RE: Brake control questions
The proportional controllers like the prodigy have one problem: When you step on the break your rig slows down, activating the prodigy, which responds to the slowing down. This activates the trailer breaks and adds to the breaking. The controller will respond to that too, accellerating the process. In effect, you have positive feedback. I had to adjust mine to a very slow response or else my wheels would lock. A controller that monitors the hydraulic pressure is ideal.
It is correct that the Prodigy, and other deceleration-based controllers, employ positive feedback. However, one should not infer that this means the Prodigy is an undesirable controller. It only means that one must take care in adjusting the Boost and Gain settings.
Positive feedback in a control system is perfectly acceptable as long as the feedback factor is less than unity. Since the trailer brakes normally will be producing less than 100% of the total braking force and since the Prodigy's Boost and Gain are easily adjusted, the positive feedback should not present any problem.
Ron
RE: new 28'TT 07Expedition SWB H E L P
I have a 2007 Ford Expedition only 119" wheel base, which was ok with 24' Palomino, but know bought new 28' 5600lb.dry weight Zinger with double slide.Power still awesome for gas motor but know white knuckling it!!!Our hitch set up is reese weight distributing bars(square style bars with 1200lb hitch rating and 12000lb overall rating, with only friction sway control. When we had crew cab pick up we didnt need sway control and bars were lighter duty, that vehicle was 138"WB
Any suggestions before we unload expedition which we absolutly love and don't want to get rid of!!!
I strongly suggest that, before you hit the road again, you take your fully loaded TV and TT to the nearest scales to find out what everything weighs.
The 2009 Zinger specs indicate TT's of your size with two slides have tongue weight percentages in the range of 14-16%. Depending on how much stuff you put in the TT and where you put it, your TW could be pushing the 1200# mark.
The 2007 Expedition specs indicate a "payload" of around 1800#. Some of the weights which must be included in payload are: total weight of passengers and pets in excess of the 150# assumed for driver, weight of optional equipment, cargo, receiver, hitch, and vertical load added to hitch via the TT tongue.
There should be a sticker on the TV's door indicating the Gross Vehicle Weight Rating (GVWR). The TV's Gross Vehicle Weight (GVW), which is the loaded weight of the TV, including the load imposed by the TT's tongue, should not exceed the GVWR.
To know the GVW, you must actually weigh the TV to measure the sum of the loads on its front and rear axles. This should be done with the weight distribution system adjusted as it would be when ready for camping.
If you do go to a scales, the TV and TT should be loaded approximately as they would be for camping, and it is good to measure the following:
1) With TT attached and with WD activated, measure TV front axle load, TV rear axle load, and TT axles load with all three loads measured on separate scales pads.
2) With TT attached and with WD NOT activated, measure the same loads as in 1).
3) Then go and drop the TT and return to the scales to measure the TV's front and rear axle loads on separate scales pads.
The above measurements should tell you what you need to know about vehicle weights, axle loads, and how the WD system is performing.
You might be a lot closer to exceeding the TV's GVWR than you think. And, adding an extra 100# or so by switching to a Hensley Arrow or ProPride would make the loading situation even worse.
Ron
RE: new 28'TT 07Expedition SWB H E L P
For the benefit of those who missed the third post on page 2:
I just wanted to thank everyone for there thoughts and expertise! I just purchased the Reese dual cam (was able to buy for 162.00 with free shipping and no tax on line at etrailer.com which I love and been buying through them for a few years), still waiting for it to arrive. I'll post my findings after I hook it up. Thanks agin
Hopefully, Frank will report back via this thread to let us know how the rig handles after he has done some towing with the properly-installed Dual Cam system.
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
(Ya'll shouldn't mess with "Ron Gratz", as "he" is actually a product of a Lawrence Livermore AI project from the 1980's).:W
Ahhh, those were the good old days. But, I decided to escape from the AI program when it became obvious that artificial intelligence was no match for natural stupidity. :W
Another take on the Hensley is this. First, for those who claim their conventional hitch method has not caused them to experience any sway, I'll bet I can follow you for only a few miles on a day with a bit of wind -- nothing high -- and with a video camera show you that the suspension on your TT is loading up on one side, regularly. Or on just a bad road, no wind. Or as you cut around a slow-mover. Etc.
