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RTurnConn 02-24-2012 07:55 PM

CAT scale results .. your thoughts
 
On our first real trip in our "new to us" 31 ft 1985 Limited I decided I would make a couple of runs as the scales.
Towing with a 2011 Suburban 2500.
First weighing was with empty TV and AS fitted out with only dishes, cookware and a few odds and ends. Pretty empty. I was not smart enough on that weighing to get a drive axle ans steer axle weights, so that kind of compounds the current situation.

Results: Steer axle 00, drive axle 7500; Trailer axle 6140, Total 13640.

Second weighing was on the way to Florida. WD bars set at what I believed to be a reasonable setting with front and rear TV movement. Trailer now loaded with clothes (wife does not pack light), food and misc. TV loaded with smarttote, tools, etc. Third row of seats taken out.

Results. Steer axle 3360, Drive axle 4320, Trailer axle 6540. Total 14,220

So TV weight was only 180 greater than empty and AS only 400 lbs more. ??? I was not happy with the set up, i.e. front and rear tire pressures were indicating more weight on rear axle and less on front.
On return trip I changed the WD set up by lift trailer and putting more wt on front of TV.

Results: steer axle 3440, drive axle 3980 (7420 total), trailer axle 6840. Total 14260

TV tire pressures (frnt vs rear) rose at about the same ratios (rear just slightly higher)
One observations is that it does not appear that we have over loaded the AS with "stuff". I was told in an earlier thread on tires that I would probably ad 1700 lbs of "stuff".........don't think so. I left the washer and dryer in the utility room at home. along with the upright freezer.
Any thoughts on these results?

slowmover 02-24-2012 09:32 PM

Well, buddy, you are off to the right start even if a step got skipped. The end result of dialing in the hitch rigging, IMO, is that the TV drives and steers pretty well as if it were solo. A goal worth working towards as maintaining lane center with no undue driver inputs is worth the effort. And the range of future adjustments -- barring a "new" TV or TT -- is then so small as to be worth it in itself: there's a narrow limit even for "major" changes to those vehicles or their loads. Peace of mind, IOW.

We start with the vehicle manufacturers guidelines, and Airstreams requirements. They are not the end of the story, but they are the beginning. Post 'em up.

I borrowed a chart from contributor Ron Gratz on Woodalls some time ago, and recommend it for the checks it provides. An "empty" TV weight (adjusted from factory shipping weight) is made with driver, full fuel and what remains permanently in truck. An "empty" TT weight is full water and propane, plus permanent trailer supplies (axles and TW). I like to have these prior to:

Ready for a trip, then onto the CAT Scale:

Weighing #1 -- TT attached and Weight Distribution Activated

Let Front Axle Load be "FA1"

Let Rear Axle Load be "RA1"

Let TT Axles Load be "TT1"

Then, while in same position on scales, take
Weighing #2 -- TT attached and Weight Distribution Not Activated

Let Front Axle Load be "FA2"

Let Rear Axle Load be "RA2"

Let TT Axles Load be "TT2"

Then, drive off scales and drop TT. Return to scales and take
Weighing #3 -- TV only -- TT Not Attached


Let Front Axle Load be "FA3"

Let Rear Axle Load be "RA3"

From the above values, you can calculate:

TV weight = FA3 + RA3

Gross Combined Weight = (FA1 + RA1 + TT1)
- should also be equal to (FA2 + RA2 + TT2) if scale weights are correct

TT Weight = Gross Combined Weight - TV Weight

Tongue Weight = (FA2 + RA2) - (FA3 + RA3)

Load Transferred to TT Axles
when WD System in Activated = TT1 - TT2

We none of us ever get this perfectly. But we can come real durn close. By coming as close as we can we can tweak back and forth on one or two adjustments till we are satisfied. It allows us to get TV tire pressure ideal (as that is always a pressure-versus-load problem) since TT tire pressure should always be sidewall maximum (or slightly higher) and doesn't change. Once dialled in it would be a quite large load change to have a corresponding TV tire pressure change trip-to-trip. The only real change is from solo to towing. Easy to maintain tire pressure even with load changes once one is "on vacation", IOW.

