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Jackknifing not actually bad?

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  • #16
    IN order for an equalizer to work properly all 3 holes should be in the same line. With the center one higher (like the trailer ones) as the front axle lifts, it puts up lift into the front hole on the equalizer causing the triangle to rotate. As the triangle rotates since the hole is lower, the moment arm from the center to the forward axle gets longer and the rear shorter. As a result the rear has to carry more load than the front to maintain the sum of moments equal to zero. In an inline hole setup (very similar to a slipper spring system) as the front hole goes up the distance gets SHORTER on BOTH.
    Joseph
    Tow
    Vehicle: 2024 GMC K3500 Denali Ultimate Diesel
    Coach: 303RLS Delivered March 5, 2021
    South of Houston Texas

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    • #17
      timelinex I believe one of the overlooked issues with "jack knifing" is the tremendous side loads placed on the sidewall of the tires. I have seen r.vs parked in tight spots with the sidewalls stretched in all directions at once for a whole stay at a campground. A friend had a tire store for years and always insisted that the side loads were the worst for a tire. Generally the side walls have much fewer plys than the tread and can be overstressed in a hurry by those side loads. An uncle that had large 5th wheels did this kind of thing on a regular basis and was constantly having tire issues and suspension problems. IMHO most of these types of problems with suspension and tires can be avoided with a little pre-planning when parking.

      Dave
      flyfshrockies, 2021 imagine 2600RB, Ford F-150, XLT supper crew 3.5 eco boost with max tow. Dave and Toni (and the awesome Aussie Bayley, he's the social one)

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      • #18
        Jlawles2
        Hi Joseph . . . I am going to have to think a bit about the equalizer triangular geometry affect that you describe . . . hmmm. I do wish Gyrogearloose Pat was still following this discussion (I know that he has sold his Grand Design) because he had the software to model the suspension loads that we were debating.

        The explanation that we were following a while back had more to do with the reaction forces to brake apply. Basically this causes the front attachment for each spring to pull down and the aft attachment to lift up. Thus, the rear axle is pullings its end of the equalizer down and the front axle is lifting its attachment to the equalizer up. Since the outer ends of the springs can't move, all the motion happens at the equalizer, as shown in the video.

        Rob
        Cate & Rob
        (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
        2015 Reflection 303RLS
        2022 F350 Diesel CC SB SRW Lariat
        Bayham, Ontario, Canada

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        • #19
          Originally posted by flyfshrockies View Post
          timelinex I believe one of the overlooked issues with "jack knifing" is the tremendous side loads placed on the sidewall of the tires. I have seen r.vs parked in tight spots with the sidewalls stretched in all directions at once for a whole stay at a campground. A friend had a tire store for years and always insisted that the side loads were the worst for a tire. Generally the side walls have much fewer plys than the tread and can be overstressed in a hurry by those side loads. An uncle that had large 5th wheels did this kind of thing on a regular basis and was constantly having tire issues and suspension problems. IMHO most of these types of problems with suspension and tires can be avoided with a little pre-planning when parking.

          Dave
          Good point Dave. This was a much greater problem when ST tire quality was so bad that many were using LT tires on their trailers. Now that ST tire quality has improved . . . and ST tires have much stronger sidewalls than LT tires . . . this is less of a problem.

          BTW . . . I agree with your "pull ahead and take another run at it" advice rather than forcing the tires and suspension into a tight jackknife. And particularly . . . don't leave them twisted like that. Yikes !

          Rob
          Cate & Rob
          (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
          2015 Reflection 303RLS
          2022 F350 Diesel CC SB SRW Lariat
          Bayham, Ontario, Canada

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          • #20
            Cate&Rob Rob, sit down and draw out the triangle. With what I do at work, it's common for us to use equalizers and those are typically setup with all 3 holes in line due to keeping the forces equal. It does not matter if the center hole is above or below, it only changes which gets longer or shorter. Hole over as most suspensions are assembled, the front gets longer as load increases, where hole under the front would get shorter.

            If someone had a way to invert the equalizer and run a test, I suspect the rear axle would skid vs the front.
            Joseph
            Tow
            Vehicle: 2024 GMC K3500 Denali Ultimate Diesel
            Coach: 303RLS Delivered March 5, 2021
            South of Houston Texas

            Comment


            • #21
              Cate&Rob Thanks Rob. As you said the new ST tires are worlds better than say 20 years ago. I cringe when I hear and see the tires on an r.v. skidding on the surface while someone parks their rig. Ouch!

              Dave
              flyfshrockies, 2021 imagine 2600RB, Ford F-150, XLT supper crew 3.5 eco boost with max tow. Dave and Toni (and the awesome Aussie Bayley, he's the social one)

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              • #22
                Cate&Rob OK, I was under the trailer adjusting the brakes (no surprise that all 4 were different) and had a time to look at the CRE system. I think the swing shackle holes are closer to in line with the pivot hole, but no where close enough to act a s a true equalizer.
                Joseph
                Tow
                Vehicle: 2024 GMC K3500 Denali Ultimate Diesel
                Coach: 303RLS Delivered March 5, 2021
                South of Houston Texas

                Comment


                • #23
                  I used to be pretty happy that my 5er could almost make a full 90-degree when backing in. Then I got to looking at the stress and strain placed on the tires and suspension and decided that it wasn’t a big deal to just take a pull-up and reduce the stress and strain.

                  As of Thursday afternoon, my unit is in quarantine in my driveway with a broken curb-side rear spring hanger that I discovered during my first pre-flight check of the season. Not a warm and fuzzy feeling, considering that the last trip of the season last year was a 4,400 mile round the country trip, with many out-of-the way and off the beaten path destinations. I’m glad that it appears to be a fresh break and only on one side of the hanger. At least I found it before the other side broke as well, potentially damaging something or someone. I’m also glad that it didn’t occur during our long trip, and having to figure out what to do in the middle of nowhere.

                  My wife was shocked and said, “But you baby this rig, how can that happen?” I can only assume that it is from the hard right turn that I have to take when exiting my driveway and the near 90-degree backing that is required to get the unit back into the driveway at the end of the trip.
                  Last edited by Tom in PGH; 05-08-2022, 09:20 PM.
                  Tom and Janice (also known as Richter on the “Other” forum)

                  First came the 18' Comfort bumper-pull, was great for 20 years.
                  Now a 2019 Reflection 303RLS, second air, double glass, table and chairs
                  2019 F350 Lariat 4x4 Crewcab with lots of goodies
                  Andersen aluminum with the puck system holding it all together
                  Cranberry Twp. PA, about 30 miles north of Pittsburgh

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                  • #24
                    When I first pointed out the LCI video and theorized on the interaction it surprised many at the other forum. Today it still surprises many but the manufacturers still make this system. Any IS will prevent front axle rise as well as a slipper spring system but here we are. When heavy braking is performed, the rear axle torques and rolls over, wraps the rear spring as verified by Pat and articulates the equalizer which lifts the front axle. What happens next is reduced traction where the rear axle, tires, springs, etc. essentially become overloaded. The rear hanger is the only solid anchor point during this dynamic condition between the overloaded rear axle and the frame. Spring wrap can result in a crack to form at the trailing edge of the rear hanger. Once this crack occurs, any motion will work at that crack to create a fractured spring hanger. The addition of the V Clip will prevent the hanger from cracking and failing in most cases.

                    Hard to imaging that the heaviest braking will result in less stopping distance but this is the case.

                    Rear hanger failure is the result from hard braking.


                    Jim
                    Last edited by Guest; 05-09-2022, 10:15 PM.

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                    • #25
                      What if my trailer does not have the V braces? It does have a tube between the hangers and the frame to raise the unit, but no V brace.
                      Joseph
                      Tow
                      Vehicle: 2024 GMC K3500 Denali Ultimate Diesel
                      Coach: 303RLS Delivered March 5, 2021
                      South of Houston Texas

                      Comment


                      • #26
                        With the rear wheel doing the lions share of hard braking, would be a good reason to rotate tires front to back from time to time.
                        2018 Dodge 3500 6.7 Cummins w Aisin and 9 cup holders
                        Not to brag or anything about my finances, but my bank calls me about every day to tell me my balance is OUTSTANDING!

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                        • #27
                          Originally posted by Scott'n'Wendy View Post
                          With the rear wheel doing the lions share of hard braking, would be a good reason to rotate tires front to back from time to time.
                          Lionshead (supplier of wheels and tires to Grand Design) recommends rotating the tires in an “X” pattern when they are off for bearing repack. The front tires can actually show more wear than the rear tires because (due to the lifting) they are more likely to slide against the road surface which creates more wear than the firmly gripping rear tires.

                          Rob

                          Cate & Rob
                          (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
                          2015 Reflection 303RLS
                          2022 F350 Diesel CC SB SRW Lariat
                          Bayham, Ontario, Canada

                          Comment


                          • #28
                            Originally posted by Cate&Rob View Post

                            Lionshead (supplier of wheels and tires to Grand Design) recommends rotating the tires in an “X” pattern when they are off for bearing repack. The front tires can actually show more wear than the rear tires because (due to the lifting) they are more likely to slide against the road surface which creates more wear than the firmly gripping rear tires.

                            Rob
                            I just finished the bearings...I'll break out the jack and do that then. Prior to that video, I couldn't think of any reason to rotate the trailer tires. It's not like they have a steering pair/drive pair like a truck.
                            2018 Dodge 3500 6.7 Cummins w Aisin and 9 cup holders
                            Not to brag or anything about my finances, but my bank calls me about every day to tell me my balance is OUTSTANDING!

                            Comment


                            • #29
                              Originally posted by Jlawles2 View Post
                              What if my trailer does not have the V braces? It does have a tube between the hangers and the frame to raise the unit, but no V brace.
                              Joseph,

                              The V Clip I believe was to provide additional support in the longitudinal direction where otherwise the thin hanger in the longitudinal direction can crack. Somewhere on this forum is a golden pic of the onset of this failure. Not sure which thread that is on.

                              The X Factor bracket will support in the lateral direction and is really needed on the center hanger but some add them to all three points. One fellow here found a clever solution in adding the X Factor bracket with hangers equipped with V Clips.

                              Jim

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                              • #30
                                Originally posted by Jlawles2 View Post
                                Cate&Rob Rob, sit down and draw out the triangle. With what I do at work, it's common for us to use equalizers and those are typically setup with all 3 holes in line due to keeping the forces equal. It does not matter if the center hole is above or below, it only changes which gets longer or shorter. Hole over as most suspensions are assembled, the front gets longer as load increases, where hole under the front would get shorter.

                                If someone had a way to invert the equalizer and run a test, I suspect the rear axle would skid vs the front.
                                Joseph,

                                The axles will always exhibit a resultant force to braking and will always want to roll forward. However with the equalizer being an unfixed point, this allows the rear axle to roll forward. The front axle would try to roll from braking torque as well, but this does not happen since the front axle is raised through the motion applied through the equalizer from the rear axle. The key is to dump the use of the equalizer and use a slipper spring system. Each axle would try to roll against a fixed point (hanger pin or slipper side) and would stay in contact with the road.

                                The original thought on this system in transferring load is interesting but its performance based on its history of so many failures on the rear axle provides enough data to say most all other systems are better.

                                Jim

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