Round Bar vs. Trunion Mount Flat Bar WDH ?

[bobinyelm]

I WAS going to use a single spring WDH to tow Casita w/ my Jeep Cherokee, but because I want to leave room on the "A" Frame for my Honda generator, I've decided to go w/ a 2-spring WDH.

They are offered in either round bar (bars have a 90 deg bend) or trunion mount w/ flat bars.

Other than ground clearance issues, I can see no clear advantage of one over the other. I asked my local RV dealer and he didn't have a clue, either.

Anyone here have any reasons for a preference of one over the other?

Thanks,
Bob

[Frederick L. Simson]

Preference?

My Fiber Stream already had the flat bar system installed which were included in the sale from the previous owner. But he did not have a trunion ball mount; apparently he was just passing along some equipment from the previous previous owner. The guy I bought the trailer from never used weight distribution. I had to go buy a trunion ball mount to be able to use the flat spring arms. The only one that Camping World sells is a heavy thing rated for 10,000 - 12,000 pounds. My spring arms are rated for 350 pounds.

[Roger H]

The trunnion system allows for the use of the Dual-Cam sway control system parts. The round bar is only for weight distribution.

Roger

[Brian B-P]

The trunnion system allows for the use of the Dual-Cam sway control system parts. The round bar is only for weight distribution.

But any WD system with two spring bars does lots more than just the "weight" distribution: the chain-linked type (any Reese product) spring-loads the tug/trailer coupling towards straight ahead, spring-loads it towards keeping the trailer and tug tilted the same amount (whether that is appropriate or not), and adds friction to the yaw (steering or swaying) motion. All of these are "sway control" features. The "cam" effect is a non-linear exaggeration of these same characteristics in the yaw axis... which means it does more of the same, more strongly centred.

I'm not questioning that in the Reese lineup Dual-Cam is the ultimate variation, and you need to use the trunnion system to get there... but it's not an all-or-nothing "sway control" situation.

[Roger H]

Brian, without something like the cam setup from Reese, or the Equal-i-zer setup, a WDH is only that... there is no effective sway control provided merely from the weight distribution system. That is why folks need to use a friction sway control bar with a standard WDH. There are, of course, weight transfer which goes to the core of sway issues, and some limited friction in the hitch, but no "sway control" per se. A WDH alone will allow a sway episode just as thought WDH wasn't in use.

Roger

[bobinyelm]

The trunnion system allows for the use of the Dual-Cam sway control system parts. The round bar is only for weight distribution.

Roger

Actually, Reese now offers their round-bar WDHs with bent flat ends like the torsion arms so they, too , can be used with the dual cam anti-sway. Picture illustrates the round bar w/ dual cam:




Bob

[Roger H]

Wow, Bob. I learn something new every day. Ok, then I have NO idea why square bars would be better than round. Maybe an email to Reese is in order? Let us know what you find out please!

Roger

[Brian B-P]

Certainly, a pure WD design would not be a sway control, in the sense that this term is normally used. The closest current design to this would I suppose be the Reese single-bar, because it responds minimally to yaw and roll motions, and has no friction in pitch motion.

Equal-i-zer uses square bars so that they are forced to twist when the trailer rolls relative to the tug - the bars go though roughly square brackets. Despite the Equal-i-zer mystique, the Reese 350 Mini WD must have at least some of the same effect, since it forces the bars to ride on flat surfaces, not pivoting on the end of a chain. Without this sort of torsional constraint, I can't imagine a functional advantage to square bars... although these are bending-beam springs, so for efficiency they should actually be flat leaves, and a square bar is closer to that ideal than a round one. My guess is that the choice of square or round in the Reese designs is just a matter of manufacturing cost.

The Dual-Cam cam action is to provide spring-loading to centre (in both roll and yaw, but mostly in yaw). All dual-spring WD systems do that... so either it doesn't matter to sway control, or all dual-spring systems do have a sway control function. I don't question that the Dual-Cam has a very strong centering action... maybe it's the only Reese variation with enough of this action to be effective.

The other aspect of "sway control" in these devices is friction. Equal-i-zer makes a big deal of their deliberate "four point" friction, and they specifically informed me in an e-mail response to a question that the primary friction location is at the spring bar pivots in the head (they call it their "tri-wing" design). All WD systems have pivoting spring bars, so all have some degree of friction at the head (and the Reese 350 Mini has it at the bar ends as well). Perhaps only the Equal-i-zer has a useful amount there. The Dual-Cam design forces the bars to slide over the cams - that's their planned friction point... and again, it may be so massively larger than a basic chained-up WD system that only the Dual-Cam is noticeably effective.

In the end, if I were buying a Cequent (Reese, Draw-Tite, etc) two-bar WD system I would want to get either the 350 Mini (with the slide pads) or something which could accommodate Dual-Cam later - why not keep the options open?

[bobinyelm]

Wow, Bob. I learn something new every day. Ok, then I have NO idea why square bars would be better than round. Maybe an email to Reese is in order? Let us know what you find out please!

Roger

Roger,

I in fact did speak with Reese (Cequent) today and asked several questions.

On was about weight and the dual cam. The techie said 400# hitch weight is the break point for recommending the dual cam unit, so I'd be fine in that regard. The Casita 17 is notoriously node-heavy with some reporting OVER 500# hitch weight with a 3300 pound trailer gross weight!

