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Author Topic: Logged speed no 'linear'  (Read 194 times)
vtraudt
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« 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
Logged

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


« 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 Smiley
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vtraudt
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« Reply #2 on: September 17, 2020, 09:28:55 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 Smiley

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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