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#1 cedarsf1

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Posted 25 February 2015 - 12:42

Hey guys. Two questions on braking for you...

 

1) On a modern car, is the fastest way to slow down using ABS, or keeping the car just short of ABS activation. On the track I initially go easy on the brake pedal to transfer the load smoothly onto the front, and then I fully engage the ABS. It seems to me like this is the fastest way to brake, but some people insist that one should brake just short of ABS activation.

 

2) How much time is there really to be gained under braking. Let's say you brake from 140 mph to 90 for a corner, and you brake 30 ft earlier than you possibly could without overrunning your turn in point. How much time are you really losing? I guess this is a math problem, and I'm terrible with that!



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#2 Stu56

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Posted 25 February 2015 - 16:16

Hey guys. Two questions on braking for you...

 

1) On a modern car, is the fastest way to slow down using ABS, or keeping the car just short of ABS activation. On the track I initially go easy on the brake pedal to transfer the load smoothly onto the front, and then I fully engage the ABS. It seems to me like this is the fastest way to brake, but some people insist that one should brake just short of ABS activation.

 

2) How much time is there really to be gained under braking. Let's say you brake from 140 mph to 90 for a corner, and you brake 30 ft earlier than you possibly could without overrunning your turn in point. How much time are you really losing? I guess this is a math problem, and I'm terrible with that!

 

My 2penny's worth:

 

1) The fastest way is to reach the maximum available grip of the tyre under braking as soon as possible, and maintain that loading until you have reached your desired (reduction in) speed. That tends to happen *just* before ABS is engaged.

2) It's more about "how" you brake. Specifically, how you choose to cope with the physics (weight transfer) as you blend off the brakes into / during the turn-in phase of the corner. The best amateurs and the top pro's are simply fast, everywhere. But, I think if you were to poll all of the driver coaches and ask them for one area where the top amateurs and the pro's make the biggest difference actually *in* the car, I reckon it would be here. 



#3 kikiturbo2

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Posted 25 February 2015 - 18:41

1. On track the recipe is to hit the brakes hard as you can and fast. For the inexperienced driver this usually means applying the force that they will find impossibly high and it takes quite a while to get used to it. This is even more important in any car with a hint of downforce.

While driving instructors (driver safety training) will usually make you activate the ABS and keep it activated, braking performance is usually better with the brakes on the verge of lock, and not in the full antilock mode..

 

It has to be said that getting off the brakes is maybe even more important as you have to get that part right and do it gradually while entering the turn... at this point it is about using the maximum circle of traction and going directly from full longitudinal deceleration into full sideways acceleration... without going trough the zero point.. if you know what I mean...

 

2. if you brake 30 feet too early your oponent on the track will have 30 ft travelling at higher speed that you.. :)



#4 Greg Locock

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Posted 25 February 2015 - 21:01

In the early days of ABS I'd have guessed a human could outbrake an ABS, because the ABS cycled over quite a wide range of slip velocities. However, since you can now buy a tunable ABS, that is only the case if you have set it up wrong, or need to spend more time/money. I'd be very wary of any tests based on stopping distances in the dry, the scatter of results from brake tests is legendary

 

Bear in mind a full ABS gives you EBD as well so you don't need to worry about brake balance.

 

Also trail braking should be easier with ABS.

 

But then I like gizmos.



#5 kikiturbo2

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Posted 25 February 2015 - 21:58

Google ABS ice mode on porsche forums, such as rennlist... quite a bit of bent metal due to gt3 ABS system thinking it got on ice when in fact people hit the some warped asphalt in the brake zones.. Had it happen to me on occasion..

Then again, I really like the active yaw contol that also works trough ABS during braking on my evo.. :)

 

I did a tire test with continental a few years ago, and one of the tests was a handling course with a full brake zone on one of the straights. Controlled wet asphalt and fully instrumented bmw 120i's. I had never seen a car with so much telemetry inside.

