A "slightly different" GVW question

[dznf0g]

Originally Posted by goldenchase

This is a very good point, I am going to work on this. I suspect lateral distribution is very important in the dynamics of trailer sway. Easy to compute with individual wheel weights.

Yes to all. I would be very interested in your feedback. I seem to have a bit of a mental block on inertia calculations, so I'd like detail. But how to apply those outcomes to a target or standard????

[Silvr_Bullet]

goldenchase. You have done a great job, very impressive. Above what I can do, so I’ll ask a silly question, how did you arrive at the CG in your examples. Thanks

[SYC2Vette]

Originally Posted by dznf0g

I agree with your methodology, and I utilized an AS provided line drawing and the GM Upfitter manual line drawings for my particular truck, along with physical weights and measures for the hitch itself. From this, I created "load stations" in the truck and trailer. My sheet has formulas assigned to each load station, so that when items are added, removed, or relocated, I get outputs for the change in weight distribution across the truck and trailer.

This however doesn't give us definitive information relative to lateral inertia while underway. We could calculate those figures, I suppose...but to what standard?

There seems to be information on the net under "Yaw moment of Inertia"

[goldenchase]

Originally Posted by dznf0g

But how to apply those outcomes to a target or standard????

That would require testing. I am not ready to go that far. But just knowing how far out of balance a trailer my be laterally provides the required information to shift payload in order to center the lateral CG. It would also answer the question about longitudinal weight distribution on the 4 trailer tires.

The CG (at 12.5% of weight on the hitch) for my trailer is just forward of the forward axle. That must mean that the forward set of tires are carrying more load than the aft set. Should pressures in the tires be adjusted accordingly?

[dznf0g]

Originally Posted by goldenchase

That would require testing. I am not ready to go that far. But just knowing how far out of balance a trailer my be laterally provides the required information to shift payload in order to center the lateral CG. It would also answer the question about longitudinal weight distribution on the 4 trailer tires.

The CG (at 12.5% of weight on the hitch) for my trailer is just forward of the forward axle. That must mean that the forward set of tires are carrying more load than the aft set. Should pressures in the tires be adjusted accordingly?

Agreed on the first paragraph.

Second paragraph....hmmm....maybe. I always see my front running pressures increase a bit more than the rears. I know my trailer is about 1/2" lower in front than back (over about a 29' span) so I always contributed the elevated pressures to more weight on front than rear tires due to tilt, but CoG certainly does contribute. I run at 80psi cold, so a lot of compensation is already factored into a large margin when comparing to tire load/pressure tables.

[dznf0g]

Originally Posted by SYC2Vette

There seems to be information on the net under "Yaw moment of Inertia"

OK, but what is safe, or recommended for a trailer/truck combination??

[JJTX]

Originally Posted by SYC2Vette

So after talking with and emailing 2 WD suppliers and etrailer folks, all agree that the entire WD should be added to the GVW of the trailer. Including the stinger, there may be some disagreement, but since this is a conservative approach I am going with it.

The tongue weight as measured with the WD installed on the trailer but trailer not connected to tow vehicle, should not exceed the allowable Tongue Weight of the tow vehicle or the hitch receiver on the tow vehicle, whichever is lower (you do get to use the WD rating). In my case the GMC rating of 1000 lbs is the lower of the two.

The total of the trailer axle weight and the tongue weight thusly measured, and adding the weight transferred by the WD yields the trailer GVW.

My measured weight, ready to travel with fresh water 50% full but no black or grey is:

Hitch weight at ball as shown in photo = 750 lbs
Axle weight = 4030 lbs
Total = 4780 lbs
Which leaves 220 lbs for WD back to trailer wheels (it is less than that).

I am ok not considering grey and black as in all our travels we have only driven a short distance at low speeds with those tanks full, and when on the road our fresh water is kept at 25% -50% full.

Hopefully that pic is with a level trailer. Its hard to tell But I will assume it's level.

What are you using for sway control? ( this is just as important as proper weight )

What is the tow rating of your tow vehicle? Including combined gross rating?

I always travel with a full tank of water. It makes calculating weight easier and if you have water in your rear tanks, it keeps distribution more towards the front where it needs to be for stability on the ball vs the opposite which can induce sway. ( most people dont drive long distances with their black/grey tanks full as theres no reason to do this other than occasional slosh cleaning of the black )

My general rule is, if your trailer actual weight, regardless of what it is, is close to the tow-vehicle max rated weight, you need a bigger or more capable/rated tow vehicle.

