TM Towing Problems

[Denny_A]

Re: my 10-03-04 post regarding "cold" tire temp s/be 70 deg F.

Assumed 70 F is considered to be the temp appropriate for a 50 psi. Question is, what would be the appropriate pressure at a different temp. Assume the tire volume is constant (in a close-enuff-fer-gumint-work way), then P2 = P1*(T2/T1), where P is in psi and T is deg. Rankin. Math indicated a Temp change of 10 F should result in a 1 psi tire pressure change.

Sampled my tire pressure 3 days ago at 40 F and today at 70 F. Result:

P(@40 F) = 45 psi. P(@70 F) = 48 psi. Tire was not adjusted in any way. Temp change of 30 F resulted in a 3 psi change.

Although this was an obviously limited test, and a larger Temp difference would have been more statistically significant, it nevertheless appears to confirm the rule of thumb: Cold tire pressure changes 1 psi for each 10 deg F change.

Time to adjust my tire pressure back to 50 psi(translation: my tire is 2 psi underinflated) .

Denny_A

Are you suggesting that I (living in hot south Texas) should lower my psi when it is 100F? Instead of 50 it should be at 47? It seems to me that would increase heat build up and lead itself to self destruct.

[Denny_A]

Originally Posted by Windbreaker

Are you suggesting that I (living in hot south Texas) should lower my psi when it is 100F? Instead of 50 it should be at 47? It seems to me that would increase heat build up and lead itself to self destruct.

No. I'm suggesting that the "cold" tire pressure of 50 psi must be defined at a particular temperature. I believe that temp to be 70 F. Therefore, if one were to be checking tire pressure when it is significantly different from 70 F, then it would be useful to have a rule of thumb in order to know what pressure is equivalent to 50 psi at 70 F. Actually I wrote:

..... rule of thumb: Cold tire pressure changes 1 psi for each 10 deg F change.

Temp higher, pressure higher. Temp lower, pressure lower. Each is a change. Therefore, at 100 deg F expect to see 53 psi if at 70 F the pressure was 50 psi. Conversely, at 30 F, expect to see 44 psi. If need be, adjust pressure accordingly.

Denny_A

[Denny_A]

Had I done a bit of investigation first, instead of fooling with the math, I would have discovered, in minutes, that "cold" pressure is always the placarded inflation pressure with the tire air at/very near the current ambient temperature. Therefore if the outside air temp (OAT) were 20 F or 100 F, set the pressure at 50 psi.

If one were to depart from freezing OAT and travel to balmy climes, then prudence would require checking cold pressure at each stopover and adjusting pressure as needed.

In the past, I have accepted the lower pressure when OAT is low, and let the warm-up of ambient conditons take care of tire pressure. But, even a few hours running with pressure as little as 10% low can cause accelerated wear.

So, At 100 F, or zero F the correct cold tire pressure is 50 psi. Bench marks, such as that which I hypothesized, don't work for "cold" tire pressure.

Denny_A

I'll give you another one to play with. Started trip @50 psi and 960 elevation. Ended trip 6000 elevation, cooled tires were reading 52psi one week later.

[Denny_A]

Originally Posted by Windbreaker

I'll give you another one to play with. Started trip @50 psi and 960 elevation. Ended trip 6000 elevation, cooled tires were reading 52psi one week later.

Easy. Standard atmosphere tables:

14.18 psi (@960') - 11.78 psi(@6000') = 2.4 psi difference.

Therefore gage pressure of tire is 2.4 psi greater due to reduced atmospheric pressure. Assumes the Cold tire temp was identical at both elevations, and atmospheric conditions (air mass system) similar during both readings.

Accuracy of the pressure gage (or lack thereof) would likely blur any air mass variable. Temp differences would result in a more discernable effect.

Denny_A

[RockyMtnRay]

Originally Posted by Denny_A

Easy. Standard atmosphere tables:

14.18 psi (@960') - 11.78 psi(@6000') = 2.4 psi difference.

Therefore gage pressure of tire is 2.4 psi greater due to reduced atmospheric pressure. Assumes the Cold tire temp was identical at both elevations, and atmospheric conditions (air mass system) similar during both readings.

