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.|
@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?
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.
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!
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Buy my book! The Physics of NASCAR
Wouldn’t 20 pounds make quite a difference on a road course?
Anybody stopped to think that it is this obsession with “parity” that has resulted in what Nascar has become?
On one hand, I agree with everything above. Moving 0.5% of the vehicle mass a tenth of an inch isn’t going to make a difference. On the other hand, the teams do everything they can to shave off every tenth of a pound.
I think basic math would tell you, two equal cars, one being .5% lighter and having a CG .1″ lower and to the left than the other will be faster. No question about that. The real-world question however is will it have any difference with two different drivers driving the car over 500 miles around in circles, factoring in pit stops, etc.
At the end of the day, this is a non-issue. Now I win our Pinewood Derby races every year by simple physics based on the CG and the initial PE of my car as compared to the others. In NASCAR, they don’t simply drop the cars down a ramp with gravity to determine the winner.
NASCAR weight rules are made to prevent driver’s weight being an factor of the car’s speed, so I think that Danica’s weight had minimal effect on great qualifying lap.
First off we are talking about a track with high banking where the driver floors it the whole lap. Banking effects the left side weight and you do not have to allow for acceleration. In my opinion I agree with PittCaleb and it does”t make a difference. Now go to Martinsville and see what a crew chief will do to get tiny advantages in left, light and lower. It is flat and you use your brakes. She weighs 40 lbs. less than the lightest driver I know of (Mark Martin.) Check with any crew chief you now and ask him if he would like to have 40 lbs. to put anywhere he wants in the car.
I also have found in the “real world” that many of these drivers can feel things in a car that we cannot fathom.