Steering control is everything. A washer or link here, a few psi there . . it is easily felt at the wheel.

Ideal hitch rigging also eliminates questions when some "new problem" is bothering our awareness. We want to take the effect of the trailer upon the tow vehicle out of consideration for problem diagnosis (so it's not just for running the roads, but keeping track of how that feels as the rig ages). Keeps the diagnosis decision tree simpler.

Two threads for your consideration:

From Post #50: The RobertCross Limited

and,

Finalcutjoe, with Diminished Hensley [Hitch] Performance?

Of course, anything written by 2Airishuman is worth your time, and especially so on hitch rigging. It isn't that one man is the authority, it is that 2Air has the full range of familarity with arguments (debates) on this subject and his links to other explanatory threads is unmatched.

Pictures of the rig and of hitch rigging (taken on level ground) are of benefit, and close-ups lend the experienced eyes around here the opportunity to question and critique (mainly each other, ha!). The Full Monte, my friend.

.

slowmover 02-24-2012 10:05 PM

Quote:

Originally Posted by RTurnConn (Post 1111341)
On our first real trip in our "new to us" 31 ft 1985 Limited I decided I would make a couple of runs as the scales.
Towing with a 2011 Suburban 2500.
First weighing was with empty TV and AS fitted out with only dishes, cookware and a few odds and ends. Pretty empty. I was not smart enough on that weighing to get a drive axle ans steer axle weights, so that kind of compounds the current situation.

Results: Steer axle 00, drive axle 7500; Trailer axle 6140, Total 13640.

Second weighing was on the way to Florida. WD bars set at what I believed to be a reasonable setting with front and rear TV movement. Trailer now loaded with clothes (wife does not pack light), food and misc. TV loaded with smarttote, tools, etc. Third row of seats taken out.

Results. Steer axle 3360, Drive axle 4320, Trailer axle 6540. Total 14,220

So TV weight was only 180 greater than empty and AS only 400 lbs more. ??? I was not happy with the set up, i.e. front and rear tire pressures were indicating more weight on rear axle and less on front.
On return trip I changed the WD set up by lift trailer and putting more wt on front of TV.

Results: steer axle 3440, drive axle 3980 (7420 total), trailer axle 6840. Total 14260

TV tire pressures (frnt vs rear) rose at about the same ratios (rear just slightly higher)
One observations is that it does not appear that we have over loaded the AS with "stuff". I was told in an earlier thread on tires that I would probably ad 1700 lbs of "stuff".........don't think so. I left the washer and dryer in the utility room at home. along with the upright freezer.
Any thoughts on these results?

There are quite a few ways to interpret your initial results. But without a full set of scale readings they are without enough foundation for even reasonable speculation.

That said, you might look at your TT axle weights and calculate what percentage of GVWR. When the wife and I full-timed in our earlier trailer a few years ago we were at .92 of maximum. A poll with a few doen responses on Woodalls showed (per Ron Gratz) that those respondin were at .85 of GVWR.

But we'd need the adjusted empty weight to make sense of it. And, as time-in-service lengthens, so (automagically, in BartS words [I love that]) does the "empty" thus "loaded" weights increase.

The end result of WDH adjustments will be: about 60-75% of TW on Drive Axle where Steer Axle is returned to "Unhitched, but Loaded" value.

A Ron Gratz quote:

" .. However, when using weight distribution, not all of the TW is carried by the TV. With a properly sized and properly adjusted WDH, it is reasonable to assume that only about 75% of the TW is carried by the TV. This means it is reasonable to assume that the load added to the TV would be around 13%x75% = about 10% of the TT's loaded weight.

So, for your hypothetical 6500# TT, you could estimate that, when using a WDH, the TT would add about 650# to the load carried by the TV."


Slick, huh?

