Yahooligan
Temecula, CA
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BarneyS wrote:Yhaooligan wrote:The friction is there all the time, the Reese DC system simply uses the detents to create MORE initial friction, however once the cam is out of the detent you have less friction working for you.
I agree that the friction is there all the time but you are mistaken about less friction once the cams come out of the detents. Once the cams come out, there is MORE friction because the very act of the cams coming out of the detents puts more pressure on the WD bars by raising them up some more. The raise is just about equal to one chain length on both sides of the A frame. This makes the trailer harder to sway than the constant pressure of the other hitch.
Are you 100% sure about that? Not saying you're wrong, but it would seem that it would take more effort to get the cam out of the detent than it would to slide on a flat surface. I equate it to pushing a car out of a rut, it takes more energy to lift AND move the car at the same time, then once out of the rut it's much easier to push. I wouldn't think the additional weight on the cams with a flat surface would have more friction than overcoming the detent and the metal-on-metal friction. If that were the case then I would think they'd forgo the detents and just have you put more weight on the bars to get more friction. Also, more weight on the bars once out of the detent would seem to have a minimal effect due to the reduced leverage (Shorter distance from the cam to the head).
Anyway, I haven't towed with a DC setup and I haven't seen or looked for anything that shows the force required to slide the bars, I'm just thinking about how it seems to work to be the most effective.
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BarneyS
S.E. Lower Michigan
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Yahooligan wrote:Are you 100% sure about that? Not saying you're wrong, but it would seem that it would take more effort to get the cam out of the detent than it would to slide on a flat surface. I equate it to pushing a car out of a rut, it takes more energy to lift AND move the car at the same time, then once out of the rut it's much easier to push.
Yes it does take more energy to "lift" the cam out of the detent but that is because the of the increased pressure (friction) on the bars as the cam moves up the detent and not due to gravity like your car example. Once out of the detent, the pressure (friction) stays higher, unlike the car where once out of the rut the pressure is not needed to lift it anymore. As you said, once it is out of the rut it is much easier to push. That analogy does not work with the Dual Cam however since the pressure (higher friction) is still there after coming out of the detent.  The very act of the cam coming out of the detent increases the pressure on the bars and that pressure (higher friction) remains there until the cams return to the center of the detent.
This is one half of what makes the Dual Cam so effective. The other half is the reduced pressure (friction) when the trailer is returning to center. Keep in mind that during normal driving and small sway conditions, the cams never do come completely out of the detents so there is always that "return to center" tendency of the hitch to force the trailer back in line. On the other hitches, except for one of the newer ones, the friction pressure remains the same no matter whether the trailer is trying to get out of line or trying to return to center.
As far as the distance from the cams to the hitch head goes, keep in mind that as one side extends, the other side retracts. Since the ramps function in both directions that would cancel out any differences between the distances.
Check out the long post made by Ron Gratz earler. He is an engineer (unlike myself) and explains it in much more detail.
Barney
2004 Sunnybrook 30FKS TT
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Yahooligan
Temecula, CA
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Awesome info, thanks Barney!  That's a great help.
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Ron Gratz
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Yahooligan wrote:Are you 100% sure about that? Not saying you're wrong, but it would seem that it would take more effort to get the cam out of the detent than it would to slide on a flat surface. I equate it to pushing a car out of a rut, it takes more energy to lift AND move the car at the same time, then once out of the rut it's much easier to push. I wouldn't think the additional weight on the cams with a flat surface would have more friction than overcoming the detent and the metal-on-metal friction. If that were the case then I would think they'd forgo the detents and just have you put more weight on the bars to get more friction. Also, more weight on the bars once out of the detent would seem to have a minimal effect due to the reduced leverage (Shorter distance from the cam to the head).
This photo provided by member John Barca shows a cam centered in a WD-bar detent.
This photo from John Barca shows the shapes of the detents for two different bar sets.
For most forward-driving conditions, the TV/TT articulation will be within +/- 10 degrees, and the cam will remain in contact with the sloped surface fore or aft of the center of the detent. The relative movement will be about 0.1" per degree of articulation.
