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"  Of the ingredients needed to make a car go around the famed 2.5-mile oval in Indianapolis at speeds in excess of 230 mph, some are familiar to even the most casual fans: plenty of horsepower, the aerodynamic wings that push the car to the tarmac and a courageous driver. But don&amp;#039;t forget perhaps the most crucial element of all: the car&amp;#039;s ride height, the distance between the bottom of the car and the track surface. If the Indy 500 teams are off by the thickness of a few sheets of paper, a once-front-running car can find itself laps down in a hurry.  &amp;quot;You don&amp;#039;t want to set the car too low because you hit the ground and lose downforce,&amp;quot; three-time Indy 500 winner Helio Castroneves says, &amp;quot;and you don&amp;#039;t want to go too high because you don&amp;#039;t make enough downforce. There&amp;#039;s a tiny, tiny window\u2014call it the sweet spot\u2014where the ride height is perfect, and, right there, that&amp;#039;s where you make the perfect amount of downforce, the tires are glued to the ground, and the handling balance of the car is also perfect. I keep saying, perfect, perfect, perfect, because that&amp;#039;s what we are always seeking.&amp;quot; An Indycar&amp;#039;s ride height is more than a uniform distance across the bottom of the car. The pitch of the car, the difference between the front and rear ride heights, is also critical. Add that to the myriad other adjustments that affect the ride height\u2014tire pressure, shock and spring rates, slight bumps in the paved surface and the angle of the wings\u2014and you have a vehicular Rubik&amp;#039;s Cube that&amp;#039;s far easier to get wrong than right, especially with the minute adjustments involved. The width of 10 sheets of printer paper (about 40/1000 of an inch) is a big change for an Indy chassis; a more granular change would be 20/1000, or five sheets of paper. &amp;quot;With such a small change in ride height, you can lose it all and the car is slow, or with one adjustment, it can all come back and feel perfect,&amp;quot; Castroneves says. &amp;quot;It&amp;#039;s crazy to think about how sensitive it is like that.&amp;quot; Finding the right setup is as much black art as engineering exercise. Most IndyCar teams use data loggers that measure the right height from two ways as the car runs on the track. Lasers mounted front and rear of the car measure the distance to the ground 1000 times per second, and potentiometers on each shock absorber capture the minutia of how the car sits at all times. Those measurements, combined with feedback from the driver, help the engineers determine where to set the car.  Then there&amp;#039;s another variable\u2014the weather. If Indianapolis were completely enclosed and had no wind or barometric pressure fluctuations, it might be possible to find and maintain a perfect ride height at all time. But as Castroneves&amp;#039;s engineer Ron Ruzewski knows, Indy is anything but a perfectly serene laboratory environment. Indy is messy, and that means constantly adjusting the car. &amp;quot;If you know you&amp;#039;ll be running in traffic, or if you know there&amp;#039;s a headwind,&amp;quot; he says, &amp;quot;you know you&amp;#039;ll have more or less air across the front of the car and have to adjust for it. If you run your car with the front higher than the rear, you&amp;#039;ll be less affected by air on the nose, while if you run nose-down, like a wedge, you&amp;#039;re more susceptible to aero changes at the front. At Indy, in particular, it&amp;#039;s all about maintaining a balance front to rear... It&amp;#039;s a constant circle we&amp;#039;re working on.&amp;quot; By raising the nose of the Castroneves&amp;#039;s car by 20/1000 of an inch\u2014 which equates to about one-tenth of a percent shift in dynamic weight from the front tires to the rear tires\u2014Ruzewski could make the car perform perfectly as he rockets through Turn One. Or the driver could find that the tiny change makes the car understeer too much to his liking.  Simply put, the difference between Happy Helio and Angry Helio all comes back to five sheets of paper closer to or farther away from the ground. Castroneves, a perennial favorite to earn pole position at Indy, found his car to be outside the narrow window of perfection during last weekend&amp;#039;s qualifying for the upcoming Indy 500. The miniscule miscalculation cost the Brazilian. His 225.216-mph qualifying average was only 2.256 mph off of Alex Tagliani&amp;#039;s 227.472-mph pole speed, but Castroneves, (who&amp;#039;s also a Dancing with the Stars winner), will start Sunday&amp;#039;s Indy 500 from 16th position. The team has already tweaked his ride height in advance of the race, but we won&amp;#039;t know until Sunday whether those fractions of an inch will put Castroneves back in the winner&amp;#039;s circle. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/adventure/sports/a6650/the-fractions-of-an-inch-that-decide-the-indy-500/>