There are many different definitions of "sway", but I certainly agree that the uneven side-to-side loading you have described can lead to yaw instability.
In short, it (sway) is happening ALL THE TIME. Better trailer design is the only real cure.
Certainly, the cure starts with better trailer design. Other essentials are proper fabrication, proper loading, proper operation, etc.
The best band-aid is hitch rigging. And the best anti-sway rigging gives the driver -- the weak link -- a better chance in that short moment between an incipient problem and one that is threatening catastrophe.
I agree 100% that the driver is the weak link. IMO, when the TT exerts a lateral force which causes yawing of the TV, most drivers will instinctively react with steering inputs which will increase the yawing and might lead to loss of control. Some drivers are able to overcome instinct and avoid making adverse steering inputs. The HA significantly reduces the TT-induced yawing of the TV and reduces the effect of de-stabilizing feedback due to incorrect steering adjustments.
I'll finish with this. I have verfied I can violently, repeatedly snap my rig from one lane to another at over 50 mph. Constant lane changes, no "straightening-out" between changes the day I had my Hensley installed.
I'm guessing that you have a "well-behaved" trailer and are not just using your HA as a "band-aid" as you mentioned above. Some people do use an HA as a "band-aid" for a trailer which is not well-behaved and/or is too large for the TV; and they might not experience the same response to a violent maneuver -- especially if they are steering instinctively.
Ron
RE: Suburban 2500...TT to big?? opinions
---If you are as 'anal' as you suggest here, then I think you'll agree that one way or another, you need to get the weight back on the front axles of your tow vehicle. Ideally, its best if both front and back of the tow vehicle drop same amount, although frequently thats not possible. But, at the very least you need get the front to same height hitched vs unhitched.
I agree you should try to get the front back to the same height hitched vs unhitched.
However, with a Suburban, it might not be ideal to have both front and back of the tow vehicle drop same amount. With some Chevrolet models, the front should not be dropped below the unhitched height.
You can find info about this subject in this post and subsequent ones in the same thread. Unfortunately, the link to BigToe's photos are no longer working, but he does give a good explanation of what the photos showed. Also, you can do a search using the keyword, "jounce".
You should check your Owners Manual or check with your dealer to find out what is recommended for your vehicle.
Ron
RE: Trailer sway question
Thanks for the responses....
I have the air pressure around 60 psi, not max.
Used to have D load rating and went to E load
Same tire/rims combo as before.
Let me know if I left something out.
How much air pressure did you carry in the old tires and what was their maximum pressure rating?
What is the maximum pressure rating for the new tires?
Did you have the new tires balanced before they were installed?
What type are the new tires (ST, LT, etc)?
Ron
RE: Towing Capacity Question
As pcm1959 points out, "For example, if you have 800lbs of of people and cargo in the truck, deduct that from the max tow rate rating. That number is then the max LOADED trailer weight in which you can tow." In this example, the maximum allowable loaded TT weight would be 6200-800 = 5400#. For this example, if you properly follow Ford's specification, you would limit the maximum TT weight to 5400/6200 = 87% of the tow rating.
It is important to note that the calculated value pertains to the TT's GVW and not to its GVWR. For the above example, if the TT had a GVWR of 7000# and you only loaded it to 5400#, you would be within Ford's specification.
Ford's tow rating assumes the projected frontal area of the TV/TT is 60 sq ft if the vehicle is equipped with a trailer tow package or a heavy duty payload package. Although it is not stated, it is reasonable to assume that the rating is based on a towing speed of at least 70 mph since that is the legal limit in many states. If so, and if your TT's frontal area is 65 sq ft instead of 60 sq ft, all you need to do is reduce your towing speed from 70 mph to 68 mph to have approximately the same amount of aerodynamic drag power requirement.
If you have a good idea of how much weight will be added to the F150 by the additional options, passengers, cargo, and hitch, then subtract that number from 6200# and you will have Ford's recommended maximum value for TT weight. Then you have to estimate how much weight you will add to the empty TT. Subtract that estimate from the max allowable TT weight to get the max allowable empty weight.
