Towing A Trailer: Why Don't These Buggies Flip Over Backward?

Discussion in 'The Perfect Line and Other Riding Myths' started by nicholastanguma, Sep 15, 2021.

  1. dirt hokie

    dirt hokie Long timer

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    For your consideration....there is also video
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  2. Center-stand

    Center-stand Long timer

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    #22
  3. Bar None

    Bar None Long timer Supporter

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    What me worry?
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  4. nicholastanguma

    nicholastanguma nicholastanguma Supporter

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  5. Cheshire

    Cheshire Been here awhile

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    Regarding weight on the hitch: tongue weight is how much weight pushes down on the hitch. If it's something like a hitch-mounted Versa rack, that's 100% of the weight. For trailers, if your load is balanced for the trailer's axle, tongue weight should be about 10% of the load.
    If your tow vehicle is rated to pull 3500lbs, max tongue weight is 350lbs. 5000/500, etc.
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  6. Norty01

    Norty01 Occupant

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    The towbar tongue acts as a "wheelie bar..." LOL!
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  7. High Country Herb

    High Country Herb Adventure Connoiseur

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    If the trailer hitch is mounted lower than the rear axle, it is technically possible to increase the downforce on the front wheels.
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  8. nicholastanguma

    nicholastanguma nicholastanguma Supporter

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    Very helpful to know, thanks so much!
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  9. Center-stand

    Center-stand Long timer

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    Not sure if you are suggesting this is a good thing or not. If the trailer is properly loaded for the correct tongue weight, I would think level trailer would be the preferred height. I'm not a mathematician, but I don't understand how weight added behind the rear bumper of any normal vehicle, at any height, could increase down force on the front wheels. I'm open to an explanation.

    The length of the trailer tongue and the weight of the loaded trailer can act as a lever when braking. If the hitch is too low it could possibly reduce the ability to steer the vehicle, if too high it could reduce rear wheel traction resulting in a jack knife.

    The following is search results that might help answer the question of hitch height.

    https://www.google.com/search?q=how...ight&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari
    ..
    #29
  10. High Country Herb

    High Country Herb Adventure Connoiseur

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    No, I wasn't advocating for a super low hitch. I was pointing out that simply pulling a lot of weight doesn't mean the front tires lift. Kind of like pulling a bowling ball by reaching between your own legs. You might even fall over forward. My point was only theoretical, and I agree with your points.
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  11. foxtrapper

    foxtrapper Long timer

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    It’s not the tongue weight, it’s the pulling load. It’s not the bumpers, it’s axle height.

    Farm Tractor 101.
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  12. Center-stand

    Center-stand Long timer

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    Initially I did not interpret High Country Herb's post as being a direct reply to the original thread title question. Instead I interpreted it as a positive suggestion for hitch height setup.

    My concern was, and is, safety. Towing is both pulling and stopping the load. Of the two, stopping is probably the more critical. Proper hitch height is important to the safe towing experience, along with many other factors including,but not limited to, tongue weight and total load.

    I provided the link because there is more good information there than I could provide in my words.

    If you provide a link to information that supports your statement I would be happy to read it.

    What I have noticed when I watch those truck and tractor pulling contests on TV, it seems the pulls most always end with the sled at its heaviest and the truck, or tractor with its front wheels in the air. Apparently there is a point of diminishing returns on front wheel downforce transfer.

    ..
    #32
  13. BikeMikeAZ

    BikeMikeAZ Been here awhile

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    The postulated front wheel downforce would only occur when pulling with the hitch point below the center of mass of the tow vehicle. The same hitch location results in some front wheel upforce when stopping. Since the tractor pulls move the weight forward on the sled as the pull progresses, eventually the weight overcomes this effect and the front wheels lift as the hitch weight to rear tires wins the see saw with the front weight to rear tires.
    #33
  14. Center-stand

    Center-stand Long timer

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    If by below center of mass you mean the hypothetical trailer hitch is under the vehicle somewhere between the front and rear axel, you have moved away from practical information for someone asking questions about towing a trailer.

    So, let's imagine a see saw with one end notched to be 10 inches lower than the pivot point when level. How do we apply weight to the notched end to put down force on the other end of the see saw?

