29 replies to this topic

[dan2k]

Whaaattttzzzuuuppp!!!

Seriously, I wanna ask you guys something.
I've been wondering about this for a long time, so I hope you guys can help me out since I don't know much about the technical side of cars.
Its about ABS and normal brakes.
Lets use F1 cars for an example, with the current brakes that F1 cars have at the moment.
If lets say, they fited in a ABS in the curent F1 cars.
In a straight line, would the ABS take longer to stop compared to normal brakes, lets say from
300 km/h to 0 km/h.
The reason I ask this is because.
Doesn't ABS brakes tap at a very fast rate, so that the brakes don't lock up, and alow you to steer.
But while breaking in a straight line, wouldn't tapping take longer to stop a car?
Compared to normal braking system, and a driver was able to brake in a straight line without any lock ups, wouldn't he stop quicker then the guy that had ABS?
I hope you get what I'm trying to say, because I really want to know the anwser to this.

[nzkarit]

The top drivers are much better at braking than ABS.

The advantage of ABS is that it can change the pressure on each brake so good if different wheels are on different surfaces. This is something a driver can not do unless Mac bring back their extra brake pedals.

[Lephturn]

In a straight line, a human can break better than ABS.

What ABS does on road cars is save the driver when they screw up. If the driver doesn't screw up, ABS is not needed.

[AdamLarnachJr]

Umm, I beg to differ. ABS systems are designed to prevent wheel lock, the valve system is designed to apply as much pressure to each brake assembly as possible. Think of this way, each wheel/tire has a different amount of grip, so simply applying an equal amount of pressure to them wouldn't really work efficiently. SO if you were going down hill and slammed on the brakes you would lock up the rear's and maybe get the tail end out, but with a good ABS system, it applies the maximum amount of pressure to each wheel/tire until it senses lock, and then continues to pulse to keep it from locking, this way each brake assembly is used to its maximum efficency and no valuable time is wasted trying to impossibly modulate the pedal or correct for slip.

[berge]

the abs equipped vehicle will always stop quicker than the non-abs vehicle. even if schumacher or senna are controlling the brake pedal. the only exceptions are heavy snow and loose gravel, in which case the non-abs vehicle stops quicker due to "compacting" of the road surface in front of the locked tires, therefore stopping quicker than the abs equipped car.
anybody who claims they can stop their car quicker without abs is overestimating their ability to compete with a computer.

[MacFan]

I have to agree with the last 2 posts. When ABS was first used on road cars it wasn't capable of modulating the brake pressure particualrly fast, or applying different pressure to different brakes, therefore it was possible for a good driver to stop a non ABS car slightly quicker in a straight line on dry ashphalt. The current systems for racing and road cars are generations removed from the primitive early versions, and much more effective than even the best driver in the world, or anybody else who is foolish enough to think he can react faster than a computer. That anybody believes they can beat a system capable of unlocking an individual brake without affecting the other 3 defies belief.

[PDA]

Addint to that previous comment - All F1 cars used ABS in 92/93, so one can assume it was fitted because it was better than non-ABS systems. It was banned at the end of 93 along with other "user aids" such as traction control.

[palmas]

Yes!

[random]

My feeling is that today's ABS braking systems are better and faster than any standard system. In addition ABS systems allow a consistency that is difficult to duplicate with standard brakes. They also allow full on braking while turning.

I've taken ABS equipped cars to the track and have been very impressed. At one corner in particular, there was no way I could have braked as late as I did without ABS. All the drivers I spoke with that had ABS equipped cars also used ABS in that corner to much applause.

There is nothing like braking later than you should humanly be able to and carry your full-on brakes through the corner. In a non-ABS car I'd have had to brake much earlier and would not have been nearly as quick through that section.

[Zeus]

MacFan, agreed, and add to that modulating the pressure serveral thousand times per second.

