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Old 09-18-2007, 11:11 AM   #15
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Thanks for your contribution to this thread. I realize that no one can ever make everyone happy, so I make it a point to try to cater to as many as possible. I agree with all five of your points, although number one has been a topic of heated debate on many occasions. I also agree with your summation as well. You need more stopping force to combat the additional force (F=ma) generated by the towed. Many people want to know more than just what is happening: they want to know why. If you wanted to dig a little deeper, you could find how many watts would be created with the addition of the towed by using the formula Kinetic Energy= 1/2 mv2 (the "2" after the "v" being exponential) and compare that to the coefficient of friction on the coach's braking system. If the coach brakes try to dissipate this heat from the additional wattage, it will result in a lock-up; or, more likely, severe brake fade. This topic can be as simple or as complicated as you like. The statement regarding more weight to stop in a panic did not refer to the towed magically gaining weight (gravitational mass) as we all remember the Lomonosov-Lavoisier law from elementary school (conservation of mass), but the fact the there is more force (perceived as weight) on the back of the coach in a panic. To make it more simple (at least to me ), I referred to force in its perceived form of weight to help readers relate. I apologize if my post seemed to cast "Fear, Uncertainty, and Doubt." My intention was to supply a "why" that was easy to understand rather than getting up on a soap box and beginning the mundane "You need a brake" speech while I shake my finger.

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Old 09-18-2007, 06:29 PM   #16
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I will .

Toads do need brakes!!
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Old 09-18-2007, 11:46 PM   #17
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I suspect I'm from the old school which tries to use some common sense. We have a 2005 Georgie Boy Pursuit, 35 foot, double slide, F53, V10. We tow a 2001 Jeep Cherokee. We use our Brake Buddy every time we tow. Now here is the common sense part. The most precious items are my family; therefore, we make sure that the coach is as safe as it can possibly be by keeping up with all the essentials; we "drive" the coach by being aware of what is around us all the time; we do our best not to get too close to any other vehicle; If we're tired we pull over; We respect other vehicles on the road; we leave in more than enough time to get where we going; We try to always know our exact route before we leave; our speed is dependant on many things including but not limited to weather, traffic, time of day. We realize that any RV does NOT handle like a sports car. We have been know to communicate to a higher source and we hope that others on the road keep their minds on the road, instead of their phone or other distractons. It's taken 65 years to get this far, we want to be careful going down the road so we can continue to enjoy this Great Nation of Ours.....
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Old 09-19-2007, 07:07 AM   #18
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I just love the ones that argue that the law specifically says trailers over XXXX# have to have a braking system. Therefore, the towed car is not a trailer and exempt from the braking requirement.

I guess that in the great wisdom of the chassis manufacturers, they have designed the chassis such it can determine if it has 3500# of rocks on a trailer or 3500# of dinghy trying to push the RV along.

I agree, the dinghy must have a braking system.

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Old 09-19-2007, 07:28 AM   #19
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I would also like to reiterate that many people "overlook" the part in underneath their coach's towing guide that states:

"Any trailer over 1,xxx lbs loaded must be equipped with its own braking system of adequate capacity."

That's coming from a coach with a hitch rated at 10,000 lbs pulling weight. This limitation is not from a "Law" or lack of a "Law," this is a chassis limitation.

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Old 09-19-2007, 08:53 AM   #20
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yes it is 'interesting' that the basic requirements for towed vehicle braking are in such dispute as they are rather well defined.

As for "you could find how many watts ... and compare that to the coefficient of friction" -

this is confusing force and energy.

In a panic stop, you are not concerned with the problems of heat dissipation. You are concerned instead with the total force you can apply. The heat dissipation or energy problem is usually only a concern on downgrades without proper engine braking or other driver compensation.

The short term energy dissipation needs from a panic stop are well handled by the thermal mass of the components.

The short term force you can apply is limited by the tire on the road and that is highly dependent on conditions.

As for physics, this does get into the problem many have in distinguishing between momentum and energy conceptually. In the example provided, I think that distinction was a critical factor. Momentum has a direction that energy doesn't have. Momentum requires a force to change it while energy does not. Energy comes in flavors while momentum does not. Energy is conserved while momentum is not.

(ever try to get across the distinction between elastic and inelastic collisions in the physics context to someone?)

The natural inclination of those facing a crash is to try to evade or avoid it. In an RV, this can often be a bad idea. You can create more damage by trying to maneuver (as in the example provided) than by just putting the effort into straight line reduction of speed.

Managing momentum gets to be a lot of fun when you start to consider the moment arm between the center of gravity and the points where you can apply a force to the rig. That gets into why you slow down on curves but that is a different topic than braking.
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Old 09-19-2007, 12:12 PM   #21
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Very good point. For the most part heat dissipation is only an issue on downgrade or high-speed braking; however, these vehicles are equipped with "adequate" braking systems for their size and weight. I have performed some skid-pad testing in the development of our systems. In most cases, without additional force from the towed, braking effort was limited to available traction; but in cases where there was an ˜un-braked' towed attached, tire skidding ( or ABS activation) was minimal (but present) and brake fade was very evident. With an efficient towed-vehicle braking system, results were very similar to what was experienced with no towed vehicle at all. These tests were performed in favorable weather conditions on asphalt, which would increase the amount of traction available to the tires.