Then, if you are concerned about having more than 60 sq ft of frontal area, keep your speed below 65 mph and you should be okay.
Of course, you also should stay within the GCWR and the GVWR.
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
There is a reason why all those folks with humongous 5vers drive around with pickups just like mine with no sway control at all. It's because their 5ver has no leverage on the TV so they don't need sway control. Figuring out how to make a hitch that takes advantage of that basic principle is so much more elegant AND effective than any friction hitch ever built.
If you want "elegance" and don't mind paying for it, go for it. You don't have to justify the purchase of a Hensley Arrow on a "need" or "superiority" basis.
Steve wrote: Ah, we’ve gotten to the crux of the discussion. See, I never said “elegance”. That implies something entirely different. But, I do like elegant solutions. Elegant solutions are by definition simple and effective. The PullRite hitch is a truly elegant solution. It’s easily mistaken for a conventional hitch most of the time, yet it completely eliminates sway under all conditions and situations AND imposes NO loss of performance compromises on the TV. And it is bonehead simple & 95% out of sight—elegant.
OMG, now we're debating "elegant" versus "elegance". Perhaps it's time to bring this to a close.
BTW, I've never owned a Monaco Dynasty.
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
The common friction-bar sway control is adujsted at the factory to produce a maximum torque of about 500 ft-lbs.and
No, you're confusing force and torque.
No, I’m not. I think you are. You said the friction-bar sway control produces a maximum torque of about 500 ft-lbs. The friction-bar sway control doesn’t produce any torque at all. It produces friction which resists the yaw force of the TT. The motion of the TT produces a force, which when applied to a lever (the 5’ that’s the typical distance between the ball and the rear axle) produces torque.
Steve, I suggest you take a look at Figure 2 of these Sway Control Installation Instructions.
The friction bar is factory adjusted to produce a friction FORCE of 1100#. Figure 2 shows that the friction bar FORCE vector passes through the front ball attachment which is 5.5" from the ball coupler. This means that the FORCE of 1100# multiplied by the DISTANCE of 5.5" produces a TORQUE of 6,050 lb-in which is equal to 504 lb-ft (I rounded the value down to 500).
The force in the friction bar is opposed by an equal and opposite force in the ball coupler, so there is no net force acting on the hitch head -- only the torque. As far as sway control TORQUE goes, it makes no difference whether the distance from the ball coupler to the TV's rear axle is 5' or 1'. If the friction bar produces a FORCE of 1100#, the TORQUE applied to the TV will be about 500 lb-ft.
Steve wrote: Since the friction-bar sway control is mounted at the ball, the overall resistance of the friction sway control is very much affected by the length of the lever the TT has to exert its force on the TV. So, if the friction sway control can develop up to 500# of resistive force at the ball, that
Looks as though something got lost here. However, the friction bar produces about 1100# of FORCE, and via its connection to the hitch head, a TORQUE of about 500 lb-ft is exerted on the hitch.
True, but I believe your attempt at applying physics has led you to grossly overestimate the effect of sway-control torque on the steering process.
Steve wrote: Grossly overestimated? Look at it this way Ron, a friction device that has the ability to tame the yaw of a 10,000# TT logically has the ability to also affect the yaw of the 5,000# TV it’s connected to. Your analysis of the tire forces necessary to turn the vehicle depended on the 12’ WB of the TV, but didn’t correct for the 5’ lever the TT & friction device has.
That's because the "5' lever" has nothing to do with how much sway control TORQUE is applied to the TV.
Steve wrote: Additionally, the friction device has two states: stationary and sliding. Very often, the stationary friction is several factors higher than the sliding friction. So, if the factory 500# is stationary, then the amount of resistance to yaw produced by the friction device drops significantly as soon as it slides. OTOH, if the 500# represents sliding friction, then the initial resistance to yaw is much higher, which when combined with the leverage can dramatically increase the amount of steering force required to turn the TV.
