: more closed diff acts as a kind of primitive ABS system which helps keep the
: rear brakes from locking. What I was trying to get accross was, you don't
: really need ABS as long as your brake balance is forward enough.
Well, I did some playing about on GPL last night and what I found was
the following for the power-on diff:
1) If you have the rear wheels very tightly locked then you get
understeer in long corners through which you have the power on. Take
the first long right hander in Monza - if you have the rears tightly
bound then the power will tend to push you to the outside. This is
because the rears "want" to move together but what you, the driver,
wants is the inside wheel to turn less than the outside wheel (think
about it, when going round a corner the last thing you want is the two
wheels turning at the same speed because then one or other of them
must be slipping). If you set the diff to tightly lock the two wheels
when the power is on then you will get dreadful understeer through
power on corners.
2) However, if you have the wheels extremely loosely locked then the
inside wheel can break away. The inner wheel when you're cornering is
the unloaded one. If your diff is set loose then when you put the power
on hard, the inner wheel will break free and spin. This will mean that
your car is being accelerated more by the outer wheel. This will, in
turn, mean that you will spin towards the inside of the corner. In my
case, a typical symptom of this is spinning off into the barrier on the
right hand side of parabolica. (And, occasionally, if the diff is very
open then powering off the road on the right hand side of the first
right hander - the name of which I forget).
I'm not sure quite what the equivalent bits of this for "power off"
diff would be. It seems it would only make a difference on corner entry
as you began to turn with the power off. Perhaps something with the
diff could stop my habit of having the rear end of the car overtake me
as I head into parabolica. Again, I think there may be a compromise
between having the wheels tightly bound (which would, as the manual
says, provide a rear wheel only ABS) and having the wheels loosely bound
(which would allow you to actually turn the corner without the tyres
slipping).
Apologies if this is obvious to everyone but me - I'd been regarding
diff settings as dangerous heavy magic and actually understanding them
really seemed to help my lap times.
(Also, driving with a very open diff improved my sensitivity on the
throttle).
--
Richard G. Clegg Only the mind is waving
Networks and Non-Linear Dynamics Group
Dept. of Mathematics, Uni. of York
www: http://www.racesimcentral.net/