Momentum and energy are most definitely related and most definitely different. How is that for profound? While the energy equivalent to a given mass may be found with the mass-energy equivalence (E=mc2 [the "2" being exponential]), the two essentially express very different values, and neither of these values directly have anything to do with motion. Momentum is where motion comes in to play. As we all know, the momentum is found by taking mass times the velocity (p=mv). So the values are related, but very different. All these factors are relevant (directly or indirectly) in the inertial reference frames of a braking situation.

Managing momentum does get hairy with one of these beasts. The coach, in effect, becomes a giant lever with far more mechanical advantage than that of a regular automobile, and when you reach the turning moment, hang on! If this change of motion takes 50% of the tires available traction, then there is only 50% left for braking, resulting in a longer stopping distance. So in short, if you are not going to clear the accident, you are better off to put 100% of available traction to stopping rather than frivolously using it for lateral movement; and the amount of available braking traction greatly increases with the "towed's rubber" in the braking picture.

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Old 11-29-2007, 02:18 PM   #22
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I have not had the opportunity to examine the SMI Brake System. I have been using the Appolo Brake from Blue Ox and have been very satisfied with the performance.
There is no question about T Toad Brake , or not to Brake !!!
Whatever you do Have one, the dynamics are nothing to fool with, you bet your life !
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Old 08-26-2008, 07:14 AM   #23
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I know these postings are old but the force of a 3,000 lb toad @ 30 mph is 90,000 lb !!
That's where all the force comes from in a collision !!!
Those are just simple numbers that I remember
for reference.
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Old 08-26-2008, 12:04 PM   #24
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the force of a 3,000 lb toad @ 30 mph is 90,000 lb !
remembering simple numbers may not remember important conditions and circumstances.

The force of the toad as described is nearly zero if not talking about the force on the road (its weight) and going in a straight line. The 'nearly' is due to friction and perhaps wind drag.

When you try to stop that toad, you'll apply a force to it. A very small force will do if you have a long time to stop. A fairly large force will be necessary if you want to stop it quickly. That 'fairly large force' is still only a fraction of the toad's weight.
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Old 10-16-2008, 02:30 AM   #25
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As someone who has had a lifetime passion for driving - anything from cruising in the motorhome to driving a race car in wheel-to-wheel competition - I concur fully with what is being said. Anyone who tows without brakes on the toad / trailer is not only asking for trouble, they're risking MY safety in the equation - should we have an unfortunate meeting.

One element of towed vehicle dynamics that you have devoted entirely too little discourse to, IMHO, is that of lever arm forces. Due to many factors, RV's (in general) do not perform well in high lateral-G scenarios. An improperly braked towed vehicle contributes a lot of inertia to the tow vehicle in any maneuver - and certainly enough in a threshold turn-brake scenario to totally upset the control parameters. It's certainly not inconceivable that even a light toad could exert ofer a ton of lateral force to the rear of a motorhome - and that is easily enough to trigger an oversteer situation in the proper circumstances. Motorhomes weren't designed to drift - and I've seen more than one rig "put on its roof" by just this situation.
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Old 05-07-2009, 11:18 AM   #26
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I have never done the math, as you did, (thank you by the way) but I have commented many times that if you rear end me. and I find you are towing without supplemental brakes (Towed brakes) on the trailer, (Exception for very light trailers) you are going to hear from Dewy, Cheatem and Howe, attornies at law (Or to be more precise whomever I hire to represent me, but you will think they are D, C & H, a name I borrowed from the 3 stooges by the way)

But that is just because I studied Physics and KNOW that all wheel breaking is better

Question.. Can you do the math for a 2-wheel dolly with brakes only on the dolly and not on the two remaining vehicle wheels?.. Thanks in advance
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Old 06-15-2009, 08:03 AM   #27
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Two things to remember.
#1 keep a safe distance in front of you to the next vehicle (from my observations most everyone follows way to close); thats the reason for most rear end crashes.
#2 a lot of motorhomers drive way past their safe driveing speed ( just because the motorhome runs so good at 75 MPH doesn't mean its safe to drive that speed. brakes on your toad are no help if your driveing past the safe speed.

safety is no accident
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Old 09-27-2009, 11:33 AM   #28
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I think one of the problems about supplemental breaking is definition. In California the laws states that any "trailer" over 1000 lbs. must have a supplemental brake system. People get the idea that a motor vehicle "toad" is not at trailer therefore a braking system is not required.

According to a CHP officer that I asked one day, "If you are towing it, it is a trailer"

The last time I looked the California Vehicle Code still refereed to motor homes as motorized house cars. Some time when the states got nothing better to do, they can up date some of the antique language. Do hold you breath.

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