The friction FORCE of 1100# is for static friction. For steel on steel, a typical value of static friction coefficient is 0.7, and a typical value of kinetic (sliding) friction coefficient is 0.6. I don't know what materials other than steel are used in the typical friction bar. At any rate, if the bar slides, the FORCE and TORQUE probably will be somewhat smaller instead of larger than when the bar is not sliding.
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
Ron:
You are incorrect.
I checked with the president of ProPride and he informed me they would offer a full refund.
Check out this link:
http://www.propridehitch.com/trailer_hitch_and_accessories/reese_straight_line_dual_cam_hitch.php?item_id=3
Here's the quote from the ProPride website:
"Purchase with confidence backed by the ProPride Towing Comfort Guarantee!
If this product does not provide you with the towing stability you desire you can apply 100% of the purchase price toward purchasing a ProPride 3P. We have you covered for total towing comfort and stability."
1) Well, it appears they've upped the ante. Last week, a post on their forum stated that they would give a 50% credit toward the purchase of a 3P. Now they are saying they will give a 100% credit.
2) You said, "they would offer a full refund." Does this mean one could purchase a Dual Cam and then return it and get back 100% of the purchase price without subsequently purchasing a 3P?
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
The airfoils on a Formula 1 car create a "downforce" which improves cornering and lateral stability. A properly adjusted WD system also can produce a stabilizing downforce on the TV.
1) Yes, the ground effects & airfoils on a Formula 1 car create tremendous downforce, which increases tire traction--not stability. There is a difference. 2) However, that downforce is created without a significant amount of weight, hence a net gain in performance. However, when you add weight to a vehicle, the gain in traction is more than offset by the gain in weight and performance is degraded. Often significantly. 3) If adding weight improved the performance of the vehicle, then race cars wouldn’t use outrageously expensive exotic materials to reduce weight. In fact, race sanctioning bodies impose additional weight as a penalty, AND the race cars faced with such a penalty always try to mount the weight as close to the center of the vehicle as possible because they know that it DOES matter where that weight is located.
1) Please explain why adding downforce on the axles cannot improve stability.
2) What you say might be true. However, as I attempted to explain several posts back, when you attach a TT to a TV, the mass of the TT remains with the TT. There is a difference between transferring load and transferring mass. When you attach a TT to a TV, you add vertical force to the TV but you do NOT add mass to the TV.
3) Airfoils do not add significant masss to the Formula 1 car and hooking up to a TT does not add any mass to the TV.
Not at all. I said, "The additional vertical force imposed on the TV, when properly distributed between front and rear axles, can improve braking, steering, and lateral stability." I did not say that the improvement is enough to eliminate the need for sway control. And, I did not say that the potential braking improvement is sufficient to stop the additional mass of the TT.
Steve wrote: Well, if you’re saying that the additional weight improves braking, steering and lateral stability then why would you need sway control with all of those improvements? Especially, if you’re towing such a lightweight, low slung and aerodynamically advantaged TT?
Because, as I indicated before, the improvement in TV stability might not be sufficient to eliminate the need for sway control.
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
Depending on the magnitudes of the vertical force and the torque, the load on both axles could be increased, and this would increase the steering effectiveness of all tires. Or, only the rear axle load might be increased. However, since the rear tires also provide steering forces, increasing the rear axle load can also improve steering effectiveness.
What you just said is that if the vertical load is between the axles the steering effectiveness is improved and you also said that if the vertical load is on only on the rear axle the steering effectiveness is improved. In other words, you’re saying that the steering effectiveness is improved no matter where the vertical load is applied. If that was true, why do Porsches drive so differently than Camry’s? And if the steering effectiveness is improved with additional weight on the rear axle, it seems there is little reason to spend money on a W/D setup because the steering of the TV already improved with the weight of the TT on hitch ball.
No, I did not say, "the steering effectiveness is improved no matter where the vertical load is applied." I did say, "---the load on both axles could be increased---". In order for the load on both axles to be increased, the resultant of the added force would have to be between the axles. And, part of the reason people spend money on a WD system is to prevent load from being removed from the TV's front axle.
