What do you think of these

[Ben_Stevo172]

Anybody bought one? And how accurate can it be? Looks like it just plugs into the cigarette lighter!

http://www.gtechpro.com/ss.html#

 

[len_beach]

I don't understand how these can possibly work without being hard wired into the ECU somewhere.

A tad cheaper: http://cgi.ebay.co.uk/GTECH-Perform...yZ122140QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[ChrisR]

I don't understand how these can possibly work without being hard wired into the ECU somewhere.

A tad cheaper: http://cgi.ebay.co.uk/GTECH-Perform...yZ122140QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

It's simple equations of motion.

All the device needs to measure is acceleration, or G, which if it has an accelerometer or whatever in it it's perfectly possible.

So by using the equation v = u + at where

v = end velocity (which on the 0-60 run would be whatever 60mph is in metres per sec)

u = initial velocity (i.e. 0)

a = acceleration (measured by device)

t = time (the unknown)

Rearrange the equation and bobs your uncle you can work out the time taken to get to 60.

 

[Justin182]

I see what he means.... how do they know the rpm ?

They claim they can pick it up from the cig lighter.

 

[d4nn3h]

I see what he means.... how do they know the rpm ?

They claim they can pick it up from the cig lighter.

Probably can pick the RPM up from the cig lighter, the alternator in the car will never produce a perfect DC voltage, there will always be some kind of interference within the supplied voltage, the device would look at this, look at the frequency of the interference (IE faster engine runs, faster alternator spins, the more frequent the interference would be) and determine how fast the engine is running in rpm.

The only time you will get a perfectly clean voltage from any supply in the car is when the engine is not running (clean voltage from the battery).

 

[Ben_Stevo172]

are these worth buying????

 

[tommyboy]

I don't understand how these can possibly work without being hard wired into the ECU somewhere.

snap

 

[ChrisR]

After clickign the link I see we're talking abotu the bigger GTech thing that does mroe than just 0-60, but as others have said you can get other info from other bits of the car without needing to hook anything up to the ecu etc.

iirc there was a heads up display system that used the cig lighter, or something to do with the coils to get the revs?

 

[Ben_Stevo172]

I copied and pated this from a website:

How does it work?
The heart of the Gtech Pro is a precision silicon accelerometer. An accelerometer is a sensor that measures acceleration, also known as G-Force. G-Force is what's keeping you in your seat as you are reading these words and if it wasn't for the seat you would be accelerating to the ground at 1G (32 feet per second per second).

Gtech Pro measures your speed and distance traveled by integrating acceleration over time. Basically, if you know how fast you are accelerating for a certain time period you'll know how much your speed has changed after that time period. So, if you start of from zero speed then you'll know what your speed is after every time period. These time periods are very small (2.5 milliseconds) and that's how Gtech Pro maintains its accuracy.

Distance is measured in the same fashion, if you know how fast you are going for a certain time period you will know what is the distance traveled during that time period.

Gtech Pro also measures delivered Horsepower, sometimes called Rear Wheel Horsepower. This horsepower includes the loss of power through the drivetrain which is usually 10-15%. The formula for Horsepower is speed times acceleration times the weight of the vehicle.

 

[C.slicker]

Can you use it to find say 50-70mph?