[SYC2Vette]

Originally Posted by JJTX

Hopefully that pic is with a level trailer. Its hard to tell But I will assume it's level. Yes, bubble level

What are you using for sway control? ( this is just as important as proper weight ) Friction style and vehicle electronic sway control (that applies trailer brakes only if called on). That said with or without sway control it is very stable, I have never had a hint of sway even with high crosswinds and semis passing me at 85 mph on toll road) our near 15% hitch weight likely helps in that regard. Never had the electronic sway control activate but nice to know it is there

What is the tow rating of your tow vehicle? Including combined gross rating? 7,000 lbs max tow 12,000 lbs GCWR.

I always travel with a full tank of water. It makes calculating weight easier and if you have water in your rear tanks, it keeps distribution more towards the front where it needs to be for stability on the ball vs the opposite which can induce sway. ( most people dont drive long distances with their black/grey tanks full as theres no reason to do this other than occasional slosh cleaning of the black ) Our tank is at the rear of trailer, which is main reason we travel at 50% or less

My general rule is, if your trailer actual weight, regardless of what it is, is close to the tow-vehicle max rated weight, you need a bigger or more capable/rated tow vehicle. our TV GVWR and typical travel load is 6,000 lbs, trailer is 5,000 lbs, I have seen 3/4 ton trucks towing trailers that weigh more than the truck but are within ratings, I don't think they are particularly dangerous, but yeah I like the theory

Good questions

[field & stream]

Originally Posted by SYC2Vette

So the bottom line for me is: do I put the full cooler with all the beverages in the trailer over the axle, or leave it in the back of my truck? LOL.

This is a lot of mental aerobics just to decide where to put the beer!

For the mathematically inclined, here is another formula: bigger TV + smaller trailer + travel light + slow down = nothing to worry about. LOL

[SYC2Vette]

Originally Posted by field & stream

This is a lot of mental aerobics just to decide where to put the beer!

For the mathematically inclined, here is another formula: bigger TV + smaller trailer + travel light + slow down = nothing to worry about. LOL

Very true on all counts! To think we used to camp with a motorcycle and a tent. At our local campground this last week a guy pulled in with a big Peterbilt 579 TV (labeled private use only not for hire) and a giant triple axle 5th wheel. Good grief!

[dznf0g]

Originally Posted by field & stream

This is a lot of mental aerobics just to decide where to put the beer!

For the mathematically inclined, here is another formula: bigger TV + smaller trailer + travel light + slow down = nothing to worry about. LOL

Is it???

I usually load 2 cases of soft drink and 2 cases of beer. That's 72#. I actually keep those in the front sofa side arm compartments.

trailer TW increase = +52#
receiver hitch weight = +48#
Trailer Axle = +19

And that's just one load category item. Sometimes you don't know what you think you know, relative to how quickly things change.

[SYC2Vette]

Originally Posted by dznf0g

Is it???

I usually load 2 cases of soft drink and 2 cases of beer. That's 72#. I actually keep those in the front sofa side arm compartments.

trailer TW increase = +52#
receiver hitch weight = +48#
Trailer Axle = +19

And that's just one load category item. Sometimes you don't know what you think you know, relative to how quickly things change.

Yeah, I think in my case it was how all the items add up to get within limits, and the coolers are certainly a part of that.

This trip add inflatable Kayak and accessories: +50 lbs
Delete one of two solar panels -35lbs
Delete BedSlide -150 lbs
Delete spare extra long 30 amp extension cord -25 lbs
Replace 2x30 lb propane with 2x20 lb = -15 lbs (not counting propane)

.....so that is net reduction of 175 lbs, not bad.

Could probably not bother with carrying our Honda 2200 propane fueled generator as so far we have never used it on our road trips

[dznf0g]

Originally Posted by SYC2Vette

Yeah, I think in my case it was how all the items add up to get within limits, and the coolers are certainly a part of that.

This trip add inflatable Kayak and accessories: +50 lbs
Delete one of two solar panels -35lbs
Delete BedSlide -150 lbs
Delete spare extra long 30 amp extension cord -25 lbs
Replace 2x30 lb propane with 2x20 lb = -15 lbs (not counting propane)

.....so that is net reduction of 175 lbs, not bad.

