[graaja]

Originally Posted by Sutripta

The biggest problem with these systems is trying to work out how much the vehicle will squat under acceleration.

There is a parameter called "Pitch" that takes care of this. The App provides guidance like what value to use for the type of suspension - soft, sporty, and very stiff suspensions. I think the app compensates for the "squatting under acceleration" based on the value entered for the "Pitch" parameter.

[Sutripta]

^^^
Question is how to get the value for 'pitch'. For the average enthusiast, it is essentially a guestimate. And it directly affects the readings computed.

Regards
Sutripta

[graaja]

Originally Posted by Sutripta

^^^
Question is how to get the value for 'pitch'. For the average enthusiast, it is essentially a guestimate. And it directly affects the readings computed.

Regards
Sutripta

I just followed the PerfExpert guideline and provided 3 as pitch for the Jetta and Polo, as these suspensions are neither very soft nor very stiff.

However, there is an interesting procedure to accurately adjust pitch described in the PerfExpert forums. You could give it a try.

http://www.perfexpert-app.com/forum/...-le-pitch.html

Use Google Translate to translate the page.

[Sutripta]

^^^
If I understood what was being proposed in the link, it was
use an independent estimator for speed
fiddle with the value of pitch till speed matches for PerfExpert and the other method.

Have I got it right?

Regards
Sutripta

[graaja]

Originally Posted by Sutripta

^^^
If I understood what was being proposed in the link, it was
use an independent estimator for speed
fiddle with the value of pitch till speed matches for PerfExpert and the other method.

Have I got it right?

Regards
Sutripta

Yes. That is what I understood from the link as well.

But I do not understand how pitch would affect speed calculation. The speed is calculated from measured acceleration and the measured acceleration is on the actual acceleration on the wheels after the losses which would include transmission loss, rolling resistance and the acceleration loss due to pitch.

There is another link in the same thread which says access denied.

http://www.perfexpert-app.com/fr/for...terminer-.html

Let me see if getting membership to the PerfExpert forum will open up this thread.

EDIT: Even after I created an account in the forum, I get "Access Denied" error

[Sutripta]

Fiddling with parameter values to match results are hardly the hallmarks of a finely tuned precision instrument!

It is not to put down this class of 'dynamometers', far from it. For its price it is a steal. But one should also know its limitations. Even better if one knows why the limitations.

Change in pitch will affect results. Applies to ALL similar setups. It is a theoretical limitation. Cannot be worked around (in the context of mobile phones) by using costlier hardware, or better crafted (= normally costlier) software, or by loading the software with bells and whistles.

Originally Posted by graaja

But I do not understand how pitch would affect speed calculation.

It comes from the fact that one can't distinguish between (and thus separate) gravitational forces from inertial forces.

Regards
Sutripta

[a4anurag]

Inspired by Graaja Sir, I too installed the App and went off for a test today morning en-route home from work. Got a closed patch of road (ORR, Hyderabad). Took advantage for 30 minutes.

Here are some images:





























Web links for the 4 run's:

Run 1

Run 2

Run 3

Run 4

[Quadrant55]

Originally Posted by graaja

Attachment 1610364

In this thread, I would like to write about an interesting Android App called “PerfExpert” that can be used to do dyno test of cars. From the data I got for my Jetta and Polo, and from the reviews by many other users online, this App is quite accurate in the dyno results.

I immediately decided to give this App a try and downloaded and installed the App from Google Play. The App costs INR 650.

Hi
Thanks for sharing this.
Gave it a shot after reading your thread, its pretty accurate if we key in the right parameters.



It costs 1100/- now. But worth every penny.