Electric Trailer Brakes, (Revisited)

sisu1a wrote:
Hi All,

By request, I am posting my electric brakes vs surge brakes article/
rambling. It is much the same info as my post on the subject before,
but written more in an article format. It is of course unfinished, but
pretty much covers my thoughts on the subject. My apologies for any
redundant redundant repetitive repetition.

You know something occured to me when I read this article. Paul talks about
using the trailer brakes only to stop the trailer from swaying. In fact, I
would think that if you hit the trailer brakes that if anything it would make
the trailer more likely to sway. Afterall, when you want to drift a car,
the easiest way to do that is to pull the emergency brake. It transfers weight
forward and off the rear wheels (on in this case the trailer wheels) and it
reduces the available traction for the tires to counter the swaying.
Admittedly, removing weight from the back end reduces the polar moment as
well.

But what did occur to me is that many new vehicles selectively apply the
brakes in order to implement stability control. It makes me wonder if you
could design a simple controller which could detect swaying and selectively
apply the brakes to counter it, either automatically or with driver
intervention.

Having towed a trailer behind a relatively light small car, I can tell you
that swaying is what freaks me out more than anything else (although inability
to stop or accelerate isn't particularly pleasant either).

wrote:
It makes me wonder if you
could design a simple controller which could detect swaying and selectively
apply the brakes to counter it, either automatically or with driver
intervention.


Already done.
Some trailer brake controllers offer this, and has been offered as far
back as the early 1980's, or earlier. Some of the new factory
installed trailer packages are including this feature on new vehicles
destined to be tow vehicles.

sisu1a wrote:
About driving 60: Although it may leave you with less energy in the
equation to manage, *I feel like driving much below the speed limit
(like doing 60 in an 80 for instance) *is far more dangerous to
yourself and the other drivers on the road, since you then make
yourself an obstacle that needs deviated around. With every car that
passes you, your odds of being hit by one of them increases. By
driving the same speed as the cars around you, you are much less
likely to be hit by one of them. Sometimes I slow down a bit too, but
usually only to get a different set of drivers around me because I've
had it with the knuckelheads around me. I am not worried about ME
crashing, I am indeed worried about one of 'them' hitting me though.
Most folks do not put much thought into driving, and it is usually
demonstrated for me every time I drive.

Eric wrote:
At 60 mph on an Interstate (most of my trailering) seems just as safe as
75, because passing is easy. Two lane roads, regardless of the speed
limit, is where the danger is. Most of that danger occurs when I have to
drive *less* than 60 mph, due to traffic, hills, and curves. Since it's
not related to brakes, I'll leave the issue for another thread.

Perhaps this is the start of that "new" thread:

The NTSB statistics on crashes between Class 8 semis (big trucks) and
automobiles (four-wheelers) reveals that ~ 70% of these accidents
involve the four-wheeler striking the big truck from behind (the
reverse is, fortunately, quite rare). Compare the rear of that
semitrailer with LED tail and marker lights, not to mention at least 8
1/2 feet of DOT tape with the rear profile and lighting intensity of
your basic glider trailer. There's little question that the risk of
being rear-ended increases in proportion to the speed differential.
Good lighting does attenuate this risk somewhat, but doesn't come
close to eliminating it.

That said, there are, as Eric points out, excellent economic and
safety/stability arguments for that 60 mph speed. (arguments I now
take seriously, BTW, since my tow vehicle is a VERY thirsty pick-
up.) Personally, however, I would have a creepy feeling at the back
of my neck with a 15-20 mph differential between me and all those SUVs
coming up behind me, even if the lane(s) to the left of me were
unobstructed. The good news is that the majority of professional
drivers deal well with these closing rates, the bad news is that so
many non-professionals don't. Here in New Jersey, I've had to move
right or left to avoid being hit from behind on at least three
occasions this past year. In one case, the car then hit the truck in
front of me.

