In trucking, what’s jackknifing?

In trucking, what’s jackknifing?

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0 thoughts on “In trucking, what’s jackknifing?”

  1. There are lots of misconceptions about jackknifing. Firstly, jackknifing is nowhere near as common as the media or traffic reports lead you to think. Trucks are often reported to have jackknifed when they actually haven’t. It just sounds sensational to say that a truck has jackknifed when in fact it has simply crashed or got stuck in the snow. Let me make it absolutely clear that jackknifing is not the result of a trailer skidding. If a trailer skids it’ll come back into line when the brakes are released and the tractor continues to pull it along. Jackknifing occurs when the TRACTOR skids, and if the skid is not corrected in time, it will be exaggerated by the trailer pushing from behind. If the tractor is pushed around until it faces backwards and collides with its own trailer, it is said to have jackknifed. Jackknifing occurs when a vehicle is empty or when a load is badly distributed so that there is very little weight over the drive axle causing it to lose traction. Preventing a truck from jackknifing is done in the same way as one would avoid a skid by allowing plenty of braking distance when the road surface is likely to be slippery, and by having the skill to correct a skid if it does occur. Most truck drivers are skilful enough to avoid jackknifing and also nowadays trucks are fitted with ABS.

    In trucking, what's jackknifing?

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  2. A jacknife is named as such because many years ago, like in the 50’s or maybe before that. A pocket knife that folded up to close the knife was called a jack knife. When a tractor trailer ends up from the result of a lot of different situations with the tractor part of the rig in contact with the side of the trailer, that’s is called a jacknife. It can happen as simply as a driver turning there steering wheel to sharply for to long while backing up, until the cab of the truck hits the side of the trailer. Or getting into a skid from slick road surfaces allowing the cab to slide around and make contact with the side of the trailer. I actually had this happen to me once.I was working in the oilfield in West Virginia and driving a rig that weighed around 130 thousand pounds. When I left the drilling location there was a really steep hill, which is common in WV. It went down for about a 150 feet or so followed by a flat 90 degree right hand turn.When I started down the sloop my trailer brakes failed, so all I had was tractor brakes.Every time I applied the brakes the trailer would start to push my tractor side ways. That’ll get your pucker factor going, I’m telling you.When I got to the turn I jammed on the brakes for a moment to try and slow as much as I could then attempted to make the turn, which right a way I knew one of 2 things was going to happen. Either I was going to roll over or jacknife and go backwards down through the woods below the road. Seconds latter my tractor slammed into the side of the trailer with enough force to throw me out the window if I hadn’t had my seat belt on. When the bulldozers built the road fortunately for me they left a big wall of dirt around the outside of the turn. I plowed through that which slowed me enough for me to have time enough to engage all my drive wheels on the tractor, put it in 3rd or 4th gear, I don’t really remember which one I chose at the time. I mashed the throttle to the floor and dumped the clutch. With the trailer still slowly moving me backwards and the tractor wheels throwing rooster tails of dirt up over my cab, the rig started hopping up and down pretty violently, which caused the tractor wheels to get enough traction to start dragging the trailer back up and around onto the road. I just held down the throttle until it bounced back onto the road. That was a bad day, but sure could have been a lot worse.

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  3. Jackknifing is where the tractor and trailer come in contact with each other.
    Jackknifing is caused by braking forces on the tractor that are uneven in combination with the trailer having too much momentum for the grip available on the back tires of the tractor. An example of this scenario would be: Coming around a corner too fast pulling a tri-axle load of 60,000LB of ice cream and suddenly the drive tires catch a patch of black ice; If the driver is unable to correct the tractor’s drift because the steering box has run its maximum cut angle limit then the tractor will continue to rotate into the trailer due to grip on the steer tires which are not a driven axle.
    The only way to correct a drift on a non-ESC truck and get back in front of the trailer is to gently apply torque to the drive axles while counter-steering. On trucks with ESC the brakes will apply on each individual wheel to get the tractor back in line with the trailer.

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