TALLADEGA, Ala. -- Precise calculations, computer-animated drafting and wind-tunnel testing are hallmarks of good engineering. But sometimes the predicted results don't match what happens in real life.

And that's the time when you pull out the reciprocating saws and "engineer on the fly." Which is why Tuesday's Sprint Cup test at Talladega Superspeedway could be considered the Case of the Incredible Shrinking Spoiler.

A truer test

Talladega is one thing, but the focus is on Charlotte.

• Complete story
• Photo Gallery

The 24 cars that participated in the test started the day with restrictor plates slightly larger than an inch in circumference and a 4 1/2-inch tall, U-shaped rear spoiler that included 2-by-12-inch extension flaps on either end. But by the time the test ended, the flaps had been sawed off and the spoiler narrowed 2 inches from its original 64 1/2-inch profile.

So the spoiler with which NASCAR may return in April may not look radically different than the one that was on the car before the advent of the rear wing three years ago. And, according to director of competition John Darby, that's why you need empirical data to confirm or disprove your theories.

"Things on paper and even on wind tunnels look very attractive sometimes, and then you turn the lights on in the room, they have a different appearance," Darby said. "The aero formula and the engine formula we came here with were correct. The relationship between the two probably wound up exactly to what we started with, but at a little bit of a lower scale by the end of the day.

"What we don't have in wind tunnels and what we don't have, even with the best engineers we work with, is the input from the guys who are out there holding the steering wheels. They're the ones actually feeling all the effects. And if they're not comfortable, then we're not going to have a good race, and that's what we're here to do."

Finding the "sweet spot," where the balance between horsepower and drag make for a competitive and comfortable car, can be a tricky formula, Darby said.

"The three things that we work with at restrictor-plate race tracks that ultimately control everything that surrounds the performance of the car are aerodynamic signature, the restrictor-plate size, and rear-end gear," Darby said. "There's a real delicate balance between the three of those that helps us contain the speeds to what we're looking for, as well as keeping the drivers happy."

The idea behind the bigger plates and wings seemed sound at first, especially when single-car speeds during the morning session were exactly as predicted. But Darby said it quickly became apparent in drafting practice that once cars lost the draft, they weren't able to catch back up.

"Right before lunch, we asked about a half-dozen competitors to go out and run nose to tail for a few laps, just to give us an early indication of what drafting speeds may appear," Darby said. "And they weren't ridiculously fast. They were still in the ballpark.

“

... we had a lot of conversations with the drivers and that's when it became apparent that we had too much drag.

”

-- JOHN DARBY

"But as you add more cars to the draft, the speeds will continue to climb. So first thing after lunch, we started a drafting session and had some pull-up speeds that were a little faster than we cared for. And we had a lot of conversations with the drivers and that's when it became apparent that we had too much drag. It was good for closing up while you were in the middle of the pack, but if somebody got shuffled to the outside, that big spoiler became a parachute and sucked them backwards just as fast. That typically doesn't make for a good race."

In addition, racing speeds began to climb above what Darby and vice president for competition Robin Pemberton felt were within their comfort range.

"I think the big bad-ass lap of the day was 202 and some change," Darby said.

"That was an average lap," Pemberton added. "There were places on the track where it was slower, and also much faster."

In fact, some drivers reported hitting speeds close to or exceeding 210 mph. But Pemberton admitted the bigger worry was the extreme closing rate between cars. Nearly every car in the garage had severe scrapes on the nose and rear bumper, the after-effects of some severe bump-drafting.

"We started off with a reasonable package that was pretty safe on restrictor-plate size and spoiler, got the guys comfortable with their cars and let them draft in the early afternoon," Pemberton said. "They gave us their feedback on what they thought their cars were doing in the draft. The feedback was the cars were stable but the closure rate was a little too much at some points. And that's what we spent most of the afternoon working on, was trying to slow that closure rate down."

So that's when the balancing act began. NASCAR officials downsized the restrictor plates twice, and then asked teams to first lop off the spoiler extensions, then narrow the blade an inch on each side, in an effort to limit drag.

"If you fall away from the draft, it's like having a huge parachute on your car and you watch the pack drive off into the sunset," Darby said. "And that's not good for competition. A lot of the spoiler trimming we did was to give the teams back the ability to stay with their competitors, have the confidence that as they raced, they not only could stay with the draft but have enough closure speed and horsepower to successfully pass each other."

At the end of the day, the package seemed to satisfy both NASCAR and a good percentage of the garage area.

"We've got a very good starting spot to go home with, maybe fine-tune on it a little bit," Darby said. "I'll predict right now we'll probably come back [in April] with a straight-top spoiler. The good thing about that is it will overlay the proposed spoiler we've got for Daytona, so the tracks in some ways come back to being more similar."

So the Talladega spoiler as it stands today would be one-half inch taller and 2 inches narrower than the spoiler proposed for tracks without restrictor plates.

And as always, NASCAR reserves the right -- all the way to the conclusion of the final practice session -- to tweak the formula when the series returns next month.