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Old 02-27-2014, 11:29 AM   #51
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Some very nice points Dave.
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Old 02-27-2014, 10:24 PM   #52
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Excellent post Dave - great points, very well presented.

Quote:
Originally Posted by ice-breaker View Post
The amount that you tow on relatively flat terrain versus steep mountain grades may influence the amount of excess towing capacity you want. Maybe you are comfortable and happy with a tow vehicle that does not have the horsepower necessary...
This is one issue which seems to confuse things. The rated towing capacity is not determined entirely (or even primarily) by power, so equating excess rated capacity to performance doesn't work.

An example:
  1. A 2004 Toyota Sienna minivan (like mine) rated for 3500 pounds of trailer, towing 3000 pounds: loaded 86% of rated towing capacity.
  2. A 2014 Ram 3500 pickup truck rated for 30,000 pounds of trailer, but only towing 15,000 pounds; loaded to 50% of rated towing capacity.
The Sienna plus travel trailer passes the Ram plus monster trailer like it was standing still, up any grade on any paved road (hey, it's not a 4x4 van ) - the one with less excess capacity performs better, because it has half the power but only one third of the weight. (Been there, done this).

Another example:
  1. A 2004 Toyota Sienna minivan (like mine) with towing package, rated for 3500 pounds of trailer, towing 2000 pounds: loaded 57% of rated towing capacity.
  2. A 2004 Toyota Sienna minivan (almost like mine) without towing package, rated for 2000 pounds of trailer, towing 2000 pounds: loaded 100% of rated towing capacity.
The two vans have exactly the same engine and transmission, and as a result exactly the same performance (although the transmission of the one with the towing package will last longer), even though one has vastly more excess capacity.

The fact that a tug has more towing capacity than another tug does not necessarily mean that it has any more performance under the same load.
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Old 02-27-2014, 10:32 PM   #53
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This towing stuff gives me a headache. I buy because I can afford it, like the way it looks (I'm visual) and the rated information from the manufactuter tells me I can tow my trailer. Fuel mileage be damned. It is what is ... I don't tow my trailer every day, when I do.. I make MEMORIES. If I'm slooow going up a hill... sorry.. but, I'm usually behind a bigger truck than mine and happy to be there. YMMV
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Old 02-27-2014, 10:55 PM   #54
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Quote:
Originally Posted by Kip in Ga. View Post
"Near stop" in my example was closer to 20 mph, by the time we reached a point of a lesser grade. Had the steep grade continued much farther, I feel we would have come to a complete stop...
Thanks for the details, Kip. I agree that this was an unacceptable situation.

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Originally Posted by Kip in Ga. View Post
Quote:
Originally Posted by Brian B-P View Post
I don't think that someone new to towing a travel trailer should be misled to think that typical travel trailer tugs can maintain any desired legal speed on any grade at will.
By the same token, they should not be misled to thinking an "adequate" TV on flat ground, with little to no margin of extra power, will be safe for unexpected situations.
I absolutely agree.

Quote:
Originally Posted by Kip in Ga. View Post
Considering these grades we are discussing. Would you recommend to a friend or loved one that adequate is fine? Do you believe a TV, with a 3000# rating, plenty good enough for a camping trailer weighing 2500# loaded?
I personally DO NOT!
I don't presume to know whether a 3000lb-rated tug performs well with a trailer weighing 2500 pounds loaded, if that rating is all I know about the tug. My 3500-lb-rated tug certainly performs very well with a 3000 pound trailer, but there are probably tugs with much less power which have the same rating, and would not have an adequate margin of performance. The rating is not to be exceeded, but other than that gives no indication of hill climbing or acceleration performance.

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Originally Posted by Kip in Ga. View Post
Quote:
Originally Posted by Brian B-P View Post
On the 8% grades of the Coquihalla and similar western mountain freeways (which have two or more lanes for traffic in each direction) and other major highways (which commonly have passing lanes in grade climbs), you're not slowing traffic down at even 2/3 of that speed limit on sustained grades... assuming you are driving in the right (meaning both right-hand and correct) lane.
So what is a marginal rig supposed to do when they find themselves on a busy 2 lane curvy road with no passing lanes and it becomes 6-8%?
A rig which must slow down by a 10% or so at 6-8% will be a little slower in the those sections, and the traffic that can't stand the several seconds of delay will pass at the next reasonable opportunity, and life will go on. Certainly this is not a disruption in traffic flow compared to the effect of heavy trucks which slow down much more.

An older economy car, or anything driven by someone unwilling to push the pedal down far enough, will have the same effect.

Quote:
Originally Posted by Kip in Ga. View Post
Quote:
Originally Posted by Brian B-P View Post
I agree that we shouldn't be roadblocks, but there's a big difference between grinding along in first gear this way and letting the speed drop moderately from the legal limit.
There we agree! Having enough TV to allow us to make the decisions is hugely better than the TV making the decisions for us.
Yes, we generally do agree, once we clarified just what performance is expected (which is not necessarily the posted limit).

