racing and Ferrari's ABS system

Does anyone understand Ferrari's ABS system? Here is the situation. My ABS went out on the racetrack when some crap fouled my wheel sensors. The result was that I feel (maybe I'm dumb) that now I can break deeper in corners. I don't think my foot is smarter than ABS but i think I like it better without ABS. O.K. here is my theory you tell me if I off the deep end. ABS is set up for street tires which limit at 1g braking at best. My huge Pirelli slicks have a 1.5 G capability. Is the ABS thinking I'm on street tires and no allowing me the full benefit of my slicks? There has to be more than just the speed of rotation that the wheel sensor picks up or else I would have a ABS pulsation with foot on brake and not moving tires at a stoplight right? Somehow the ABS is sensing the car is moving AND the wheel speed? Second bit of theory...I'm safer on the racetrack without ABS because if I spin and "put both feet in" (standard technique) my locked wheels will have no adhesion and I spin in a predictable straight line and people don't hit me. If I spin with ABS the car trys to get grip by controling lock-up and I may veer off in an unpredictable way as my tires grip the track. O.K. what do you guys think?

 

Stop me if you've heard this before...

ABS does not shorten braking distances; it acutally lengthens them. Optimal braking is done right on the very verge of locking up the wheels. ABS never approaches this high of a threshold.

So you're right on: I'd prefer the loss of ABS, too. I'm sure that it actually does let you brake deeper into a corner.

I actually pull the ABS fuse from my daily driver during snowy and slushy conditions for the same reason. It dramatically shortens the stopping distance. I figured that out after coasting right through an intersection during a nasty Pittsburgh February, with my ABS pulsing all the way...

--Matt

 

Yes, I would agree you are better off on the track w/o ABS. If you are skilled at all, you don't need it on the street either.

The ABS system works by comparing the rotational speeds of all 4 wheels. If there is a significant difference between any 1 wheel speed and the average of the other wheels, then the system intervenes.

 

Which is why you don't feel the pedal pulsating at a stop light.

 

OK, the following is just my $.02, and no disrespect is intended toward anyone. A few random points about ABS.

First off, ABS *is* worse than locked up tires ONLY in heavy snow and gravel. Why? Because a locked up tire will cause a pile of snow or gravel to build up in front of it, thereby shortening braking distance. But if you're on ice or just packed snow, forget it. As always, the coefficient of friction for a rolling tire is greater than that of a locked tire. In other words, you'll stop in a shorter distance if your tire is not locked up. If the driver is good enough to threshold brake the car while driving on ice, god bless him/her. Me, I'll take the computers any day. In the winter, I try very hard not to trigger the ABS, because, if I'm successful, I'll have slightly shorter braking distances. But if I'm hitting the brakes hard enough to trigger ABS, then I do want the system in place, especially if I'm trying to steer as well (a locked tire cannot steer). Keep in mind that modern ABS works a lot better than older systems; with more powerful computers, cycles get much faster and the "pulses" get to be much quicker. So the effectiveness of ABS on, say, a 1989 328 will not be the same as on, say, a Challenge Stradale.

Second, modern, four channel ABS works by calculating incipient wheel lockup, but NOT just by sensing when a wheel IS locked up, then releasing it. Common misconception. Rather, it senses the wheel rotation, compares tiny tiny tiny differences in the rate of rotation at different wheels (three channel looks at each front wheel and both back wheels as one, four channel looks at all four individually), looks at its algorithms and calculates the ideal slip angle for braking, then dances back and forth around it. ABS, when engaged, NEVER allows a wheel to lock. Rather, the wheel is question will be rotating SLOWER than the other wheels; when the difference in the rate of rotation reaches a certain point - the slip angle has increased beyond a permitted parameter - then the ABS intervenes. That intervention occurs before the slip angle reaches 100% (a locked wheel).

So, yes, a theoretically perfect driver can brake the car at 100% of the tires combined braking force, at the maximum effective slip angle. Whereas a good ABS system will be slightly below that, because it's never at the max, but rather always just below and then just above it (not locking the wheel, BTW). But I know *I'M* not that good!

The magic of modern ABS is that it can MODULATE EACH WHEEL INDIVIDUALLY. The driver can, at best, reduce pressure at all four wheels. As one example, at New Hampshire International Speedway, turn 9, there is a dip as I enter it. I always lock up my left rear wheel. The ABS fixes that. If I didn't have ABS, I'd either have to live with that one locked wheel (and decreased braking ability), or else reduce pressure overall to get that wheel rotating again (decreased braking ability too).

Third, for those who believe that ABS makes cars slower on the racetrack, let me ask you a question. If ABS does make the car slower, then why has almost every sanctioning body banned ABS? Is it because they want cars to go faster? For example, ABS was in F1, but the FIA banned it because it made the cars too easy to drive - as well as faster. Teams didn't adopt ABS because they wanted to turn in SLOWER lap times, right? If the world's best and highest paid drivers run faster lap times with ABS installed in their cars, do you think you'd benefit from it too?

Third, to address your concerns specifically, FBB, it shouldn't matter which tires you're running on the car, as the 355 Challenge ABS system isn't any different (I'm reasonably sure of this, but could be wrong). Yes, it is possible that changing to slicks does cause some problems for your car's ABS, but why not just test it? Do some practice stops, and measure your distances - street tires v. slicks, then with ABS and without.

As for the concern about "two feet in" when you spin, it's a question that's been discussed a lot. Generally, I'd much rather AVOID SPINNING IN THE FIRST PLACE. A lot of spins are caused by ineffective trail-braking or panic-braking while cornering, and ABS might help with that. So I'd just as soon not spin. But what happens if you do spin? Well, ABS doesn't help much if you're spinning. If the tires are rotating at a PERPENDICULAR to the car, it doesn't matter whether the tire is rotating or being locked by a brake - the car will continue to spin (albeit perhaps at a different rate). Also, keep in mind that "both feet in" is pretty much bending over and saying your prayers. After all, you could just as easily be spinning directly into the wall, where ABS might have helped you send the car off in a safer direction. There isn't an easy answer to this question, IMHO, other than to say that I'd rather have the ABS to help prevent the spin in the first place, rather than worry about the potential effects AFTER I've failed miserably and the car is out of control.

Don't believe me? Check out:
http://www.geocities.com/nosro/abs_faq/#What%20are%20the%20advantages

Have fun on the track!

vty,

--Dennis

 

Dennis, really good points.

ABS is good in that you can steer while braking hard - especially in snow and ice.

However, while race cars may benefit from advanced ABS designs, I have found road cars to be somewhat lacking ABS performance. In some of my vehicles, I could brake shorter on icy streets by myself w/o ABS. I believe ABS was added to road cars more as a safety feature to save the average driver in emergency situations, not to shorten braking distances.

On the track, I find the ABS intervention disconcerting when I'm trying to finesse the brakes. Maybe that is just a misperception on my part.

 

The 4 channel system of the 360 Challenge or N-GT car is sensational. They are very sensitive also to the use of grooved discs, cooling and various pad choices. The balance, bite and feel can be changed a fair amount by experimenting with component hardware.

The 3 channel of the 355 Challenge is far less effective, but still faster than non ABS on slicks in racing.

We've tested a 360 with the ABS disconnected.....and also Michelotto say it's about 2 seconds slower without ABS around Fiorano.

 

i have a f512m and the abs is turned off all the time just a little switch on the dash but never had this on previous ferraris that i have owned another reason for not to sell it