And . . . what's handy about all this is one can ignore the no-need-for-WDH crowd (getting my bow shot in early) as these are static measured values of a few hundred pounds standing in for what, potentially, can be many thousands of pounds of force. All applied at the wrong time. Distribution takes away the bad pressure points, so to speak. Loss of control is generally over-correction by the driver (it is surmised) so let's keep him within familiar territory (is the back story).

Onward.

.

dznf0g 02-25-2012 08:05 AM

Geez, Rednax, I don't see anything wrong with your post at all. I don't think it's a bow shot. The only thing I'd do differently is, I don't travel with anymore water than necessary to flush the toilet and wash up from lunch, etc. So my "baseline" would be a little different than you prescribe. Good post!

slowmover 02-25-2012 10:51 AM

I was having some fun with the idea out there, that, there's a hundred different opinions on how to set up a hitch, and, that one does not need WDH (for a variety of ill-considered [non] thoughts); thus, that our threads on these subjects degenerate from the outset. None of which is quite true, but apparently it salves those who won't/can't/don't want to read their way through.

Numbers are the standard that work.

.

ROBERT CROSS 02-25-2012 01:11 PM

Quote:

Originally Posted by dznf0g (Post 1111499)
Geez, Rednax, I don't see anything wrong with your post at all. I don't think it's a bow shot. The only thing I'd do differently is, I don't travel with anymore water than necessary to flush the toilet and wash up from lunch, etc. So my "baseline" would be a little different than you prescribe. Good post!

dzn,

Just to illuminate...it's the TV loaded for camping un-hitched weight that will establish the amount of weight transfer needed on the steering axle....

KEEPING the TV/Trailer level when hitched with WD set and proper transfer is the goal.

Bob
:wally:

DreamStreamr 02-25-2012 01:31 PM

Yeah Bob,
You hit the nail on the head -- the direct measure of proper weight distribution is the measure of the front and rear of the tow vehicle from the ground.

One suggestion is adjusting weight distribution so the front of the tow vehicle lower than "coupled without wd" heights and the rear of the tow vehicle between uncoupled and "coupled without wd" heights.

We can follow this simple guideline, then confirm with weight scales -- it's always worked for ours.

RTurnConn 02-25-2012 01:51 PM

Quote:

Originally Posted by DreamStreamr (Post 1111611)
Yeah Bob,
You hit the nail on the head -- the direct measure of proper weight distribution is the measure of the front and rear of the tow vehicle from the ground.

One suggestion is adjusting weight distribution so the front of the tow vehicle lower than "coupled without wd" heights and the rear of the tow vehicle between uncoupled and "coupled without wd" heights.

We can follow this simple guideline, then confirm with weight scales -- it's always worked for ours.

I just did a readjustment of my WD "settings"....increased the height of the ball from the ground and thus increased the number of chain links. Result was front end dropped 1/2" and rear end dropped 1". Not sure how much I can tweek that. I guess I could play around with the number of washers in the receiver..........I'll try your approach the next time I have the AS home.

ROBERT CROSS 02-25-2012 02:20 PM

Quote:

Originally Posted by DreamStreamr (Post 1111611)
Yeah Bob,
You hit the nail on the head -- the direct measure of proper weight distribution is the measure of the front and rear of the tow vehicle from the ground.

One suggestion is adjusting weight distribution so the front of the tow vehicle lower than "coupled without wd" heights and the rear of the tow vehicle between uncoupled and "coupled without wd" heights.

We can follow this simple guideline, then confirm with weight scales -- it's always worked for ours.

Jim,

Measurements can work for an initial set-up.....

When we got the Hensley this procedure got us close.:blink:

Measure the truck height through the center of each wheel to the edge of the wheelhouse when loaded for trailering, on LEVEL ground.

Hook-up and measure again with NO tension on spring bars.

Adjust the bars to transfer about 1/2 the difference to the front axle.

Example: If you have a 4inch rear drop when hitched, adjust bars so 2inches are transferred to the front.