 

Anyhow,.. the conti engineers were verry insistant on two things during the brake test... 1. Super fast ramp up of pedal pressure, 2. full on braking with ABS working full time.

I nedeed some time to get used to hitting the brakes so hard in the wet, but had a major fight with them on the issue of braking on the ABS limit (what I did constantly) and being in the zone of ABS modulating the brake pressure (what they wanted me to do). Now, I do understan why they insisted... because that way the brake force was more constant and we had the opportunity to see the difference in the tires more, but after comparing the decel graphs they concured that our brake performance was quite similar. And I am no Senna..



#6 gruntguru

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Posted 25 February 2015 - 23:14

2. if you brake 30 feet too early your oponent on the track will have 30 ft travelling at higher speed that you.. :)

A lot more than 30 ft.



#7 cedarsf1

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Posted 26 February 2015 - 09:11

So how much track time do you actually lose braking 30 ft early from 140 to 90 mph?

 

I always thought that maximum braking is with the ABS activating. So the consensus opinion is that this is not true? Why did F1 have ABS brakes in the past? I know old ABS systems aren't as good as a good driver, but I thought modern ones are better.



#8 Stu56

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Posted 26 February 2015 - 11:14

So how much track time do you actually lose braking 30 ft early from 140 to 90 mph?

 

I always thought that maximum braking is with the ABS activating. So the consensus opinion is that this is not true? Why did F1 have ABS brakes in the past? I know old ABS systems aren't as good as a good driver, but I thought modern ones are better.

 

It's possible you may gain time, depending on how you are braking. I've raced competitively at club level in the Lotus Elise Trophy and have gb's of data showing that braking later and harder is actually much slower than braking earlier and upsetting the car less. Stowe corner at Silverstone is a prime example. It's all about the transition into braking (especially in the wet) and off the brakes.  Just offering my own experience having gone from one style to another. 



#9 cedarsf1

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Posted 26 February 2015 - 11:34

It's possible you may gain time, depending on how you are braking. I've raced competitively at club level in the Lotus Elise Trophy and have gb's of data showing that braking later and harder is actually much slower than braking earlier and upsetting the car less. Stowe corner at Silverstone is a prime example. It's all about the transition into braking (especially in the wet) and off the brakes.  Just offering my own experience having gone from one style to another. 

Yes, I understand that. My questions is theoretical I guess. I'm really just wondering how much time you actually lose braking early for this specified distance.



#10 Stu56

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Posted 26 February 2015 - 12:32

Yes, I understand that. My questions is theoretical I guess. I'm really just wondering how much time you actually lose braking early for this specified distance.

 

every 10mph is 14.7 feet per second.

So 140mph = 205ft per second. 

Work that back, if you brake 30ft later, you would be braking 0.14 seconds later on the stopwatch. On the borderline in terms of human judgement. Visual if you had a reference point but that changes every lap. 



#11 bigleagueslider

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Posted 27 February 2015 - 07:38

The quickest lap time usually results from carrying the most speed through the corners. Braking late and getting on the throttle early. There is no driver that has better brake control than a modern ABS system does.



#12 Lee Nicolle

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Posted 27 February 2015 - 08:25

In the early days of ABS I'd have guessed a human could outbrake an ABS, because the ABS cycled over quite a wide range of slip velocities. However, since you can now buy a tunable ABS, that is only the case if you have set it up wrong, or need to spend more time/money. I'd be very wary of any tests based on stopping distances in the dry, the scatter of results from brake tests is legendary

 

Bear in mind a full ABS gives you EBD as well so you don't need to worry about brake balance.

 

Also trail braking should be easier with ABS.

 

But then I like gizmos.

ABS limits braking. A standard road car ABS increases the braking distance. Turn it off by whatever means and on a racetrack you will be faster under brakes. 

ABS is handy on inclement conditions, loose surfaces or when towing. And learn to live within its limits.

Early Ford ABS was dreadfull. The pedal would sink when a wheel locked giving you that 'oh ****' feeling. OK these days.