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
A WD system does exert a vertical force at some distance behind the TV's rear axle. However, the WD system also exerts a pitch-axis torque on the hitch head. It is this torque which causes the vertical force to be distributed between the TV's axles. The resultant vertical force is moved from the hitch to a location which might be directly over the TV's rear axle or somewhere between the axles.The static vertical force of the TT tongue is shifted forwards by the W/D hitch, but as you said where? While shifting the vertical force forward is definitely better than not doing so, the improvement in vehicle performance does not approach that of the TV without the TT.I said, "over the TV's rear axle or somewhere between the axles". I assume the resultant "downforce" on a Formula 1 car acts somewhere between the axles. Are you suggesting the downforce on a Formula 1 car does not improve the performance relative to having no downforce?
Steve wrote: Plus, When the trailer is braking, the TT pitches on it's axles making for considerable weight transfer onto the tongue. Weight transfer on a passenger car can exceed 80% of the total weight of the vehicle onto the front wheels, so it’s reasonable that the weight transfer of the TT onto the tongue could be in the range of 50%. That’s 3-4 times the static tongue weight and bound to have dramatic effect on the handling of the TV as several thousand pounds of force is suddenly applied on the hitch ball—far more than the W/D hardware can compensate for.
Hmmm -- if what you say is true, I'm wondering why receivers and WD hardware aren't being destroyed everytime a TT's brakes are applied.
Let's assume my 5000# Award has its CG 3' above the ground and the brakes are causing it to decelerate at 0.25G. The added downward force on the ball would be about 5000*0.25*3/18 = 208#. This might add about 300# to the Explorer's rear axle and remove about 100# from the front. At the same time, the TV is also braking, so that causes some of the weight of the TV to be moved from its rear axle to the front. Seems to me that the added downward force on the ball would help compensate for some of the TV load shift.
Steve wrote: Worse, if this happens in a turn, then that downward force on the ball tends to lift the front wheels of the TV AND the forward momentum of the TT that can’t stop as quickly as the TV pushes on a 5’ long lever. The result is sway with a simultaneous reduction in steering traction. Not pretty.
If this is true, I surprised we're not reading about many more TT accidents.
If the TT is braking, the TV probably is braking also. If the TV is braking, load from the weight of the TV is being shifted onto the TV's front axle. I'm guessing that the net result of braking is to increase the load on the TV's front axle.
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
The TT has its own brakes which are designed to stop its mass. Since the TV has more load on its tires without a corresponding increase in mass of the TV, its braking effectiveness is increased.Yes, it's true the TT has it's own brakes. The same marginally effective brakes that came on a 1950's 4,000# Oldsmobile are supposed to stop a 10,000# trailer? They do meet the requirement that the trailer has brakes, but their effectiveness is pathetic compared to the effectiveness of the TV’s brakes.I'm quite certain that my 1994 Award TT did not have brakes from a 1950's Oldsmobile.
Steve wrote: The test results I've seen show that a 3/4-ton pickup with 4-wheel disc brakes takes 150% as long to stop when towing a 10,000# trailer so I think it's safe to say the braking effectiveness is definitely NOT increased when the TT is connected.
Do you have a reference for the test results? Do the results also apply to a 1994 Explorer towing a 5000# TT? It would be interesting to see the details.
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
Well, this thread has been off track since the end of Page 2 -- so as long as the OP and the moderator don't mind:
As regards Award trailers -- the phrases "very low", "steeply sloped roofs", "extreme light weight", and "much less affected by" might be a bit misleading. The overall height of a 2005 Award is listed as 9' 6". The lateral roof slope is about 9" over 4'. My 1994 Classic 27 had an empty weight of 4000# and a GVWR of 6000#. Because the Award has less ground clearance, it is more difficult for side winds to pass under the TT and the wind load might not be significantly different from the load on a taller TT.Height: Your Award's overall height is 9'6", but sidewalls were only 8'9" high. By comparison, my Holiday Rambler was 10'3" high at the sidewalls, plus 15" for ACs etc. That makes the HR nearly 20% taller than the Award--a very significant difference.
Weight: The dry weight of a 27 HR Aluma-Lite was 7,176# (heavier than the GVWR of the Award) and the GVWR of the Aluma-Lite was 10,000#. A full 30% heavier than the Award.