[CADBLACK]

RE: ABS

A good racing driver can certainly out-perform a conventional ABS system by perfect mudulation of the brake pedal -- with a perfect longitudinal brake-bias set-up. The driver wants -- provokes -- a bit of lock-up, that is, the wheel-tire turning something like 15% slower than it would if it were "geared" to the ground.

Two things, however, the come to mind: There probably could be an ABS system (with a really fast computer) to simulate what the driver is doing in a perfect braking situation (i.e. getting that perfect 15% slippage).

But also, there would be other things lost. Not only would the ABS probably not "feel" right, but on occasions a racing driver is deliberately try to provoke a bit short of lockup; sometimes to adjust the car, let the tires purposely slip to allow the car to move in its inertial direction (say on turn-in while trail-braking) maybe due to undue a slightly too-shallow line (at corner entry).

Also, certain (very sophisticaed) drivers use both left and right feet while driving: One on the brake, one on the gas to keep the trottle open slightly even under braking (thus keeping the rear wheels turning a bit while the front ones are verging on lock-up).
A lot of things are going on here. By this, a driver can be minutely adusting the car's fore-aft attitude (its "dive" angle) -- thus changing the aero center of pressure on the car's longitudinal axis and hence changing its oversteer-understeer characteristics. I.e.: one end of the car may be being pressed down harder into the pavement than the other for a few milleseconds.

Also, there are other things going on -- that have only to do with mechanical grip; that is, squatting the car in a certain way because of certain shock-valvings, etc -- all kinds of things.

So finally, with conventional brakes, you have a thousand little things you can modulate -- a lot of it intuitive; but measurable on telemetry. All kinds of things are happening.

ABS -- no matter how sophisticated -- would take a lot of these weird abilities away from you.

Also, at certain times, you simply want to "drop the pegs," that is,
just lock up all four wheels to purposely let the car go directly with its inertia instead of "taking a set" -- this usually done when you've lost control and are going to hit the wall...and you're trying to quickly adjust how you you're going to hit it (a glancing blow, straight in, side, front or rear of the car, etc.)

Anyway with ABS -- any ABS -- a lot of control is taken away from you.

I think most good racing drivers can get a lot more from the car with full manual control of the brakes.

There are just too many situation for a computer to comprehend!

CADBLACK@aol.com

[mkane]

I remember seeing a documentary about racing a few years back. It had Mario Andretti driving an Eagle Talon. Not a rocket, but that is besides the point. One of the things done was a comparison between ABS and non-ABS breaking in a strait line. Mario Andretti could brake from speed faster in the ABS car. IS this an absolute definitive answer? No. Just my input.

Matt

[berge]

[QUOTE]Originally posted by CADBLACK
[B]RE: ABS

on occasions a racing driver is deliberately try to provoke a bit short of lockup; sometimes to adjust the car, let the tires purposely slip to allow the car to move in its inertial direction (say on turn-in while trail-braking) maybe due to undue a slightly too-shallow line (at corner entry).

--if there is no wheel lock-up, abs does not kick in,

Also, certain (very sophisticaed) drivers use both left and right feet while driving: One on the brake, one on the gas to keep the trottle open slightly even under braking (thus keeping the rear wheels turning a bit while the front ones are verging on lock-up).

--if there is no wheel lock-up, abs does not kick in,

I think most good racing drivers can get a lot more from the car with full manual control of the brakes.

--in dtm abs is used. in 92-93, abs was used by none other than senna, schumacher, mansell, etc.. I did'nt hear any of them saying they could drive the car better without abs. Senna was quoted as saying in 93 " I can compete with anybody, I can't compete with a computer."

[desmo]

A couple of points, "if there is no wheel lock-up ABS does not kick in". Actually ABS systems prevent lock-up, the wheel never "locks up"- stops rotating- with ABS. The ABS senses incipient lock-up at some predetermined decelleration inferring some degree of tire slip and backs off the system pressure until some other point is reached at which point the ABS allows the pressure to rise back to the initial point at which it was activated. This recurs cyclically until the braking input is eased off.