#13 Lee Nicolle

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Posted 27 February 2015 - 08:26

So how much track time do you actually lose braking 30 ft early from 140 to 90 mph?

 

I always thought that maximum braking is with the ABS activating. So the consensus opinion is that this is not true? Why did F1 have ABS brakes in the past? I know old ABS systems aren't as good as a good driver, but I thought modern ones are better.

F1 had ABS? When?



#14 Greg Locock

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Posted 27 February 2015 - 09:38

It was banned in 1994, as part of a package to slow the cars down.  So, obviously, at least some teams thought ABS was quicker.

 

A good driver can beat ABS in the dry, given various provisos, such as forewarning. Whether he can beat it after 70 laps, or when tired, or surprised, or on split mu surfaces is another matter. At least one reasonably successful driver uses ABS on track.



#15 Stu56

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Posted 27 February 2015 - 12:21

ABS limits braking. A standard road car ABS increases the braking distance. Turn it off by whatever means and on a racetrack you will be faster under brakes. 

ABS is handy on inclement conditions, loose surfaces or when towing. And learn to live within its limits.

Early Ford ABS was dreadfull. The pedal would sink when a wheel locked giving you that 'oh ****' feeling. OK these days.

Seconded. Note that ABS only kicks in when the tyre loses adhesion, not before. Therefore, a human being will also be able to optimise braking by that very sole fact. 



#16 Joe Bosworth

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Posted 27 February 2015 - 14:09

Allow me to put some real numbers on braking things to try to answer your questions.  I have taken the liberty to convert your basic question into metric measurements bacause over time I have developed dozens of metric based programmes including such things as lap time forecasting based on max G, HP and weight inputs.  I am too lazy to convert any of these to non-metric units.

 

So I have inputted your question into braking from 225 kph to 145 kph and your braking 30 feet early to 9.1 meters early.  I have also assumed that your vehicle has a maximum braking capability of 1G.

 

These numbers result in the 225 to 145 slowing effort will occur over 116.52 meters and take 2.27 seconds, (I am reporting in two decimal place accuracy).  To compare this to your alternative of braking 9.1 meters earier I am assuming that the car will be held at 225 kph for these 9.1 meters which then adds .15 seconds to the late braking alternative.  So this now has you taking 2.42 seconds to traverse 125.62 meters.

 

Now the early braking alternative finds you now braking at .93G and taking 2.44 seconds to traverse the same 125.62 m distance.

 

We can analyse any series of corners in a lap to find out what the effect on lap time is for early braking but this example shows that there is very little in it.  I reality there are two factors which make the real scenario  a bit worse for the early braker and those are that the late braker will continue to accelerate for those 9.1 extra meters and the early braker opens themselves up to an easier passing move by the late breaker if it is close enough.  I have always found that optimum lap time comes from trail braking after the turn in has started and thereby getting some free and easy yaw control and resultant higher exit speed.  The complexities of this are best kept to a differnet thread.

 

On the issue of how good are ABS systems I can throw in a few items from my experiences.

 

For both optimum braking and for optimum acceleration the best results occur with a bit of slip between rubber and road.  In other words, for braking tyres are spinning at less than true vehicle speed and for acceleration they are spinning at greater than vehicle speed.  The amount of slip for best performance is quite variable over a small range.  The best slip is dependant on rubber compund, track suface and both track and tyre temperature.  Others might offer better data but I find that the best performance is developed at slip ratios of 104 t0 112 percent of true vehicle speed.  A  good starting point for testing is 108%.

 

Now Greg has highlighted adjustable systems.  I have nerver come across one that doesn't require a computer to set and I can absolutely advise that unless you have a good data collection system on your car that you will never get there by seat of the pants.  I also know that your day to day driver sold by tthe tens of thousands have ABS systems that are set so far into the average driver's frailities that it is quite easy for a good driver to get into such a car, turn off the ABS and out perform the factory set ABS.  Not the least of problems are that the slip ratios are set below optimum and the cycle rate is slow enough and wide enough that the tyes are constantly cycling outside the best real setting.  A good driver and I note that there are not too many of these found day to day can feel the point of optimum slip and hold the car at that point without much if any cycling.  I know from experience that even the the Vette ZO6 factory system can be beaten by a big margin by an accomplished driver.  I also accept that in the electronic days of F1 that they developed systems that couldn't be beaten.  The real problem was that these systems cost far more than the cost of 99.9% of the total cost of cars bought today.

