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Snatching from towbar.

Discussion in 'General 4x4 Discussion' started by boobook, May 17, 2018.

  1. boobook

    boobook Well-Known Member

    We all know not to snatch from a towball right? And lots of people advocate towing from the tow bar, for example using the tow pin or a recovery tow hitch. Like the pictures below.

    But the snatch straps are rated at 8000kg or 11000kg, and there are lots of 4wd stress tests on these in the magazines. every one puts so much importance on the breaking strain being over the rated value, and not under the value, even by a small amount. That would be a dangerous fail.

    But tow bars and the pins are only rated at 3500kg.

    So why is this form of snatching considered ok? In theory the towbar or tow pin is rated at less than half the snatch strap and could be a missile.

    I don't get it.
    [​IMG]

    or this
    [​IMG]
     
    Dead End Dendo, Jaye, Muddled and 3 others like this.
  2. billolga

    billolga 4x4 Earth Contributer

    I love my Cargo Barrier when I am snatching from the Tow Bar & avoid as much as possible pulling from the front (Not hard snatching).
     
  3. mac_man_luke

    mac_man_luke Well-Known Member

    My thoughts are:
    Tow bars ideally should be rated to a WLL (working load limit) which is generally 5-10x breaking strain, eg 3.5T tow bar should be able to handle 17.5 to 35T
    Snatch straps are rated to breaking strain eg 9000kg strap will break around 9000kg

    Also likely find tow bars are massively over engineered and tow ratings are more based on vehicle capability, safety and legalities than actual engineered strength.
    Most tow bars would be much stronger than any of the bolt on recovery points people are happy to use, often held on by a few m10-12 bolts and are "rated" to 5-10T on occasion.
     
  4. billolga

    billolga 4x4 Earth Contributer

    The problem I see is if the bar is stronger than the Recovery gear what happens when it breaks when your watching it come at you. A fair few have died when something comes through the Windscreen.
     
  5. boobook

    boobook Well-Known Member

    Well that definitely makes sense Luke, except for one thing... the Tow ball should be rated in an identical way to the tow bar. - 3.5Ton WLL or 17.5 to 35 tons.

    So why is it ok to accept the rating of the tow bar, pin, bolts, hitch, but not the ball??? After all none of the towing assembly is being used in the way it was designed to be used.
     
  6. 80lover96gxl

    80lover96gxl Moderator

    Seems to me that the ball itself is fixed at one point by one nut and a spring washer at a point around one third the overall length of the ball to the tounge of the towbar, in a vertical manner. When used as a recovery point the sheer factor due to design, and no fixed point securing the top of the ball leaving it venerable to snapping, hence the light rating. All other points of the towabar, hitch assembly are all fixed points by multipul bolts or welds. I think the difference being the towball is designed to work in a vertical fashion whereas hitch recievers are horizontal allowing their rating to be largely increased safely.
     
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  7. mikehzz

    mikehzz Well-Known Member

    If you hook over the ball then you get a bit of a leverage action trying to bend the ball around the tongue. I think it's that and the shock load of someone going back and forward repeatedly as seen on umpteen youtube clips.
     
    Luthy likes this.
  8. Tink

    Tink Well-Known Member

    I dislike using just the pin with a strap if it is not a dead straight recovery. I just get this bad feeling that any sideways tension on that pin is asking for trouble.
    And there is also the chance of damaging the strap on the edges of the square receiver when it is not a straight snatch. The stress of being stretched around a sharpish corner is not something that the strands of the strap are designed to handle I would think.
    Tink
     
    Spooner likes this.
  9. Cokedaddy216

    Cokedaddy216 Active Member

    Tow balls have 30 or 40 mm of thread after the nut , that is part of there design , I don't know the engineering behind that it has to be that way for a reason .
    The tow hitch pin would wear a fair load as the van or whatever slows down or accelerates .
     
  10. mac_man_luke

    mac_man_luke Well-Known Member

    The only thing that should break and become a possible projectile should be the snatch strap which should be slowed with dampers.
    People tend to die when the recovery point rips off or someone uses a shackle to join straps, big piece of metal is going to do much more damage than a fabric strap.
     
