

(required)

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>