Text 27102, 176 rader
Skriven 2009-02-02 10:56:38 av Michiel van der Vlist (2:280/5555)
     Kommentar till en text av Roy Witt (1:397/22)
Ärende: Trailer brakes
======================
Hello Roy,

On Thursday January 29 2009 10:20, you wrote to me:

 MvdV>> A common misunderstanding, even among caravaneers. Engine braking
 MvdV>> will help keeping the brakes of the tow vehicle cool, but it has no
 MvdV>> effect on the brakes of the trailer. It does not matter what method
 MvdV>> is used to control the speed of the tow vehicle: disc brakes, drum
 MvdV>> brakes, engin braking or the Flintstone method; the trailer brakes
 MvdV>> will activate when going down a steep slope.

 RW> I think you misunderstand the concept. By alternating between systems,

You are the one who fails to understand. There is just the one system: the suge
brakes on the trailer. Nothing to alternate between.

 RW> the brakes of both vehicles will be kept at a minimum. Engine braking
 RW> will keep both brake systems from engaging until they're needed, the
 RW> trailer braking system being nuetralized by the speed. By shifting up
 RW> a gear, the trailer brakes are then engaged, as the tow vehicle picks
 RW> up speed.

You don't "pick up speed" when going down a prolonged 5-10% slope with at
camper trailer. That is suicide. 50 kph is the maximum safe speed under those
conditions.

 RW>>> But as stated, in combination with low gearing and engine
 RW>>> braking, disc brakes will stay cooler longer, even with a heavy
 RW>>> load in the trailer.

 MvdV>> No, see above. It seems to me you do not really have much
 MvdV>> experience with trailers with surge brakes in combination with
 MvdV>> prolonged steep descents...

 RW> I have enough experience to know about it.

Obviously not. Or you would not claim that you can keep a surge brake from
activating by using engine braking.

 RW>>> I beg to differ. Disc brakes are mechanically as simple as you
 RW>>> can get.

 MvdV>> They are more complex than drum brakes, if only for the
 MvdV>> hydraulics.

 RW> Drum brakes also have hydraulics,

Not here. Not on trailers behind passenger cars.

 RW> Anybody who does is endangering their lives and those of others on the
 RW> road.

Bullshit. Surge brakes with mechnicall linked drum brales are a proven concept
that is very reliable and safe.

 MvdV>> Recreational trailers do not make many clicks. The brakes do
 MvdV>> not wear out. I have mine for 15 years now and I never had to
 MvdV>> replace anything. I inspect them every spring through an
 MvdV>> inspection hole in the drums.

 MvdV>> With hydraulic disc brakes, there would be the rubbers that
 MvdV>> crack, and oil that leaks.

 RW> Maintenence of hydraulic brakes on you trailer would be no different
 RW> than the hydraulic brakes on your tow vehicle.

The difference is that trailers are not subject to a mandates yearly
inspection.

 RW>  i.e. those 'neoprene' seals don't crack over a season. It takes many
 RW> years before they deteriorate to such a state.

Trailers last much longer than cars. Mine is over 25 years old. The seals can
not be expected to last that lomg.

 RW>  If you see oil, then you haven't done any maintenence on them.

There! They require maintenance. A pulling rod does not.

 MvdV>> It is the same with tyres. It is tear rather than wear that
 MvdV>> limits their life. After 6 to 8 years, there is hardly any
 MvdV>> visible wear.

 RW> On a trailer with very little weight to tire ratio.

Again you show ignorance. Tires on camper trailers are nearly always loaded to
the maximum.

 MvdV>> Profile is still perfectly ok, but little cracks develop on the
 MvdV>> sides and then it is time to to replace them.

 RW> Those cracks aren't from use, they're from environmental conditions.
 RW> Tires age exponentially in the sun vs your garage.

I know that....

 RW>>> If so, they have far less braking power than a hydraulic system.

 MvdV>> Another misconception.

 RW> Wrong again. It is a proven fact that mechanical brakes will not have
 RW> the stopping power of a hydraulic system. That's why mechanical brakes
 RW> were outlawed here in 1939...

You are comparing apples and oranges. For _trailer surge brakes_  the
hydraulics are just another way to link the sliding part on the coupler to the
moving parts on the brake. It has no effect on the stopping power as the forces
remain the same fir a direct mechanical link or an indirect mechanicak link via
hydraulics.


 RW>>> That was the difference between getting insurance on my 1937
 RW>>> Ford vs my 1940 Ford. The former had mechanical brakes, while
 RW>>> the latter had hydraulic brakes. The latter being considered the
 RW>>> safer system by the insurance companys.

 MvdV>> Apples and oranges.

 RW> Mechanical vs hydraulic brakes. Hydraulic known to be superior.

As Bob Bashe explained to us: that depends on your perception of "superior".

 MvdV>> No, that is not he problem. One problem is "spots" where the
 MvdV>> brake pads rest on the disc.

 RW> Pads don't rest on the disc. They're always a few mm away from them.

Look again. The space is much less. And if they are not in perfect rder, the
pad can touch the disc.

 RW> If you find that they're touching the disc, you haven't done
 RW> your maintenence.

I prefer systens that require no maintenance at all.

Anyway this is leading nowhere.

I was discussing going dwnhill in the Alpes. With a camper trailer behind a
passenger car. And that means surge brakes. With machanical drum brakes.
Because that is what is in use here.

 MvdV>> Here the automatic speed traps detect vehicle length. If it is
 MvdV>> over nine metres, it assumes it is a truck or a combination and
 MvdV>> it triggers at the lower speed allowed for trucks and trailers.

 RW> Meanwhile law enforcement is having coffee and donuts at the local
 RW> donut shop.

Maybe in your part of the world. Here the spped traps are handled by robots,
while the real cops are busy catching real criminals.

 RW> By the same token, the surge brake will engage when the vehicles are
 RW> going down a steep grade, whether the tow vehicle applies its brakes
 RW> or not.

As I have been saying all along...

 RW> This system is inferior to the electronic controlled system

That depends on your POV on "inferior".

 MvdV>> Certification is a long and slow process. Much red tape to be
 MvdV>> cut. Let us hope the manufactures of the "caravan Descent
 MvdV>> Control", as it is called, will not go broke before it gets
 MvdV>> officially certified for use on public roads.

 RW> If it works and is safe, then it should be certified.

Agreed in principle, but who decides if it is safe? Surely not the
manufacturer. Transport authorities do not make decisions like that overnight
and for good reasons.

Cheers, Michiel

--- GoldED+/W32-MINGW 1.1.5-b20070503
 * Origin: http://www.vlist.org (2:280/5555)