I've ordered a new set of LED tail and marker lights, a round brake
light to place high on the back of the fin and some DOT tape for the
trailer and, when they're installed, will reduce my maximum towing
speed a bit with the clear understanding that I'm balancing economics
and risk. I'm applying the DOT tape all the way 'round, but that's
another story...

Ray Warshaw
1LK

On Jun 6, 2:10 pm, wrote:
In fact, I
would think that if you hit the trailer brakes that if anything it would make
the trailer more likely to sway. Afterall, when you want to drift a car,
the easiest way to do that is to pull the emergency brake. It transfers weight
forward and off the rear wheels (on in this case the trailer wheels) and it
reduces the available traction for the tires to counter the swaying.
Admittedly, removing weight from the back end reduces the polar moment as
well.
At one time I drove semi's and they have two ways to apply brakes; one
(a pedal) worked exactly like your car (operated all the brakes) the
other was a lever in the cab to operate the trailer brakes only. The
rig could be slowed down or stopped using the trailer brakes only,
theoretically a sure way to prevent jackknifing. I can tell you that
tapping that trailer brake took the sway out very nicely. While it
worked very well, owner/operators were rumored to use only the trailer
brakes to save on their tractor brakes. This would cause premature
brake failure of the trailer brakes and that would lead to some
interesting situations during panic stops or runaway conditions with
very effective tractor brakes and no brakes on the trailer.

Anyway, I think maybe you are not understanding the use of the E brake
in a drifted turn, which is done to break traction on the wheels
(inducing drift) and not primarily for weight shifting (I think).

Controlling sway with that lever in the cab of a semi (it's called a
trolley bar BTW) works only if the rear duals have some level of
adhesion, in which case you didn't need to use it in the first place.
If the trailer duals are already loose (or on the edge), really bad
things can happen when you yank the trolley bar. I suspect the effect
is similar with an electric brake controller.

Most owner-operators have compression (Jake) brakes fitted to the
engine and use the air brakes mostly to hold the rig in place at
stoplights and the like, the exception being panic stops where you
need all the help you can get. No need for brake-saving strategies if
you don't use them much in the first place. It's very much like a
spot landing, you want to run out of enery right at the stopping
point.

The above suggests a good strategy for towing any trailer - think far
enough ahead of the combination that you can do much of your slowing
with engine braking, keep the rig rolling slowly when approaching a
stop-light (stopping and restarting costs fuel and adds wear and tear)
and, as much as possible, use the brakes only to hold the vehicle in
place when stopped. Change lanes to permit vehicles entering an
interstate to merge. In this way, you won't be forced to slow down
and if they do something stupid ( I once saw a four-wheeler stop and
back up), you're already by them. Amuse yourself by trying to predict
what the drivers around you are likely to do next. With practice you
can get surprisingly good at it.

Ray Warshaw
1LK





there was the least bit On Jun 9, 12:20*pm, brianDG303
wrote:
On Jun 6, 2:10 pm, wrote:
* In fact, I would think that if you hit the trailer brakes that if anything it would make
the trailer more likely to sway. *Afterall, when you want to drift a car,
the easiest way to do that is to pull the emergency brake. *It transfers weight
forward and off the rear wheels (on in this case the trailer wheels) and it
reduces the available traction for the tires to counter the swaying.
Admittedly, removing weight from the back end reduces the polar moment as
well.

At one time I drove semi's and they have two ways to apply brakes; one
(a pedal) worked exactly like your car (operated all the brakes) the
other was a lever in the cab to operate the trailer brakes only. The
rig could be slowed down or stopped using the trailer brakes only,
theoretically a sure way to prevent jackknifing. I can tell you that
tapping that trailer brake took the sway out very nicely. While it
worked very well, owner/operators were rumored to use only the trailer
brakes to save on their tractor brakes. This would cause premature
brake failure of the trailer brakes and that would lead to some
interesting situations during panic stops or runaway conditions with
very effective tractor brakes and no brakes on the trailer.

Anyway, I think maybe you are not understanding the use of the E brake
in a drifted turn, which is done to break traction on the wheels
(inducing drift) and not primarily for weight shifting (I think).