Steeply sloped roof: 9" slope in 4' is the same steepness as a 19% grade.---
As for the wind load being increased by the lower ground clearance of the Award? First, due to the friction of the wind passing over the ground the wind speed at a point just 1 foot off the ground is only a fraction of what it is 10 feet off the ground. Plus, the wind force on the additional 15” height of the HR has far more leverage on the coach and therefore a much greater effect on it’s behavior.---
I think we're making some progress. We now understand:
1) a "very low" TT is one with a 9' 6" overall height compared to your HR with 10' 3" sidewalls plus 15" for AC etc,
2) a TT of "extreme light weight" has a GVWR of 6,000# compared to your HR's 10,000#, and
3) a roof with a slope of 9" in 4' is considered to be "steeply sloped" when compared to a highway grade. However, it might make more sense to compare a TT's roof slope to the slope of a house roof, in which case I think most of us would agree that a slope of 2.25 ft in 12 ft would not be considered "steeply sloped".
As for the wind load -- the vertical profile of mean speed for turbulent wind flow can be approximated with reasonable accuracy by the power law expression V = Vref*(H/Href)^K where Vref is the reference speed at the reference height, Href, and K = 1/7 for open flat terrain (CBD-28. Wind on Buildings).
So, if we can accept the equation and the coefficient of 1/7 as being sufficiently accurate, wind speed at a point just 1 foot off the ground would be 72% of what it is 10 feet off the ground. Or, if we wanted to use the coefficient of 1/10 which is recommended for wind gusts, the "fraction" would be 79%.
Yes, the wind force on the additional 15” height of the HR would exert "more leverage". However, the (I assume) wider track of the HR and its nearly 2X greater weight would provide much more resistance to the "leverage".
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
A conventional friction hitch has its pivot point about 5' behind the rear axle of the typical TV. The 4-bar linkage of the Hensley projects that pivot point forward to about 20-24" behind the rear axle.---
Partially true. When the TV and TT are aligned with zero relative yaw angle, the VPP might be about 20-24" behind the T's rear axle. When the relative angle reaches 4 degrees, the VPP will be about 50-54" behind the axle and about 18" away from the TV's longitudinal centerline. With an angle of about 15 degrees, the VPP is very close to the straight-ahead location of the ball coupler.
Steve wrote: This is the same as eliminating over 50% of the yaw-force the TV experiences.
No, you're confusing force and torque. The 4-bar linkage has relatively little effect on the lateral force induced on the TV by the TT. The significant effect is on the yaw-inducing torque and not on the lateral force. At a relative yaw angle of zero degrees, the torque might be reduced to about 40% of what it would be with a conventional hitch. At a relative yaw angle of 4 degrees, the torque might be around 85% of conventional. And, at 15 degrees, the torque would be greater than the conventional value because the VPP is actually further from the TV's rear axle than would be the ball of a conventional hitch.
Steve wrote: As for the PullRite? Well, the pivot point of the PullRite hitch is only 11" behind the rear axle, so the leverage is reduced by half again compared to the Hensley.
Unless you have the 90 degree model -- in which case, the pivot point probably would be closer to 20" behind the rear axle.
Steve wrote: There is a reason why all those folks with humongous 5vers drive around with pickups just like mine with no sway control at all. It's because their 5ver has no leverage on the TV so they don't need sway control. Figuring out how to make a hitch that takes advantage of that basic principle is so much more elegant AND effective than any friction hitch ever built.
If you want "elegance" and don't mind paying for it, go for it. You don't have to justify the purchase of a Hensley Arrow on a "need" or "superiority" basis.
Steve wrote: A friction hitch, when adequately tightened can make a good TV/TT combination behave well enough to satisfy most people. However, the more friction force the friction hitch employs to force the TT to behave, the more steering torque is required to turn the TV when the road turns.
True, but I believe your attempt at applying physics has led you to grossly overestimate the effect of sway-control torque on the steering process.
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
I think it's interesting to note that a Hensley Arrow does not generate yaw-axis torque unless there is some amount of relative yaw between TV and TT. It does not tend to "lock" the TV and TT together as a friction-based control does. Instead, the HA works by moving the pivot point closer to the TV's rear axle.
