Collyn Rivers on towing dynamics

[Skater]

Originally Posted by REDNAX

For all others, traveling with fresh full water improves handling, or, maybe we can say that it dampens the tendencies of untowards behavior.

You've made a good case. I may try filling the tank for our upcoming trip to see how it handles. Not that it handles badly now, of course - the only gripe we have now with our rig is when you're passing a truck and the wind is coming off the truck, causing the trailer to bounce around a bit. I never thought much about it, but it bugs my wife a lot.

I am used to running 'dry' because I did with the B190 as much as I could. But that's a totally different situation.

[Skater]

Originally Posted by Skater

You've made a good case. I may try filling the tank for our upcoming trip to see how it handles. Not that it handles badly now, of course - the only gripe we have now with our rig is when you're passing a truck and the wind is coming off the truck, causing the trailer to bounce around a bit. I never thought much about it, but it bugs my wife a lot.

I was thinking about this while I was getting the hose to fill the tank, and I remembered something: The tank was full on our last trip when my wife was driving. We'd filled it at home before our Disney trip in January, just in case we had to stop for the night at a non-campground location (truck stop, Wal-Mart, etc.) due to bad weather.

At least on the way down, it was. I assume I filled it for the trip back, but I don't remember doing so, nor do I recall draining the tank when I went to winterize after the trip. Hmmm. She grumbled about the bouncing on the way home, not the way down there.

I plan to crank the sway control a little tighter for our upcoming trip and see what that does, if anything...

[Skater]

Yeah, so they're doing some construction on the PA Turnpike (weird, I know), and there is one lane through the Kittattiny and Blue Mountain tunnels, so basically you're facing traffic head on. On a side note, my wife was THRILLED I'd driven that stretch.

Anyway, the speed limit is 40 mph, but even with that closing speed and trucks going the opposite direction mere feet away, the trailer was totally solid. I couldn't detect any sway at all. Of course I didn't want to stare into the mirror too long, being mere feet from death were I to stray into the other lane, but with a couple quick glances during passing trucks I couldn't see even a slight wiggle.

I love our rig.

[slowmover]

Okay, now run the Ho Chi Minh Trail. At night. In the rain. (Familiar with the reference?)

Good news. TT tires at max pressure? TV tires set load against pressure? (Details that also count). Continue your experiments. The range of adjustments for any of our rigs is limited. Knowing them is what separates us out.

[Skater]

Originally Posted by REDNAX

Okay, now run the Ho Chi Minh Trail. At night. In the rain. (Familiar with the reference?)

Good news. TT tires at max pressure? TV tires set load against pressure? (Details that also count). Continue your experiments. The range of adjustments for any of our rigs is limited. Knowing them is what separates us out.

No, don't know that movie. My first thought was it had something to do with the "Smokey and the Bandit" movies but a quick search makes it look like you were referring to a different movie. I'm more of an Airplane! guy. "We're going to have to come in pretty low to land this, Elaine." (Actually that's Airplane! II but it still feels relevant.)

The TT tires are at 60 PSI, but I forget if their max is 60 or 65 PSI. I do want to get the rig weighed (in particular I think the lifter bars are too heavy - they're 1200 lb bars).

I've already made a number of adjustments to the hitch setup since I got the trailer (with hitch) last summer. The PO wasn't putting any weight on the lifter bars at all, for example, but I tightened them up over time especially after 'enjoying' some porpoising. The lifter brackets were not attached at the right spot, so the lifter bar chains weren't straight when the rig was straight. The sway control was merely a decorative attachment - he told me to set it way too loose. And of course the first time we got on the highway taking it home, a pickup towing a large cargo trailer zipped by at high speed and sent us a-swayin'. So the situation is already very much improved over what I started with, which is why I'm so happy with it right now.

It's hard to see how further adjustments are going to make it much better, when trucks passing in the opposite direction at high speed in the next lane don't even give a wiggle. I didn't mention it above, but I was in a similar situation on the open road last fall - two lane road, speed limit 55 mph both directions, a little cross wind, and the passing trucks produced NO movement of the trailer that I could discern.

