Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. It only takes a minute to sign up.
Sign up to join this community
Yesterday I was towing my friends car to a repair shop. I was towing it on a rope. But due to my inexperience every start was akin to game of paddle ball. The rope is kinda elastic and my car is abour 300kg lighter than his.
What is the reason for the tow rope to be elastic? If it was rigid I think there would not be such a problem with every start. It would be similar to using tow bar.
EDIT: I have changed flexible to elastic, to better capture my intent.
Tow rope is specifically made to be elastic because it allows for diffusion of energy when the rope is tightened.
Imagine towing with a chain, which has essentially no elasticity. While the chain is loose, the car in front can move freely forward while the car in back is stationary. At the instant the chain tightens, the car in back would go from zero to the speed of the car in front instantly, causing a very uncomfortable jerk, and putting an immense amount of force on the parts attached to the chain.
Its impossible to keep a chain perfectly taut the entire time while towing so at the very least this would make for an uncomfortable ride and at worst do serious damage to both vehicles.
An elastic rope in contrast stretches when under tension and allows the rear vehicle to slowly accelerate to the speed of the front vehicle.
A tow bar is different because it is rigid and therefor always taut.
This is the same reason why rock climbers use elastic (or dynamic) rope rather than static rope for climbing. When falling on a dynamic rope, the climber slowly decreases speed from a freefall to stopped. With a static rope, the climber would stop immediately the instant the rope becomes taut, exerting a large amount of force on the climbers body, and the bolts holding the rope to the wall.
Edit: In answer to the second part of your question, it looks like the rope you linked to in the image was not made for towing. If you buy one made specifically to tow cars there will be less stretch so you won't be bouncing around so much
All types of rope have a certain amount of stretch possible - the amount depends on the material and weave and this is good to absorb small shocks.
When towing, the person driving the car that is being towed has to keep the rope taught - so it does not drag on the road (causes wear) and does not get caught under a wheel...
One rope I had with a 10 ton capacity had a stretch rate of 45% which meant that it would increase its length by half as much under load - worked very well for what I wanted.
Snatch towing or more properly kinetic energy recovery is something that a stretchy rope is good for - can’t do that with a solid bar - the likelihood of something breaking is very high, but KE recovery needs the mounting points to be perfect : have seen a chassis member come off before...
All rope stretches to some degree. And besides when being towed it's like a cushion between the two vehicles so one does not pull the others bumper off or tie rod or radiator support or wearever the rope is fastened to.
