Understanding Braking Capacity

Discussion in 'Experienced Truckers' Advice' started by Hammer166, Dec 2, 2024.

  1. Brandt

    Brandt Road Train Member

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    Here is something else I was trained by company that runs the mountains. They took us up Parley Canyon. We all drive up to the top and turned around drove and halfway down and stop and switch driver. With a loaded trailer so we could all see it works. That part of my training was probably not normal for most drivers. It’s not a requirement of CDL training and most people don’t live were the bigger mountains are so they don’t teach this. Someone in Florida is not going to get training in driving in the mountains because its flat land.
     
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  3. REALITY098765

    REALITY098765 Road Train Member

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    Quote'''Braking uses friction to convert a vehicle's kinetic energy into thermal energy, which is then dissipated into the atmosphere. ''end quote''

    It's the ability to dissipate the energy that stops the truck.
     
  4. Oxbow

    Oxbow Road Train Member

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    I don't even know about that Hammer. Dragging 10 psi at 55 mph for 15 minutes straight and I think some that are adjusted tighter will be smoking. Maybe discs are better, but heating dums so that they expand and reduce the maximum braking power seems pretty dangerous to me. At 20 mph not so much. I think the smell at the Arrowhead truckstop, or the southbound Cajon scales, or the bottom of any grade with substantial length supports my opinion somewhat, but I really don't know, because I NEVER ride my brakes from top to bottom of any grade that is longer than maybe a 1/4 mile.
     
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  5. Hammer166

    Hammer166 Crusty Information Officer

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    Sort of... It's the ability to dissipate the energy that allows the truck to KEEP stopping ability.

    One could technically design a brake system with extremely poor heat dissipation but a huge thermal mass that could stop the truck quite effectively... once. Then it would be ineffective until such a time as the components cooled.
     
    Last edited: Dec 6, 2024
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  6. Hammer166

    Hammer166 Crusty Information Officer

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    I was kind of giving them their point that a perfectly balanced brake system could effectively handle some light braking input for extended periods without overheating.

    But yes, we all know that isn't gonna happen often in the real world. All of us geezers remember watching the trucks go by looking like meteors at the bottom of the grades.

    I was really hoping to get it to sink in that any extended brake usage was not good idea, but I realize this morning that relieving myself upwind into gale and staying dry is a far more likely outcome.

    It's also amusing to listen to one tell a bunch of old heads who learned the mountains without jakes that we basically just don't understand how it works.
     
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  7. Brandt

    Brandt Road Train Member

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    If you have been driving a long time how could you NOT know this stuff. It not anything new. You really don’t think you can ride the brakes at 10psi without the brakes over heating or being able to stop if needed is not a problem.
     
  8. AModelCat

    AModelCat Road Train Member

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    Adjusted tighter or looser. Always wondered about that. With a service brake diaphragm being more or less a constant surface area through out its entire stroke the braking force should be nearly equal regardless of adjustment would it not? Force = Pressure x Area. Assuming you're not overstroked of course. The slack adjuster angle would change the force slightly but probably not enough to make a huge difference.
     
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  9. Hammer166

    Hammer166 Crusty Information Officer

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    The angle plays a small part in any application, but at low application pressures, spring tension, component geometry, and differing levels of wear & friction in the brake system can all add up to make the pad pressure vary quite significantly. It is quite literally why the recommendation was switched from light steady to snub. Testing showed a much greater variation in brake temps under light steady.

    So long as the descent speed is the same, the total heat generated by the descent is the same, snub merely spreads it more equally among the brakes. The biggest issue with snub is that drivers tend to spend too much time above target speed (velocity squared is a #####) without realizing it, and thus put more heat into the brakes than they realized.
     
  10. tscottme

    tscottme Road Train Member

    Can confirm. East of I-35 you can use almost any technique you like and not smoke the brakes on those little hills. Some drivers drive their whole career and the most dangerous "mountain" they experience is Monteagle, NOT Mount Eagle, on I-24 in TN. Black Mountain near Ashville, NC is another "monster" for Easterners. Fancy Gap or Pilot something is another. Those are reasonable and need attention but easily manageable, also. Out West is the varsity section. East is the JV section for mountains. Some places in WV on the state highways are sporty.
     
  11. Hammer166

    Hammer166 Crusty Information Officer

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    I'll never forget when they opened Sandstone, couldn't believe they built a brand new piece of Interstate with that long steep grade.
     
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