If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:6:25

Optimal turns at Indianapolis Motor Speedway with JR Hildebrand

Video transcript

this is Sal here with famous Indy car dryer driver smiling when I said famous junior Hildebrand and since you're here I thought I would ask a question that that's always been on my mind yeah we have a picture here of the of the Indianapolis Motor Speedway yeah and and I've always wondered you know how you it seems like turning is a very important part of this is absolutely an important part of the reasons get fixated on the car going straight but the turning Park City where a lot of the skill comes into it and I've always wondered you know what is what is optimal do you all try to minimize your distance and kind of take the turn as as quickly as in the short of a distance as possible by kind of really hugging the hugging the corner by going like that or but when you do that you have to kind of you have to turn more there's more g-forces there's more kind of centripetal force that you that your your tires have to deal with the cabin has to deal with versus versus taking the outside where you have to cover more distance but the the centripetal acceleration the g-forces aren't going to be as dramatic so how do you think about that well every track ends up being a little bit different but when we we take any Annapolis here as the example if you're all the way on the inside and it's like the 800-meter runner is kind of path it's the shortest distance you can kind of get from point A to point B the lap is the same every time so it doesn't actually depend on your running a specific distance or not for us in this example the car actually just won't do that if you think about being all the way on the inside being all the way inside through the corner and then exiting all the way on the inside it's having you the most work to follow that path and in Indianapolis we're approaching turn one at upwards of 240 miles per hour well and that turn one is not it's it's hardly banked it looks quite flat in person so as opposed to you know NASCAR running at Talladega or Daytona these big giant super speedways the car is having to do quite a lot of work to get through the corner here so how do so do take the outside or is it well so then you know you look at that and I think if you if you noted sort of the radius that we like if you feel if you do a full circle out of that each of those arcs let's do that so let's say this is the shortest distance path this is kind of a circle that looks something like my best let me scroll over a little bit so that we can see a little bit better so this would be a circle like this if you were to keep that arc right going would be a circle that looks something like this so that's a pretty that's a pretty small circle small some things here yeah and for the larger one the circle would look something like would look something like this right so you have a larger radius a larger turning radius so you would have to have less centripetal acceleration inward acceleration and less fewer g-forces on this outside one right wise that circle is in a different way to look at it if you looked at the car trying to just go around these two different circles and it's going to be going the same speed on either one it's doing a lot less work to get around this outside circle and therefore the speed that you could carry around that then sort of goes up you know the car has a limited ability to stick to the racetrack so the thing that up definitely makes it that's an important point at least in Indianapolis your full throttle the entire way yeah so when you're saying I mean obviously if you hit the brakes the car could do what you know yeah very small turning anyways yeah but but you're you're a full problem you're not you're not gonna have any chance if you had all let off the gas that's right when you qualify it Indianapolis you've got to put in four laps four of your best laps of the season of your career in an Indianapolis to qualify and that you are absolutely flat chat the whole way around the racetrack there's no lifting there's no braking and so that's why you're saying are just wouldn't do that if you're going all out the cards wouldn't even be able to make this this exactly so from a drivers that's a good point from the driver's perspective you have to stay flat out if you're going to go faster you're going to set a lap time that's relevant you have to be able to stay flat out and so at that point then you're searching for the line around the racetrack that you can do that most efficiently right and so then in this example moving that increasing that radius by going from the from our green circle out to the purple circle does that rather effectively I see we're going for the purple to the green back like so you're saying like this well yeah and so then to find the actual optimal line what we end up doing is starting out on the outside of the track then bending the car into the inside of the track and going back to the outside of the track really using all of the road that's available to us right so that's interesting so you know I posed the question it was kind of like I was my brain was just looking at these two circles but right you realize there's a bigger circle that you could fit here that there's an arc like this and this would be you know if you imagine this would be a part of a circle that's way huger than even that even that purple circle that we're drawing yeah that's the center of that circle is like here or something right so you have a lot less centripetal acceleration that you have to place inward acceleration that you have to place on the car exactly and therefore the car is able to carry a massively increased level of speed through the corner and that that's that's really what we're looking for you consider I think it's it's a very interesting when I think about what I'm doing is the driver I don't think I really am consciously thinking that much about the the mathematics that go into finding this optimal racing line you sort of instinctually just gravitate towards what the car feels like it wants to do but when we look at it from this perspective you've got the car going down the straightaway here it's a at 240 miles per hour that's almost as fast as the car is going to go so it's just a sort of terminal velocity the drag of the air hitting the car won't allow it to go engines giving all the power yeah your house just out setting the drag of that so you can't accelerate exactly it's almost like you're hitting a hot wall of air you're not going to be able to accelerate any faster and so what you're really trying to do is you're trying to in order to set that fastest lap time which ends up equating to the like highest average speed around the lap that's what's the lowest number in terms of a lap time perspective you're trying to get the car to most efficiently get through the corners so that you can allow it to accelerate down the straights right as much as you can you're sort of getting into diverge from this intended course that it's going on here as efficiently as you can and so by creating the largest radius around corner that's how we end up finding that optimal line that's fascinating