Accuracy of the pressure gage (or lack thereof) would likely blur any air mass variable. Temp differences would result in a more discernable effect.

Denny_A

As someone who experiences each day in my traveling around Colorado as much as 7000 feet of altitude gain/loss...and as much as a 50 degree temperature swing, I just go with the gauge on a "cold" tire before each day's travels. It's too complicated to try to calculate the effects of temperature and elevation changes during the day...I figure that as long as my start-of-the-day tire pressure is 50 according to my gauge, I'll be fine for the rest of the day. If it's above that the next morning, I let out a little to reach 50; if it's a little below that, I pump the tire up with a portable compressor until I have 50. Basically the K.I.S.S. principal in action.*

Enroute I do check the temperatures of all the TV and trailer tires at each rest stop using an ultra sensitive probe (the back of my hand ). As long as they're all about the same reasonable temp (usually just a little warmer than ambient)...and I've got my weights within the tire limits...I figure I shouldn't have any problems. So far, so good, too...

*Keep It Simple Stupid aka Don't Get Fancy.

Latest update to the 'towing problems'......

Took our 2720 out yesterday for our 'inaugural' towing experience; and shake-down jaunt for the unit as a whole. Experienced some things that my feeble mind just cannot decipher; so hopefully, some of the more knowledgable brethern here can help. The unit was 99% fully loaded with water, food, 'stuff', etc.. Have an Eaz-lif #3 hitch with weight distributing bars.

First the statistics....
I'll post them all so that the ones usable can be analyzed. Probably more here than needed; but one never knows.

First, measured the tv clearances in driveway; pre-hook up was 12.75 inches on the front wheels; with 16.5 inches on the rear.

Next, hooked up wd hitch. Clearances changed to 12.25 inches on front; and 15.5 on the rears.

In connecting the wd bars, went to the 3rd link down from the end of the chains.

Tongue weight, pre-hook up, comes in at a weighted 450 lbs.

Went to the local scales after hooked up and weight for front axle was 2260.
Rear axle was 2660... and total package was 8400 ... indicating tm was 3580, and that tv was a combined 4920 ..l. which by the way is a Jeep Liberty.

Also have an adjustable brake controller; setting at time was at 3.5 on scale of 5.0.

Tires set to specificied psi plus an additional 5 lbs. for the trailer due to noticable wearing of thread on outer edges.

Now, here's the part that concerns me.....
In cresting a slight grade just after starting out, decided to pull over at the bottom due to traffic. Grade approximately a 3-5% down grade.

As I took my foot off of the accelerator, the unit began to fishtail noticably; at least at my end of the equation that is. No braking as of yet.

Applied brakes slightly, and fishtailing continued about the same; but decreasing as the braking began to take ahold. Was able to stop w/o any problems ... but action/response confused and concerns me.

So, can anyone shed light on the above for me.

Could my wd bars be too tight? If so, how to correct?
Could my controller be set too tight?
Could my excessive tongue weight (per TM's stated tongue weight) be in excess of manufacturer standard?
(In front of axle, had tool box full of tools; couple of containers with food and some other odds & ends; nothing overly heavy singularly or combined. One full tank of propane and the other 1/3 full. Nothing in the rear of the tv.)

As mentioned in other postings, have anti-sway unit 'in the mail', but have not yet received it so it has not been utilized or tested yet.

Analysis and ALL comments welcomed.

Hope I've 'splained it sufficiently.

Paul

[RockyMtnRay]

Originally Posted by paul street

Tires set to specificied psi plus an additional 5 lbs. for the trailer due to noticable wearing of thread on outer edges.

This bothers me enormously. First of all, you should never exceed the specified maximum PSI on the tire. NEVER. On a 2720 with the 14 inch tires, that number is 50lbs. You should never travel with less than that either. Use a quality, preferably digital tire pressure gauge and set your tire pressure to exactly the maximum tire pressure stated on the tire.

Secondly, your trailer tires should not under any circumstance be showing uneven wear across the tread. That they have noticeably greater outer edge wear is a very strong indicator that the previous owner ran those tires at grossly underinflated pressures for a substantial distance. That means those tires have very likely been badly damaged and are far more likely to have a blowout. Do NOT try to compensate for previous underinflation by overinflating...it simply puts more stress on an already damaged tire.