 

So, if you really are good enough and can prove, it switch off the factory electronics for best performance on your evey day driver.  Otherwise leave it on because even the factory settings will beat your performance. The proof only can come from lap time on the track.

 

Regards



#17 Greg Locock

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Posted 27 February 2015 - 23:54

I'd add that the ABS works off the wheel speed sensor, and can detect the acceleration of the wheel, so it knows when it has passed peak braking force because the rotational acceleration of the wheel increases. So it could find the optimum 

 

Here's some real results for a submission zero tire (ie the first attempt to meet a given spec), run at various loads. I've normalized fx by the vertical load so effectively it is a plot of mu vs slip %age, As you can see, the optimum is actually pretty broad, so if an ABS cycles from 5% to 15% slip then its average braking will be within 5% or so of the peak.  Note that the basic advice for a non ABS in a straight line to just press very hard actually isn't a bad option, the downside of going too deep is not as bad as not hitting the peak.

 

8p7s9v99zl9qwrn4g.jpg


Edited by Greg Locock, 28 February 2015 - 21:46.


#18 rdyn

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Posted 28 February 2015 - 11:47

Hey guys. Two questions on braking for you...

 

1) On a modern car, is the fastest way to slow down using ABS, or keeping the car just short of ABS activation. On the track I initially go easy on the brake pedal to transfer the load smoothly onto the front, and then I fully engage the ABS. It seems to me like this is the fastest way to brake, but some people insist that one should brake just short of ABS activation.

 

If you press the brake pedal down slowly, estimating the vehicle speed can be difficult -> ABS performance and stability is hindered.
 

=> press clutch pedal

=> press brake pedal (fast)

=> let ABS do the work


Edited by rdyn, 28 February 2015 - 11:48.


#19 cedarsf1

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Posted 01 March 2015 - 03:36

If you press the brake pedal down slowly, estimating the vehicle speed can be difficult -> ABS performance and stability is hindered.
 

=> press clutch pedal

=> press brake pedal (fast)

=> let ABS do the work

If you slam on the brakes, isn't the sudden load transfer going to be detrimental? When I mean that I smoothly hit the brakes, I mean for a split second I apply some brake pressure to put some load on the front tires, and then immediately floor the brake pedal and let the ABS do its thing.



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#20 cedarsf1

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Posted 01 March 2015 - 03:48

Thanks for all your great replies! You guys have given me a lot of things to think about.

 

I suppose one other factor to consider is that if I brake early and realize before I get to my turn in point that I'm slowing down too much, I would let off the brakes a bit, so the speed lost isn't as much as if I actually slowed all the way down to my turn in speed too early.



#21 cedarsf1

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Posted 01 March 2015 - 03:54

I always thought that ABS does the work of threshold braking, that it senses tire slip and then does its thing. But from what I understand you guys saying, ABS waits until a tire has actually locked up to release pressure, and then allows a tire to lock up again until it releases pressure again. Thus, whereas a good driver in a non-ABS car is modulating the brake pressure to allow just a little bit of tire slip without the tire fully locking up, the ABS cycles between locking up a tire and unlocking it.



#22 bigleagueslider

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Posted 01 March 2015 - 05:21

Conventional ABS systems function by bleeding fluid from the hydrostatic brake circuit at very high frequency when the speed sensor at any wheel detects loss of traction. This results in the braking torque applied to the wheel being modulated so that the tire operates right at the limit of sliding and gripping. The ABS functions at a very high frequency that no human driver could ever replicate. In fact, the most effective use of ABS would be to apply the brakes while also applying the throttle going into a turn, and thus letting the ABS system function as a traction control system. Exiting the turn you would release the brakes and the engine with open throttle would immediately be producing power out of the turn.



