From: Ashton Crusher on 22 Apr 2010 21:06 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.
From: gpsman on 22 Apr 2010 21:31 On Apr 22, 9:06 pm, Ashton Crusher <d...(a)moore.net> wrote: > On Thu, 22 Apr 2010 21:47:45 +0000, Alexander Rogge > > >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. Under most conditions, a vehicle with a good anti-lock brake system can stop in a slightly shorter distance than -an average driver- could accomplish in the same vehicle without ABS; however, that is not the main purpose of ABS, and the difference is generally not great enough to notice or be of any real use. ABS can actually lengthen stopping distances on some surfaces, such as loose snow, dirt, or gravel, because of effects that occur during locked-wheel skidding that are unique to those surfaces. http://www.aaafoundation.org/resources/index.cfm?button=abs#stop ----- - gpsman
From: Ashton Crusher on 24 Apr 2010 21:31 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.
From: Ashton Crusher on 24 Apr 2010 21:43 On Fri, 23 Apr 2010 16:35:55 +0000, Alexander Rogge <a_rogge(a)yahoo.com> wrote: >Ashton Crusher wrote: >> On Thu, 22 Apr 2010 21:47:45 +0000, Alexander Rogge >> <a_rogge(a)yahoo.com> wrote: >> >>> 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. > >That would depend on the sophistication of the ABS program, along with >the stability-related properties of the car. Most of the programs on >the cars that I have tried will miss the threshold at which braking >pressure is optimised for minimum stopping distance. Instead of the >tyre providing the expected friction against the road surface, the ABS >program attempts to guess about when the wheel should not skid, and as a >result the program delays the application of maximum braking pressure. No modern ABS "guesses" at anything. It's true that back in the early 90's there were some really crappy ABS systems out there. When you say the cars you have tried miss the "optimum", how are you making that assessment? Unless you have done multiple instrumented tests there is no way to know. In addition, a modern system will module pressure on at least three circuits separately, the most you can do it modulate overall pressure on the pedal, i.e. a single "circuit". For a human to beat a modern ABS is essentially impossible. Most likely you are also basing your assessments on braking on dry pavement. Although ABS will win there, where it really shines is on wet pavements and on pavements that have highly variable friction levels transversely and/or laterally. A 3 or 4 circuit ABS can easily handle such surfaces, a single circuit, i.e. human on the pedal, can't hope to handle it at anything close to what the ABS can do.
From: Matthew Russotto on 25 Apr 2010 15:41
In article <0rr8t5935sf8ejbiduealdjju2ksp44joi(a)4ax.com>, Scott in SoCal <scottenaztlan(a)yahoo.com> wrote: > >In reality, it's a quantized approximation of threshold braking. That >pulsation you feel in the pedal is the brakes being applied and >released several times per second as the wheels go into and out of >lockup and the system modulating the braking pressure to compensate. >TRUE threshold braking would not involve the wheels locking up, even >for a few milliseconds. Remember also that "locking up" is not as binary as we normally make it out to be. The slip ratio actually varies continuously (but nonlinearly) between near-1 (not braking) and near 0 (locked up). There's an ideal slip ratio for maximum braking, and good ABS will keep the tires near (but oscillating around) that ratio; if you have stability control as well, it will also try to keep the car straight (which may result in a longer stopping distance... would you rather stop short sideways or stop a little longer straight? The answer unfortunately is dependent on the situation). -- The problem with socialism is there's always someone with less ability and more need. |