If I were in your position, I would immediately replace both tires with new Marathons and while I was at I would also insure that the axle was properly aligned...especially if the existing tires are showing any cupping or feathering on the tread edges.

Could my wd bars be too tight? If so, how to correct?

No, the nearly equal drop of your Liberty's front and rear suspension indicates to me that you have the WD bars almost perfect for your current loading of the trailer. They are definitely NOT too tight. As a point of reference, I use a 5 link drop on 750 lb bars with my 2720SL...that you are getting equal drop on your TV with just 3 links indicates to me that your TM is verly likely not loaded correctly.

Could my controller be set too tight?

Not likely, if anything the controller settings might not be tight enough. First of all, you experienced fishtailing BEFORE you put on the brakes and the brake controller's settings do not come into play until you put on the brakes. Equally importantly, when you did apply the brakes, it didn't reduce the fishtailing...normally application of sufficient trailer brake is an excellent way to stop fish tailing. That it didn't tells me you may not be getting enough trailer braking for the amount of TV braking.

BTW, exactly what brand, model, and type (e.g. inertia, time delay) of brake controller are you using? If it's one of the low cost time delay controllers, you're going to have braking problems. Period. No ifs, no ands, no buts. You will have braking issues.

Could my excessive tongue weight (per TM's stated tongue weight) be in excess of manufacturer standard?
(In front of axle, had tool box full of tools; couple of containers with food and some other odds & ends; nothing overly heavy singularly or combined. One full tank of propane and the other 1/3 full. Nothing in the rear of the tv.)

As we've told you before, totally forget TM's stated tongue weights. For real world purposes, they are completely bogus and useless because they are taken on a completely empty, no options trailer. DON"T USE THEM!!!!!!!!!

If anything, your tongue weight is about 50 to 100 lbs too light. It should be at least 500 lbs, more likely closer to 550 lbs on a 2720 with a full toolbox ahead of the axle.

Given your exceedingly light tongue weight, I strongly suspect your fishtailing is caused by trailer loading...or the trailer tires/axle. There should be nothing of any weight behind the TM's axle. I towed a 2720SL for thousands of miles over serious mountain grades behind a Jeep Cherokee and never had even the slightest indication of fishtailing. Since the Cherokee has virtually the same wheel base and front/rear weight bias as your Liberty, the difference has to be in the trailer loading...or the trailer tires. My tongue weights on the 2720SL have never been less than 525 lbs...I currently have a nearly 550 lb tongue weight. In '03, my TM weighed 3570 and had a 525 lb tongue weight. That you have an almost identical trailer weight but 75 lbs less tongue weight is strong indicator you do not have a properly loaded trailer.

As mentioned in other postings, have anti-sway unit 'in the mail', but have not yet received it so it has not been utilized or tested yet.

Do NOT use the anti-sway device until you correct the cause of your fishtailing. That you were having fishtailing at all indicates that something (loading, tires) is very, very wrong with your trailer or its loading. Using the anti-sway device is only a bandage or mask for the problem...it will not fix the problem and sooner or later the underlying problem will result in a serious accident whether or not you have the anti-sway device.

[Bill]

Paul -

Yup, I also agree with Ray on most points, but with a slightly different conclusion.

o Ray is right about the tires - follow his advice - but like Ray, I don't think it has anything to do with the fishtailing.

o When you hook up, the back end of your Liberty squats by 1" and the front end squats by 1/2". In an ideal world, the squats would be equal. You are pretty close, but as Ray said, if anything you are on the light side. Just for the fun of it, try picking up one more link and measure the squats again. And one big question - once you have raised the springbars, is the TM level? It should be. But again, I'm not convinced that any of this is related to the fishtailing.

o Counting chain links and comparing your count to someone else's is meaningless. The number of links depends on the mfr of the hitch, the springbar ratings, the firmness of the suspension of the tow vehicle, the angle of the ball mount, the tongue weight of the trailer, and probably a few more parameters I haven't thought of. For example, Ray drops 5 links on his TM, I drop 4 links on the exact same year and model TM. Why? Probably because my Explorer is sprung softer than his Tundra, we have different hitches, and we have different springbar ratings. We may also have somewhat different final squat, though we've never compared.