Could probably not bother with carrying our Honda 2200 propane fueled generator as so far we have never used it on our road trips

Good for you, for paying attention to these kinds of details!

Sure wish I had your scales!

I tried to score a set a few years ago. My son worked for Dale Coyne Racing (indy car team). They were upgrading their scales. I had my son inquire about selling me the old ones. Apparently it is common practice that used equipment is handed down to lower class, more financially burdened, "feeder" series teams.

Can't argue with that....but I was bummed.

[Profxd]

You guys as usual are over thinking something simple. The WD is not added the trailer GVW in the manufacturers rating.

[dznf0g]

Originally Posted by Profxd

You guys as usual are over thinking something simple. The WD is not added the trailer GVW in the manufacturers rating.

Correct, the Ratings (GVWR) never changes. However the hitch components and the effect of WD do affect GVW, as hitched and loaded ready for running down the road.

[foobar]

Originally Posted by dznf0g

Yes and no, IMO. Certainly you can be under on coupler weight and under on axle capacity (some ASes have a lot more CCC than others (mine had more than 2k# when delivered) and have a poorly distributed weight. You are right, locating heavy items to the extreme rear of the trailer in order to compensate for a heavy coupler weight leaves a lot of mass at the front and adds a lot of mass to the rear....all with a potential inertia about the axles to create a problem during some evasive maneuver. BUT, I know of no "standard" calling out any formula with a recommendation "not to exceed". We are kind of left with making a conscious effort to concentrate individual loads toward the axles where we can, given the designed in base weight distribution of the floorplan and available storage locations.

Apologies for not being an active participant in this thread for a couple of weeks. I was out of town visiting relatives 500+ miles away (Yeah, Texas is big, LOL) and just managed to catch up with chores after my return home.

Rich and others are correct. Meeting the gross vehicle weight rating for the trailers provides "very little" information with respect to the stability of the trailer when it is being towed.

So, let's start by ignoring the effect of the trailer being hooked up to the tow vehicle for the moment in order to try and discuss a little bit about dynamic stability. This is a complex topic, so please forgive the rather simplistic explanation below.

My intuitive understanding of the basics of dynamic stability comes from my experience with larger sail boats. In the world of sailboats, placing loads at the ends of the sailboats is evil (allow me a little intentional exaggeration here) :-).

If you place large loads far from the center of gravity of the yacht, the yacht becomes less stable and will develop a tendency to act like a hobby horse in response to minor wave impacts on the hull (in trailer terms, this is analogous to the dynamic input from road imperfections). I.e. a small wave hits the rear of the sailboat, causing it to lift up slightly. After the wave passes, the rear of the boat attempts to return to it's former position. But because the excess weight in the front and rear of the sailboat, the sailboat acts like a double ended pendulum around the axis created by the sailboats center of gravity. Once you move one of the pendulum weights from the equilibrium position, the boat will start rocking back and forth around the pivot point (i.e. acts like a hobby horse). A trailer with loads distributed away from the center of gravity will behave the same way, even if the loads are equally distributed to the front and rear of the pivot point (e.g. the trailer axles). The trailer will tend to want to rock back and forth and jerk up and down on the trailers connection to the tow vehicle as the TV + TT travel down the road and run over road imperfections. This occurs even if the total loads on the trailer are within the GVWR spec for the trailer.

In another scenario, if too much load is placed in the rear of the trailer, this causes the tongue weight to reduce (like putting a heavy person on the end of a see-saw or teeter totter at a playground causes the other end of the teeter totter to rise up). As we all know, this can cause all sorts of tow stability problems if there is insufficient tongue weight (porpoising, sway, etc).

Unlike the yacht analogy, in towing a trailer, we actually desire a modest imbalance of weight. We want the center of gravity to be slightly forward of the pivot point of the trailer (the axles) in order to keep enough weight on the trailer hitch so that the combination of trailer plus tow vehicle is less sensitive to dynamic inputs from the environment (cross winds, air pressure waves from passing trucks/busses, and road imperfection inputs and any emergency steering maneuvers). This is where the requirement comes from that tongue weight should be somewhere within 10-15% of the travel trailer mass.

I'm sure the more technical among us will pick apart the admittedly simplistic analogy above, but please understand that I'm simply trying to pass along an example that might help folks better understand stability issues at a "gut level".