  11. mac_man_luke

    mac_man_luke Well-Known Member

    I think tow balls failing is just due to forces not taken into account when manufactured and no doubt quality of manufacture.
    Most pics i have seen of snapped tow balls have been rusty and well used with no doubt pre existing fatigue (not that you should use one anyway!)

    Guess that might be a reminder to check and replace all recovery gear if suspect. Im sure most use straps more than they should just trying to save replacing a $50-100 strap etc
     
  12. Cokedaddy216

    Cokedaddy216 Active Member

    Tow hitch pins would be made from a steel like 44/40 or something like that , if you tried to shear it in your cropper it would jam the machine or smash the blades , that's most likely the reason you can use them as a point for the recovery point .
    Strong with a high shear strength ;)
     
  13. Luthy

    Luthy Active Member

    Its like trying to snap a twig. Imaganine holding a stick (in this case towball) even a sall one upright and pulling the top towards you of coarse it will snap. Then lay the stick (towball) towards you and pull it towards you it wont break at all. Same physics apply to using a tow hitch reciever or pin. General forces will move along the direction of pull ie. Along the receiver and into you chassis which i agree are probably way over engineered, but if you use a towball the weakest link is said towball. The pin should be made out of high tensile steel as tow hitchs are generally removable therefore need to be shock loaded as a car speeds up and decreases speed it will move and therefore have to be strong enough not to shear off especially in an emergency. The tow bar needs to take a fair load to say have a 40ft caravan on it loaded up and travel at speeds on a usually rough surface to not have the bar shear away from the car and let the whole lot career down the road with the bar still attached to said caravan. In saying that how many ppl tow or do recoveries and regulary check there tow bars for stress fatigue?

    Not an expert, just my thoughts.
     
  14. silkwood

    silkwood Member

    Engineer from work (reworks the trucks and machinery for the concrete factory) will only use a hitch receiver, not the pin on its own (he has now shifted to a rear bar with built in towpoints). His reason is not that the pin will shear, but that he has bent a couple, making it very difficult to remove. The pressure on the pin when using a hitch receiver recovery point is spread across the material, lessening stress and eliminating bending. Not a formal engineering opinion from testing, but I've seen the stuff he works on and tend to trust him.

    Cheers,

    Mark
     
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  15. rogerazz

    rogerazz 4x4 Earth Contributer

    I remember when buying my first snatch strap, the bloke who was into recovery etc. said not to get a strap with a very high breaking strain. You have to take into account weights of vehicles, what forces should/should not be used etc. , virtually impossible to work out.
    Using dampners and straps that break easier so to speak would be better than straps that never give and break something else.
    Having said that, I have only snatched once in five years and maybe if again , very slow and steady. My shovel, tracks, winch etc. is good enough for me.:).
     
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  16. Cokedaddy216

    Cokedaddy216 Active Member

    Hitch pins are not given weight ratings because they are built with such extreme weight bearing capabilities that the trailer hitch, ball mount or trailer coupler is more likely to fail than the hitch pin.
    From a site on the net ;)
     
  17. CaptainBanana

    CaptainBanana Active Member

    A cars towing capacity is a capacity based on a cumulative number of factors and not directly related to what the towbar itself can hold but this has been mentioned already.
    Snatching of a towbar pin which passes through two sides of a hitch and evenly spreads load is less likley to break than a tow ball being levered.
    Also IF the pin were to snap and manage to work out of the hitch it wouldn't matter as it's mass is so low it's unlikely to project anywhere.
     
  18. Spooner

    Spooner Well-Known Member

    Thats my thoughts as well.
     
  19. Spooner

    Spooner Well-Known Member

    Back in the real world , if you can't dislodge after 1 or 2 or 3 gentle snatches letting the strap do its work using its own energy , then you ain't going anywhere regardless of how hard you tug , pull or full revs dump it .
    Thats why we have a thing called a winch ;)
     
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