#23 Greg Locock

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Posted 01 March 2015 - 06:43

I always thought that ABS does the work of threshold braking, that it senses tire slip and then does its thing. But from what I understand you guys saying, ABS waits until a tire has actually locked up to release pressure, and then allows a tire to lock up again until it releases pressure again. Thus, whereas a good driver in a non-ABS car is modulating the brake pressure to allow just a little bit of tire slip without the tire fully locking up, the ABS cycles between locking up a tire and unlocking it.

 

 

No, your first guess was closer. An ABS does not slow the wheel to zero rotational speed, in fact that is why the ABS cuts out at low speed, and is not as good on snow or gravel.



#24 rdyn

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Posted 01 March 2015 - 09:27

If you slam on the brakes, isn't the sudden load transfer going to be detrimental? When I mean that I smoothly hit the brakes, I mean for a split second I apply some brake pressure to put some load on the front tires, and then immediately floor the brake pedal and let the ABS do its thing.

Braking slowly will probably cost you more time

 

I always thought that ABS does the work of threshold braking, that it senses tire slip and then does its thing.

ABS cannot sense tire slip. Tire slip depends on wheel speed and vehicle speed - vehicle speed has to be estimated



#25 imaginesix

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Posted 01 March 2015 - 16:40

If you slam on the brakes, isn't the sudden load transfer going to be detrimental? When I mean that I smoothly hit the brakes, I mean for a split second I apply some brake pressure to put some load on the front tires, and then immediately floor the brake pedal and let the ABS do its thing.

The reason for giving time for the load to transfer to the front is to avoid prematurely locking up the front tires at the initial braking phase. With ABS, there is no risk of locking up the tires, obviously. The load will transfer to the front just as with any other car, but without the need for modulation from the driver.

#26 Fat Boy

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Posted 01 March 2015 - 19:31

None of you guys are talking about a good racing ABS. A properly tuned ABS on a racetrack does a better job than a human. I'm not talking about a road car system that has to deal with all sorts of road conditions, just a racing system on a race track. They do not have to wait until a 'tire loses adhesion' (I'm not even sure what that means, exactly). Good systems have predictive qualities.

 

30 meters, 2 car lengths or 0.14 seconds is getting to 'the borderline of human judgement'? Not even close. A good racing driver will hit braking points *much* tighter than that. 3 meters or less would be expected. A world-class driver will be closer to a 30 cm resolution than he will be to a 30 meter one.

 

The fast way (on a racetrack) to use the brakes is to use them all at once and then get off of them. If you have ABS, then hit them hard enough the ABS is on as soon as you touch the pedal. Keep in mind, the brake release is more important. It's _a lot_ earlier than most people think. Tire scrub, rolling frictions, aero drag, etc. will be slowing the car even after brakes are released and it has a very large effect. Here's food for thought. Friction will be slowing the car even after throttle application has been initiated, especially in a fast corner.



#27 RogerGraham

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Posted 02 March 2015 - 11:11

And if I understand correctly, with very-high-downforce non-ABS cars (e.g. F1), after initially smashing the brakes you need to be gradually releasing them as your speed slows, due to the loss of downforce reducing the mu.



#28 Fat Boy

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Posted 02 March 2015 - 14:57

Not really gradually. You have to hit the pedal with as much leg as you have and then over the course of maybe two seconds, release the pressure back down to zero. It has to happen in a controlled manner while down shifting and presenting the car to the corner. Ultimately it starts to be a muscle memory thing, but initially a lot of people struggle to come to grips with it.

#29 RogerGraham

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Posted 03 March 2015 - 04:40

Yes, "gradually" is relative given the braking power of such cars!  :)  

 

I meant, between the initial smashing of the brakes and the "eventual" release of the brakes.