[foobar]

Originally Posted by goldenchase

This is a very good point, I am going to work on this. I suspect lateral distribution is very important in the dynamics of trailer sway. Easy to compute with individual wheel weights.

Agree that lateral weight distribution matters too.

We tend to focus on how trailer load distribution moves the center of gravity forward/aft of the trailer axles. That's certainly a primary concern.

How we distribute weight to the left/right within the trailer also impacts TV + TT handling (I.e. stability) when towing.

It's not very difficult to place too much weight on one side or the other when loading the trailer. An easy example would be when larger lithium battery banks and inverter are added inside a twin bed version of a trailer. This can easily add a few hundred lbs of weight concentrated on one side or the other.

[Profxd]

Originally Posted by foobar

Apologies for not being an active participant in this thread for a couple of weeks. I was out of town visiting relatives 500+ miles away (Yeah, Texas is big, LOL) and just managed to catch up with chores after my return home.

Rich and others are correct. Meeting the gross vehicle weight rating for the trailers provides "very little" information with respect to the stability of the trailer when it is being towed.

So, let's start by ignoring the effect of the trailer being hooked up to the tow vehicle for the moment in order to try and discuss a little bit about dynamic stability. This is a complex topic, so please forgive the rather simplistic explanation below.

My intuitive understanding of the basics of dynamic stability comes from my experience with larger sail boats. In the world of sailboats, placing loads at the ends of the sailboats is evil (allow me a little intentional exaggeration here) :-).

If you place large loads far from the center of gravity of the yacht, the yacht becomes less stable and will develop a tendency to act like a hobby horse in response to minor wave impacts on the hull (in trailer terms, this is analogous to the dynamic input from road imperfections). I.e. a small wave hits the rear of the sailboat, causing it to lift up slightly. After the wave passes, the rear of the boat attempts to return to it's former position. But because the excess weight in the front and rear of the sailboat, the sailboat acts like a double ended pendulum around the axis created by the sailboats center of gravity. Once you move one of the pendulum weights from the equilibrium position, the boat will start rocking back and forth around the pivot point (i.e. acts like a hobby horse). A trailer with loads distributed away from the center of gravity will behave the same way, even if the loads are equally distributed to the front and rear of the pivot point (e.g. the trailer axles). The trailer will tend to want to rock back and forth and jerk up and down on the trailers connection to the tow vehicle as the TV + TT travel down the road and run over road imperfections. This occurs even if the total loads on the trailer are within the GVWR spec for the trailer.

In another scenario, if too much load is placed in the rear of the trailer, this causes the tongue weight to reduce (like putting a heavy person on the end of a see-saw or teeter totter at a playground causes the other end of the teeter totter to rise up). As we all know, this can cause all sorts of tow stability problems if there is insufficient tongue weight (porpoising, sway, etc).

Unlike the yacht analogy, in towing a trailer, we actually desire a modest imbalance of weight. We want the center of gravity to be slightly forward of the pivot point of the trailer (the axles) in order to keep enough weight on the trailer hitch so that the combination of trailer plus tow vehicle is less sensitive to dynamic inputs from the environment (cross winds, air pressure waves from passing trucks/busses, and road imperfection inputs and any emergency steering maneuvers). This is where the requirement comes from that tongue weight should be somewhere within 10-15% of the travel trailer mass.

I'm sure the more technical among us will pick apart the admittedly simplistic analogy above, but please understand that I'm simply trying to pass along an example that might help folks better understand stability issues at a "gut level".

Your analogy is a very good one. Unfortunately most on these forums believe as long as you are in the weight limits everything will be good. If not then tighten up the WDH little more or spend $2k for a HA/PP. The trailer loading solution goes ignored.

[dznf0g]

Originally Posted by Profxd

Your analogy is a very good one. Unfortunately most on these forums believe as long as you are in the weight limits everything will be good. If not then tighten up the WDH little more or spend $2k for a HA/PP. The trailer loading solution goes ignored.

Now, c'mon, let's not get into the hitch wars here. No brand or style is an excuse for improper balance and loading.

You do make a point though. Just like a 2500 or 3500 will probably mask an improper load better than a half ton, giving the driver a false sense of security....so too, will a PPP hitch mask an improper load better than other WD hitches.

So, nobody should chime in and say, "I have a PPP, so I don't have to worry about inertia, 'cause the trailer can't swing on its own."

Physics is a fickle friend when you try and cheat too much.