As long as the contact point remains on the sloped surface, both the normal force and the friction force will affect the resistance to sway. And, the resistance would be different from that of a cam on a flat (horizontal) surface.
The friction force resists relative movement of cam and bar both when the cam is moving away from center and when the cam is moving toward center. The normal force resists movement when the cam is moving away from center and promotes movement when moving toward center. The promoting of movement gives rise to the "self-centering" effect.
Quote:Anyway, I haven't towed with a DC setup and I haven't seen or looked for anything that shows the force required to slide the bars, I'm just thinking about how it seems to work to be the most effective. For chain tension = 1000#, coefficient of friction = 0.7, and bar slope angle relative to horizontal = 30 degrees, the horizontal force between cam and bar will be about 2000# when the bar is moving away from center and about 20# when the bar is moving toward center of detent.
Ron
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JBarca
Dublin, Ohio, USA
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Cool, my hitch is in the pictures now!! Glad they can help out.
I take it we have now convinced most folks that the Reese DC is a high friction anti sway device.
And as Ron stated static friction is stronger the sliding friction. Meaning the force to breakaway an object at rest takes more force then one that is sliding. And sliding up hill takes more force then sliding level.
The actual friction formula is pretty straight forward. Coefficient of Friction = force to move the mass / the mass itself.
In our case of a hitch, the cof. of friction is between the 2 rubbing surfaces. The mass itself is the force of the WD pushing the 2 rubbing surfaces together. The force to move the mass is the effect of sway against the TT. In order to increase the stiffness of the anti sway device you either increase the force of the WD bar or the coef of friction.
In the case of the DC, as the WD bar raises off the cam, the force increases, this is something the Reese SC or the Equalizer does not have. The force there is constant.
The next thing about the Reese SC verses the Reese DC is the actual coefficient of friction.
On the Reese DC, the WD bar is tempered steel, the cam is cast steel I do believe. Point is the hardness is less on the cam them the WD bar. An estimate on cof. of friction on hard steel to mild steel is approx around 0.7 ish. Dry. The exact would have to be tested. http://www.engineershandbook.com/Tables/frictioncoefficients.htm
The Reese SC unit uses a similar WD bar is tempered steel, the friction pad is a type of brake pad material. Good question is what is the brake pad cof. of friction. It could be 0.4 or really high performance and ~0.6. which I doubt, but could be. Here is one racing site I could find brake pad material on. http://www.thebrakeman.com/tbrake_pad_selection
Here is another car site http://www.autospeed.com/cms/A_0351/article.html
And anotherhttp://www.ctbrakes.com/faqs#friction2
Point: The Reese DC appears to have a higher cof. of friction dry then the Reese SC. Wet the SC may loose more friction then a wet DC. The DC has an advantage that the force can rise as the WD bar rides up the cam increasing the resistance.
Hope this helps
John
PS Ron, that last link you sent on Trailer handling and Braking Standards has 4 volumes..... I was in contact with them to get the 4th volume to work on line. 448 pages in total. I’m still reading and compiling a response. There are a bunch more over on the SAE site but I have to pay for them.
* This post was
edited 11/25/09 05:58am by JBarca *
John & Cindy
2005 Ford F350 Super Duty, 4x4; 6.8L V10 with 4.10
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Yahooligan
Temecula, CA
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Thanks for all that great info, John!
I knew going into things that the DC was superior to the SC, but I chose the SC over the DC based on complexity vs advantage. Cost, not so much since the DC and SC aren't too far apart in price. I'm definitely not disappointed in the SC one bit and have no desire to switch. The SC may not be as effective, but the simplicity can't be beat and I can't imagine that it's less effective than an Equal-i-zer, which many people are very happy with as well.
My personal feeling, as I said before and after towing with the SC in 35+ MPH gusts, is if you feel you NEED to spend $2500+ on a hitch in order to feel safe then you might want to evaluate your existing setup and TV to determine what the actual problem is. I have NO doubt that anyone that uses a friction bar and then tries the ProPride or Hensley will love it and be sold. I know I thought the friction bar on a borrowed trailer was completely useless. However, I don't know that the same could be said for someone going from a DC to a Hensley if they could compare back-to-back with the same TV and TT and I certainly don't think they would think the Hensley was roughly 5-7x better than a DC since that's how much more expensive they are.