NOT a substitute for accurate CAT weights!!

Bob
:wally:

slowmover 02-25-2012 05:58 PM

Measurements = rough it in
Weight #'s = dialed in

dznf0g 02-25-2012 06:25 PM

Quote:

Originally Posted by REDNAX (Post 1111703)
Measurements = rough it in
Weight #'s = dialed in

I agree.

DreamStreamr 02-26-2012 11:14 PM

We weigh 2X yearly and more when we reset or rebuild the hitch head. Not disagreeing on tuning with scale weights, but it seems wrong to start without properly setting it up by accurate measure. Yours was the first post to acknowledge this requirement is all I'm saying. Thanks.

Jim
https://dreamstreamr.com

slowmover 07-08-2017 08:06 AM

This thread was linked in a recent discussion.

So, what's the story five years down the line?

Mollysdad 07-08-2017 09:23 AM

I once attended an RV rally where a company weighed your rig. You stopped, they placed super thin scales by every wheel, you pulled up on them and they read each, then mailed you the results. It was well worth the small fee to have every tire's weight. It led me to determine the correct tire pressure.

JamuJoe 07-08-2017 06:29 PM

Quote:

Originally Posted by Mollysdad (Post 1974307)
I once attended an RV rally where a company weighed your rig. You stopped, they placed super thin scales by every wheel, you pulled up on them and they read each, then mailed you the results. It was well worth the small fee to have every tire's weight. It led me to determine the correct tire pressure.



I did the same by borrowing a set of four racing scales from an auto enthusiast. Weighed at the four trailer wheels, then the tongue, hitched and unhitched. Significant differences right to left, front to rear on my FC23FB. Played with adding weight on the trailer rear bumper to simulate carrying bikes or a generator back there. Nice to do this in your own level driveway. Much more accurate, informative and convenient than dragging repeatedly through commercial CAT scales (done that too).

slowmover 07-08-2017 06:55 PM

Quote:

Originally Posted by JamuJoe (Post 1974567)
I did the same by borrowing a set of four racing scales from an auto enthusiast. Weighed at the four trailer wheels, then the tongue, hitched and unhitched. Significant differences right to left, front to rear on my FC23FB. Played with adding weight on the trailer rear bumper to simulate carrying bikes or a generator back there. Nice to do this in your own level driveway. Much more accurate, informative and convenient than dragging repeatedly through commercial CAT scales (done that too).



The new telephone app makes the CAT Scale easier to use.

Goal15 07-08-2017 08:49 PM

I did CAT scales right after we got the Airstream but haven't gone again because really felt my travel trailer was in the way of the big rigs. Anyone else had similar experiences?

Dana

uncle_bob 07-08-2017 08:58 PM

Hi

If I felt uncomfortable at one of the local scales, I'd drive off to another one. Doesn't everybody have four of them within a few miles of home? :)

Actually it's worse than that. The trailer is stored 20 miles down the road. If I go out that far, the count goes up to six.

Bob

SteveSueMac 07-08-2017 09:13 PM

Quote:

Originally Posted by Goal15 (Post 1974634)
I did CAT scales right after we got the Airstream but haven't gone again because really felt my travel trailer was in the way of the big rigs. Anyone else had similar experiences?

Dana



Well - sure, you don't want to get on the way of commercial truckers. But it's just 3 measures. So you get there all hooked up with you WD loaded - so take that as your first run through. Then get off the scales, release the WD tension and circle back for your second measure. Then go park and unload the trailer and go back for your last solo tow vehicle measure. At that point, you've got the 3 key measures you need. You could always hitch back up and go back for a fourth measure with a bit more WD applied than before - now you'll really know how to dial it all in!

Just be quick and don't get in the way of commercial drivers. They'll be fine!

slowmover 07-10-2017 08:04 AM

Speaking as someone who is on those scales several times daily, you aren't in the way. No matter how many passes you make.

Sure, be mindful. Just do what needs doing.


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