Like I said above the one thing I want to check is the lifter bars - the original owner added a third battery and a huge inverter (it'll run everything but the A/C) under the front gaucho, so I wouldn't be surprised if our tongue weight is above what you'd normally expect for a 1995 30' Excella, but I still think the lifter bars are a touch heavy. I haven't done anything yet because (a) these are obviously working, (b) we haven't had a bunch of extra money to spend on it, and (c) I wanted to limit the number of variables I was altering at once.

[slowmover]

Running the PA Turnpike brought up an old truck driver name for US-209 and in reference to the North Vietnamese jungle logistics route through neighboring countries. Turn, blind curves, traffic . . all was difficult driving, but a time-saving route nonetheless.

Using a CAT Scale to "dial in" the WDH is the time-honored method of getting it really right.

.

[Collyn]

Originally Posted by slowmover

I found an interesting set of discussions from Down Under on towing dynamics and stability. Let's start with Collyn Rivers on Caravan Dynamics

The clarity is outstanding. As are the references. These links (and this thread) are for those who find the technical aspects of trailering of interest.

This link goes into a bit of depth: Caravan World Article and Sway

And a calculator as a help to both links above: Kilograms to Pounds (kg to lbs) Conversion

Another good page discussing stability on the Australian caravanersforum.com. Very interesting posts by Collyn Rivers there from Nov 16 through Nov 18, 2011. With a nod to the value of 2airishuman's great input on such subjects, I originally had a lengthy quote from Collyn Rivers in my original post re: independent suspension from this last link on that forum. A bit much per copyright concerns. But let's summarize that...

As with aerodynamics, the science of suspensions goes back to the beginnings, sometimes to the very beginning (1903 in this case) and much was accomplished by the 1920's (IFS FA with leaf sprung RA on a TV for instance) and the quote ended with the idea that the interactions between the axles on a TV (in this instance) are already complicated enough before one adds the TT. The difficulty of prediction.

A quite interesting aside about engineer Maurice Olley and his influence to this day. From the post on Nov 18:

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Have just joined this forum - and this is my first posting.

The interaction between a trailer and the tow vehicle is hugely complex and not feasible to even begin to cover on any forum posting. I have been studying it for some 45 years, following an initial interest whilst working at GM Research (Vauxhall/Bedford) in the UK - and being fortunate enough to have attended lectures by Maurice Olley.

Following the above kind mentions regarding some of my writing in this area, (the Australian experience is not dissimilar from that in the USA) and receiving a lot of queries from USA readers (and also some most interesting technical exchanges with Airstream) I feel it may be worth directing members' attention to my most recent writing in this area: ([url=http://www.exploroz.com/Vehicle/Caravans/Caravan_Dynamics.aspx]

It does I fear use metric units - as Australia has been using the system since 1951 - but the generality should I hope be clear. Ditto re none US English spelling.

That piece will be presented in a less colloquial form as the keynote speech at the major Conference to be held in Australia (in 2014) on this topic - of which I am also the moderator.

This piece primarily covers the trailer, as that is the major cause of the instability, but I am currently working on a longer fully referenced version that includes the dynamic behaviour of tow vehicles and the interactions between the two.

Re the many recent queries regarding WDHs - the best way to see them is as a truss used to assist remedy a condition that is far better addressed at source - by eliminating its need. This is the way this matter is being addressed in Europe - by keeping length to less than 20 ft, mass to under 1600 kg (about 3500 lbs), and particularly by centralising the major masses within the trailer.

As with Australia, the USA will inevitably be faced with the situation where tow vehicles become ever shorter and lighter. This is already a very serious issue in Australia as the big Fords and Dodge Rams are now very rarely used - due to our increasingly stringent emission requirements. Our most popular big tow vehicle is the Toyota Land Cruiser in turbo diesel form, but many are turning to smaller units - that have a tow ball loading max of a typical 150 kg (about 330 lb).

A very quick solution is - where a trailer longer than 20--21 ft is sought -is to use the fundamentally far more stable fifth wheel format. If wished I can offer this forum an article on this topic (explaining why) for publication.

(There has been a fair bit of US research in this area - but mainly in the later 1970s).

Re copyright issues - this can be problem on some forums as the ofetn site provider seeks to own 100% copyright. This is simply not feasible for me - so prefer to ask readers to refer also to my own main website: www.caravanandmotorhomebooks.com

Collyn Rivers
Caravan & Motorhome Books (also Technical Editor of the Caravan Council of Australia).
Sydney