Ah, but here is the beauty of the Hensley & its new kin, the ProPride. Since the Hensley does not tend to "lock" the TV & TT together, the drive of the TV is free to point the TV anywhere he needs to go without ANY resistance from the hitch. Steering feel is greatly improved, as is steering response since there is no turn-resisting torque to overcome.
Not true. As you well know, if you are rounding a curve with an angle of, say, 4 degrees between TV and TT, the HA's virtual pivot point will be moved about 18" laterally from the TV's longitudinal centerline. Unless you are coasting, the TT will be exerting a rearward pull on the TV due to aerodynamic, rolling, and friction forces which might be in the range of 500-1000# depending on speed, terrain, etc.
Since the rearward pull from the TT is acting at the VPP, the 500-1000# of force acting over the distance of 18" will translate to a yaw-axis torque of 750-1500 lb-ft. This torque will tend to straighten the combination as you round the curve. You will have to introduce more steering angle to maintain the 4 degree relative yaw angle.
With a friction-based sway control, you will have to introduce more steering angle at the beginning of the curve; but once into the curve, the SC will tend to keep the yaw angle constant until you are ready to steer out of the curve. So there are advantages and disadvantages to both the HA and friction-based systems. The thing to remember is that for either type of system. The steering changes required to overcome the hitch-induced torques are quite small.
Steve wrote: What makes the Hensley, ProPride and PullRite so incredibly more stable than any friction hitch is the simple fact that the pivot point is moved much closer to the rear axle of the TV and as a direct result the yaw-inducing force of the TT has much less leverage on the TV.
I must agree with you on this point since I've often made nearly identical statements in these threads.
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
Also, a friction-based sway control resists relative yaw between TV and TT and tends to turn the TT into a "tag axle" for the TV. A single friction bar can generate about 500 ft-lb of yaw-resisting torque. A Dual Cam or Equal-i-zer can generate several times that amount.
Let's assume that your figures are correct. So, if a single friction bar can generate 500 lb-ft of yaw-resisting torque, that also means that it resists the front wheels of the truck with the exact same amount of torque. Since the friction bar is mounted 5 feet behind the rear axle, then that means it's developing 2,500 lb-ft of turn-resisting torque because of the 5' lever it has on the truck. If the WB of the truck is 144", then the front wheels have a 12/5 advantage which gives 1040 lb/ft of turn-making torque required by the front wheels before the truck would even begin to turn.
First, some basic physics -- torque is the product of force times distance. Sometimes, it is expressed in units of lb-ft. The product of torque times distance, as you have introduced above, is meaningless. Torque is torque. Whether torque is applied at the hitch, or at the rear axle, or at the front axle, or anywhere else on the vehicle, makes no difference.
To determine how much front tire lateral force is required to balance the 500 lb-ft of torque, you can assume the torque will tend to make the TV pivot about a vertical axis through the center of the rear axle. The required front tire force would then be: force = 500 lf-ft / 12 ft = 41.7#. Each front tire would have to generate a lateral force of about 21#.
Assuming each front tire carries a load of 1800# and the tire is operated within its linear range of lateral resistance, an additional steering angle of about 0.12 degrees would be required in order to balance the 500 lb-ft of yaw-axis torque exerted at the hitch.
Steve wrote: When you consider that my Duramax makes a maximum of 605 lb-ft of torque & that's enough to propel 20,000# of truck down the highway & up grades, 1040 lb-ft of torque just to start a turn certainly explains why friction anti-sway devices are so dangerous--because they can make a TV difficult to turn.
No, that does not explain anything. The torque produced by your engine has absolutely nothing to do with the added steering angle required to overcome the sway control torque.
Steve wrote: Then, you said that the Dual Cam or Equal-i-zer can generate several times that amount. If so, that's even more scary. Since that much yaw-resisting torque is also turn-resisting torque a rig equipped with a Dual Cam or Equal-i-zer would turn about as well as a vehicle with locked differentials. Not at all.
