I have a G-Tech Pro and like it. Here's how it works. Its basically a
very accurate accelerometer, a stop watch and some clever computer
programming. There is a single 3-position switch which also acts as a
button and a LCD display. There is only one accelerometer. So at any
time you can either measure forward/backward acceleration or lateral Gs
but not both. To get accurate measurements the unit must be dead level
and pointed exactly forward or exactly 90 degrees sideways. This is not
hard because the unit will read 0.00 when its level and the car is
sitting still. This is the only tedious/annoying thing I have found.
It is a little bit smaller and lighter than the smallest radar detector.
It mounts on the windshield using a suction cup bracket and then velcro
to the unit itself. The suction cup is very strong. I was concerned that
high Gs might loosen its grip but to date it has never come loose of its
own accord. To measure acceleration or braking use the velcro to stick
the unit to the mount in a fore and aft direction. If you want to
measure lateral G's turn the unit 90 degrees so it points to the drivers
side a pillar.
It plugs into the cigarette lighter and that's the only external
connection. On both my cars the coiled cord was stretched a little and
kept pulling the unit out of level. A quick trip to Radio Shack for a
12v extension solved the problem.
The unit operates in several modes and after a few minutes reading the
instructions its easy to set up.
Lateral G's - There a two lateral G modes - I for instantaneous and C
for Continuous (continuous actually measures the highest value that is
held for a minimum of 3 seconds)
Acceleration - The unit will measure 0-60 time. 1/4 mile speed and time.
And 60-0 braking time.
Peak HP - If you have an accurate weight of your car you can get a real
world horsepower measurement. You input the weight by tipping the GTech
until the correct number is displayed. Then accelerate through 1st and
2nd gears at full throttle. The GTech calculates HP by determining the
max acceleration during your run. It does not take into account wind
resistance.
Accuracy - I know that its consistent. I know that the acceleration
numbers I got were in line with published stats. My Audi A4 2.8 30v gave
me 0-60 of 7.3 - Audi says 7.1. My Honda delSol (1.6L SOHC VTECH) turned
in an 8.4 which seems about right.
I think the g-Force numbers are a little optimistic but again they are
very consistent. My A4 with Eibachs Bilstiens and 38psi Michelin Pilot
SX GT pulled 0.92 in continuous mode clockwise around a 100 ft circle.
Around the same circle my Honda delSol pulled -
.84 with 185/60-14 Pirelli P600 at 1/2 tread depth
.91 with 205/40-16 Nitto 450
.99 with 205/55-14 BFG g-Force R-1
All the CCW numbers were about .07g lower.
While I think all these numbers are high (I would guess the Audi really
pulls .85 - .88 as I have it equipped) what is important is that the
differences are exactly what you would expect. As a tire comparo these
numbers mimic the delSol write up that appeared recently in
GrassRootsMotorsports.
All in all I really like the GTech. Its reasonably quick and easy to
use, its tiny (I leave it in the glove box), inexpensive and its
consistent. One suggestion - if you have some buddies see if they want
to go halves (or thirds or quarters) on one. Its not something you need
more than a few times a year and it will probably last forever.
Hope this helped,
Alan
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