    If every thing in front of the rear axle of a tow vehicle is on one end of the "see saw" and every thing behind the rear axle is on the other end of the "see saw", how low below axle height does added weight on the hitch have to be to increase down force on the front axle?

    When pulling or moving the load, the "pivot" point, or rear axle, has to rotate against the weight of the load. How and when does that forward rotation increase down force the the front wheels? A rotating wheel acts as a lever. I don't understand how a typical tow vehicle, when moving a load forward, can transfer weight, or increase down force, to the front axle.

    An accelerating vehicle tends to lift the front of the vehicle, reducing down force on the front wheels. How does adding weight at the extreme rear of the vehicle increase down force to the front?

    I'm not saying you guys are wrong, but my simple mind doesn't understand. I need a better explanation to be convinced.

    ..
    #34
  15. foxtrapper

    foxtrapper Long timer

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    I already did. Here’s another, an oldy but a goody:



    The OP was about pull over, not trailer safety in general. That’s what my initial reply addressed. The above link is broader.

    To go back to simple pull overs, it’s simply a lever and leverage.

    With your motorcycle, when you wheelie, you rotate the bike around the rear axle.

    If you attach a lever to the rear axle going straight up, and pull it backwards, you can rotate the bike into a wheelie position. The longer the lever, or the harder you pull, the more you lever the bike into a wheelie.

    That’s what hitching a trailer above the axle does.

    Now put the lever under the axle. When you pull it, you pull the front tire down. This is why a trailer hitched below the axle will not make the bike (or tractor) wheelie from tugging it.

    Does that mean a motorcycle or tractor cannot wheelie while pulling? No. They still can, if the tire has enough traction to rotate the motorcycle or tractor around the wheel. That’s why being on the motorcycle, with your mass in front of the rear wheel, levering down, doesn’t prevent a wheelie either. Just means you need s bit more traction and power to get that front wheel up.

    Equally true is when things are reversed. Like stopping hard while going down a steep hill with a heavy trailer with no brakes, the whole lever and forces equation reverses. Is it enough to cause a wheelie while stopping? Almost always the answer is no, you’ll skid first.
    #35
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  16. Center-stand

    Center-stand Long timer

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    You probably should go to the 11 minute mark and rewatch the video.

    I began operating tractors and farm trucks with various loads on trailers, wagons and implements in the hill country of Eastern KY 60 years ago. Was lucky to have good guidance and learned lessons without tip over or injury.

    Go back to High Country Herb's statement above which says putting the hitch below the rear axle makes it technically possible to "increase" down force on the front wheels. I suppose we should ask increase from what, and when.

    While hitch height may have a relative effect on front wheel down force when the vehicle is applying power, higher being less and lower being more, compared to the static downforce on the front axle by the unladen tow vehicle, there is no connection point behind the rear axle that will " increase" the downforce on the front axle. The difference in front wheel downforce is a product of applied power and the lever length but it never increases from what it is static.

    When you attach a vehicle to a load having tongue weight you decrease the down force on the front wheels. When you apply power to the tow vehicle with a load you decrease the down force even more. If you do it right you achieve a balance that is safe relative to the vehicle, speed, road or terrain surface, etc.

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    #36
  17. foxtrapper

    foxtrapper Long timer

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    The difference between the words below and behind are not insignificant, or irrelevant.

    Your casual mixing of them leads you to erroneous conclusions, and misunderstandings of what people write/say.
    #37
  18. Center-stand

    Center-stand Long timer

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    You may be casual reading. Let me try again. I am trying to clarify what people are saying, for myself as well as others. My confusion, questions started with High County Herb's statement in post #27, which I think he understood, and accepted the information I offered in the link for readers to self discover.

    I agree, the words are not insignificant or irrelevant, and the point being; there is no point behind the tow vehicle's rear axle, above or below axle height, to attach a load that will increase the down force on the front wheels.

    Quite frankly, " no " connection point behind the rear axle " should be self explanatory and includes all positions regardless of plane.

    The down force on the front axle will change relative to hitch height, but static, or under forward power, it will always be less than it was before the load was attached, not more.

