Re: bigger wheels

[Eliot Lim <eliot@lanmola.engr.washington.edu>]

> Yes, aluminum alloy is heavier than natural rubber, like over double if you 
> compared. 

before the physicists come after me, i better use the word "denser" rather
than "heavier".  i don't think there was any misunderstanding though..

>I seem to remember Audi alloys to be very lightweight though, 
> ever try to buy a replacement from the factory, pretty expensive? Don't know 
> the exact material.  
> 	The amount of exchange, rubber for aluminum alloy in this case, 
> produces a negligible difference in unsprung weight.  Its a good point though,
> especially on Audi's since they are kinda underpowered to begin with. 
> (relatively speaking, and excluding the S4)

while i have never gone into the mathematics of suspension design, i
understand that unsprung mass is extremely significant in the overall
performance of suspension and engineers go into extremes to keep it
down.  the use of questionably soft metals is one example.  for
another, look at mazda.  they comissioned bridgestone to make special
light weight tires for the miata.  imagine all that effort just to
save a few ounces.  Audi also said that one of the reasons why they
did not go to 16 inch wheels for the v8 is the extra unsprung mass..
though i wonder how much they saved with those "friction rings".

i have snow tires mounted on steel wheels.  the difference in ride is
instantly noticeable.  also, when my car was switched from the friction
rings to regular discs there was a dramatic improvement in ride *and*
handling.  if i were to shop for 16 inch wheels, i'd make sure that they
weigh not an ounce more than the factory alloys.


eliot