G-Analyst Helps You Improve Your Technique

Find The G-Spot In Seconds … Electronically

By Greg Raven
Photos by C. Van Tune
VW&Porsche magazine
July-August 1987, page 71

High performance is a game of numbers; the better the car the better the numbers. And when the enthusiast modifies his car it is usually done in search of better numbers. Some of the numbers, such as those for straight-line acceleration and deceleration, are easy to come up with. Others, such as lateral acceleration (cornering force) are more difficult.

The problem is compounded when you need to know what your acceleration is through a corner. The stopwatch can still tell you how fast you are from point A to point B but it is bereft of suggestions as to how you might be faster. For maximum performance you need to know not only where you are going but how to get there, as well.

Enter the g-analyst. Using three accelerometers in an orthogonal (right angle) alignment, the g-analyst can simultaneously measure acceleration (positive or negative) and cornering. The g-analyst then reports both numerically and visually what it has measured so in addition to the raw numbers you have a graphic representation of what they relate to.

Before it could display information numerically the g-analyst had to simplify the way in which the numbers were presented. Instead of using seconds to measure acceleration, distance to measure stopping, and something else to measure cornering, the g-analyst uses one measurement for them all: the g. The g is acceleration in feet-per-second divided by the acceleration of gravity (which is also expressed in feet-per-second). This gives us a number that is not only quite accurate but is also easy to relate to. Now we are getting somewhere.

To aid in the visual representation of its measurements, the g-analyst makes use of a concept known as the friction circle. The friction circle is an idea that has been gaining currency among engineers and race car drivers since around 1960. For ideal performance the car and driver would both be able to attain maximum acceleration in all four quadrants of the friction circle in a smooth and continuous manner. In real life this is extremely difficult to achieve, but with the g-analyst it is possible for the first time for the average person to measure his performance against the friction circle. Erratic driving is clearly shown on the g-analyst, allowing the driver to find a smoother and faster way through a turn, a series of turns, or through the entire course.

As valuable as the g-analyst wil be for some, it is not for everybody. Not only is the price a factor, but proper use of the g-analyst requires a good-size expanse of otherwise vacant pavement on which you can drive like a maniac while exploring the limits of your vehicle. A race track would be another fine test site for using the g-analyst, but this adds even more to the cost of using the g-analyst, putting it farther out of reach of the average consumer.

Another disappointment of the g-analyst is that there is no way of getting an average g rating over longer than 1 second. A longer average would allow the g-analyst to be used for skid pad testing as well as friction circle work.

Finally, accelerometers such as the g-analyst must be calibrated to the vehicle in which they are mounted. This fudge factor, if not accurate, will skew the results to one side or another. Fortunately the g-analyst is relatively unaffected by this problem, as Valentine Research claims there is less than 2 percent of measurement error for each degree of calibration error. Furthermore, using their calibration table you will usually be within 2 degrees of the correct actual calibration, which translates to less than 0.02 g of error at 0.90 g of acceleration. Any discrepancies would of course be important only when comparing one car to another. For comparisons involving one car with the same springs and anti-roll bars, the actual number generated is less important than the relative change in performance due to driver improvement, tires, etc.

The g-analyst comes with complete instructions, a learning guide, background reading suggestions, and all the hardware necessary to do your own friction circle work. If you cannot afford one yourself, one alternative would be to share the cost with several friends or with the members of your car club. The g-analyst is available from Valentine Research, Dept VWP, 10280 Alliance Road, Cincinnati, Ohio, 45242, telephone (800)331-3030.


  1. All controls are located in the display head. The accelerometer transducer is mounted separately.
  2. After entering the calibration and selecting the recording mode, the g- analyst waits for you to press the Now button.
  3. The friction circle display shows you all four vehicle dynamics simultaneously.
  4. To zero in on acceleration and braking you can eliminate lateral force from the display.
  5. Lateral acceleration can be isolated by choosing the left/right display.
  6. The axes formed by positive/negative acceleration and lateral acceleration divide the friction circle into four quadrants.
  7. The friction circle is a graphic representation of a car’s adhesion limits.