proper way to decend grade

[Jerry Liebler]

Chaz,
     You're right that Ohio and Indiana don't have real problem hills, at least that I've found. But Kentucky, Tennessee and especially North Carolina have some pretty bad ones  From my experiences in Wash Oregon California, Utah,Idaho, Colorado the nasty hills are very well marked with all kinds of warning signs, much more so than in the eastern states.  Any time you have a 5% or more grade lasting 1/2 mile or more or sharp curves with climbs and descents, it's time to slow down, gear down and be extra cautious.
Regards
Jerry 4107 1120

[Chaz]

Thanx guys.
  I'm hip to the signs, Russ. Just wasn't sure if there was anything else. Thanx.

  Tom, Do you find that they are ALWAYS marked well enough to give plenty of notice?

  Jerry, thanx for the more specifics. I was kinda looking for a "rule of thumb" like that.

   'preciate it,
     Chaz

[Brian Diehl]

Do you find that they are ALWAYS marked well enough to give plenty of notice?

Hi Chaz,
No they are not always marked, especially on secondary highways.  However, the interstates are usually marked pretty good.
-Brian

[niles500]

I propose that; all other things being equal (properly adjusted brakes,distance,weight,etc.), the amount of 'total' heat produced by the brakes is the same with continuous brake pressure or brake stabbing (i.e.- your stopping the same weight over a certain distance). The biggest difference would be your speed - the higher your speed the more air cooling is provided to the brakes,hubs,etc., slowing the bus down too slow will decrease the air cooling - So whether you're stabbing or applying continuous light pressure you're creating the same heat, though at different rates - how you're going to deal with the heat is most important question - Jakes allow you to remove most of the brake heat from the equation by transfering that heat to the mill, and that's how I choose to deal with the heat.

[Jerry Liebler]

Niles,
   You are on absolutely sound ground with you proposal.  If the speed is the same at the top and bottom and the vehicle's mass is the same the energy that must be lost, as heat, is the difference in potential energy at the top and bottom of the hill.  It simply doesn't matter how, when or where the heat was dissipated.  This is because of  a very fundamental law of physics called the conservation of energy.  Going slower down the hill allows more time to dissipate the energy.  Dissipating most of it through he engine means less for the brakes to deal with.  'Snub' braking gives some assurance that the brakes share the energy more equally, that's it's only virtue.  Continuous light braking means that the brakes are dissipating the energy all the time rather than in bursts which will average to the same total amount of energy but must have a higher peak rate of energy flow to make up for the time when no energy flow is occurring.  The only way to get a higher energy flow through the brakes is by them being hotter.
Regards
Jerry 4107 1120

[Len Silva]

I think I'll just stay in Florida.  As long as I avoid Mount Dora, should be OK.
Len

[oldmansax]

This is an excellent thread!!

It's good to be able to benefit from all the experience and knowledge represented here.

One thing that has not been mentioned is the relationship between speed and resistance. The faster a vehicle goes the more resistance it encounters, both from air and rolling (frictional) resistance. This translates into some amount of braking going downhill or less fuel mileage on flats. If you are on a road that would allow unlimited speed, you could safely not use any brakes, ASSUMING YOU WOULD NOT BE REQUIRED TO STOP. At some point, the resistance would overcome the forces of gravity on the incline and speed would level off. This is why an empty truck or bus can safely descend faster than a loaded one. Not only does it have more braking power per pound, but it also has less gravitational pull down the incline.

This is just another reason to do any tests using the same grade, and the same equipment in order to get reliable results.

Just another variable in the mix ......

[gus]

okieman,

What you say may be true about a bus but it is not about a big truck.

Big truck springs and brakes are designed for max braking when loaded. An empty 18 wheeler will skip the tires with full brake application unless it has some kind of automatic brake system. Just notice all the black skip marks on the highway, this is the cause of them.

Strange as it may seem, a loaded truck will brake better than an empty one.

[HB of CJ]

Wow....looks like, "What we have here is a failure to communicate!!!"  (that's supposed to be a joke from Cool Hand Luke)    What I used to do is select the proper road gear and the appropriate very low road speed, then turn on the Jake and...if everyting else was correct, never had to touch the brakes at all..all the way down.  BROOOMMMMMMMMM......sounded soosss b.t.."in! 

Automatic transmission retarders have their place, but sometimes (nearly always?) may not survive coming down our endless Western Interstate grades.  Seems the tranny cooling system is overwhelmed by the heat generated by making it work as a service brake system.  The result may be a severely cooked (ruined!) automatic transmission.  $Ouch$ 

[Chaz]

Nice to know HB. When time comes, that would be or could have been an option.

    Chaz

[buswarrior]

The trick with an automatic transmission and keeping its retarder from cooking the internals is to also select a lower gear that gives high engine RPM.

High RPM lets the cooling system deal more effectively with the massive heat the tranny is trying to dump into it.

On the unlimited downhill run, years ago, training films from the Colarado State Troopers suggested that a run-away 18 wheeler could easily attain 110 to 120 miles an hour on some of the interstate descents.

I assume run-away means the brakes are gone, and the novice driver attempted a downshift, thus losing all engine braking, when he couldn't get it back into any gear.

As noted, great ride, as long as there isn't a bend at the bottom....!!

happy coaching!
buswarrior

[niles500]

BW - Colorado has plenty of Runaway ramps, and to quote a popular comedian, THEY USE 'EM.

[oldmansax]

Gus

The thrust of my post was frictional resistance; however, I did make this statement:

"This is why an empty truck or bus can safely descend faster than a loaded one."

Are you saying a loaded truck can safely descend a grade at the same speed as an empty one?

Also, the "black skip marks" are left when a driver applies the brakes excessively while stopping. The trailer wheels will lock up because that set of axles have less traction empty then the tandem or steering axles. This situation can usually be overcome with proper driving techniques. There were very few "skip marks" left on the highway 40 years ago when we had a better educated (in driving) and more conscientious driver pool. 

[Tony LEE]

We shouldn't lose sight of the fact that whatever technique is used as far as the brake application goes, the CORRECT technique requires us to be in a low enough gear that almost no braking is required anyway. Those who get to the bottom with smoking brakes maybe forgot that.

[buswarrior]

Thanks tonylee for the idea jostle, try this on for size:

Remember, the point is to be descending slowly enough that the engine, in a lower gear, is able to, for the most part, prevent the coach from accelerating down the hill, with only a small amount of infrequent brake application.

The goal is little use of the brakes. Choose a speed and gear to accomplish this.

Remember folks with experience, we gotta get it all in there in a way that the first timer gets the point without having to find out missing bits the hard way!

happy coaching!
buswarrior