Thursday, September 01, 2011

Of G's and dBs (Lancer v. Jetta v. Element)

Ever since Jeremy Clarkson road-tested the Nissan GT-R in Season 11 of Top Gear*, I have wondered how many G's I might pull in my car on the average drive to and from work.

[How many G's do you feel when accelerating quickly?]

G-force is a measure of acceleration due to gravity. On Earth, an object accelerates down at 9.8 meters per second per second. Sitting at our desks, we experience this as 1G in the downward direction, but zero G's in the forward-backward and side-to-side directions.

Anyone who has accelerated quickly onto the highway knows, though, that feeling of being pushed back into your seat as the force of the car pushes against your back. It's the same thing you feel when accelerating quickly on a roller coaster ride. So how many G's do I pull doing that quick acceleration onto the highway?

To find out, I took an accelerometer home with me last night in my 2006 VW Jetta GLI. I experienced the most acceleration when I went from a near dead stop up to highway speeds on the interstate on-ramp. Even then, my peak forward-backward acceleration was only 3.0 meters per second per second -- less than a third of how strong gravity pulls down on me all the time! I was expecting more, frankly.

[Echo Romeo's peak acceleration of about 3.0 meters per second per second when getting on the highway: Pretty weak sauce. Click on the graph for a bigger view.]

To see what a car with a real racing engine could do, Buzz Skyline took his car, a 2005 Mitsubishi Lancer Evolution VIII RS, out for a spin. The difference was amazing. With almost twice the horsepower, the Mitsubishi throws the driver back into the seat much more violently than the VeeDub. Buzz got about 0.85 G's on his quickest acceleration. But his is a race car. (The 'RS' stands for Rally Sport.) What about the other extreme? What about a strict commuter?

[Buzz Skyline's peak acceleration of 8.5 meters per second per second translates to about 0.85 G's. Click on the graph for a bigger view.]

To find out, The Mathlete took our accelerometer to work in her 2006 Honda Element EX-P. Though there are some high peaks in her data, they lasted for a split second and weren't sustained accelerations of 5-10 seconds like Buzz and I recorded. Looking only at the sustained accelerations, it looks like Mathlete's maximum acceleration was about 2.5 meters per second per second. Just by comparing graphs, though, you can see the Mathlete is a much steadier driver than Buzz and I with her near-constant acceleration.

[The Mathlete's accelerations which peaked around 2.5 meters per second per second. Click on the graph for a bigger view.]

So there you have it. If you're a tame driver, you're likely experiencing the same accelerations as The Mathlete. If you have a sportier car, then your numbers might be more like mine. If you have a tuned race car, then Buzz's numbers might be what you'd expect. In any case, I was disappointed to find that none of us pulled anything close to the Six Flags Superman ride no matter how hard we mashed down on the accelerator pedal.

Just because I was having so much fun using gadgets in the car, I decided to also see how loud my commute is. When I leave work, the weather is usually so pleasant that I drive for a while with my windows down. It's not until I've been on the highway at interstate speeds for a few miles that I finally get tired of the noise and roll up the windows.

So I wondered: Sitting in traffic with the radio turned up and noisy trucks idling and revving next to me, or speeding along with the wind whipping through the window, how many decibels (dB) of noise am I exposed to? Enough to do damage to my hearing?

A free decibel-o-meter app helped me to find out. Yesterday, with the windows down, I recorded a peak of 99 dB. The average noise, however, seemed to stay between 80 and 90 dB. According to the National Institute of Deafness and Other Communication Disorders, prolonged exposure to noise levels of 85 dB or more can cause noise-induced hearing loss. Oops.

My only consolation is knowing that Buzz is likely subjected to more noise in his race-enhanced Lancer. Knowing that he'll go deaf faster than me makes me feel a little less sad that he can pull three times as many G's as me. Can't win 'em all.

*Watch this video starting at 6:00 minutes to see what I'm talking about.


  1. This post makes it sound like I drive like a grandma. Those of you that have driven a pre-2007 Element understand that the car itself has a complete lack of acceleration, it accelerates like a tank. There are many lovely things about the Element, it has lots of room and the interior is water proof making it easy to wipe off bike grease or maple syrup. Acceleration is not its strong suit. It's not me, its my car!!! In my old Mazda3 I was quite the speedster! Oh, and "GET OFF MY LAWN! AND I'M NOT GIVING YOU YOUR BALL BACK!"

  2. @Mathlete - The data speaks for itself, lady!

    P.S. - Never thought I'd see the day when "lovely" and "grease" were used in the same sentence.