Not really sure. http://en.wikipedia.org/wiki/Accelerometer ?

Steve

I got one of these a couple of years ago, tried it once then stuck it in the glovebox. I was running Revo at the time and not many other mods, 0-60 was 6.something IIRC. I'll have to dust it off and give it another go.

speed = distance over time

An acelerometer can measure distance by sencing g-force it can measure time with a clock devide one with the other you have speed ,thats how it works.

Just like if you sit in a ferrari with your eyes closed and a punto with your eyes closed and both acelerate to 60 you cant see the speedo but im sure you could tell which is the ferrari .you do this by feeling the g force and estimating the time.The g-tech does exactly that but obviously more acurate

thats rubbish though because some cars feel faster than others even though they are slower. one obvious one springs to ming but won't mention it here

speed = distance over time

An acelerometer can measure distance by sencing g-force it can measure time with a clock devide one with the other you have speed ' date='thats how it works.

Just like if you sit in a ferrari with your eyes closed and a punto with your eyes closed and both acelerate to 60 you cant see the speedo but im sure you could tell which is the ferrari .you do this by feeling the g force and estimating the time.The g-tech does exactly that but obviously more acurate[/quote']

absolute bobbins!! all it could work out from that is what sort of g-force was being produced, and for how long...

If it knows the rate of acceleration and the time then it can calculate distance and speed. It's fairly simple physics. However I have doubts over how accurate the accelerometer is, I think it even has a statement in the documentation saying it loses accuracy on cars with a 0-60 of less than 8s or something like that.

I have very big doubts over the accuracy of these too...

I use a AP-22. Best standard was 8.6sec to 60 with the fuel light on..

I reckon mine's slower once the fuel gets low - does the car drop the pace slightly to extend the range or just suffer fuel starvation?

I reckon mine's slower once the fuel gets low - does the car drop the pace slightly to extend the range or just suffer fuel starvation?

It might be a case of the fuel getting hot as theirs less fuel so quicker to heat up.

Just done another time run last night remapped. best was 7.6sec to 60. So an empty tank made no difference. Sounds about right. As I have 160bhp and a PD160 autocar done in 7.1 and these make around 170-180bhp on the rollers.

it is simple physics,this model is acurate to + or - 1/10 second the latest models are acurate to 1/100 of a second and you can plug it into your PC after and it will give you lots of fancy graphs ect. I have tested 10 cars with it and it is very consistant and gives the expected times therefore after playing with it for a while i am convinsed it is acurate thats more than can be said of my spelling

but if it has no accurate reference points as it doesn't actually know how fast your going how far you've gone :confused:

Surely it uses the GPS sensor for that?

Steve

The version of g-tech I have doesn't have GPS, it's all calculated.

also gps isn't that quick in my experience

Some info on performance meters plus a test of a several different meters.

http://www.caranddriver.com/features/9380/do-inexpensive-performance-meters-work-page6.html

but if it has no accurate reference points as it doesn't actually know how fast your going how far you've gone

The reference point for an ecelerometer is 0 inotherwords stopped

The reference point for an ecelerometer is 0 inotherwords stopped

what is that supposed to mean?

if it has no feed from the car how does it accurately know how fast you are going or what distance you have convered?

The cheap ones that I believe we are talking about here don't use GPS.

Ben you should know what they are like you've used mine!! Remember losing the instructions??

doesn't mean i understand or trust the results though

It explains it in the instructions.

magic?

I've got the basic G-Tech model too - it's a fairly fun device, but is definitely better than trying to 'feel' the performance fo a car by your own perception.

It does work out the speed and acceleration from 'G' force, note that G is a measure of acceleration (for reference 1 G equates to an acceleration of 1 metre per second, per second, or in more common units, adding 22 mph per second)

If you know how fast something is accelerating, and you know how long it has been doing that, you can work out what speed it is travelling at. E.g. if you take a car accelerating at 1 'G' for 2 seconds, it will be doing 44mph. (hence the unit knows how fast it is going.

If you know how long a car has been doing a speed, you also know how far it has travelled.

For this example, the car will be averaging 22mph over two seconds, it will have travelled 19.7 metres. (hence it knows when it has done 1/4 mile etc.)

To do these calculations, the unit has to be kept level, (so you need to attach it level to the widscreen) and you need a straight and LEVEL piece of road. Also every test has to start from rest, since the unit needs a base point.

I think it's generally good enought to get a reading within +/- 5 %. I think power always tends to read (almost shockingly) low compared to flywheel figures because it measures power accelerating the vehicle, much 'unmeasured' power is going into losses such as aerodynamics, transmission losses etc. etc.

Thanks Franv8 I was just going to say all that

LOL @John - yes, thanks for the useful post

Steve