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Re: driving in rain and snow (Re: 4000 Quattro Question

Guillermo S. Christensen wrote: 
>> >address.  First, a few years back while I was in Germany a friend of mine
>> >who owned a Quattro coupe, would routinely lock the center differential
>> >when driving at moderately high speeds (approx. 120-140 km/h) on a WET
>> >autobahn.  This, he claimed, settled the car down and improved braking at
>> >higher speeds in the wet. 
>On Sun, 13 Nov 1994, Bruce Bell wrote:
>> The car has 4 wheel brakes whether or not the center differential is locked.
>> 4 Wheel drive, Audi's nor anyone elses, does not help braking. 
Elliot Lim (Glen Powell & Mikes Garage also agree)wrote:
>if the center diff is locked, braking loads are redistributed over the
>two axles, thus influencing the braking characteristics of the car.  i
>don't know if it actually *improves* braking, but it will most
>certainly be different over a 2wd or unlocked diff quattro.
>i also recall that the victorious quattro racing drivers (hans stuck,
>hurley haywood) also said that because of quattro they had a braking
>advantage over their competitors.

OK,  I can see how 4wd will help braking if you are using engine
compression. I  use this technic in the snow because it is more stable and I
have more control. Of course in that situation, I'm not looking to brake
that much faster becaue I'm allowing extra room. On a race track where
picking up a couple of hundreths of a second can make the difference between
wining and losing I can also see the value. These cars also have stiff
suspension that helps keep the weight from pitching forward to the front
tires. On the street, I don't beleive the difference in braking is enough to
keep you from slamming the car in front. If any of you guys have numbers
that show a significant (meaningful on the street) difference I'll roll
over. Until then I hesitate to give someone a sense of security that could
be very expensive in terms of lives and $$$. 

>>Driving at
>> that speed on a wet highway puts the car in danger of hydroplaning.
>it is always dangerous to over generalize.  i punted a v8 on a wet
>race track once at speeds in excess of 100 mph in complete confidence.
>after that the skip barber instructor took the wheel to show us how to
>drive a quattro and went even faster than that.  i think that tires
>make a big difference on what speed is safe.  there is no one safe
>speed that applies to all conditions and all cars.
I pointed out in my post that tires road surface etc. were all factors that
determined at what point a car will hydroplane. Yes, with good tires I too
have travelled very fast on wet roads.  Where we live many of the highways
are rutted and will, even in a light rain, fill with an inch of water which
can provide some surprises. 
>> If the
>> car hydroplanes at that speed no brake is going to stop you. The Audi owners
>> manual has a warning about quattro drive and hydroplaning. Seems the 4 wheel
>> drive makes you think all is well until the last wheel floats. 
>yes, this is very true.  i think the key to uninhited quattro motoring
>is to always use the right tires for the conditions.  using bald
>tires in snow is asking for trouble.. you may be able to pull off
>but you won't be able to steer or stop.
Right,  but perhaps this is enen more important if you don't have a quattro.

>> I do use the center diff when ever the roads start getting slick. I have
>> found the Quattro drive really helps to stabilise the car at speed on a
>> slick surface but as above I use it with the knowledge it won't help me
>the first year i owned a 4000q i took it to the mountains for skiing
>and found that the impressive traction really led one into a false
>sense of security about how grippy the road was when in fact it was
>butt-busting slippery.  :)
Me too


The bottom line on braking is the mu coefficiant between tires and road. 

Eliot, I'd like to hear more about your experiences at the Skip Barber school. 


bbell@csn.org (Bruce Bell)