Episode 180 – Indy 500 by the Numbers

In today’s podcast episode, the topic is the Indy 500 by the Numbers.

This coming Sunday, May 30th, will be the 105th running of the Indy 500, so we thought we would do a simple analysis of the track and the drivers; hopefully, it will make watching the race more enjoyable.

Welcome to the Indy Motor Speedway

Listen to the Podcast

Let’s take a look at track dimensions

  • The Indy 500 oval track is 2.5 Miles or 4 Kilometers in length.
  • The track consists of:
    • Two long straightaways that are each 3,300 Feet or 1006.5 Meters in length
    • Two short straightaways that are 660 Feet or 201 Meters long
    • Four corners that are 1320 Feet long or 399 Meters

Looking at those numbers, an Indy 500 driver will spend 40% of their time in a turn.

Some Numbers

Over the last decade, the average straightaway speeds are approximately 225 MPH or 362 KPH. These are approximate race speeds; qualify speeds are in the 238 MPH or 383 KPH range. Due to pit stops, the average speed for the entire race is much less.

For the sake of easy math, we will lower that max speed number down to a boring 220 MPH or 354 KPH, which is 323.4 feet in a second or 98 Meters Per Second, more than the length of a US football field in a second. When you consider that blinking your eyes takes .2 seconds, the vehicle will travel 64.6 Feet or 20 Meters in a blink of an eye. At 220 MPH /354 KPH, it would take the vehicle 10.2 seconds to go the length of the long straight, and 2.04 seconds to travel the short straight, and 4.1 seconds in each corner.

Pit Stops

How vital are pit stops? For every second spent in the pits, the driver will give up 323.4 Feet or 98 Meters of track space. In five seconds, they give up half a straightaway of distance. This means that if two drivers enter the pits simultaneously, and one leaves the pits a half-second quicker, that driver gains 162 feet or 49 Meters of distance on the other.

Corners

Depending on the vehicle’s path and speed, the cars will produce approximately 3.8 G’s pushing on their Center of Gravity. That means there is 3.8 times the weight of the vehicle pushing the vehicle away from the corner and towards the wall. Also, four times a lap, there is 3.8 times the weight of the driver pushing on the driver. If a driver weighs 175 Pounds, 79 Kilograms, there will be 665 pounds or 301 Kilograms pushing on their neck four times a lap.

An Explanation

Every time they drive through a corner, the path of the vehicle creates an arc with a given radius. The arc is created by the amount the driver moves the steering wheel. You will hear the announcer call the arc – “the line the driver is taking through the corner.” The driver’s speed, where, and how much they move the steering wheel will determine “their line,” which determines if they make it through the corner, spin the vehicle, or hit the wall, or both. During the 200-lap race, a driver will make these decisions 800 times.

Even at Indy, it’s all about the driver’s equation.

Old Scotti School and Vehicle Dynamics Institute (VDI) students are familiar with the phrase “The Driver’s Equation.” The less the driver moves the steering wheel, the bigger the radius – the bigger the radius, the faster the driver can move through the four Indy corners. The faster the driver moves through the corner, the higher the force pushing on the race car’s center of gravity. With too much force, the driver will lose control – too little they are not maximizing the vehicle’s capability and will lose track position.

You will hear the announcers talk about “Push” and “Loose,” which refers to Understeer and Oversteer.

Understeer (the “push”) is the condition where the front tires lose adhesion while the rear tires remain in contact with the pavement. The car tends to travel straight ahead, even though the driver is turning the wheel; too much understeer results in hitting the wall.

Oversteer (“loose”) is the condition where the rear tires lose adhesion while the front tires remain in contact with the pavement. The back end of the car will slide out; actually, snap out is a better explanation.

To get a clear understanding of understeer and oversteer, a basic discussion of the laws of physics is required. When the driver turns the steering wheel, there is energy pushing on the race car’s Center of Gravity (CG). The amount of energy (which can be measured in G’s or pounds or kilograms) is determined by how much the driver moves the steering wheel and how fast they are traveling. The more speed and the more steering, the more energy is pushing on the vehicle. Think back to high school physics and the laws of motion, “for every action; there is an opposite and equal reaction.” So, if there is a force pushing on the CG of the race car, there has to be an equal and opposite force pushing back – that force pushing back is created by the friction the tires make with the track.

