ur-quattro suspesion changes (was Wheel rate v. spring rate)

[Dave Eaton <Dave.Eaton@clear.net.nz>]

i thought my point was quite clear actually.  with a 17" rim and wide tyre, 
you are adding many kilos of unsprung weight on each corner of the car, 
designed originally for the weight of the 15" time and tyre.  therefore, 
this will have a detrimental affect on handling and transient response 
(which you mention as a benefit of the heavier wheels!??) of the vehicle on 
the road.  last year "performance car" magazine did a series on wheel/tyre 
upgrades which identified and covered this issue.  from memory, in all 
cases they found that changes in the spring and shock absorbers were 
required to improve the feel and handling of the car......

there is also fable (which you also mention) about the lack of change to 
the ur-quattro suspension during the life of the car.  while it is true 
that the suspension *setup* information did not change, there were *many* 
revisions to the design.  as to audi's attitude to the different wheels 
offered on the early quattro (6x15 fuchs) versus the ronal 8x15 on the 
later ones.  i would offer the following observations from the parts 
fiche...

the major changes were at the end of the '82 model year for the '83 year. 
 this was at the end of 85-c-902-000, and the start of 85-d-900-001.  as 
you probably know this was the start of the "series 2" cars, with the cibie 
lights, the slanted grille and the (of major interest here) 8x15" ronal 
wheels.

at the front,  the changes involved new lower wishbone, ball joint, and new 
shock absorbers and anti-roll bar (along with their rubber mountings).  the 
wishbones and ball joints also changed again for the 20v.  there was a 
change in front springs at 85-e-900-324 (nov '83, during the '84 model 
year) in addition to a different front springs identified for vehicles with 
air-conditioning.

at the rear (again from 85-d-900-001 - the '83 model year); the anti-roll 
bar was deleted and a new wishbones specified (changed again at 
85-h-901-001 and finally at 85-l-000-001 for the 20v), tie rod (changed 
again at 85-j-900-622), and the ball joints (single part replaces the 
lhs/rhs part).  the rear strut also changed for the '83 model year.  the 
rear shocks changed at 85-e-900 901, and the coil springs at 85-e-900-329 
and again at 85-h-901-001.

so, clearly audi changed all suspension components throughout the life of 
the car, the major changes being made for the '84 model year, the time 
where the 6x15" fuchs wheels wearing 205/60 15 tyres were replaced with the 
8x15" ronals and 215/50 15 tyres.  in summary, these changes involved new 
wishbones and ball joints front and rear, new shocks and anti-roll bar at 
the front, the deletion of the anti-roll bar at the rear, along with a new 
design of tie rod, and a new rear strut.  for the '84 model year a change 
was made to the springs front and rear, and rear shocks.

so in summary, your point about audi not caring about the change in wheels 
and tyres from 6x15" to 8x15" is patently not the case.

dave
'95 rs2
'90 ur-q
-----Original Message-----
Date: Fri, 22 Jan 1999 00:01:40 EST
From: JustaxPHX@aol.com
Subject: RE: Wheel rate v. spring rate (was 17" wheels on an Ur-Q)...

>and also increases the unsprung weight by a not-insignificant number of 
kgs
in each corner.

... and your point is?  Every decision that's made about how a car should 
be
equipped -- be it by the factory's engineers before it's put into 
production
or at a later date by the car's owner -- involves weighing various 
trade-offs.
My decision to run 17" wheel-and-tire combos on my two cars is no exception
and was made with full knowledge that there was a price to be paid for the
additional benefits they offered.  Better transient response, for one, and
room for bigger brakes, among others...

>discussing this with an old rally buddy of mine who was talking to the guy
who recently won the regional rally in his wrc->spec subaru.  he was
discussing the pedant for uprating wheels and tyres on subaru's.  "if i had 
my
way they would sell >them with anything but 15" wheels.  handle much better
that way."
>
>makes you think.

Actually, what makes *me* think is whether Audi originally designed the 
Ur-Q's
suspension around 205/60-15 tires on a 6x15 wheel or 215/50-15 tires on an
8x15 wheel.  So far as I can tell, the suspension geometry wasn't changed
much, if at all, to compensate for the change and given the difference in
diameter between the two, they both can't be correct.  Is anyone else 
puzzled
about this like I am or privvy to the logic behind Audi's decision? 
 Perhaps
it was just one of those "happy accidents" that worked out far better than
anyone thought?