That's an interesting deduction. I think we all know that a rig equipped with a Dual Cam or an Equal-i-zer can be turned. It might take an added 0.12, or even 1.0 degrees of tire angle to make a turn; but, the TV does turn
Steve wrote: It's worth noting that even if your numbers are wrong, the fact remains that 100% of the yaw-resisting torque of a friction hitch is also turn-resisting torque. And that is not a good thing when the driver needs to turn the vehicle. And what if road conditions are slippery? It means that just when the driver needs to finesse the steering, he can't because the friction hitch is trying to force the entire rig, including the TV to go straight.
Please see this post for my response.
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
The additional vertical force imposed on the TV, when properly distributed between front and rear axles, can improve braking, steering, and lateral stability.Hmm, very interesting. While the addition vertical force can increase tire traction, the increased kinetic energy of the the additional mass results in longer stopping distances.No, the additional mass remains in the TT. Force distribution or load distribution is not the same as mass distribution. The TT has its own brakes which are designed to stop its mass. Since the TV has more load on its tires without a corresponding increase in mass of the TV, its braking effectiveness is increased.
Steve wrote: The same holds true for steering. It's also hard to imagine any real world vehicle that can gain an improvement in steering by adding weight approx 5 feet behind the rear axle.
A WD system does exert a vertical force at some distance behind the TV's rear axle. However, the WD system also exerts a pitch-axis torque on the hitch head. It is this torque which causes the vertical force to be distributed between the TV's axles. The resultant vertical force is moved from the hitch to a location which might be directly over the TV's rear axle or somewhere between the axles.
Depending on the magnitudes of the vertical force and the torque, the load on both axles could be increased, and this would increase the steering effectiveness of all tires. Or, only the rear axle load might be increased. However, since the rear tires also provide steering forces, increasing the rear axle load can also improve steering effectiveness.
The airfoils on a Formula 1 car create a "downforce" which improves cornering and lateral stability. A properly adjusted WD system also can produce a stabilizing downforce on the TV.
Steve wrote: If what you said was true, then it seems that the combination of these 3 improvements in vehicle dynamics that you've described would render any form of sway control, or even auxiliary braking quite redundant and unnecessary.
Not at all. I said, "The additional vertical force imposed on the TV, when properly distributed between front and rear axles, can improve braking, steering, and lateral stability." I did not say that the improvement is enough to eliminate the need for sway control. And, I did not say that the potential braking improvement is sufficient to stop the additional mass of the TT.
Ron
RE: Hensley Arrow Hitch - Is it worth it? edited
---When I'm towing with the Hensley, the combination was actually more stable in most conditions that cause sway than the truck was without the TT. You just can't say that with any friction-based sway control.Actually, an almost identical statement has been made by at least one user of a Dual Cam.
Also, when I towed an Award TT with a Ford Explorer using a single friction sway bar, it was my opinion that the combination was more stable than the Explorer was without the TT.
Award trailers are very low and have steeply sloped roofs, so they are much less affected by side winds than conventional TTs & impose less yaw force on the TV because of their extreme light weight. So, it's pretty easy to envision a friction sway control stiffening up the connection to the point that it resisted turning strongly enough to make the TT behave somewhat like a tag axle.Yes, there are a variety or reasons why a TV/TT combination with a friction-based sway control has potential for making the combination seem more stable than the TV without the TT. That feature is not unique to the Hensley Arrow.
As regards Award trailers -- the phrases "very low", "steeply sloped roofs", "extreme light weight", and "much less affected by" might be a bit misleading. The overall height of a 2005 Award is listed as 9' 6". The lateral roof slope is about 9" over 4'. My 1994 Classic 27 had an empty weight of 4000# and a GVWR of 6000#. Because the Award has less ground clearance, it is more difficult for side winds to pass under the TT and the wind load might not be significantly different from the load on a taller TT.
Of course, that same friction sway control also has the effect of trying to prevent the TV from turning easily and there are cases of TV's failing to negotiate turns because of overly tight friction sway devices.I've done a lot of searching on ORF regarding this subject. I've found only one case where a driver had some difficulty in (as opposed to "failing to") negotiating a turn. However, he was driving on an unusually thick layer of freshly-placed uncompacted gravel. If you have references to other cases such as you have described, I would be interested in reading about them.
Ron