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    #38
  19. foxtrapper

    foxtrapper Long timer

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    Lets see if I can explain with pictures then.

    By and large, most of us understand how a wrench works. We put a force across an arm.
    01.jpg

    This creates torque, and if we create enough torque, the thing turns. Usually a nut or bolt, but really it can be anything.
    02.jpg

    Now in order for it not to turn, there's got to be a resistive force, countering the torque we're creating.
    03.jpg

    If fact, that resistive force (green arrow) will be proportional to our force (red arrow). The harder we push one way, the harder the resistive force pushes the other. Otherwise, it rotates. If you're looking at that image wondering why it isn't lifting up, gravity is the invisible downard force. But, let that red arrow be strong enough, and you would lever it up into the air.

    We can get the same torque with the arm in a different position. Say here.
    04.jpg

    Again, it's creating the same torque.
    05.jpg

    And it doesn't matter what the shape of the thing is. Round is convenient, but it could be say rectangular.
    06.jpg

    The reactive forces to resist it rotating would be the same. Where it is can of course be different. But there has to be a reactive force to prevent rotation.
    07.jpg

    In fact, we can put things in between that reactive force that's resisting rotation. Like say a tire.
    08.jpg

    That load is creating a counter-clockwise rotation, and the front tire onto the ground is what is resisting it. The harder that load, the harder it pushes the front tire...into the ground. This is why when plowing, the front wheel dig such ruts. The pull of the plow through that lever arm actually pulls the front end of the tractor...down.

    This is also the time to show why hitching up a load ABOVE the rear axle is such a bad idea.
    09.jpg

    With the load above the axle, the load is trying to lift the front wheels off the ground. The stronger the load, or the longer the lever arm, the easier the front wheels come off the ground. That is why hitching up high is generally a very bad idea. The only thing resisting the vehicle from flipping is gravity, through the center of mass.
    10.jpg

    Is there more to it than simply this? Of course! That's why 5th wheels are not inherently bad, why that little Beetle is not really in any danger, how tractors rear up some while doing pulling competitions, etc.

    But, as a very general rule, when pulling loads, keep it below the axle, not above it. With a tractor, use the drawbar, never the top link.
    #39
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  20. Center-stand

    Center-stand Long timer

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    Your illustrations make absolutely no sense to me.

    In what world would someone try to make a point by comparing a tractor with a plow stuck in the ground to a road vehicle pulling a trailer with wheels.

    But since you did, ......

    If we tie a tractor to an immovable object, say a stump. Two assumptions, both attachment points are behind the rear axle and the tractor has ample torque and traction. First we use a seat height mounting point, then, the lowest hitch point on the tractor. As we attempt to pull the stump from the ground with either attachment, the forward rotation of the wheels will raise the front of the tractor. The only difference is the amount of torque it takes to do the job. In neither scenario will the torque applied by the rear wheels increase the down force on the front of the tractor.

    A properly setup tractor and plow utilizes a three point hitch that places the plow level in the ground to cut and flip, or turn the furrow over, not dig in pulling the back of the tractor down. They are called turning plows for a reason.

    A three point hitch is designed to attach implements that are sized to the tractor and capable of being lifted and driven safely in that position. Trailers, or more likely wagons, are usually connected to a fixed height hitch mounted low on the tractor that is also used for implements that are towed and not lifted.

    Go take a ride and notice all the modern pickup trucks and SUV's with receiver hitches and notice the height compared to the center of the wheel. Most who tow will use a dropped ball to match the height of the trailer coupling when trailer is level. If the trailer weight matches the tow vehicle specs, none are in danger of flipping their vehicle over backwards.

    After all this exchange there is still only one point I was trying to make. Let me say it again. You can't attach a typical utility, boat or RV trailer to the rear of a typical SUV, pickup or auto tow vehicle utilizing a typical receiver hitch in such a manner that the tongue weight or the load when moving forward under the power of the towing vehicle, increases the downforce on the front axle of the tow vehicle.

    Let me try another way. I don't see how one could place a lever over a fulcrum and apply down force on one end that also produces down force on the other end. Down force on one end will lift the other.

    If you want to continue arguing the point then stick to the point.

    ..
    #40