Anyway, I'm not meaning for this to be a debate or argument, there's a lot of great info in this thread and I really don't think anyone can go wrong with any of the good SC/WD hitches listed. This discussion could go on forever, much like gas vs diesel or 1/2, 3/4, or 1-ton trucks.
Take care and have a great Thanksgiving, everyone!
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HappyTrails2U2
Atlanta, GA
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b_salgado wrote:Depending on what gear ratio you have in that truck, you might be hating your towing experience.
I'm pretty sure it's not going to be an enjoyable experience I've already said that. I only plan to tow it one time with this truck. I'm using this trailer to live in during the week over the next 3 years while I'm working in Mississippi and not to pull around on vacation. It should stay in the same parking spot the whole time unless I find a better RV park near by that I might move it to. By the time this job is over in 3 years I'll have a new truck to tow it with and I'll get one with a bigger engine next time or else I might just sell the trailer because I'll probably be sick of living in one by that time.
Greg
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Mike Up
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The matter of the fact is that the friction that the equalizer uses, is sliding friction that doesn't prevent the sway. The DC is locked, by a friction locking system, but doesn't use sliding friction to cotrol sway. It uses a locking system to prevent sway. The way Reese states it, E-trailer states it, it's not a friction sway control. Everything has some form of friction in it.
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Ron Gratz
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Mike Up wrote:---The matter of the fact is that the friction that the equalizer uses, is sliding friction that doesn't prevent the sway.
The Equal-i-zer utilizes both linear friction between bars and L-brackets and rotational friction between bar sockets and hitch head. The yaw-resisting torque resulting from friction at the socket/hitch contacts is probably more than twice as great as the torque generated by bar/L-bracket contact.
As for "sliding friction that doesn't prevent the sway" --
every friction-based sway control (including EQ and DC) utilizes static friction rather than "sliding" friction to attempt to keep the TV and TT "locked" in a straight line. These devices prevent relative yaw up to a point at which the yaw-producing torques exceed the static torque resistance of the sway control.
When the static resistance is exceeded, the friction forces transition from static to kinetic friction and the yaw-resisting torque will decrease by perhaps 15%. The sway control is still resisting sway -- just at a slightly reduced level.
Quote:The DC is locked, by a friction locking system, but doesn't use sliding friction to cotrol sway. It uses a locking system to prevent sway.
There is no "lock" -- there are only normal forces and friction forces acting between cam and bar. When the longitudinal force in the bar exceeds the longitudinal component of normal force plus static friction force, the bar will slide relative to the cam. Once relative movement begins, the sliding (kinetic) friction force is working to resist sway.
Quote:The way Reese states it, E-trailer states it, it's not a friction sway control.
The Reese literature contradicts itself. The promotional literature, perhaps written by marketing people, implies the DC does not use friction. The installation and operating instructions, probably written by technical people, clearly states that the DC utilizes metal-to-metal friction. In technical matters, I would go by what the technical people say.
Ron
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b_salgado
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Hey Ron, I really don't think Mike understands the difference. He clearly doesn't understand how either hitch operates or how they reduce sway. I am wondering if he has seen another hitch or used another hitch. The Equal-i-zer head is definitely unique. The Reese head is the same across the lineup. ALL trunion bars set the same, ALL round bars set the same. They ALL have friction points where the bars sit.... Metal to metal...... never mind.... you already covered this over and over. I can't believe I actually got called out by a member on this forum! How childish is that? All I asked is where Mike got to after the tech spec's got posted.... Was that wrong? I don't think so.
HEY MIKE...... do us a favor, go to bed! wake up on the other side and have a Happy Thanksgiving! This is only an internet forum. I am sorry is you don't understand the hows and why's of the hitch's above. Just be thankful that they do work and rely on FRICTION to keep your trailer safely behind your tow vehicle. Make sure it is set up properly and you are loaded correctly. Have fun and go camping! Geesh! Some people
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