eriklane at gmail.com
Sat Nov 28 23:29:27 PST 2009
On Sat, Nov 28, 2009 at 7:47 PM, <decker at toledotel.com> wrote:
> Hi Eric;
> You and Val can argue about physics but in a real world of stopping a
> big diesel tractor and a long semi-trailer or a set of doubles I can tell
> you about how they brake since I have done it for 50 years. If you are empty
> and in a panic stop you put on the air and the tires will almost invariably
> smoke (skid) and then bounce so you have to back off on the air till they
> start rolling again and have some adhesion to the pavement. Between air time
> and skid time you do very little braking. If you are loaded to say 100,000
> pounds you have so much mass moving that when you put on the air and the
> wheels lock the tires skid and you aren't stopping well. If you are lightly
> loaded you have a pretty good balance between the mass you are trying to
> stop and the adhesion your tires have on the pavement so you stop rather
> quickly. Read about ABS brakes. A big share of you new cars have them
> because the computer can sense when the tires would skid and can modulate
> brake pressure to prevent you from skidding them no matter how had you press
> on the brake pedal.
> One of the tough things about driving a big rig in traffic is when you
> leave enough following distance to be safe most likely some stupid car
> driver will pull in front of you and behind the rigs in front of him.
> Apparently they don't comprehend that they have just driven their mobile
> coffin into emanate danger till you can back off enough to have a safe
> following distance. Sometimes it feels like you are driving your truck
> backwards. When you are drafting you don't bother me since what is behind me
> has to look out for themselves. Last year we had a driver with a set of
> doubles just barely get stopped because some fool in a motor home just
> stopped in the road in front of him for no apparent reason. It would not
> have been a problem except that the new Ford pickup that was following to
> close got eaten up when he hit the back trailer. It probably was inattention
> since he should have been able to stop faster than our doubles driver. He
> wasn't hurt it totaled his pickup.
> Brian Decker
If the tires start bouncing then of course that would change things.
Is it the heat that does that? I'd like to see some actual tests that
scientifically show that there is a significant difference with the
With that said, I drive much more carefully when pulling large
trailers and loads. They feel different. But I still suspect that with
operating brakes and all wheels locked up they'd stop pretty well.
Maybe the large tires are made for economy and have much less grip on
the road than consumer tires, but other than the material differences
the stopping distance should still be about the same. Unless there's
more advanced things that I don't know about. In that case I'd *love*
to be educated.
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