The cyclic rate is actually around 1/2 second due to the tire dynamics. Claims of ABS modulating the braking tens or even hundreds of times per second aren't honest figures.

As was pointed out the best advantage of ABS is it's ability to modulate each wheel seperately, something impossible with a dual-circuit conventional system. A driver- no matter how skilled- cannot manage the braking torque laterally with a conventional system as long as both wheels are given equal pressure. In real world terms this means that one of the wheels in each circuit will be braking below it's potential. I think if a conventional system can outperform an ABS system all else being equal, it tells me that the ABS system is simply not sophisticated enough. Before ABS was outlawed, in '93 I think, all or most of the teams were using it.

[berge]

understood.
should have chosen my words more carefully. I was replying to a statement such as "a driver applying the brakes just short of lock-up." my response(ill worded) was if the driver is just at the threshold of lockup, the abs will not kick in, therefore it is a moot point to compare abs and non-abs for that situation.

[dan2k]

Thanks for the help guys.
But I'm still abit confuse.
Some of you say a driver would out brake another driver that had ABS, others say it wouldn't.
Anyways, wouln't ABS be more useful for drivers braking while they are tackling the corner, because with ABS their wheels don't lock up? There for, they car still steer.
But for sure, if it was rainning, ABS would certainly beat normal braking systems.
So lets say if ABS where alowed in F1 now, how much improvement do you see in lap times?
Could it be really huge time gain, or not much?
Do you think ABS will ever allowed back in F1 again?

[OLEV]

Originally posted by desmo
A couple of points, "if there is no wheel lock-up ABS does not kick in". Actually ABS systems prevent lock-up, the wheel never "locks up"- stops rotating- with ABS. The ABS senses incipient lock-up at some predetermined decelleration inferring some degree of tire slip and backs off the system pressure until some other point is reached at which point the ABS allows the pressure to rise back to the initial point at which it was activated. This recurs cyclically until the braking input is eased off.

I beg to differ. Try a brake-test on a concrete road on a hot day and check out the skidmarks you leave...

Originally posted by desmo
The cyclic rate is actually around 1/2 second due to the tire dynamics. Claims of ABS modulating the braking tens or even hundreds of times per second aren't honest figures.

I dunno, 1/2 sec is a pretty long time. Back in 1985, once, when I was in a Mercedes with the then-latest ABS, their claimed freq was 0.25, which sounded about right when we tried it.
I reckon present-day cars "hum/pulse" at an even higher freq than that.

[Al.]

I would be suprised if ABS were allowed again in F1 because in theory it would make overtaking harder.
I guess the main advantage is that you could brake a little later and start to turn in to the corner with the brakes applied. Some drivers can do that now ( I think it's called trail braking - but I stand to be corrected ) but they reduce the pressure on brakes as they turn in. The disadvantage without ABS is that it can lock a wheel if you brake to hard as you turn. If that is a front you understeer wide, if that is a rear you risk spinning as you oversteer. This can be compenstated with front/rear brake balance but never as well as independant modulation as with ABS.
So with ABS you can brake all the way to the apex of a corner and then be straight on the gas.
I drive a 2000 VW with ABS ( the first car with ABS I have owned ) When it activates there is a pulsating that comes back through the pedal that makes it difficult to have confidence to knowingly push the car beyond the limits of the tyres under braking.
I suppose this could be damped out and with companies such as ZF dabbling with fly-by-wire brakes ( and steering ) for road cars, it will all help. However I think with certain top teams struggling to make cars move off from stationary due to electronic or software glitches, I think fly-by-wire brakes are a little way off yet.

[Amadeus]

Originally posted by Al.

I drive a 2000 VW with ABS ( the first car with ABS I have owned ) When it activates there is a pulsating that comes back through the pedal that makes it difficult to have confidence to knowingly push the car beyond the limits of the tyres under braking.
I suppose this could be damped out and with companies such as ZF dabbling with fly-by-wire brakes ( and steering ) for road cars, it will all help.

I dunno - I prefer to get the pulse - at least it is feedback on what the car is doing and where you are at with your adhesion limits. If it was 'damped out' you'd end up with a pedal like a wooden block, no feel and no idea what was going on.....

[random]

The ABS pulse on many newer sports cars is just enough to let you know ABS is working.

To agree with Desmo and Berge, almost anything you can do with non-ABS system, you can still do (and do better) with a quality ABS system.

ABS systems do not prevent threshold braking, they just make it safer. If you are a perfect threshold braker and never lock the wheels, you'll never even notice the car is equipped with ABS. The ABS will only kick in if you screw up and brake too hard.

Admittedly, the early ABS systems suffered from softer pedals and such, but no longer. My feeling is that a quality, modern ABS system is almost impossible for the human non-abs driver to beat.

[desmo]

OLEV, you are correct that the cyclic rate can be significantly less than 1/2 second. The data I've seen suggests a range in the order of 0.2-0.9 second, I was generalizing. The skid marks do not necessarily indicate lock-up. ABS systems may have a threshold of 20-40% tire slippage, more than enough to produce skid marks. This figure can be significantly higher if the wheel sensors infer that a loose or gravelly surface is present. In some low traction conditions lock-up is the quickest way to stop, albeit at a significant loss of vehicle control. ABS systems may allow up to 80% tire slip if it senses these conditions.

[bugeye]

I agree that the claim of a super skilled driver being able to stop faster with ABS are outdated, it just doesn't make any sense.

Desmo, you had alluded to ABS systems being sophiscticated enough to detect low CF surfaces like ice, sand or gravel. and that they would use a different algorithm for braking under those circumstances. What I am wondering is: Is the braking protocol the same for all low CF surfaces? more locking in gravel seems intuitive, but would the same thing work on ie or snow?

FWIW: ABS has saved my bacon in the snow many a time.

FWIW2: We have two early ABS equiped cars, an 87 Mercedes and an 89 SAAB. The ABS system on the Mercedes is far superior...which strikes me as odd, you'd think they would use the same vendor (BOSCH in the SAAB's case)

[Jaxs]

One of the first production cars to have ABS, Dunlop Maxaret system with four wheel drive was the Jensen FF, the film to advertise the difference between 'normal' braking and drive system used a ' normal' Ford Zodiac and the Jensen running between a series of post on wet grass, the Jensen was able to accelerate, steer and brake effectively whilst the Ford demolished all the posts. The difference between ABS and non ABS as only become greater over the years.. Non ABS will not take into account the moment the wheel lifts off the ground and returns locked up, the ABS will, the ability to steer under heavy braking remains as effective, Don't try it in a non ABS system. Slippery suface braking becomes controlable, the cloud of smoke from the inside wheel on fast corners becomes almost nothing with ABS

Regards

Jaxs

[Yelnats]

The effectivness of ABS in F1 has very little to do with the very hypothetical situation mentioned by the poster of this thread, dan2k. The situation he is reffering to is straight line decleration where the braking forces are laterally balanced and presumably the brakes have been setup with perfect front/rear bias. In this situation ABS would offer very little advantages to the super skilled drivers in F1.

But on corner entry during a racing situation where we see numerous cases of the unloaded inner front wheel lockups, even the crudest of ABS systems would offer great benifits to even the best F1 pilots.

[Ben]

I would definitely agree with Yelnats on that last point. Mike McDermott in Race Tech recently calculated a plausable pitch frequency for an F1 car of 10Hz. The maximum frequency of muscle contraction is about 5Hz, ergo drivers can't cadence brake, at least not in a feedback sense, maybe in a predictive sense.

This means that ABS would definitely be better under trail braking while turning into a corner.

