How We Test: Behind the Numbers with Edmunds Vehicle Testing Team

How We Test: Behind the Numbers with Edmunds Vehicle Testing Team

Acceleration test is done once the brakes are cool. While we’re waiting, let’s review our fuel policy. Generally, we use the minimum required fuel octane for our test runs, and if a manufacturer recommends a higher grade “for best performance”, we’ll use that. The only exception is when 93 octane is recommended, a grade of gasoline that is not available here in California and many other states. Fortunately, the number of cars that present this problem are few and all of them list 91 octane as the minimum requirement, a fuel that we can easily obtain. If the runs come out a little slower than the manufacturer claims, that’s okay. It is the manufacturer’s fault if it optimizes the engine for a grade of fuel that is not widely available.

All published acceleration data – quarter-mile times and trap speeds plus 0-60 times and all intermediate speeds – come from best single runs. In other words, we don’t mix and match. But that best race requires a skilled driver who can realize the ideal launch technique that optimizes speed yet doesn’t damage the car. This is no easy task due to the wide variety of vehicle configurations, engine outputs, transmission types, gear ratios and tires on the market. And then there’s the traction control system, launch control, and a variety of sport settings.

When testing a car with multiple adjustments, we’ll do a first pass with all settings at default, ignoring electronic enhancements to establish a baseline number. After that, more aggressive settings are engaged to see if they represent any real improvement.

For vehicles with manual transmissions, some cars are quicker with moderate wheelspin at launch, while others are quicker without any. Some cars like a little clutch slip; Others require instant clutch engagement and lots of drivetrain shock. Trial and error is the only way to know for sure which technique is best.

Vehicles equipped with automatic transmissions don’t require as much imagination. If this gives a better test result, we will brake-torque the vehicle by revving the engine to the start line while the brakes are held in check. Often, a simple break-off, throttle-on technique is best, as electronic stability control in many cars will not allow simultaneous brake/throttle application.

Automated manual transmissions require a similar brake-torque technique, even though there is usually no torque converter and the transmission may be damaged. The use of simultaneous brake/throttle application on such a transmission can, at times, result in rapid acceleration. This is a technique we use under the assumption that most of these cars have drivetrain protection that will prevent this behavior from destroying the clutch pack. It’s an unrealistic technology for real-world driving, but some cars are significantly slower without it.

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