RE: unsprung weight...

[JustaxPHX@aol.com]

>it is extremely difficult to find this information about wheels.  the
>manufacturer's don't seem to publish this information (wonder why not?). 

And when they do, my experience has been that it's usually a *very* optimistic
figure...

>the 15x8 et35 weights 8.4kg,
>the 17x8 et35 weights 10.8kg

In my garage, I have an OEM Ronal 8x15 and a Compomotive MO 8x17, both with
and without tires ... this weekend, I'll take them to my local Post Office and
weigh them on the digital scale in the lobby.  (If you're a racer, you'll find
this is a great place to weigh parts: 24-hour access, a scale that's accurate
to .1 ounces and reads to 75 pounds ... I've weighed everything from flywheels
to brake calipers and even rear seats on it in my quest to the find the
lightest parts!  You may be surprised to learn that otherwise identical
looking parts can vary in weight by several ounces, if not pounds, and with
some time and a big pile of parts to sift through, you can remove quite a bit
of weight from a car without anyone figuring out how you did it ... in my
case, I lightened an '81 4k by an additional 85 pounds simply by mixing-and-
matching such things as caliper brackets, starter motors, etc.)
 
>thus an increase of 2.4kgs (5.3 pounds) per wheel.  to put it another way,
>by going +2, you have increased your unsprung weight from the wheel alone by
>30%.

Which, depending upon the total unsprung weight of the car, might actually be
as small as 3 or 4 percent ... I will admit that every bit helps but I still
maintain that there are benefits to be had from using larger wheels.  I'm also
finding that on the Ur-Q in particular, using a larger diameter wheel
preserves the suspension designer's original geometric relationship ... but
more on that at a later date, when I can bring some hard numbers to the
discussion.

JG