Quote:
Originally Posted by Kip in Ga. View Post
Just as important, or more so, I want to decide the downhill speed as well. With enough "Engine Braking" and wheel brakes and chassis to handle the trailer, even if it's brakes fail!
One thing to keep in mind is that regardless of the tug, the rig will have limitations. You can have great braking, but you can't have infinite braking, so at some point you may not be able to stop in time to avoid that animal crossing the road. You can have great handling and lateral acceleration, but at some point you may not be able to dodge that oncoming driver you just moved into your lane. You will never be able to decide what the rig can do arbitrarily, because it will always be limited by physical abilities, and the road, and the surrounding situation. The trick is to find a level of performance which suitably exceeds that required in normal conditions, but is still reasonably obtainable.

I'm not concerned with engine braking. I use it - it is absolutely essential for proper operation on long downgrades - but there's a lot more available in a typical recreational rig with a trailer only about the weight of the tug than is needed. There's certainly excess engine braking available in our van.

The question of braking with failed trailer brakes is controversial. Those big trucks - the tractor-semitrailer rigs weighing tens of tons - cannot stop without trailer brakes at a performance level which we would consider acceptable for a car. On the other hand, they have some system redundancy which our electric-braked travel trailers do not, so we run a higher risk of needing to slow the rig without trailer brakes. This has nothing to do with engine power, and mostly a matter of tow vehicle weight and GVWR... neither of which has much to do with tow ratings. My 4500 pound van with a 3500 pound trailer (its limit) is much more able to stop without trailer brakes than a slightly lighter and much shorter Jeep Liberty with a 5000 pound trailer (its limit). The trailer rating does not tell the whole story.
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Old 02-27-2014, 11:03 PM   #55
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I only have one question.
If one uses engine braking to slow tow and trailer, does that increase fuel consumption over applying the brakes?
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Old 02-27-2014, 11:16 PM   #56
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Quote:
Originally Posted by gbaglo View Post
I only have one question.
If one uses engine braking to slow tow and trailer, does that increase fuel consumption over applying the brakes?
That depends on the vehicle...

In my 2004 van, whenever the engine is above idle speed and the accelerator pedal is not depressed, fuel flow is cut off entirely. As I descend a grade using engine braking, I'm consuming absolutely no fuel. This may have been new behaviour with this new-that-year model.

In my same-year car (which I didn't use to tow, but it's the example I have), the fuel flow was not cutoff, and (just like a carburetor) fuel in proportion to air continued to be supplied. Since engine braking means forcing the engine to turn faster, it would consume more fuel than using a higher gear and the brakes, or coasting (in neutral) and the brakes. The continued fuel delivery also means that the engine is producing power (enough to idle at the elevated speed), so the effectiveness of engine braking is reduced (although there is still significant engine braking). I assume this was the result of an outdated engine management system (the model having run for some years unchanged). I still engine braked on extended grades, valuing preservation of brake effectiveness (by avoiding overheating) over fuel consumption, but the waste annoyed me.

Diesels should cut off the fuel flow, or at least run just enough for low-speed idle, so there should be no fuel penalty to using engine braking; however, they don't have a throttle, so they have essentially no useful engine braking unless they have an added exhaust brake or internal compression release braking system. The machine-gun noise from big trucks is the result of a compression release braking system, commonly called a Jake brake (after Jacobs, an early manufacturer); pickup trucks typically have just an exhaust brake, if anything.
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Old 02-27-2014, 11:17 PM   #57
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I'll add another engine-braking question: I assume that a proportional brake controller will apply the trailer brakes when you use engine braking in the tow vehicle. That suggests you still need to worry about your trailer brakes overheating when using engine braking down a long grade. Is this true?
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Old 02-27-2014, 11:21 PM   #58
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Vehicle-specific note: since the 2008 V6 RAV4 uses the 2GR-FE engine which replaced my 3MZ-FE, my guess it that it cuts off fuel flow like my van, which is the desired behaviour. If you have a fuel economy meter - either built-in or a OBDII port gadget - you should be able to see this clearly: select L/100km (not MPG), and the reading goes to zero when the fuel flow cuts off. You don't need a long grade for this - a few seconds with any engine speed much above idle will do.
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Old 02-27-2014, 11:27 PM   #59
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Quote:
Originally Posted by dbailey View Post
I assume that a proportional brake controller will apply the trailer brakes when you use engine braking in the tow vehicle.
Yes, it brakes in proportion to deceleration, regardless of the reason for the slow-down... but only if the brake lights are on.

Quote:
Originally Posted by dbailey View Post
That suggests you still need to worry about your trailer brakes overheating when using engine braking down a long grade. Is this true?
Maybe, brake heating might be a concern if the brake pedal is held at all. I say this because on the descent maintaining constant speed (by providing enough resistance with engine braking) the rig is not actually slowing down. The only reason for the controller to apply any braking is that is leaning downhill, which would look to a pendulum-type proportional controller like gentle braking; a modern accelerometer-type controller usually measures in two perpendicular axes, and may not be confused.

Since the brake controller will only apply power to the trailer brakes if the tug's brake pedal is pushed (triggering the switch), during any time that you are not touching the pedal at all, there is no trailer braking action and thus no heating.

In practice, I have never noticed my trailer's brakes being hot (by smell or reduced performance - I haven't directly checked) after long and steep grade descents under engine braking... engine braking is appropriate to keep both tug and trailer brakes from being overheated.
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Old 02-28-2014, 08:32 AM   #60
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Right... while engine braking you're not actually decellerating normally... I missed that point.

The brake controller only applies trailer brakes if the TV's brake lights are on? I didn't know that.

Theory is good, but experience is better...
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