factory limited slip differential

[Josh.Hignight@phoenix.edu (Josh Hignight)]

We finally know what unobtanium is! 


Joshua Hignight
Student Services/Technical Services
New Mexico Campus
(505) 821-4800

-----Original Message-----
From: 16V Jason [mailto:jason@scirocco.org]
Sent: Wednesday, January 23, 2002 5:12 PM
To: Mash; Neal Tovsen; thescirocco@juno.com
Cc: scirocco-l@scirocco.org
Subject: RE: factory limited slip differential

At 01:59 PM 1/23/2002, Mash wrote:
>--- Neal Tovsen <nealtovsen@yahoo.com> wrote:
> > Thanks! So...yeah, the factory unit isn't worth
> > much. :)
> > Neal
>
>Yes, but it is better than nothing (from experience).

Really?

Assume for a second that I am at full throttle in 2nd gear at 3000rpm.  My
left wheel hits unobtanium, which has a ZERO coefficient of friction --
i.e. black ice from hell.  My right wheel is on dry pavement.

At 3000rpm, a 1.8 puts somewhere around 98 lb-ft of torque to the output of
the tranny.  Of course, this is multiplied by gearing.  2nd gear on a 16V
is 2.12:1, the final drive is 3.67... so the overall ratio is
7.78:1.  Therefore, the torque acting on the wheels is 762lb-ft.

With a 2% limited slip, the torque acting on the wheel on dry pavement is
2% of 762 lb-ft, which is 15 lb-ft.  On a 185/60-14 tire, which has a
radius of 0.67 feet, the thrust is only 10 lb... and this is at full
throttle!

10lb of thrust is basically negligible, so it's really not better than
nothing; it really *is* nothing. :)

If the Scirocco had a 30% limited slip, that value would jump from 15lb-ft
to 190.5 lb-ft. or 127lb of thrust.

On a 5% grade, the Scirocco would be pushing downhill with (2350lb * 5%) =
117lb of thrust.  So basically, if you were trying to climb a 5% grade with
a 30% limited slip and one wheel getting 0 traction, at best you would just
about stand still and not roll backwards down the hill, as you would have a
net thrust of (127-117)= 10lb of thrust pushing you up the hill.  That
ain't much.

However, you're better off than with no limited slip, where the car would
roll down with 117lb of thrust.  The 2% limited slip would drop that down
to 107lb.. but when you hit the guard-rail at the bottom, you'd probably
say that the 2% LSD did just about nothing.

Physics lesson over -- and hey Meze -- no comments about how you don't have
snow or ice where you live.  The way you drive, you need all the fucking
help you can get. :)

Jason


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