From: Alan Baker on
In article
<9bd36917-1c4c-48ba-bb9b-7061a9d6afca(a)z7g2000yqb.googlegroups.com>,
Dave__67 <spamTHISbrp(a)yahoo.com> wrote:

> On Apr 22, 9:04�pm, Ashton Crusher <d...(a)moore.net> wrote:
> > On Thu, 22 Apr 2010 05:08:07 -0700 (PDT), Dave__67
> >
> > <spamTHIS...(a)yahoo.com> wrote:
> > >On Apr 21, 11:55�pm, "Nick Naim" <orb...(a)ix.netcom.com> wrote:
> > >> I pegged her at 70 years old plus minus.
> > >> She pulled �out of a fast food on my left in a heart beat
> > >> I,m in the left lane of thru traffic.
> > >> I,m on the binders on ABS and they are working on overtime.
> > >> I come to a stop 3 feet from her right front fender.
> >
> > >If your ABS is kicking on on dry clean pavement you need better tires-
> > >you're throwing away stopping distance!
> >
> > >Dave
> >
> > How do y9ou figure that? �ABS works, wet or dry, to maximize the
> > amount of time the tire is at or near peak friction level. �
>
> No, it does not.
>
> ABS is designed to allow you to still steer while mindlessly whomping
> on the brakes. To do so it has to leave a little traction on the
> plate.

Again, not quite. ABS will reduce the amount of force applied to the
brakes whenever conditions result in the tire starting to lock up.

One of those conditions could be a change in the friction of the
surface, but one could also be that you've turned the wheel.

So there is no traction "left on the plate" in the way you meant.

>
> Anyway, on dry pavement, if you can lock up the brakes, your brakes
> are better than your tires. If you improve the grip of the tires
> you'll stop faster.

Not just on dry pavement. :-)

--
Alan Baker
Vancouver, British Columbia
<http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg>
From: Alan Baker on
In article <mk7bt51g12uq8cvh2anf8aj2c1ek85bnip(a)4ax.com>,
Scott in SoCal <scottenaztlan(a)yahoo.com> wrote:

> Last time on rec.autos.driving, Ashton Crusher <demi(a)moore.net> said:
>
> >I'm not sure what point you are trying to make.
>
> In general it has been true that a skilled driver can threshold-brake
> better than an ABS system. Now maybe ABS systems have gotten better in
> recent years and this is no longer true, but at one time ABS was only
> an advantaged for unskilled drivers.

I very much doubt it was ever true except for a tiny fraction of the
very best drivers.

One advantage you get from ABS is that there is no need to spend any
time approaching the threshold.

--
Alan Baker
Vancouver, British Columbia
<http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg>
From: Ashton Crusher on
On Mon, 26 Apr 2010 05:29:33 -0700 (PDT), Dave__67
<spamTHISbrp(a)yahoo.com> wrote:

>On Apr 22, 9:04�pm, Ashton Crusher <d...(a)moore.net> wrote:
>> On Thu, 22 Apr 2010 05:08:07 -0700 (PDT), Dave__67
>>
>> <spamTHIS...(a)yahoo.com> wrote:
>> >On Apr 21, 11:55�pm, "Nick Naim" <orb...(a)ix.netcom.com> wrote:
>> >> I pegged her at 70 years old plus minus.
>> >> She pulled �out of a fast food on my left in a heart beat
>> >> I,m in the left lane of thru traffic.
>> >> I,m on the binders on ABS and they are working on overtime.
>> >> I come to a stop 3 feet from her right front fender.
>>
>> >If your ABS is kicking on on dry clean pavement you need better tires-
>> >you're throwing away stopping distance!
>>
>> >Dave
>>
>> How do y9ou figure that? �ABS works, wet or dry, to maximize the
>> amount of time the tire is at or near peak friction level. �
>
>No, it does not.
>
>ABS is designed to allow you to still steer while mindlessly whomping
>on the brakes. To do so it has to leave a little traction on the
>plate.
>

Not so. It makes use of all available traction within the limits of
reasonable target values to prevent going into lockup. If you aren't
steering then all available traction gets used for braking, if you
decide to steer then some of the traction is used for steering and the
rest for braking.