Another question was round bar vs. trunion, and he said the trunion gives better ground clearance, by putting the spring bars closer to the trailer frame, and is rated to 12,000 pounds trailer weight (vs. 10,000 for the round bars). Other than that, he said they are functionally identical.

I further asked him if their Hidden Hitch line WDHs could be used with the Reese dual cam setup, and he said that they are virtually identical, and thet the dual cam works perfectly with Hidden Hitchs, which is nice, because Reese and Hidden Hitch are the same price, BUT Reese does NOT come with the draw bar, but HH does (that's a $100 piece of metal if you don't have one lying around).

Brian-

If I understand the principle right, the cams use the fact that to move the spring relative to the cam, the spring assumes greater displacement, so that adds to the friction effect?

Friction alone damps sway, but it does noting to encourage a straight-ahead position. Friction bars are as happy to have the trailer at an angle (any angle) as straight, offering equal resistance to resuming straight-ahead as they do to the turning maneuver.

I am surprised that no one has designed a side mount anti-sway (would mount to balls like the friction antisway) where a center cylinder is machined into an hourglass shape that passes through an outter cylinder (tube) that has spring loaded balls that compress inward against the inner cylinder, encouraging a return-to-center when displaced. One could seal the device and add hydraulics to it so it has spring force PLUS hydraulic damping.

Hmmm....I need to patent that idea!

Bob

[Pete Dumbleton]

I am surprised that no one has designed a side mount anti-sway (would mount to balls like the friction antisway) where a center cylinder is machined into an hourglass shape that passes through an outter cylinder (tube) that has spring loaded balls that compress inward against the inner cylinder, encouraging a return-to-center when displaced. One could seal the device and add hydraulics to it so it has spring force PLUS hydraulic damping.

Hmmm....I need to patent that idea!

Bob

Might want to check existing patents because many of us have expressed thoughts along those lines for sway dampening for small trailers without the current need for WDH and without the (sometimes scary) limitations of friction sway control. OTOH, maybe it's been all talk and no action so far!

BTW, I think the 'round bar equals no sway control' idea may stem from the small round-bar WDHs with only ONE bar for one-beam trailer tongues:

http://www.etrailer.com/pc-WD~3204.htm

According to ETrailer's site, Draw-Tite makes dualcam sway bars in both round and trunnion shapes.

[Brian B-P]

If I understand the principle right, the cams use the fact that to move the spring relative to the cam, the spring assumes greater displacement, so that adds to the friction effect?

Friction alone damps sway, but it does nothing to encourage a straight-ahead position...

The cam action increases the friction, but it also forces the trailer towards straight, since that is where springs have minimum displacement - the springs "fall down the ramp" of the cam. The Equal-i-zer and Mini 350 designs do not have the cam shaping, so I agree that they only resist changes in direction, and don't encourage a specific direction.

I am surprised that no one has designed a side mount anti-sway (would mount to balls like the friction antisway) where a center cylinder is machined into an hourglass shape that passes through an outter cylinder (tube) that has spring loaded balls that compress inward against the inner cylinder, encouraging a return-to-center when displaced. One could seal the device and add hydraulics to it so it has spring force PLUS hydraulic damping.

Hmmm....I need to patent that idea!

The logic makes perfect sense to me. Blue Ox used to sell a pneumatic sway control device - basically a fluid shock instead of the cruder mechanical friction device - but discontinued it a year or two ago. I asked them if it provided an air-spring based return-to-centre, but never received a response.

Many motorhomes and off-road trucks use "steering stabilizers"; these are fundamentally the same thing as the friction-type sway control device, but using a horizontal hydraulic damper (shock absorber) instead of mechanical friction. They mount on the steering linkage They are available with coil springs, like an "overload" spring on suspension shock, but clamped so it is spring biased to the central (straight ahead) position. One of these could be mounted as Bob describes (to ball mounts) and serve functionally as almost the same thing as the "patent pending" device. I have not heard of anyone doing this... it would certainly cost a bit more than the mechanical friction devices.

Bob's cam design would have one advantage over the coil-on-damper alternative: it could have a curved cam (not just straight slopes), to allow tuning of the spring behaviour.

[Roger H]

The other aspect of "sway control" in these devices is [b]friction. Equal-i-zer makes a big deal of their deliberate "four point" friction, and they specifically informed me in an e-mail response to a question that the primary friction location is at the spring bar pivots in the head (they call it their "tri-wing" design). All WD systems have pivoting spring bars, so all have some degree of friction at the head (and the Reese 350 Mini has it at the bar ends as well). Perhaps only the Equal-i-zer has a useful amount there. The Dual-Cam design forces the bars to slide over the cams - that's their planned friction point... and again, it may be so massively larger than a basic chained-up WD system that only the Dual-Cam is noticeably effective.

Brian, Equal-i-zer may be different, and I have no experience with them, but all of the Reese components are greased at the hitch head end; both the top and bottom pivots of the trunnion bars get greased to diminish friction and wear. The trunnion bars should swing freely with the trailer tongue around the ball, even under load. The stock Reese WDH setup without the dual-cam does nothing for sway control; hence the need for a friction sway control assembly or the Dual Cam in addition to the WDH.

Roger