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When you buy a tow rope it is usually marketed as something like "4000 kg tow rope" or similar. Does that rating mean that the rope is suitable to tow vehicles with a mass of up to 4 tonnes, or does it mean that it has a safe working load of 4000 kg, i.e. the rope can safely sustain a force up to 4000 kgf?

Obviously one wouldn't, or rather, shouldn't use an uncertified rope for any critical applications or at least without testing and verifying. I also don't trust any 'cheap' product I could buy at my local grocer, but I am curious about this number and what it is supposed to mean, disregarding marketing hype.

  • I expect the design load for a tow strap is essentially the same as the weight of the vehicle. Figure you need to allow for towing up hill and handling a certain amount of shock. In any case a good strap will also be labeled with its actual breaking load rating. – agentp Mar 20 '18 at 11:18
  • No, it means normal "flat towing" of such a weighted vehicle. You can't dead lift it with a crane. Maybe you could, but that's not the intent of the rating. A "strap" with a 4000kg lift rating would be one hell of a strap. Compare it to welded link chain with the same rating... – SteveRacer Mar 21 '18 at 0:56
  • I don't mean dead lift, I mean running highway speed up a grade and being less than perfectly steady on the gas. If you are rating a tow strap to sell to the public you need to assume someone will do that. – agentp Mar 21 '18 at 1:15
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It is rated for vehicles up to 4000kg...

It is not rated for lifting operations ie use as a sling on a crane...

It is not rated for KE recovery - kinetic energy recovery - where the stuck vehicle is made to move by accelerating the towing vehicle and “snatching” or jerking the stuck vehicle free...

Edit: some people will use a strap for heavier vehicles than the strap is rated for, as there is a "margin of safety"... While it may work and is not recommended, if it goes wrong then the insurance company may not cover the incident...

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