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Old 11-16-2012, 01:43 AM   #1 (permalink)
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Talking effect of lsd on mpg

I've been wondering for quite a while what effect installing an LSD would have on my mpg. The last time I was out in Tahoe skiing w/ my friend who lives there, I couldn't hardly get out of his driveway w/ my 2wd truck, even with chains on. An LSD diff would have helped there.

I'm eyeballing the Detroit trutrack LSD. It uses worm gears in some sort it f fancy arrangement to provide continuously variable power to whichever wheels have traction.

Does anyone here have any insight into what kind effect this hardware would have on mpg in either foul weather or fair?

It's possible that an alternate gear arrangement could increase mechanical losses in the diff (or the inverse), but it's also possible that reduced wheel slip in less than perfect conditions could have a positive affect, not to mention being all kinds of fun to drive in the corners (I'm sure there are unusual circumstances in which one's ability to effectively utilize power transfer through the wheels to alter a line in a corner could have a positive effect on mpg ;-P. )

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Old 11-16-2012, 01:48 AM   #2 (permalink)
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From what I've heard, it would be a strange trip.
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Old 11-16-2012, 02:38 AM   #3 (permalink)
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I've not noticed any difference from installing an LSD on my car, but I wasn't paying attention to any differences when I did it.

If it's a helical, you won't really notice any extra drag or frictional losses... Dunno about clutch-type or viscous LSDs.
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Old 11-16-2012, 09:32 AM   #4 (permalink)
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I think viscous LSDs have a little bit of parasitic drag, probably not much. Nothing to worry about IMO, because you don't hear about LSDs having significant cooling issues. If they dissipated a lot of energy as waste heat (to the point of it being a concern) they would need an actual cooling solution.
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Old 11-16-2012, 10:16 AM   #5 (permalink)
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limited slip diffs, whether they're clutch (cone, disc, or 'phantom') or helical or even hydraulic piston (varilok) or dog-clutch (Aussie, Detroit, etc) don't have any way of affecting mileage when you're traveling in a straight line with equal pressure in your tires, because the business parts of the system are all built into the carrier, and essentially static when there's no difference in rotational speed between the left and right wheels.

When you turn a corner, clutch type LSD's necessarily scrub but as serialk11r points out, if they really created much drag they'd need cooling because that energy has to go somewhere. Helical systems are more about leverage than friction and when there's very little difference in the torque distribution between wheels (turning a corner, both wheels on pavement, there is wheel speed difference but not a drastic difference in torque delivery, both are receiving power from the engine pushing the vehicle forward) - they don't have any more excuse to create drag than the gears in your transmission.

I can think of no time a traction aid would affect mileage, except by improving it when you would have been stuck & spinning a wheel, and instead you're moving.
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Old 11-16-2012, 02:54 PM   #6 (permalink)
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translation: Limited Slip Differential (LSD), not Lysergic acid diethylamide (LSD).
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Old 11-16-2012, 04:11 PM   #7 (permalink)
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Ooooooooooooh...

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