When to lock diffs; Was: Draggin' & VW Books

[paul.heneghan@bbc.co.uk (Heneghan,Paul)]

From: Simon Allcorn
>So do you drive along a 'fast bendy road' turning the diff lock on and
>off ? (given that to turn a corner turn it off / to drive a fast bendy
>road turn it on )

I do.  When driving very fast along country lanes in the dry (or just 
 fast in the wet), I lock the centre diff.  As I reach the 30mph sign 
 at the outskirts of towns, I unlock it.  The difference in handling is 
 remarkable (even to a novice like me).  The car goes around bends as 
 if it's on rails, and appears to lean much less.  

You get the added benefit of poor man's ABS.  If one wheel looses 
 traction, it will not lock up as long as the other wheel on that axle 
 has some grip.  It also means that the rear brakes are actually 
 contributing to the braking action of the front wheels (via the 
 transmission). 

>And theres not a problem with having the center diff on and doing 60 -
>70 MPH ?

I've done a lot more than that with the centre diff locked.  So have 
 all the Audi rally drivers.  On some courses, they are doing more than 
 100mph down appalling roads, and most of them have no centre diff at all!

To be honest, for most of my driving (under normal conditions), I don't 
 lock any diffs.  When I'm really in a hurry, particularly when it's 
 wet, I lock the centre diff.  I locked the rear diff once only, this 
 was in order to get up a hill in the snow.

Driving in snow with the diffs locked can give you a false sense of 
 security.  You can get enough traction to get going, but at 30mph with 
 standard tread tyres (not M&S), you get virtually no braking - very 
 frightening!  I even think that both locked diffs in snow is more 
 likely to cause all the wheels to lock - this usually makes the car 
 rotate and slide off of to the side of the road until the brakes are 
 released and steering is regained again.  I'm looking forward to 
 another couple of days of snow this year so I can do more experiments.

Paul
paul.heneghan@bbc.co.uk
1984 Audi 80 quattro
1983 Audi 100 Avant