Anti-Lock Brakes

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There was no problem with brake lockup because brake lockup is not a problem. They still could and did lock up the wheels if the driver applied enough force to the brake pedal.
That said, the setup that you describe while typical of race cars is not at all typical of a street car of 50 years ago. The typical street vehicle had a single reservoir/single circuit master cylinder, and the brake "proportioning" such as it was was taken care of by careful sizing of the front and rear wheel cylinders. (that is, there was no proportioning valve per se.)
Even when a system is correctly proportioned front to rear, brake lockup can and does still occur. The proportioning, however, ensures that the front wheels lock up slightly before the rear wheels so that if a driver does inadvertantly lock up the wheels the car won't become unstable.
nate
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Yes, actually: they did.
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Alan Baker
Vancouver, British Columbia
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Cars have never had a problem with brake lockup. It's drivers who have the problem with brake lockup.... --scott
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"C'est un Nagra. C'est suisse, et tres, tres precis."

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I can't resist one more braking dynamics point:
A racing motorcycle...even a sportbike quickly converted to racing...can lift it's rear wheel off the ground during maximum braking. The front wheel...with 100% of the motorcycle and rider weight on it...does not lock up. Of course the front brake system and the rear brake system are separate...
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See...maximum-braking is defined as 100% weight transfer. Well...define maximum-braking as the most braking that a particular vehicle can achive in practice. Then...define ultimate-braking as 100% weight transfer to the front wheels. Next...just say that a racing motorcycle on dry pavement and with racing tires...can achive ultimate-braking. But the racing motorcycle achieves ultimate braking without front wheel lock-up. And the racing motorcycle during ultimate-braking has 100% of the weight on the front wheel and the front brake is getting 100% of the brake force since the front brake system and the rear brake system are separate. And that's a proof...
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And that's a proof...that wheel lock-up can be avoided with hydraulic brake proportioning relative to vehicle front-to-rear weight distribution and relative to vehicle weight transfer.
(A related item is that tires can achieve more than 1 G of force because they interlock with the pavement.)
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See...the motorcycle does achieve ultimate braking before front wheel lock-up. And there can't be anymore braking than the 100% weight transfer of ultimate braking.
There might be more hydraulic force to the brakes...possible...but not more effective braking than 100% weight transfer.
So...for simplicity sake let's choose one part...say the master cylinder...and work with that. Now put a small master cylinder on the motorcycle front brake and the rear wheel does not hold off the ground during maximum braking. Now put a slightly larger master cylinder on the motorcycle front brake and the rear wheel does not hold off the ground during maximum braking. Now go to the next size master cylinder on the motorcycle front brake and the rear wheel does hold off the ground during maximum braking. So now stay with that last master cylinder size on the motorcycle front brake. And ultimate braking has been achieved without front wheel lockup...
Now the motorcycle could have front-to-rear hydraulic brake proportioning such that at maximum braking the front brake gets 100% of the hydraulic force with the rear brake getting 0% of the hydraulic force...and now the motorcycle brake system is working like a car system. And the rear wheel is off the ground at maximum braking, the front wheel is not locked, and actually ultimate braking of 100% weight transfer has been achieved...on dry pavement.
But posters here have suggested that car brakes are so large that they will always lock-up the brakes...even in a straight line...and even on dry pavement...and in spite of correct front-to-rear hydraulic brake proportioning.
I'm saying that if the car brakes are about the right size...then with correct front-to-rear hydraulic brake proportioning...there will be very little problem with wheel lock-up...in a straight line...and on dry pavement...and without the use of ABS. Then on wet pavement the ABS is needed to avoid wheel lockup...because the brakes are sized for dry pavement.
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If a motorcycle can lift its front wheel (100% weight transfer) under braking, then maximum braking force is achieved AFTER that has occurred. That's true no matter how you propotion braking force. If the front wheel doesn't lift and it is capable of lifting, you haven't provided maximum braking force.
This is true for cars as well, but most of them can't lift their rear wheels under braking.

That's right. Properly functioning car brakes can always lock up the wheels.

Brakes sized such that they could just barely lock up the wheels under dry conditions would be horribly undersized in practice.
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Matthew Russotto wrote:

And brakes so wimpy would probably heat soak after the first hard stop, and suddenly it's 1960 (again.) Although even by that date good brakes were available on *some* cars (Studebakers always had decent brakes after 1954; Buick was using aluminum drums on production cars in an attempt to shed heat faster, some imports were coming through with disc brakes by that point.)
nate
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Switching from a modernish 1996 car to a 1964 Commander OHV6 with stock brakes can be a lesson in automotiive advancement
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I forgot about the six cylinder brakes. Can't remember the last time I drove a Stude six :)
nate
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And you are -- in every possible detail -- completely wrong.
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Alan Baker
Vancouver, British Columbia
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Alan Baker wrote:

Much more eloquently stated than any rebuttal I could come up with.
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PolicySpy wrote:

False. You are correct in so far as that the shortest stopping distance is achieved with wheels that do not lock. You are also correct in that if the rear wheel of a motorcycle is pulled off the ground that said motorcycle is at or near the maximum deceleration that it can physically achieve. However, you are completely wrong that that is all the more stopping force that you can get out of the brakes on a typical car (or motorcycle.)
Think about it. My grandmother has to drive a car. If we set up the brakes in her car so that she can achieve maximum stopping force, then what happens when I, who outweigh her by about a factor of two and am proportionally (if not more so) stronger, drive the same vehicle? Of course the brakes will lock up long before I run out of leg strength.
It is the driver (or the ABS) that determines whether the wheels will lock or not, not the engineers that designed the brakes. The engineers design the brakes so that they are correctly proportioned and (hopefully) that a 5th or 10th percentile driver will still be able to panic stop successfully (that is, in other words, that a person of average size and strength will me more than able to force the wheels to lock if he pushes as hard as he can on the brake pedal.) In a good car, the engineers will also design the brakes to be fade resistant, such that a car can make repeated maximum deceleration stops from high speed without glazing the brake pads or causing them to outgas to a degree that stopping power is noticeably reduced. They will also design the brakes to be responsive to the driver, such that he can "threshold brake" successfully with a minimum of wheel lock.
nate
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Not at all. My ex managed to lock up the brakes on a motorcycle while learning to ride. Unfortunately it was my motorcycle, too. --scott
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"C'est un Nagra. C'est suisse, et tres, tres precis."

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PolicySpy wrote:

Sure there can, you MORON.
Riddle me this: by your theory, a motorcycle will stop fastest if the rider leans forward to achieve 100% weight transfer sooner during braking.
So why do motorcycle riders (in the real world) shift their weight REARward to keep as much weight on the REAR wheel as possible? To allow them to fully use the braking power of both wheels!
You're claim that "maxiumum braking is defined as 100% weight transfer" carries about as much weight as a truckload of post-holes.
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PolicySpy wrote:

Yes. The point being that under those conditions ALL the wheels will lock up AT THE SAME TIME.
"Wheel lockup" is only a "problem" for a driver when either the rear wheels or the front wheels lock up before the OTHER pair of wheels has reached maximum braking potential. If the rear wheels lock up when the front wheels are only at 80% of their braking capability, the system is out of balance and will take longer to stop than if all 4 wheels lock up at approximately 100% capability.
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This isn't what the ABS exists to prevent, though. The ABS exists to prevent inadvertent lockup by inexperienced drivers who jam down on the pedal and lock the brakes in cases when they could have come to a controlled stop by feathering the pedal. The ABS automatically feathers the pedal for poor drivers who don't know how to do it themselves.
And this is a reasonable thing to do, especially seeing that nobody thinks clearly in a panic situation. But personally I will pass. --scott
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wrote:

The problem I have with ABS brakes is that they don't increase overall safety. Studies of similar vehicles with and without ABS brakes show that the cars with ABS brakes are involved in fewer accidents of some types and more accidents of others. NHTSA spent millions trying to figure out why a supposed safety device did not improve safety. In the end they pretty much gave up, but said ABS is good, but we can't require it becasue statistics show it actually decreases safety. However, in the end, they got the last laugh. NHTSA decreed that all light vehicles will have electronic stability control (ESC), which effectively mandates ABS as well. And this time NHTSA didn't bother to study whether or ESC was actually improving safety, they essentially said, we know it is a good thing, so all light vehicles must have it and we are not going to take risk finding out that it is not useful. So now Americans will be spending billiuons for what is at best a marginal safety device because a zealous bureacrat who has probably been wined and dined by the ABS/ESC manufacturers, decided we should have it. Total rot. Billions for ABS/ESC/Air Bags, while the roads crumble under the cars. Idiocy.
Ed
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wrote:

Vehicle stability being one effect of abs (Sliding sideways doesn't help anybody) the main point of ABS is to maximize the braking ability. The MAXIMUM braking ability occurs at the moment before wheel lockup, (as it was explained to me in a aircraft maintenance class, the millisecond before the slide would start. A Slide has less braking ability, even though we feel like "we tried our hardest to prevent the accident-look at the skid marks" Feathering the pedal is a way of stimulating a abs for a car without abs, but there is no way you could do it as often as a computer can. I've been driving a lot of years, and my 92 F-250 is the only vehicle that has had ABS (not counting the Subaru-still undriveable) I've only had it's rear abs activate two or three times. (once in Phoenix rush hour with a camper on it- was glad I had it!) Once while driving a suburban in Minot North Dakota, its abs helped me stop on a sheet of wet ice. I did go into the intersection, but feel confident the abs stopped me shorter than I could have.
I like and trust ABS, but think if you feel it often, your driving to recklessly. Steve
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