TM Towing Problems

[RockyMtnRay]

Originally Posted by Bill

So let's get to the heart of the matter - fishtailing. Fishtailing is never good. But you described a very specific situation - you were decelerating on a downhill grade when the fishtailing happened. You didn't push the brake pedal, but in fact you were braking the TV (via engine braking) without applying any trailer braking. In this situation, the unbraked trailer will ALWAYS try to take over and push the car around - I don't care how the trailer is loaded. The question is how well the car can resist it. Given that the Liberty is a reasonably light vehicle, and has a reasonably short wheelbase, I am not too surprised that a small amount of fishtailing occurred under these conditions - again, the conditions are braking the tow vehicle without braking the TM.

I'm very glad that Bill raised this point of using engine braking on the Liberty without any use of wheel brakes on the Liberty or TM because it is indeed a situation that could lead to the trailer really trying to push the tow vehicle around.

However, I never once experienced such fishtailing with my Cherokee (virtually identical to a Liberty in weight and wheelbase)....even on long descents of 7 to 8 percent grades at fairly high speed (60 to 65 mph) using only strong engine braking (engine turning 3500 RPM in 3rd gear with my foot completely off the throttle). If I was going to have fishtailing from engine braking, I sure would have had it during descents off the Continental Divide on Interstate 70...on both side it's steep, it's fast, and it's got a lot of curves...and I depended almost entire on engine braking to control my speed.

So why didn't I have my rig have any problems and the Liberty/TM did? My strong suspicion is that the answer lies with a difference in tow vehicle tires. I had my Cherokee equipped with Light Truck (LT) series Goodyear Wrangler A/T tires...a tire that has a very stiff and strong sidewall. That sidewall stiffness means the Cherokee was highly resistant to being pushed from side to side by the trailer. By contrast, I strongly suspect that Paul's Liberty still has the OEM P-series (passsenger car) tires...AFAIK every manufacturer uses P series tires on all SUVs and even their half ton pickups. P-Series tires have a much, much less stiff sidewall than LT tires...and it would be much easier for the trailer to push the Liberty from side to side in a fishtailing manner.

[fcatwo]

Three points:

The first is to repeat again the importance of the manual control on your electric brake controller. The instructions for all brands I have seen say to correct sway by accelerating the TV while applying trailer brakes with the manual control. This is of course not easy to do in a panic situation or going downhill on a curving road but it's the book remedy.

The second is to muddy the water by saying the instructions for my WDH said to return the front end to only where it was before hitching unless the rear sags more than 1-1/2". IMHO it's inportant to keep considerable weight on the TV's rear axle or the WDH could contribute to sway. Again, that's my opinion and I would back off of it in cases where a TV has equal weight on both the front and rear axle before hitching. This can happen if you carry enough passengers and gear in the TV to offset the normal front axle weight bias most vehicles have standing empty.

The third is to make sure Bill gets credit for coining the phrase "FINAL SQUAT". It so clearly describes an important element in any RV discussion that I predict it will gain standard usage in the RV community regardless of the type RV being discussed.

Frank

WOW! So much good information. Lots of valuable stuff to assimilate and try to absorb.

RockyMtnRay, Bill, fcatwo, etc, REALLY appreciate your time and input. Just took your comments and went back out to do some more statistical checking. Will try to fill in the blanks that some of you brought up; and then post doing's of today.

First off, the U-Haul installed hitch receiver is an Eaz-Lift CLASS #3; rated at 5000# max gross weight and 500# max tongue gross weight when used as a w/d hitch. The wd bars are rated at 1000#. The hitch 'head' is one of the multi-use type, shaped like an "L" with 5-6 holes for adjustments; and we have had to turn it over in order, with the long leg being down, to have it clear the rear mounted spare of the Jeep.

The controller is a Draw-Tite/Activator II.

Level of the tm remains fairly constant all throughout. More on that in a second.

The 2002 , 4-wheel drive (not all the time) Liberty is automatic and did not have factory installed tow package. We have done that since by having the hitch, the controller, the wiring and the transmission cooler installed locally. Tire pressure was checked this morning and were at suggested capacity with the exception of the RR; which was about 5# over; since been corrected. Have not yet adjusted down the tm tires yet as wanted to get this posted. Have Good Year years all around on both vehicles; but have not yet checked into the specifications yet. Will do that tomorrow or this evening.

OK.......then went out this morning to hook up the system, along with the bars, and take additional measurements to post for this follow-up.

