jscott82

I expect this will end up being like asking about engine oil... But here goes.

When threshold braking:
I think we all agree with modern motorsports ABS you can/should rely on ABS to maximize braking performance. Just hammer the pedal and let the magic box sort it out.

But what about modern street car 981/991 ABS? Still better than a human?

My real question is this though... What about previous Gen 987/997? Specifically street ABS on r-comp tires.

winders

ABS, flappy paddles, traction control......whatever happened to driver control!

A432

I did a season with a stock 987R switching back and forth between NT01's vs. R7's and Pagid RS29's vs. PFC with data logging and was fastest with "nibbling" ABS but not deep into it.

Imho the reason was two fold.....the softer suspension responded better to smoother application or "feel" otherwise it would get upset and the full ABS had a lower average decel. than at the threshold.

By barely getting some ABS, the car wasn't using that suboptimal programmed decel rate as in full ABS. I was also smoother putting transitions together by thresholding without full ABS because the ramp up and down of braking was smoother.

That said, someone without many reps and seat time in the car might be faster using full stock ABS....it's understandable that at days like the PEC teaching new students,

they want them to feel what the car can do and how high the limits are in full abs. But with the stock ABS, stock suspension, R tires and some time, there was the opportunity to do better with experience and feel.

While instructing that year it played out the same with most people who could feel what the car was doing and adapt.

That's probably the tunable motorsports ABS difference, the adaptability to the specific car's setup, track, conditions and driver while the stock ABS is limited to a one size fits all for any conditions and driver inexperience.

Veloce Raptor

^^this^^

sjfehr

ABS works by rapidly switching back and forth between overloading the tires and releasing the brakes, neither of which is ideal for stopping; it's way better than locked brakes, but not as fast as braking right at the threshold.

CCA

Beyond the argument about lap times, the constant hammering of ABS can cause some brake pads to crumbling and/or delamination, though most race pad manufactures have worked to correct this issue. The hammering impacts other aspects of the suspension as well, ball-joints, wheel studs, etc, so something else to consider.

HenryPcar

What ABS cannot do is modulate the braking pressure. Once activated during a lockup it is either on or off in the pumping cycle. Humans can modulate the amount of brake pressure even on a 4-wheel drift and especially on a wet road the driver can still control the car while braking.

996AE

Smooth is fast

This is on off braking, shifting, wheel inputs and throttle control

DTMiller

There's a very good thread here: https://rennlist.com/forums/racing-a...-it-bad-2.html that talks about these issues and despite the very expert input from people who really really know what they are talking about it still gets really murky really fast; and you're asking the right question. It seems clear to me that there exist race cars where the ABS system is far superior to humans but the tricky part is figuring out whether you, the casual HPDEr or not-brand-new race car driver, are driving one of the cars where ABS is universally superior.

Thundermoose

After flat spotting two sets of tires when my ABS became disabled, I'd say that MK60 ABS is superior to my skills.

fleadh

Over the last few years I've driven a lot of race cars with (motorsport) ABS and the cars are always fastest when staying out of the ABS if it activates on more than wheel at the same time and you can feel it in the pedal:

Straight line braking over bumps? You're going to have a hard time making the corner, if you're on the limit.
Straight line braking w/o bumps? It's not as bad as above, but it generates so much heat in the system you generally don't want to drive this way. Also, the more you rely on the ABS the harder it is to come off the brake pedal and have it transfer the weight as you'd expect. Still will slightly increase the length of the braking zone.
Heavy trail braking into a bumpy corner? Very inconsistent and you won't slow the car down much. Point above about coming off the brake pedal multiplied by 8123394x. Avoid when possible.
Heavy trail braking into a smooth corner? Over loads the front tires and car simply won't turn.

Once you activate ABS bleeding off the pedal doesn't necessarily release a proportionate amount of pressure from the brake calipers, which makes control of the weight transfer slower and less predictable.

In my experience there's only 2 places where ABS in a race car shines. In the wet: you still want to avoid feeling it in the pedal for all the reasons above, but it gives you such a larger buffer for keeping the car under control while braking / entering a corner. And, stopping the flat spotting of inside front tires in certain corners where you really want to carry a good amount of brake pressure into the corner but the car is so unloaded on one side that without ABS after a couple laps you'll have a big flat spot.

With the motorsport ABS systems I don't doubt that if you spent a day working on a single corner under a finite set of tire, car and track conditions you could probably get the fully activated ABS to be better than a good driver for that one corner at that moment in time. However, every corner is different and the same corner changes lap by lap as conditions and tires change. The same programming that works for one corner at one time won't work for another corner at another time and that's why the motorsport ABS is good, but not a catch all for making the car go around the track as fast as it possible can. At least not with currently available technology.

Just my 2c anyway... Happy New Years everyone!

-mike

ProCoach

For the OP's car and purpose, this is very good advice and a very good observation.

All true on the latter. Motorsports ABS is a different beast. M4 and M5 Bosch are FAR superior to converted OEM Mk60 Teves systems.

Actually, it's the rate and amplitude of the DRIVER input that overloads the tires. It's the ABS system that releases individual wheel brake pressures, but yes, the quickest deceleration occurs just at the threshold of lockup, with wheelspeeds from 0 to a range of 7-12 per cent slower than the vehicle speed.

Excellent point. Good thread (starting out, as you say), too.

Bingo, in bold.

Happy New Years to you too, Mike!

ProCoach

I will add that there are a fair number of competition prepared cars that have never checked bias (including those with fixed rear pressure reduction), set up the treadle and pushrod length correctly on the adjustable master cylinders or taken into account changes in calipers, rotor size (for swept area) and pad compound.

This means the system can be compromised from the start.

sjfehr

I agree completely that it's the driver's input driving this. However, ABS will not engage on a wheel if braking pressure is below the threshold for lock-up. So if ABS is engaging, you can assume the tires are overloaded to the point of locking, and thus not giving optimal braking force during brake engagement periods of ABS engagement, either. Beats flatspotting a tire, and allows the driver some modicum of control, though!

jayzbird

All these nannies are a double-edged sword. Yes they allow you to get on track and protect you from your own inexperience, but also make it much harder to actually gain more advanced skills. I have been humbled at just how bad my braking skills are racing schools, where I had huge problems locking up the brakes on a SM or formula car despite having a lot more track experience than most participants. Couple that with the extreme speed so many street cars are capable of these days, making disabling the nannies quite risky, and it can be very hard to really learn how to drive at the limit. In retrospect I wish I had spent more time learning the basics in a less capable car than a 911 turbo.