#30 cedarsf1

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Posted 04 March 2015 - 06:20

So, it sounds like the consensus opinion here is:

 

1) On a good ABS system, it's best to use the ABS.

2) Most street cars don't have great ABS, so it's better to modulate the brakes just short of ABS activation.

3) Stopping 30 ft early from 140 to a 90 mph corner loses about .15 seconds (which is think is a very significant amount to lose in just one braking zone).

4) It's better to slam on the brakes in a car with good ABS because you don't have to worry about the wheel locking.



#31 Greg Locock

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Posted 04 March 2015 - 10:51

2) Most street cars don't have great ABS, so it's better to modulate the brakes just short of ABS activation.

 

I dunno, yes, if you can catch the peak mu, otherwise the penalty for overshooting optimum slip ratio doesn't seem a whole lot worse than going under.



#32 Fat Boy

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Posted 04 March 2015 - 13:13

Pretty much agree with this. I would add to #4 that most people are much too timid on initial brake application, which is a massive time waster on the track.

I also agree with Greg, most road car systems aren't worth much and can be beat regularly. Racing systems allow _big_ slip ratios compared to street systems.

#33 carlt

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Posted 04 March 2015 - 13:20

2) In a competition environment with a street type car, yes.

On the street, in an everyday situation, I would suggest one is generally not driving with the same personal absolute peak of potential performance as in competition, therefore when an emergency occurs and max brake retardation is required , mash the pedal as fast and hard as possible and let the ABS etc sort you out.



#34 DaveW

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Posted 04 March 2015 - 13:32

Greg,

 

Thanks for the Tyre Load/Angle curves you posted above.  I was intrigued by the trajectories above the peak load.  I guess that the tyre was treaded, and I suppose that the rather interesting shapes "post stall" were caused by individual tread blocks "stick/slipping".   Would you care to comment?



#35 Ross Stonefeld

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Posted 04 March 2015 - 16:01

Ive never locked a wheel in the dry in a road car. But I've never been near enough to an accident to have to. I'm usually checking up much earlier.

 

But I live in the midwest so the ABS on my (90s) Ford Explorer is constantly kicking in. I actually preferred it before I got it fixed because at least I didn't have a tendency to overcharge corners. Now it's just "screw it, I'll brake when I feel like it".



#36 CSquared

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Posted 04 March 2015 - 16:44

2) Most street cars don't have great ABS, so it's better to modulate the brakes just short of ABS activation.

I dunno, yes, if you can catch the peak mu, otherwise the penalty for overshooting optimum slip ratio doesn't seem a whole lot worse than going under.

If I understand what you're saying, the penalty for overshooting can include flat spots.

#37 gruntguru

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Posted 04 March 2015 - 23:56

Greg,

 

Thanks for the Tyre Load/Angle curves you posted above.  I was intrigued by the trajectories above the peak load.  I guess that the tyre was treaded, and I suppose that the rather interesting shapes "post stall" were caused by individual tread blocks "stick/slipping".   Would you care to comment?

I would be very surprised if those wiggles repeat (overlay). They look more like oscillations unique to the testing method than chracteristics of the tyre.



#38 Greg Locock

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Posted 04 March 2015 - 23:58

Dave - I'm tempted to say that they are something to do with bending wave speed of the belt, I haven't done a mu plot of many tires (usually we need the fz vs Fx characteristic obviously), so I don't know if it is unusual.

 

Csquared, true, I was thinking about the braking force, not practicalities.



#39 gruntguru

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Posted 05 March 2015 - 00:05

If I understand what you're saying, the penalty for overshooting can include flat spots.

No, the ABS keeps the wheel rotating at all times provided vehicle speed is above the threshold. The wheel never locks, it just cycles between very high and moderate slip ratios.

 

http://inform.wabco-.../8150101943.pdf See diagram on pdf page 10.



