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Calculating torque at the wheels w/GTech
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<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial size=2>In an
attempt to pacify myself until Saturday when I hope to have my car on a chassis
dyno, I decided to try to calculate torque at the wheels from forward
acceleration measured in G's by a GTech Pro performance
meter.</FONT></SPAN></DIV>
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size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial size=2>The
front tires break loose in 1st gear at about .50 Gs, but in 2nd I can pull .40
Gs max. So I begin by conservatively estimating gross vehicle weight at
2700 pounds including driver and passenger. Where the rubber meets the
road the force must be equal to .40 times the vehicle weight, or 1080
pounds. To get foot-pounds of torque, I need to know the feet (of
leverage), so I take the wheel diameter of 22.7 inches, divide by two to get
radius, and divide by 12 inches to get feet, yielding 0.946. Actual torque
at the wheels is then calculated to be 0.946 feet times 1080 pounds, or 1021.5
ft-lbs.</FONT></SPAN></DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial size=2>To
calculate theoretical torque at the crank I must divide by the final drive ratio
(3.67) and again by the 2nd gear ratio of 1.94 (which is what my semi-wide ratio
A3 gearbox has). The result this final calculation
is...</FONT></SPAN></DIV>
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size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial size=2>143.5
ft-lbs of torque.</FONT></SPAN></DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial size=2>I'm
assuming this is about what I might see on a chassis dyno or maybe even
less. It should truly be "net torque" after all losses. If
losses through the drivetrain were 20%, I'd be pushing about 179 ft-lbs of
torque. </FONT></SPAN></DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial
size=2>Say... we're talking about the likes of VR6 torque here, are we
not? :)</FONT></SPAN></DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial size=2>Can't
wait until Saturday!</FONT></SPAN></DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial
size=2>Bradley</FONT></SPAN></DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial size=2>'86
Scirocco 16V 2.0 "T"</FONT></SPAN></DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial
size=2></FONT></SPAN><SPAN class=54371305-12101999><FONT color=#000000
face=Arial size=2><A
href="http://dns.effervescent.com/vw/">http://dns.effervescent.com/vw/</A></FONT></SPAN></DIV>
<DIV><SPAN class=54371305-12101999><FONT color=#000000 face=Arial
size=2></FONT></SPAN><SPAN class=54371305-12101999><FONT color=#000000
face=Arial size=2>(updated with turbo pics)</FONT></SPAN></DIV>
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