Logged speed no 'linear'

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Topic: Logged speed no 'linear' (Read 2112 times)

vtraudt

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	Logged speed no 'linear' « on: September 17, 2020, 08:36:49 AM »

What is causing the logged speed (here: TT225, 6 spd. Me7.5, Me7Logger) not showing a linear behavior with rpm.
The logged speeds are too high at low and high rpm, and too low at midrange rpm.

Obviously, with fixed gear ration and tire size, the relation should be linear.

https://scontent.fdet1-1.fna.fbcdn.net/v/t1.0-9/119789025_3243989205655901_194649457966324830_n.jpg?_nc_cat=101&_nc_sid=825194&_nc_ohc=cOJyEj1T_YwAX_vz8-7&_nc_ht=scontent.fdet1-1.fna&oh=96bb54601e7e8dffe16b44d346dc7cef&oe=5F892B76


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2002 Allroad 2.7T 6spd stage 2
1998 A4 1.8T 5spd stage 3
1996 A4 2.8 auto stock

timus

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Polo 86c2f 1.8T AUM

	Re: Logged speed no 'linear' « Reply #1 on: September 17, 2020, 09:13:03 AM »

I would guess that's because of the fact that car speed is received from abs/cluster once per some time by can message, and rpm is measured direct from crankshaft. This introduce precision loss on vss and some lag between one and another.

Or maybe someone else have better explanation


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vtraudt

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	Re: Logged speed no 'linear' « Reply #2 on: September 17, 2020, 09:28:55 AM »

Quote from: timus on September 17, 2020, 09:13:03 AM

Wheel speed sensor (i.e. wheel revolutions) would be my guess.


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2002 Allroad 2.7T 6spd stage 2
1998 A4 1.8T 5spd stage 3
1996 A4 2.8 auto stock

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