Again, the Jeep, unhooked, is running at 12.5 inches up front and 16.5 inches at the rear.

Hooked, no wd bars yet, they change to 12.75 inches up front; and 15.25 at the rear.

Hooked, with wd bars (4 links down), front 12.75 inches; rear 15.5 inches.
Hooked, with wd bars (3 links down), front 12.75 inches; rear 15.25 inches.

Throughout the process, the tm stays fairly constant at between 15+ to 16 inches at all 4 corners.

In my limited ability to analyze the forces here, I look at that if I increase the wd bars linkage in an attempt to create more force on the jeep, based on the 3 to 4 link effect above, all that it 'appears' to be doing is creating a "V" effect; that being that the back end of the jeep is being forced down while the front end is forced upwards which, again in my limited ability, would seem to be part, if not all, of the noticed effects of the other day while traversing the slight down grade of 3%; foot off controls; no wind; no traffic; smooth asphalt roadway.

But, let me assure all of you that I am not versed in this new aspect of my life yet. Have not towed before, too busy raising our family, and have no experience or knowledge to relate to.

So, other than adjusting the tire pressure of the tm, and analyzing the tire specifications, does this new bunch of added details provide anything further that you can advise me on?

Thanks
Paul

[Bill]

Paul -

Re your hitch. A Class 3 hitch is the right one. A capacity of 5000 pounds is OK. Thousand pound springbars are fine. But the tongue weight capacity of 500 pounds is too light - your loaded-to-roll TM has more tongue weight than that. But you knew that. If you keep this setup, you may find metal bending or welds failing in a couple years - it has happened on this board.

The fact that your Liberty doesn't have a factory tow package probably means that it has a numerically-low rear end ratio - the one thing you can't fix. This will improve your gas mileage on the flats when you're not towing, but will make it hard to tow in the mountains. What are the towing specs and GCWR specs for your Liberty?

Unfortunately, your brake controller is one of the dreaded Time Cycle controllers. I checked the installation and checkout instructions on the web at http://65.196.229.70/pdf/N5500.pdf. On page 4 there is a bench test procedure. A light bulb is substituted for the brake magnets, and when the brake pedal is depressed, the procedure says "The display should step up to 10 and the bulb should start out dim and slowly get brighter". This is the hallmark of a time cycle controller, and it scares me to death. If you translate it, it says:

When the driver puts on the brakes, the controller has no way of knowing whether he is braking gently or braking hard. So it applies the trailer brakes just a little bit, and then gradually increases brake force as several seconds go by.

This is truly idiotic. If you are in a panic stop situation, the last thing you want is trailer brakes that don't come on NOW! A time-cycle controller gives you lots of braking when you don't need it, but no braking when you do need it. Wow! What a concept!

Sorry, my firm suggestion is to replace the controller with a "proportional controller". Many people feel that the Tekonsha Prodigy is the best in the world, and I don't disagree. As it turns out, I had an unusual problem with the Prodigy, so I switched over to the Jordan Ultima, which has been great.

Sounds like your rig is properly adjusted for level, and that's good. The difference between 3 links and 4 links doesn't look significant, so go with whichever you prefer.

As far as the "V" effect with the spring bars. For me, the easiest way to visualize what the springbars are doing is to think of them as the handles of a wheelbarrow - the tow vehicle being the wheelbarrow. The higher you lift the handles, the more weight is transferred from the back end of the wheelbarrow to the front wheel.

HTH. You have some thinking to do.

Bill

[Denny_A]

Originally Posted by Bill

Re your hitch. A Class 3 hitch is the right one. A capacity of 5000 pounds is OK. Thousand pound springbars are fine. But the tongue weight capacity of 500 pounds is too light - your loaded-to-roll TM has more tongue weight than that. But you knew that. If you keep this setup, you may find metal bending or welds failing in a couple years - it has happened on this board.

Thoughts regarding Hitch Capacity (500 lbs) and tongue weight (over 500 lbs.)

The cool thing about a WDH is that it transfers Up-to 1/3 of the tongue weight to the trailer's tires. If the tongue weight were 600 lbs, then up-to 200 lbs is on the trailer, and as little as 400 is on the hitch. That is, on the hitch affecting the loading placed on receiver and frame mounts.

As far as the "V" effect with the spring bars. For me, the easiest way to visualize what the springbars are doing is to think of them as the handles of a wheelbarrow - the tow vehicle being the wheelbarrow. The higher you lift the handles, the more weight is transferred from the back end of the wheelbarrow to the front wheel.

