Signal to Noise	Mercedes-Benz Specs	Coupes	Convertibles	Sedans	Miscellanea

If you read enough magazines, you may notice that some test numbers vary wildly between publications. Many of them vary by a half-second or more in the quarter. Some people may say, "that's due to the drivers", but I can assure you that's not true. Magazines use professionals, and they know how to drive. One writer may be faster than his or her peers, but the difference is not a half-second in a straight line. In an attempt to get to the bottom of this, some owners have gone to their local drag strip (or used their G-Tech, which can be off). To their surprise, many have found that they cannot replicate the numbers they see in the pubs.

I can tell you first hand why the numbers are at odds; the testing methods differ. That sounds easy and makes sense, but you still don't know "why".

Internet posters are full of theories, but the "why" is probably rollout. I can explain how rollout is used in testing, but first there a few things you have to understand.

At an NHRA drag strip, each lane has a staging area. That's the area the driver is supposed to be in when the light turns green. The staging area has two light beams that cross the lane. Those lights are used to help the driver position their car in the staging area. In each lane, the light emits from one side, and is picked up by a sensor on the other side. When the tires interrupt the light beam, that triggers the staging lights, which the driver can see. The first light beam is the pre-staging light. Its sole function is to alert the driver that they are getting close to the second light, which is the staging light. Once the second light is illuminated, the driver comes to a complete stop.

This is how it works from the driver's perspective: the driver slowly pulls the car into the staging area. They creep forward. At some point, their tires interrupt the first light beam, and the pre-staging light turns on. The driver then creeps forward very slowly until the tires interrupt the second light beam, and the staging light comes on. At that point, the driver stops the car waits for the green light on the tree.

After both drivers are staged, the yellow countdown lights will start. First the top countdown light will illuminate. A half-second later, the second countdown light will illuminate. A half-second later, the third countdown light will illuminate. After another half-second, the green light will illuminate. At that point, the driver will press the gas pedal and go. However, the timing clock won't begin until the pickup from the staging light is receiving a light signal. It will not receive that signal while the tire is in the way. The tire must roll forward before that happens. Typically, the car has to move forward about a foot. At the point where the tire has moved forward enough to clear the staging light, the car is traveling at a speed. That speed is about 3 MPH, and that's called "rollout".

This brings us to why many owners can't duplicate the numbers at a track. Car magazines don't typically use tracks. If they did use tracks, they'd have to rent them for months on end. It would be cheaper to simply buy a track. For performance numbers, most publications use data acquisition boxes. These electronic boxes are extremely accurate, and eliminate the need for a track. For example, a Racelogic VBOX can