What does it do and is it worth getting? Planning to get '01 A4 1.8T later this year. I'm planning to add the xenon headlights and quattro awd, but not sure I sure get this ESP thing. Btw, how much would I be looking at for the '01 A4 1.8T with the mentioned options?

 

It is pretty much an Active Handling System. Low $30s based on your options.

 

Some info on ESP vs. Quattro
Posted by mm on 2000-07-27 15:17:00:

There seems to be a lot of confusion regarding the benefits of ESP versus Quattro, so I
thought I would include a brief (or perhaps not so brief) write up on the subject.

ESP is Audi's Electronic Stability Program. It is an option available on most MY2001 Audis
and also on other makes and models of cars. It basically uses the brakes, the ABS
system, and a number of additional sensors to maintain vehicle directional control,
particularly while changing direction, swerving, or cornering.

The various ESP sensors basically compare the cars actual yaw (turning) rate against
the car's steering wheel angle and speed. From this comparison, the ESP system can
determine if the car is over steering (i.e. when the rear end of the car slides/skids out
towards the outside of the turn) or under steering (i.e. when the front end of the car
slides/skids out towards the outside of the turn). If the ESP system determines that the
car is over steering, it uses the car's ABS system to individually brake the outside front
wheel to bring the car back into the proper cornering line. If the ESP system determines
that the car is under steering, it uses the car's ABS system to individually brake the
inside rear wheel to bring the car back into the proper cornering line. Basically, ESP
compares where the car is going and how it is cornering (i.e. yaw rate) against where
the driver appears to want it to go (i.e. steering wheel angle and car speed). If from
this comparison it determines that the car is not behaving/cornering as the driver
intends, it attempts to use the brakes to correct the situation and keep the car under
control and out of the ditch.

ESP basically keep track of how the car is responding with regard to lateral (i.e.
sideways) traction and attempts to correct situations where lateral traction is lost or
compromised. This type of system is available on BMWs (they call it DSC-Dynamic
Stability Control), Mercedes, Porsches, and Corvettes among others, and now on Audis.

So then, the question is often asked whether or not ESP can provide much benefit for a
Quattro AWD car. The answer is unequivocally yes, without a doubt. Quattro does
nothing to address the issue of lateral traction directly or in the same sense that ESP
does, so the benefits of ESP on a Quattro AWD car are essentially and in most ways the
same as they are for a FWD or a RWD car.

The important thing to remember about the Quattro AWD system is that it's primary
function and intent is to maintain, balance, and distribute propulsive traction, and not
lateral traction (at least not directly), between the four driven wheels. Now then, the
since the Quattro AWD system does distribute propulsive force between four wheels
rather than just two as in a FWD or RWD car, it does offer some side benefits which can
enhance available lateral traction to some extent. Since the propulsive load on a
Quattro AWD car is divided between the four tire contact patches instead of just two,
the overall tractive load on each driven tire is generally less than it otherwise would be
for a 2WD car. This essentially allows each tire contact patch to provide a better
balance between propulsive and lateral traction before the threshold where traction is
lost is exceeded.

Basically, each tire has a certain limited amount of traction available. If the total force
on a tire exceeds the amount of traction available, the tire slips, skids, or slides, it loses
traction. For a tire to maintain traction, the sum of the lateral and propulsive (or
braking) forces must remain below the tire's available traction. If the lateral force
exceeds the tire's available traction, the tire will slide. If the propulsive or braking force
exceeds the tire's available traction, the tire will slide. If the combination of the lateral
and propulsive (or braking) forces exceeds the tire's available traction, the tire will slide.


This is why RWD cars are generally more prone to over steer at the cornering extremes.
The front (non-driven) wheels generally just have to contend with lateral (and braking)
traction, while the rear (driven) wheels have to contend with both lateral and propulsive
traction at the same time. Thus, at the extreme, the rear wheels on a RWD tend to get
overloaded and lose traction first, resulting in an over steer condition when cornering.
It's similar for a FWD. The front (driven) wheels on a FWD have to contend with both
lateral and propulsive traction at the same time, while the rear (non-driven) wheels are
only concerned with lateral (and braking) traction. At the extreme, the front wheels
tend to get overloaded and lose traction first, resulting in an under steer condition when
cornering. Of course, the overall balance and weight transfer will affect this all
significantly too, but that's the gist of it.

This brings us back to my original point about Quattro AWD and lateral traction. The
primary function of the Quattro AWD system is to maintain propulsive, and not lateral,
traction. While the Quattro system can, in essence, free up more of each driven tire's
traction for use in the lateral direction by reducing the propulsive tractive load for the
driven tires below what it would be for a 2WD car, it does nothing directly to ensure
that lateral traction is maintained. ESP does, which is why it can and will be of benefit
even on cars equipped with Quattro AWD.

This is all a bit of an oversimplification, but while it may be lacking in technical detail
and some nuances, I hope it helps to explain the benefits of ESP, and how they do
apply even to a Quattro equipped car.