Here you make the weight transfer case, sorta! Additionally, the weight of the hitch must be accounted for. Mine is 80 lbs, counting the springbars. Since the spring bars(15 lbs ea.) are cinched to the trailer frame, they don't count as hitch weight. Assuming a perfect distribution of forces, I can accept a tongue weight of 675 lbs.(WDH unconnected) w/out exceeding the 500 lb Class 3 Receiver limit when rigged for travel. I.e ---
Wt = 50 + (2/3)*675 = 50 +450 = 500 lbs.

Denny_A

Ray,
I am planning to add two Trojan 6V batteries to the rear of my 2005 2720SL. This will add about 120 to 144Lbs. My TV is a 2004 F150 4x4 Supercab 5.3L 3.78 with a 6.5' bed. I haven't had any problems with sway. Will this upset the cart. Will the 24Lbs make a difference if I go to the smaller battery. This mod was posted by mjlaupp in electical on 03-07-2004.


Thanks

[RockyMtnRay]

Originally Posted by Mountain Trippers

Ray,
I am planning to add two Trojan 6V batteries to the rear of my 2005 2720SL. This will add about 120 to 144Lbs. My TV is a 2004 F150 4x4 Supercab 5.3L 3.78 with a 6.5' bed. I haven't had any problems with sway. Will this upset the cart. Will the 24Lbs make a difference if I go to the smaller battery. This mod was posted by mjlaupp in electical on 03-07-2004.
Thanks

I did that exact modification. Like you I tow with a half ton truck (Toyota Tundra 4X4, 4.7L V8, 3.91 axle) though your Ford is a few hundred pounds heavier and has an additional 5 inches of wheelbase.

Even with my lighter, shorter truck the only effect that I noticed was the rear of the truck was a little more prone to be bouncy (probably because the hitch weight was a bit lighter and there wasn't quite as much weight on the rear springs...and there was a little more weight behind the trailer's axle). What I didn't notice was any increased tendancy to have sway.

You are actually only adding just 60 lbs or so (Grp 27 RV/Marine is around 63 lbs, T-105s are about 61 lbs each), and the weight is ahead of the rear bumper (unlike a bike rack which puts 60 to 70 lbs a couple of feet behind the rear bumper).

I later started traveling with a couple of hardwood cabinets (about 30 lbs each when filled) in the front of the trailer and tightened my WDH's bars one more link. No more bounce at all.

So if I had no real issues, you certainly shouldn't with a longer, heavier tow vehicle.

Ray,
Thanks for the input. My battery box arrived today so I guess I am ready to start. Thanks again

[RockyMtnRay]

Originally Posted by Mountain Trippers

Ray,
Thanks for the input. My battery box arrived today so I guess I am ready to start. Thanks again

Glad to be of help. You're going to love having the extra battery power while boondocking. In addition to having over twice the rated amp-hours of the Grp 27 battery, the T-105s are true deep cycle batteries and you can take them down to about 20% of charge repeatedly with no significant battery degradation.

The Grp 27 RV/Marine is designed to be a boat engine starting battery (the "Marine" part of the name) as well as a "deep cycle" RV battery. Hence its plates are much thinner than those in a true deep cycle battery...to allow high starting currents...and those thin plates deteriorate much faster on deep discharges. My gut feeling is that any discharges below about 40% on a Grp 27 RV/Marine battery really shorten its life. Basically that means that the T-105s actually have about 3 times as much usable storage capacity as the Grp 27 battery.

Just be sure to treat them well...only distilled water and keep some kind of float charger (3 stage charger) on them when they're not in use. My local battery guy told me that a well maintained T-105 should last around 8 years!

On my last trip with my GMC Envoy pulling the TM 3326, I had a very eerie feeling when I came to a curve in the road. This particular 2-lane road had several such curves. It felt like the TM was pushing me into the turn and like I had to counter steer to keep the TV on track. It felt like the force normally needed on the wheel in a turn was reduced. I towed it 2000 miles on the first trip and had not felt this before. The two variables I think are important are a) the freeway curves of the first trip are more gentle and b) I had readjusted the WDH to put less weight on the front of the TV (it had been seriously incorrectly adjusted by the dealer).

After reading these posts, I am wondering if my TV wheelbase is too short for this trailer. Also, to agrivate this effect, the hitch looks to be extra long between the ball and the TV. I can even get into the rear of the TV with the TM open. The hitch measures 12 inches from where it exits the receiver to the ball.

Any words of wisdom on this subject from the mathematical wizards out there would be appreciated.

Bob