The average Indy car weighs 1600 Pounds or 725 Kilograms. If the Indy car is driven around a corner that created 1600 Pounds or 725 Kilograms pushing on the CG of the vehicle, that would be 1 G is pushing on the CG of the vehicle.  The tires would be pushing back 800 pounds or 363 Kilograms front and rear in a perfect world. This would be called neutral steering.

You will also hear the announcers talk about the vehicle changing from under to oversteer, or vice versa, as the car is moving through the corner. The driver will be in the 1320-Foot turn or 399 Meters for about 4 seconds, and at the rate of 220 MPH or 354 KPH, which is approximately 323 Feet in a Second or 98 Meters in a Second, all while the rear tires are breaking loose (oversteer) or the front tires are losing adhesion (understeer). If the vehicle oversteers, the rear of the vehicle will more than likely hit the wall. If the vehicle understeers, it more than likely is the front of the car that hits the wall.

With oversteer, a small movement of the steering creates a big movement in the rear of the race car. With understeer, the driver is moving the steering wheel, and the vehicle is not turning and heading toward the wall at 220 MPH or 354 KPH.

With the advent of cameras in the vehicle, you can look at the driver’s hands; when entering the turn, there should be one steering wheel movement. If their hands are moving while in the corner, they are trying to balance the car, and nothing good will happen—more on balancing the car later.

Forces on the Race Car

If the Indy Car weighed1600 Pounds or 725 Kilograms at 3.8 G’s, there would be 6080 Lbs. or 2759 Kilograms pushing on the car’s center of gravity.

Which would mean that both the front tires and rear tires would have to push back with 3040Lbs or 1379 Kilograms to keep the car balanced.

Also, you will hear the announcer say the driver is chasing the balance – what that means – is with their hands – (the steering wheel) and their foot (the gas pedal) – they are controlling the amount of force pushing on the race cars center of gravity and the force pushing back.

From a driving standpoint, what is hard to do and considered by many to be a dangerous characteristic, is a vehicle that goes quickly from understeer to oversteer, or vice versa. You hear it often when watching an Indy race; the announcer or commentators will say that the car was a push (understeer) entering the corner and loose (oversteer) coming out. This condition is one of the very few that will cause an Indy driver to slow down.

Driving an Indy Car through a Slalom Course

For those who have attended a Scotti School in the past or a VDI program in the present, a good reference point would be the slalom course. Those former students are all familiar with the 80% requirement. So what would the numbers be if you were to drive an Indy car through the slalom? What numbers would you need to reach the 80% requirement?

Using 100% of the 3.8 G’s of the Indy car’s capability would produce a speed of 83 MPH or 134 KPH. To achieve the 80% goals, you need to drive through the slalom exercise at 74 MPH or 119 KPH. Also, consider that at 74 MPH and 119KPH, you would be moving 109 Feet Per Second or 34 Meters Per Second. You would have about .6 seconds from cone to cone.

The difference between using 100% and 80% is 23MPH/ 34Feet Per Second or 37 KPH/10Meters Per Second.

Those who have achieved 80% in the slalom know the level of skill required to accomplish that.

Back To Indy

The radius of the corners is approximately 840 Feet or 256 Meters. Using those numbers, if a driver moves through the corners at 200 MPH or 322 KPH, they are pulling 3.2 G’s. At Indy, that is slow and low loads on the car.

If the driver is using 220 MPH or 354 KPH, they are pulling 3.8 G’s.

A phrase often heard in our training past and present – small changes in speed produce big and dramatic changes in the vehicle’s behavior.

As the driver is moving through the corner at the speeds mentioned, a small change in throttle position or steering wheel angle can produce devasting results. A change of 10% in speed has produced close to a 20% change of the force pushing on the vehicle’s center of gravity.  All this happening at 220 MPH or 354 KPH – that’s why those guys and gal need to be the best of the best.


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