Van

The wheel offset was changed in '87 specifically to make room for the ABS components in the wheel hub. If you want ABS, sell the car and get a later one that has it.

But, if you don't have ABS, it's nothing to worry about. Lots of people track pre-ABS cars, and they've learned to modulate the brakes (pad compound can play a large role in the modulability).

The people with ABS should still learn how to modulate the brakes - it's not a good idea to just hammer the brakes and let the ABS do the work for you. The only time ABS should come on is when you're already braking at the threshold, and there is some unanticipated surface change (like a slick spot or a bump) that causes a wheel to become unloaded and lock up. Obviously, in a non-ABS car, you'll feel this and respond accordingly (let off of the brake so you don't flat-spot a tire.)

For "spirited street driving" I doubt you'll ever notice a difference.

Potomac-Greg

I would only worry about it if you drive it in snow or ice. I have managed to lock the rear wheels up on track 3 weeks ago (ask me why I am buying two new rear tires this week), but I was actually experimenting to find the lock up point. I prefer NOT having the driver aids.

racer

Wow.. Its been nearly 20 years of ABS availability.. Guess that means there is at least "1" generation, if not more, that may never have driven a car WITHOUT it.

heck, its like Manual Windows, Carburators, Points etc... Time marches on.

You'll be fine without ABS.

Heck, this is part of what made SUPERCARS so exotic.. Gobs of HP and no real way to control it except to be a good driver.

Get crackin on those car control classes

krystar

sounds like there's darwinism at work heheh

ilikemy944

Cars are more fun without all that 'safety' stuff anyway

Cole

If you need something to drink I suggest you get up and go get it now, maybe get a small snack too. ABS is a HUGE pet peeve of mine and I am about to write a short book that should be worth the read. Just bare with me for a few.

I have taught performance driving since 1992 from beginers to Indy Car drivers. ABS is one of the most mis-understood concepts ever.

Lets' look at a few basic concepts here first. First you must understand the concept of traction. Imagine for a moment that your car has 100 "units" of available traction. You can use these "units" for any action in the car individually or as a combination.

Example:

-100 units to accelerate with.
-100 units to stop with.
-100 units to turn with.

or some combination there of.

-60 to turn and 40 to brake.

etc.

As soon as you go over the 100 unit mark and try to use 101 units the car will slide. How it slides depends on which direction you were trying to use too many units.

To do ANY action in the car with the most efficiency you must use ALL 100 units for that action ONLY. So to get the most powerful turn out of the car you want to use 100 units to turn with. Which means you can't be applying throttle or brake, it must be constant.

To get the MOST braking power you want to use 100 units to brake with. If you use too many (101) then the car skids. What is also true about using 100 units to brake with is that you no longer have any units to steer with. If you are at maximum braking and turn the steering wheel, the car will continue straight.

It is this action of losing steering control that created "Anti-lock braking" systems. ABS was NEVER intended to stop the car in a shorter distance. What it was designed to do was keep you from using too many units of traction for braking and actually give you some left over units to steer the car with.

So what happens? Here is how the system works. You the driver stomp down on the brakes and use up 101 units of traction. The computer senses a wheel has stopped moving and it releives brake pressure down to say an 80 unit of traction point. Leaving you 20 units of traction to steer with. Guess what? Your foot is still planted firmly on the brake pedal and quickly raises the brake pressure back up over 100 units and the cycle starts all over. All the time you are requesting more pressure and everytime it stops a wheel, the computer releases pressure from the system. This is the pulsation you feel in the pedal.

If you learn what is known as "threshold braking". The act of braking up to the 99 unit of traction point and holding it there you will have much more stopping power than a system that is constantly releasing pressure down to 80 units on you. It takes practice and a fine touch, but anyone can become very good at it.

We taught this on a skid pad and the stopping distance with "threshold" braking is consistantly 2-3 car lengths shorter than ABS at 20 mph.

The other thing to consider on older ABS systems is that it only takes 1 wheel to stop moving to trigger the release of brake pressure to the WHOLE system. So a heavy corner entry the makes 1 rear tire light can trigger a release of brake pressure to the other 3 wheels that have great traction.

More modern ABS systems now have 4 valve systems that can control each brake individually and do things a driver does not even have the controls to do. Those systems are VERY impressive. The systems in the older cars can do more harm than good to a skilled driver. To a driver that does not know any of this it can be a nice fail safe for their lack of skill.

There were some great comments by people on this thread. I just quoted a few below.








Brian is describing Threshold braking in this post below.

Krystar hit on Threshold braking and smoothness here. "smooth" does not mean "slow" it is the way you apply the force. Very important for EVERY action in the car.



ABS does in deed fail. Learning to drive without it is best. Use the ABS as a back up to your own skill.


