Does overly biased tandem weight add drag?

Discussion in 'Experienced Truckers' Advice' started by Pmracing, Nov 10, 2017.

  1. MACK E-6

    MACK E-6 Moderator Staff Member

    48,765
    225,333
    Sep 19, 2005
    Baltimore, MD
    0
    Interesting.

    I’m going to show this to my co-workers who would slide their trailer axles up to the landing gear if they could.
     
    x1Heavy and Oldironfan Thank this.
  2. Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.

  3. x1Heavy

    x1Heavy Road Train Member

    34,017
    42,135
    Mar 5, 2016
    White County, Arkansas
    0
    Now you did it. Make me LOL.

    WHAT is tarnation is going on up there in your neck of the woods eh? //teasing.

    Merry Christmas to you and yours. Ive valued your posts.
     
    MACK E-6 Thanks this.
  4. MACK E-6

    MACK E-6 Moderator Staff Member

    48,765
    225,333
    Sep 19, 2005
    Baltimore, MD
    0
    Well, we just have more than a few non-driving knuckleheads who in apoplexy and abject fear insist on running around with trailer axles slid as far up as possible.

    I’m proud to count myself among the few who absolutely refuses to do that except to make scale weight.
     
    x1Heavy Thanks this.
  5. AfterShock

    AfterShock Road Train Member

    6,645
    11,601
    Sep 19, 2007
    Inland Empire, California
    0

    Interesting thread.

    I wonder though, is comparing internal combustion power with electric power an accurate gauge? A Big truck uses diesel power directly applied to the drivetrain, which transfers torque and power to the wheels, to the ground.

    A locomotive uses internal combustion diesel engines to turn a generator that produces electricity which supplies current to the electric motors that provide the power that makes the wheels go 'round.

    Has anyone here seen an electric vehicle, like a Tesla, launch off the line from a stand-still? It would take an internal combustion powered vehicle with a bunch-0-horsepower getting to the ground with minimal tire spin, without snapping an axle, to out accelerate electric power.

    Out here on the lower west coast, southern section, there's the Cajon (Ka-Hone) Pass. Big trucks use I-15 to get over it, trains stick to the tracks, except when they go down too fast, which has happened with disastrous results. To pull a 100+ rail-car load up and over the hill they'll position 4 or more locomotives up front pulling, two or three near the middle, and another 3 or 4 in the rear pushing to git-er-dun.

    Descending, the lead locos hold the load back while those in the middle and the end provide braking drag to prevent a run-away.
    Locomotives also have their Dynamic to assist their descent, --- an electric Jake Brake, of sorts. Think what happens when electric poles to the motors are reversed to provide resistance. Going forward with motors trying to go backwards.

    (A simplified explanation for a complex action.)
     
    x1Heavy Thanks this.
  6. x1Heavy

    x1Heavy Road Train Member

    34,017
    42,135
    Mar 5, 2016
    White County, Arkansas
    0
    Dynamic braking is the term. Literally dispensing the electricity generated in the traction motors as waste heat up top where cooling fans carry it away. A ordinary toaster on the kitchen counter is exactly how the waste resistance and heat is disposed of.

    One part of the railroad scenario is coupler strength, many railroads have policy as to how many driving axles may be up front versus a coupler with 340,000 pounds of pressure roughly, give or take 40,000 in slack running. They usually break beyond 400,000 pounds of force.

    Railroad downgrades are roughly 1 to 2% in between by percentage. Highway grades are 7% at most unless provided with a much steeper problem approaching 25% which is truly steep. Our interstate is engineered to accept 7% or less generally with curvature able to accept a 70 mph vehicle.

    Many railroad engines will lose adhesion at around 5% Saluda Mountain is one of the steepest on the USA Mainline system at around 3.8 to 4.3% with a manned safety switch at the bottom.

    Cass Scenic Railroad in the Cass West Virginia-Spruce area which is in the New River Bridge region, has grades upwards of 11 to 12% in spots beyond which are a few 14% spots. They use steam shay design engines which are specifically for extreme steep logging where ordinary engines cannot go. A ride on the Cass watching the brake man teach me about the mountain downgrade braking provided me at that time a very powerful education in physics and what is possible or not. Each of our pax cars were being hand braked in addition to the engine's train braking system downgrade from the switchback.

    There is nothing that prevents a semi truck from using a small engine up front running at RPM to feed a generator to feed electric to the wheels.

    I must say that system must be overly complicated for steering wheel holders in this industry of which there are a large percentage. The copper value alone of the traction motors on each axle or wheel will attract predators in no time.

    Also the capacity of the motors electric to accept a thermal loading is fixed. You can always apply more power in amps that will be converted eventually to a level of heat at which the traction motor, even with blowers feeding cold air must fail. When it does, the entire locomotive must go to a heavy shop to be fitted with a new motor or motors plural. No one has time for that.

    I have raced sports cars with a bobtail a few times, a truly unrestricted tractor has won a few of these races on the 1/4 mile street and top end. Unfortunatly given a long enough distance, say half a mile the tractor has reached it's top end and the car must pass at 140 and beyond. If you had enough fuel pump and a engine that will accept 3000 rpm you can get it up there. Now you must also consider that you willl break the transmission eventually on the tractor because using just three gears (High 5th to start, then 8th and 9th to finish) will eventually tear the clutch assembly out.

    Also railroads are incredibly structured in signalling and rules. They have 16 hours in which the train crew may do work. At 16 hours and one second they cannot and will not move a inch. That whole train will sit there however long until a rested crew gets to the engines.

    People on our interstates are a definition of complete chaos and destructive behaviors and are not able to adhere to any kind of rules. And so it goes.
     
    AfterShock Thanks this.
  • Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.