o I have taken a look at the Eaz-Lift web site, and I can't identify which hitch you have. Eaz-lift #3 doesn't seem to mean anything, unless I missed it. Can you translate this into a model number that the web site talks about? Also, what is your springbar rating - 500 pounds? 600? 750? 1000?

o Ray is also right about tongue weight. The numbers that appear in the TM catalog (or any other manufacturer's catalog) are the tongue weight of a completely un-optioned, unloaded trailer. And please note that the number is intended to be a piece of information - it is NOT intended to be a spec that you have to meet.

o The "strength" of your brake controller must be set according to the manufacturer's instructions, and I assume that you have done so. Proper adjustment means that the TV/TM combination will stop in about the same amount of road as the TV alone (when the TM is not there). Cranking it up arbitrarily is not a good move under any circumstances. At any rate, as Ray pointed out, this is irrelevant to the fishtailing question, since the fishtailing happened when the brakes were not being applied.

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. And let me say again, fishtailing is never good.
By the way, does your Liberty have a standard or automatic transmission?

So here is where I may diverge a bit from Ray's analysis (and I am far from an expert). I'm not sure that sway is the same as fishtailing in the situation you described. After all, 18-wheelers can't sway - but they can jacknife, which is what your TM is trying to do.

To me, sway is something that occurs when you are moving at a more-or-less steady speed, and something upsets the equilibrium of the rig (such as a gust of wind, an 18-wheeler, or a fast movement of the steering wheel as in dodging an obstacle). The trailer responds by whipping back and forth and trying to yank the tow vehicle with it, and the tow vehicle is barely able or unable to control it. Sway is VERY bad. A properly-loaded trailer (such as the TM) does not sway. But in your case, none of these things happened. So here's a question - did you experience any kind of sway in any situation other than the one you described? If so, something is wrong. If not, maybe there is hope.

OK, having said that, what should you do about your fishtailing?
First, Ray's comments with respect to proper loading and weight distribution are extremely important. But your description says that the tongue weight is 13% of the TM weight (which is apparently 3480, not 3580), and this doesn't seem out of line to me. I'm not sure that further increasing the tongue weight is going to help.
Second, fishtailing occurred when you had engine braking and no trailer braking, at high speed on a reasonsably steep downgrade. Learn to recognize this situation in advance, and react to it! Your trailer brake controller has a hand control, which allows you to apply the trailer brakes with or without the TV brakes. Learn to use it! Apply some manual trailer braking before the fishtailing starts. This is not a great solution - in fact, it is pretty poor - but it is better than nothing.
Third, when you applied the brake pedal, the fishtailing should have stopped almost instantly. Like Ray I am very concerned that it did not. Tell us about your brake controller - make and model. It sounds like a time-delay/time-cycle controller. I used one of these for a few days when my TM was new, and it was just plain scary. If you have one, I am right on top of Ray - GET RID OF IT.

So where does that leave us?
1. I'm not sure the Liberty is a great tow vehicle, but it is what you have, it is not grossly lacking, and other folks on the board have had good results with one. By the way, what year is your Liberty? Did you buy it with a factory towing package? And were its tires properly inflated? Soft TV tires invite handling problems.
2. Your fishtailing occurred in a very specific situation. If it doesn't occur in any other situation, then your temporary fix may be to recognize this situation, try not to get into it, and deal with it promptly if you must.
3. Make sure you have a decent brake controller. When you touch the brake pedal in the tow vehicle, you want the TM brakes to respond immediately and in proportion - not after a leisurely wake-up and stretch and yawn.
4. Let me say it one more time - fishtailing is not good. Nothing can make it good. But if you drive conservatively, with that in mind, perhaps you can live with it for a while.
5. But if you add a sway control, you will get complacent, and forget to drive appropriately. I really recommend against it, if for no other reason than that.

Folks, I know there are a lot of opinions that differ from this. Let us hear from you.

Bill