BINGO!

lovemyp-car

great post, good info...that's what this site is about!!!

Van

As I'm sure you know, Cole, the 944s have 3 channel ABS - it can release the front wheels independently, but the rear wheels have to work together as a pair. This means, if the computer senses that the front right wheel is turning less rapidly than the rest of the wheels (or it's locked up), the ABS system can release the hydraulic pressure to that wheel.

If the rear right wheel is locking up, the ABS system has to release pressure to both rear wheels.

More modern systems are 4 channel and have faster sensing and pulse rates. That is why people are trying to adapt Boxster ABS systems to 944s.

Cole

The problen with old systems like the Porsche is more the software. It senses 1 wheel lock up and then just runs a set "cycling" program that runs through and releases all channels. They just were not very inteligent systems. They simply could not store enough software back then to make it ideal.New systems have the processing powere to actually control individual tires.

It also took some years of learning to update the systems. I have had many Porsches on a skid pad and you can watch and feel the whole system release pressure to all the wheels on a set program.

EDIT:


Couple of other interesting notes. Many early systems were marketed as "3 channel" because they had 3 sensors, not because they could actually control the front wheels independently. If you take a look at many early ABS control modules you will see 2 brake lines leaving the module, not 3 or 4. This means that no matter how wheels have sensors on them, the most the system could ever physically control is front/rear pressures.

If anyone has good detailed pictures of a 944 ABS pump/control unit could you post them. How many lines in and out?


As an interesting side note. The one performance school I worked for years ago had a fleet of track prepped 944s as student cars and a couple 951s for the instructors.

Potomac-Greg

That is VERY interesting!

Another thing I often wonder about is how ABS contramands the benefits of going "both feet in." In an older, non-ABS car, both feet in locks up the tires, and STOPS any steering forces. In a classic tank-slapper, that could save you from darting into an inside wall. Basically, the tires turn into big rubber erasers, and you proceed on a vector based on where you were headed when they locked up, without regard to where the tires are pointed.

But wouldn't ABS prevent this? If ABS stops the tires from locking up, you WILL maintain steering force and the car will go where the tires are pointed, which could be a hard spot across the track.

Cole

This is the whole point of ABS to retain steering control. Contrary to most peoples instincts you can steer out of trouble MUCH faster than you can brake out of trouble.


Consider this simple scenario.



Driving down the freeway at 65 mph.

Something falls out of the truck in front of you.

How much time and distance does it take to change lanes at 65mph?

How much time and distance does it take to stop from 65mph?

It is MUCH quicker to steer around something than to try to stop. Go back up to the "units" of traction discussion and you will see that the FASTEST and most controlled way to steer around something is to use all 100 "units" of traction to steer with. Meaning, you don't want to brake at all, (or accelerate). A constant speed will give you the fastest change in direction.


WARNING RANT ABOUT TO HAPPEN!!!!


The biggest problem is that "most" drivers think they can drive and when something goes wrong they blame the car or environment. VERY few take the time to study driving and learn how to be better, safer drivers.

Because of this attitude of blaming the car and environment we add safety systems to our cars and roads to MAKE UP FOR THE LACK OF DRIVER SKILL AND EDUCATION.

Don't get me wrong I love some of the technological advancement and think things like airbags, ABS, ESP, traction control, etc are all good things for the "average" driver on the street.

What I hate is the lack of personal responsibility that has lead to the straightening of our twisty roads in the name of safety and cars that are fast but so muted in their driving experience that you may as well take the bus.

Cole

Here is a great picture to illustrate the problem with early ABS systems. (I should point out that some modern cars still run these early systems)

Some of you may want to stand up and try something for me really quick.

Put one foot in front of you and lean your weight on it. Not try to slide that foot across the floor. Hard to move it right? Now simply lean back to take the weight off of it and try to move it. Slides easy right? A loaded tire will have much more grip than a light one.

A heavy turn and brake will put the weight firmly on 3 tires, causing only 1 to go light. The extra down force on the 3 tires is enough for full control. But the light tire can trigger the ABS system into the preset program that releases brake pressure to ALL of the wheels. Giving you the opportunity to learn how to steer at a faster speed Up until the latest high end ABS systems I would prefer to have a tire off the ground fully locked up and drive with the other 3.

vt951

I don't have ABS, and my brakes work great on the track. The only thing I wish I had ABS for is stopping in the rain.

Van

Jfrahm

For the real world with wet roads, oily patches, wet painted asphalt, puddles, ruts, expansion joints, light rail tracks and even fuel spills I think ABS is better to have than not have assuming it's not a pathetic and outdated system.

From my limited track and AutoX experience in my 944S2 I found the ABS to be very nice. There are probably some very good Stig-level drivers out there that can do better than the 944 ABS under track conditions but in the real world... I'm not so sure.

-Joel.