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Old 10-08-2020, 12:16 PM   #15
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Quote:
Originally Posted by Seon View Post
As for trailer jackknife, it appears the major cause is the excessive swaying.
Trailer sway undoubtedly accounts for the vast majority of travel trailer jackknife incidents. However, a heavy bumper-pull trailer tends to kick out the rear end of tow vehicle in turns at speed. This phenomenon is called "oversteer".

Countermeasures to reduce oversteer include
  • Shorten the distance between drive axle and hitch articulation point
  • Increase drive axle tire pressure / reduce steer axle tire pressure (increases understeer)
  • Ensure tires are in good shape with healthy treads and strong enough sidewalls
  • Get a heavier tow vehicle (relative to trailer)
  • And most importantly: Drive slower. Speed is the main factor in all of these incidents
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Old 10-08-2020, 12:47 PM   #16
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Posts: 159
Quote:
Originally Posted by JayBauman View Post
Trailer sway undoubtedly accounts for the vast majority of travel trailer jackknife incidents. However, a heavy bumper-pull trailer tends to kick out the rear end of tow vehicle in turns at speed. This phenomenon is called "oversteer".

Countermeasures to reduce oversteer include
  • Shorten the distance between drive axle and hitch articulation point
  • Increase drive axle tire pressure / reduce steer axle tire pressure (increases understeer)
  • Ensure tires are in good shape with healthy treads and strong enough sidewalls
  • Get a heavier tow vehicle (relative to trailer)
  • And most importantly: Drive slower. Speed is the main factor in all of these incidents
All good points. I would only add that you should have a tow vehicle with electronic sway control. I believe most modern vehicles have this as standard now. The ESC will detect trailer sway once it becomes dangerous and then selectively apply the left or right tow vehicle brakes while simultaneously cutting the throttle to slow you down.
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Old 10-08-2020, 01:47 PM   #17
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Let me just add one more point. Oversteer and the tendency to jackknife is increased by taking weight off the rear tow vehicle axle. If you are using a weight distribution hitch you should only apply as much spring force as necessary to keep your axle from overloading. Some people think you should increase the spring force to restore the load on the front axle to its unloaded condition, but this is wrong. Truck manufacturers warn not to exceed 50% (in some cases 25%) FALR (front axle load restoration).
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Old 10-08-2020, 01:50 PM   #18
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Originally Posted by move on View Post
Let me just add one more point. Oversteer and the tendency to jackknife is increased by taking weight off the rear tow vehicle axle. If you are using a weight distribution hitch you should only apply as much spring force as necessary to keep your axle from overloading. Some people think you should increase the spring force to restore the load on the front axle to its unloaded condition, but this is wrong. Truck manufacturers warn not to exceed 50% (in some cases 25%) FALR (front axle load restoration).
Another excellent point. Owner manual for my 2020 GMC HD says no weight distribution is necessary, even up to the maximum tow limits of the vehicle. But if I really want, I can add 25% FALR.

Based on CAT scale and driving comfort data, I have found that in my rig the most comfortable driving conditions equate to about 25% FALR. This is nothing close to the 50% or 75% that I see a lot of others doing. Stay safe, folks.
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