From: Ashton Crusher on
On Mon, 26 Apr 2010 03:01:28 -0700, Alan Baker <alangbaker(a)telus.net>
wrote:

>In article <57q9t5lr4jhb5hervqhb2q51b3poff1eig(a)4ax.com>,
> Ashton Crusher <demi(a)moore.net> wrote:
>
>> On Sun, 25 Apr 2010 14:32:51 -0700, Alan Baker <alangbaker(a)telus.net>
>> wrote:
>>
>> >In article <dp67t55v3elj8vebi9ti24rlrqtr2hhl8b(a)4ax.com>,
>> > Ashton Crusher <demi(a)moore.net> wrote:
>> >
>> >> On Thu, 22 Apr 2010 21:48:20 -0700, Scott in SoCal
>> >> <scottenaztlan(a)yahoo.com> wrote:
>> >>
>> >> >Last time on rec.autos.driving, Ashton Crusher <demi(a)moore.net> said:
>> >> >
>> >> >>On Thu, 22 Apr 2010 21:47:45 +0000, Alexander Rogge
>> >> >><a_rogge(a)yahoo.com> wrote:
>> >> >>
>> >> >>>Nick Naim wrote:
>> >> >>>> I pegged her at 70 years old plus minus.
>> >> >>>> She pulled out of a fast food on my left in a heart beat
>> >> >>>> I,m in the left lane of thru traffic.
>> >> >>>> I,m on the binders on ABS and they are working on overtime.
>> >> >>>
>> >> >>>The ABS should not be activating on a dry surface, as this increases
>> >> >>>your stopping distance.
>> >> >>>
>> >> >>
>> >> >>ABS will activate on a dry surface the same as on a wet surface
>> >> >>whenever the tire is about to lock. And in the process it shortens
>> >> >>your stopping distance, not increases it.
>> >> >
>> >> >It shortens your stopping distance vs. screeching to a stop with
>> >> >locked brakes, sure.
>> >> >
>> >> >But true threshold braking is the shortest stopping distance of all.
>> >>
>> >> ABS is threshold braking. And any decent ABS is able to do it far
>> >> better then a human can, particularly on wet pavement.
>> >
>> >No. ABS is very close to threshold braking, but it is not. It is a very
>> >rapid sequence of going slightly beyond the threshold and then back to
>> >less than the threshold.
>>
>> Where you are getting that definition from? It makes no sense to me
>> and is contrary to what people have claimed in the past. What's your
>> definition of the "threshold" point?
>
>The point of maximum deceleration, of course. Isn't that obvious?


If that's your definition I don't see how human can successful
threshold brake for more then a very very short period before they
lock their tires or lose the peak. Critical slip for dry is about 26%
slip and wet about 13%. That's the point of peak deceleration and it
drops off on either side. If you put the tires there and the pavement
changes slightly the wheels will either lock or you will no longer be
at your defined threshold. I'm sure people call it threshold braking
but I'm also fairly certain it's not actually where they're at since
the peak is not likely to be a point a human can maintain, it's not a
stable point on the chart. More likely, when people think they are
"threshold braking" they are slightly off peak so they can feel
changing surface friction and react to it before a tire locks.

From: Alan Baker on
In article <r1uct5hggm69oh0jhjpv7gdceodkjadlvp(a)4ax.com>,
Ashton Crusher <demi(a)moore.net> wrote:

> On Mon, 26 Apr 2010 03:01:28 -0700, Alan Baker <alangbaker(a)telus.net>
> wrote:
>
> >In article <57q9t5lr4jhb5hervqhb2q51b3poff1eig(a)4ax.com>,
> > Ashton Crusher <demi(a)moore.net> wrote:
> >
> >> On Sun, 25 Apr 2010 14:32:51 -0700, Alan Baker <alangbaker(a)telus.net>
> >> wrote:
> >>
> >> >In article <dp67t55v3elj8vebi9ti24rlrqtr2hhl8b(a)4ax.com>,
> >> > Ashton Crusher <demi(a)moore.net> wrote:
> >> >
> >> >> On Thu, 22 Apr 2010 21:48:20 -0700, Scott in SoCal
> >> >> <scottenaztlan(a)yahoo.com> wrote:
> >> >>
> >> >> >Last time on rec.autos.driving, Ashton Crusher <demi(a)moore.net> said:
> >> >> >
> >> >> >>On Thu, 22 Apr 2010 21:47:45 +0000, Alexander Rogge
> >> >> >><a_rogge(a)yahoo.com> wrote:
> >> >> >>
> >> >> >>>Nick Naim wrote:
> >> >> >>>> I pegged her at 70 years old plus minus.
> >> >> >>>> She pulled out of a fast food on my left in a heart beat
> >> >> >>>> I,m in the left lane of thru traffic.
> >> >> >>>> I,m on the binders on ABS and they are working on overtime.
> >> >> >>>
> >> >> >>>The ABS should not be activating on a dry surface, as this increases
> >> >> >>>your stopping distance.
> >> >> >>>
> >> >> >>
> >> >> >>ABS will activate on a dry surface the same as on a wet surface
> >> >> >>whenever the tire is about to lock. And in the process it shortens
> >> >> >>your stopping distance, not increases it.
> >> >> >
> >> >> >It shortens your stopping distance vs. screeching to a stop with
> >> >> >locked brakes, sure.
> >> >> >
> >> >> >But true threshold braking is the shortest stopping distance of all.
> >> >>
> >> >> ABS is threshold braking. And any decent ABS is able to do it far
> >> >> better then a human can, particularly on wet pavement.
> >> >
> >> >No. ABS is very close to threshold braking, but it is not. It is a very
> >> >rapid sequence of going slightly beyond the threshold and then back to
> >> >less than the threshold.
> >>
> >> Where you are getting that definition from? It makes no sense to me
> >> and is contrary to what people have claimed in the past. What's your
> >> definition of the "threshold" point?
> >
> >The point of maximum deceleration, of course. Isn't that obvious?
>
>
> If that's your definition I don't see how human can successful
> threshold brake for more then a very very short period before they
> lock their tires or lose the peak. Critical slip for dry is about 26%
> slip and wet about 13%. That's the point of peak deceleration and it
> drops off on either side. If you put the tires there and the pavement
> changes slightly the wheels will either lock or you will no longer be
> at your defined threshold. I'm sure people call it threshold braking
> but I'm also fairly certain it's not actually where they're at since
> the peak is not likely to be a point a human can maintain, it's not a
> stable point on the chart. More likely, when people think they are
> "threshold braking" they are slightly off peak so they can feel
> changing surface friction and react to it before a tire locks.

Yup.

That's the challenge of threshold braking.

But although I do think that threshold braking is sufficiently difficult
that there are very few who can actually better a good ABS system's
stopping distances, you must remember that unless graph of slip vs
friction is very different from most physical phenomenon, almost all of
the benefit can be achieved by getting *close* to the value of maximum
slip. Typically, such curves only have a very modest slope near their
maxima and thus as you approach the peak you get smaller and smaller
increments of increase in the y-axis value (in this case: friction) for
the constant increases in the x-value (slip).

IOW, you get almost all the benefit of the maximum friction from nearly
reaching the maximum slip.

And you have your two figures backwards, BTW. It's 13% for dry pavement
and 26% for wet.

<http://www.mm.bme.hu/~stepan/mm/journal2003/olson_shaw_stepan_vsd.pdf>

Note the shape of the curves, BTW, and you'll see that particularly for
wet braking, you can have considerably less slip than the amount for
maximum possible friction and still be doing pretty well.

You'll also see why in a car without ABS it can be more effective to
simply kick the brake pedal to lock all four wheels as close to
instantaneously as possible (and getting more than 90% of the maximum
possible braking) rather than try and find the threshold point (and
moving very quickly while trying to find it).

--
Alan Baker
Vancouver, British Columbia
<http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg>