Re: quattro-digest V3 #1108

[Dave Eaton <dave.eaton@minedu.govt.nz>]

there are a number of people on this list with a better engineering grounding of the ins and outs of suspension design vis handling and traction, but i'll put in my $0.02...

traditional racers have taken as folklore that rwd makes a better racecar than awd, but analysis of race regulations and results doesn't bear this out.  awd banned in f1, likely to be banned in class 1 racing (although that looks to have just died with alfa and opel pulling out...), and rumours of being banned in class 2 racing with the runaway success of the a4q's in the british, german, south african and australian series this year (all the while carrying a substantial 45kg weight disadvantage over the rwd bmw's and 95kgs over the fwd cars).  then of course there was audi's success in imsa during the late 1980's...

my understanding of the awd advantage is that, because tractive effort is spread through 4 tyres rather than simply 2, this leaves more of the tyres adhesion (which is a constant, ignoring slip) for steering and cornering.  the other advantage (and one that i don't understand fully) is in braking, least-ways, that is what some of the audi advantage in class 2 racing is being put down to.

the case against awd in racing is most usually weight and friction, this is significant in the fixed formula such as class 2 where the engines are rev limited and so all the top cars are probably within a few hp of each other.  audi have spent a great deal of time and money on low friction diffs and diffs that spread the tractive effort appropriately for the type of surface/track.

wrt normal awd road cars, i love the quattro system.  the speed of the torsen is it's major advantage over the viscous systems employed by toyota in it's gt4 and subaru.  i haven't spend much time in a impreza but a good friend has a gt4 and in low traction conditions, or when cornering hard, the centre diff takes a perceptible time to get going....

-dave
'93 s2
'90 ur-q

..>From: Fringe Ryder <fringe@ai.net>
..>Date: Sun, 29 Sep 1996 11:00:21 -0700
..>Subject: Re: Fastest stickiest Audi? Opinions welcome.
..>
..>No, stock.  Which is actually probably the better way to measure - WE may
..>change our tires (heck, on my current car, which is not an Audi (the Audi
..>has been on order for six weeks), I've replaced the entire suspension and
..>wheels), but this is NOT normal behavior.  Further, since I'm leasing the
..>A4Q (all the better to get the 5-valve cylinders with in a few years), I
..>won't be making any drastic changes to it.
..>
..>Philosophically, I guess the question would be:
..>
..>Is AWD theoretically superior in dry conditions?
..>
..>Practically, the question is:
..>
..>Does the Audi AWD *package* perform as well as the BMW RWD *package* in dry
..>conditions?
..>
..>There are lots of variables you could fall back on... suspension pressure,
..>weight, engine, red cars having more propensity to slide sideways than
..>silver cars, etc., but what the typical person cares about it - will this
..>car perform better than that car?  Not "can it be souped up or modified to"
..>but "will it when I drive it off the lot".
..>
..>I haven't seen any evidence that AWD is superior in dry conditions, but that
..>may be simply because BMW focuses on sportier driving than Audi.
..>Extrapolating that dry is just like wet and slick, only less so, I'd
..>- -expect- better performance pressing the limits, but Audi doesn't get it there.
..>
..>Regards
..>
..>        Fringe (who is eagerly looking forward to his A4Q, and isn't a BMW
..>fan, really.)
..>