RE: Speedline weight

["Duff, Ian" <IDuff@charter.com>]

Couple of points: the Speedlines are cast, not forged, and they are one
piece, not three. They have the row of bolts to look like 3-pc, but
aren't. Audi marketing talking to styling, and ignoring engineering.

The following is all based on my understanding, without a very good
explanation, caveat emptor. Unsprung weight gets accelerated 100% over
every road irregularity, whereas sprung weight gets accelerated *much*
less, due to the suspension absorbing the irregularity. Imagine a very
light wheel traversing a speed bump. The suspension doesn't have to work
hard at all to absorb the rise as the wheel goes up, and then also
doesn't have to work very hard to keep the wheel in contact with the
back surface of the speed bump. The spring gets to store all the
potential energy of the wheel rising, with the shock absorber having to
damp very little. Now replace the light wheel with one weighing a ton.
The spring needs to be stiffer to force the wheel to stop accelerating
up, then to accelerate down to follow the contour of the bump, the shock
needs tighter valving to control the stiffer spring, meaning it will
absorb more energy, which is bad news.

There is secondary order problem with unsprung weight where wheels,
tires and anything rotating is concerned, namely that the engine and
brakes have to work that much harder to get the car going or stopping,
due to increased rotational inertia.

I did take physics *once*, but it's been a while. Sorry if any of this
is wrong, please correct as appropriate, 'cause I'd like to understand
it better, too.

-Ian Duff.
	-----Original Message-----
	From:	RELAYER@aol.com [SMTP:RELAYER@aol.com]
	Sent:	Thursday, 24 July 1997 6:21 PM
	To:	audi-20v@avs.com
	Subject:	Speedline weight

	I weighed my speedline wheels before I sent them to Bill
Reigelsperger and I
	think they weighed around 18 pounds with out tires.  Funny thing
was that my
	new BBS one piece wheels weighed 2 pounds more per wheels than
those nice 3
	piece speedlines.  I guess that's why forged 3 piece are so
popular, they do
	save weight.  But, I am still confused on how the unsprung
weight has more
	impact than regular weight.  I know it's true, but have never
heard the
	explanation.

	PS-I will be getting around to researching the K&N cone and
clear turn signal
	discount soon as I get my data line up and running at work, I
used to read my
	email during lunch at work where I have a faster computer,
printer and modem.

	Christian