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#40 kikiturbo2

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Posted 05 March 2015 - 14:03

Not really gradually. You have to hit the pedal with as much leg as you have and then over the course of maybe two seconds, release the pressure back down to zero. It has to happen in a controlled manner while down shifting and presenting the car to the corner. Ultimately it starts to be a muscle memory thing, but initially a lot of people struggle to come to grips with it.

 

When I drove a BMW formula Junior car we had a brake pressure display on the steering wheel, which was totally useles except for getting the fell for the pedal when stationary... that way the instructors could tell us the "number" for optimum brake force on initial brake application and we had something to try while waiting to go..  It was something like 90 or 100 kg on the pedal.. but was some time ago.. might not remember well..

 

Truth be told, your average driver will never ever apply max brake force, even in emergency ....that is why modern ABS tends to have panic stop algorithms that increase the brake force automatically...



#41 Ross Stonefeld

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Posted 05 March 2015 - 21:50

90kg sounds like a lot for a Formula BMW.

 

I'd think a brake pressure guage would be interesting, it'd help you calibrate what you should be feeling in your leg to what the car will feel like. Probably less helpful once you get your head around the car, but when you're learning proper race car brakes, a bit of downforce, etc it would seem to be a useful "here's a good starting point".



#42 Greg Locock

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Posted 06 March 2015 - 00:39

I would be very surprised if those wiggles repeat (overlay). They look more like oscillations unique to the testing method than chracteristics of the tyre.

 

It's a pretty slow test, so it isn't a dynamic effect. Also note that the same pattern is seen in both slip directions, which probably kills my bending wave theory. 



#43 gruntguru

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Posted 06 March 2015 - 04:47

I was trying to say the oscillations (probably stick/slip as Dave suggests) would repeat but randomly phased i.e. not actually a function of slip %.



#44 imaginesix

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Posted 06 March 2015 - 06:57

Greg,
 
Thanks for the Tyre Load/Angle curves you posted above.  I was intrigued by the trajectories above the peak load.  I guess that the tyre was treaded, and I suppose that the rather interesting shapes "post stall" were caused by individual tread blocks "stick/slipping".   Would you care to comment?

The squiggles could be just as common at low slip angles as high slip angles, but we wouldn't notice them because the slope of the plot is steeper so the squiggles would be masked.

Edited by imaginesix, 06 March 2015 - 06:58.


#45 DaveW

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Posted 06 March 2015 - 09:08

The squiggles could be just as common at low slip angles as high slip angles, but we wouldn't notice them because the slope of the plot is steeper so the squiggles would be masked.

 

Possibly.  Or it could be that the angle shown on the plot is not the angle of the tyre at the contact patch (Greg's "belt", I guess).



#46 gruntguru

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Posted 07 March 2015 - 07:17

Guys the X axis is not angle - its slip ratio - the plot is for longitudinal grip.



#47 imaginesix

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Posted 07 March 2015 - 08:03

Guys the X axis is not angle - its slip ratio - the plot is for longitudinal grip.

Thanks. But we're all good with "squiggles"?

#48 gruntguru

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Posted 07 March 2015 - 09:41

Its an Aussie thing.

 

https://www.youtube....h?v=zdmsE-Bff7k



#49 mariner

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Posted 09 March 2015 - 10:59

I dont have enough engineering knowledge or racing experience to add any technical info. to this very interesting thread but I can pass on what a professional race driver told me about traction conrol (TC)  benefits.

 

He races in both modern sports cars , Spa 24 hours etc, and Historic racing where he has driven a Porsche 917 at Le Mans in the wet - so not just ABS cars.

 

He view was that TC wasnt any quicker than the driver's control when the driver and tyres were fresh but as the driver tires on a long stint and the tyres get worn then TC is definitely quicker.

 

I woner if the same is true on ABS?


Edited by mariner, 09 March 2015 - 11:01.


#50 gruntguru

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Posted 09 March 2015 - 12:56

I would guess more likely to hold for TC. With very grippy tyres, a greater percentage of the circuit can be negotiated with WOT - engine power is finite. A good braking system should always be able to lock wheels - at any speed and regardless of tyre condition.