Ben

[FucF1]

Well I would say that ABS helps in braking for, or during a series of corners but in a perfectly straight line non-ABS is more effective if you know how to brake properly.
As you all know, but doesn't seem to be expressed here, the shortest braking distance is achieved by *not* locking up, locked tyres are sliding tyres and in my opinion non-ABS is better (if you don't screw up)

Me and my mates used to road race (I know, I know, but we were young and foolish) I wasn't the fastest, but my speciality was braking! I could haul a car down from speed to a dead stop in insanely short distances, we used to have bets to see how far you could push it.

In a challenge to my superiority (I was accused of being good because my cars brakes were better, they were non-ABS) we tried it in each others cars, both ABS and not.
I beat everyone but the point I'm getting to is the non-ABS cars were more effective than the ABS, they gave more control and feeling for the limit of adhesion.

So, yes, non-ABS is better for braking

And its also another theory of mine that many car accidents are avoidable but the drivers make the fatal error of panicking and standing on the brakes, locking up and losing control, I get myself out of seemingly impossible positions more than once by not panicking and applying the brakes correctly (off course I had to get myself *into* the difficulties in the first place)

I feel a much larger emphasis should be placed on learning how to brake properly and avoid the panic lock up, it would be very effective in cutting accident rates.

[berge]

Originally posted by Yelnats
The effectivness of ABS in F1 has very little to do with the very hypothetical situation mentioned by the poster of this thread, dan2k. The situation he is reffering to is straight line decleration where the braking forces are laterally balanced and presumably the brakes have been setup with perfect front/rear bias. In this situation ABS would offer very little advantages to the super skilled drivers in F1.

But on corner entry during a racing situation where we see numerous cases of the unloaded inner front wheel lockups, even the crudest of ABS systems would offer great benifits to even the best F1 pilots.

you cannot have "perfect" front/rear bias. braking is a dynamic situation and you cannot set it up perfectly with a "fixed" front/rear bias adjustment. It is impossible to do. you would need a dynamic means of adjustment such as an abs system.

[Yelnats]

FucF1, Welcome to the club!

I recall approaching a stop at about 100k and not begining my braking until well inside a "300 ft to stop" sign. My passenger remarked that he though I was leaving this a bit late and as we deliberatly on a fast drive I though otherwise. I bet him I could stop in far less than half that distance including reaction time. The money was put on the table and we proceeded along at 60 mph until he yelled "STOP".

He measured the distance back to the object he had chosen as his marker and arrived at 140 ft stopping distance including reaction time. Allowing 1/3 second for reaction at 88 fps give a little over 110 ft, a figure only recently matched by ABS systems on road cars. This was in 1964 in a TR3 with very narrow tires and a figure I found easilly repeatable.

I recently had the misforture of broadsiding a left turning minivan (the driver was charged) in an ABS equiped vehicle and I recall thinking that these brakes ar totally ****ed just before I hit him and rolled him unto his roof. The next car I bought was an ex-police cruiser of the same make (Ford Crown-Victoria). The police do NOT use ABS!! Case closed!

[Yelnats]

berge, of course you are correct for practical situations but for the purposes of this hypothetical case the brakes could have been setup "perfectly" for this situation and the co-efficient of friction at this location. Thus all wheels would have been operation at there ideal locking point any increase or decrese in the friction level (or passenger load or gradient of the road) would make this situation impossible.

[Jaxs]

This is sliding into an ego massaging situation as ' how quick I can brake without ABS'. Where the vehicles the same weight?, Where the tyres the same make and size? Road conditions? Disc and pad condition? Make of pad? Friction material? There are too many imponderables to even confirm or deny your arguments.

A small car with large wheels and tyres will outbrake a large vehicles with standard tyres. For normal every day braking there is very little difference between ABS and a non ABS system but for extremes of braking in virtually any conditions the ABS system will be superior. Use of the local public weigh bridge will give a good indicator of weights and co-efficient of friction if you want to establish a sound agrument either for or against ABS but conjecture in one off situation does nothing to resolve the original argument.

Regards

Jaxs