Time for a Change

[adept99]

Cut right to the chase. We're getting some waggle out of our trailer. With the Smart loaded and both motorcycles loaded, you don't notice it too much. Take the Smart off the truck and things get sloppy quickly. I've talked to Trey & Susan and had them weigh the rig, wheel for wheel. Bottom line is that we're really light at the pin and heavy at the tail. We're already a tad overweight so just adding weight isn't really a good answer either. Most of the heavy stuff can't really be moved, like motorcycles and washers and dryers.

SO.....

Has anyone else tried moving the rear axle mount(s) further to the rear?? Yes, I understand I need to verify the design load and a wad of other issues. First among them would be determining the distance needed to move. Any "Nuts...Didn't think of that" items??

Paul 

[Alie&Jim's Carrilite]

Move the front/most forward trailer axle to behind the rear.

I/we did this on a 3 axle boat trailer- 3 7k axles- that had zero hitch weight with one design we built.  Moving it made a new trailer out of it.   

You do need to look at the frame, but primarily the slide outs and any wheel fairings around them.

[adept99]

Jim;

Do you remember trailer size vs how far you moved the mounts? Can't use your numbers, but would give me a vague idea of where to start This is a three axle 7000 kb with walking gear

 

 

[Alie&Jim's Carrilite]

This was a 34' trailer.  We had to have an overhang for the style hull on this particular craft.  We kept the same spacing.  Just moved front to rear.  

An easy way to see how much you need to move- Measure everything from the pin back- all the tank locations and heavy interior items- Washer/Dryer, fridge, hot water heater, furnace, etc.  

Send the measurements and known weights to DollyTrolly and let him work his magic.....

[spindrift]

Phew!  When I read, "Time for a Change", I first thought you were going to go with that Ford Ranger and Pop-up combination you saw at the County Fair.  

 

 

[mptjelgin]

3 hours ago, Alie&Jim's Carrilite said:

An easy way to see how much you need to move- Measure everything from the pin back- all the tank locations and heavy interior items- Washer/Dryer, fridge, hot water heater, furnace, etc.  

Send the measurements and known weights to DollyTrolly and let him work his magic.....

Actually, unless you are planning to move one or more of those heavy items, all that is required at this point is the weights that have apparently already been acquired, along with the distance from the pin to each of the individual axle locations. From that the current  trailer CG can be determined, as well as the effect of specific axle relocations. 

[Exile]

Biggest danger would be increasing the "bridge" length between your front axle and the pin increasing the bending moment.  

The frame will see additional loading there, and increased stress at the knuckles where the frame transitions from lower part to upper part, because more of the weight will be on the pin.

Frame behind your axles might not be as beefey as above your axles, and might require local stiffening for the shear load.

i would say definitely doable, but if the frame is not real strong, it might be easier to move tanks forward inside frame. 

If it is a strong frame, and the same behind the axles, i would say go for it.  

Fairings might look a little silly, and could get dicey with locations of slides.

solutions: 

weld square tubing to the underside of the frame in front of the axles (or inside the frame)

remove front of trailer sheathing under overhang and add brackets

add flat plate stiffening or tubing inside frame above new axle location if the frame is lighter back there. 

Dont burn up trailer while welding

[CrazyCooter]

I have done work like this quite a few times. The last one I did was my own toyhauler which was originally tandem axle running at or above axle's max and light hitch weight while loaded. I cut all the hangers off the ibeam and added a third axle with the wheelbase 7" longer it I'm remember right. This was a good time to add box tube under the ibeam, mounts for good shocks, and Correct Track spring hangers. I had it all photo documented, but with the photobucket shakeup.......

Divided the wheelbase divided be how much the axle group moved.  I took the scaled axle weight and subtracted the estimated unsprung weight to get sprung weight. Multiply the % of additional wheelbase by the sprung weight and you should have how much your hitch weight increased. I'm no engineer, so I assume some will correct me if I'm wrong on this.

[rickeieio]

On 8/20/2017 at 9:10 PM, spindrift said:

Phew!  When I read, "Time for a Change", I first thought you were going to go with that Ford Ranger and Pop-up combination you saw at the County Fair.  

[spindrift]

LOL...just a little photo shop?

[Exile]

On 8/21/2017 at 9:15 PM, CrazyCooter said:

I have done work like this quite a few times. The last one I did was my own toyhauler which was originally tandem axle running at or above axle's max and light hitch weight while loaded. I cut all the hangers off the ibeam and added a third axle with the wheelbase 7" longer it I'm remember right. This was a good time to add box tube under the ibeam, mounts for good shocks, and Correct Track spring hangers. I had it all photo documented, but with the photobucket shakeup.......

Divided the wheelbase divided be how much the axle group moved.  I took the scaled axle weight and subtracted the estimated unsprung weight to get sprung weight. Multiply the % of additional wheelbase by the sprung weight and you should have how much your hitch weight increased. I'm no engineer, so I assume some will correct me if I'm wrong on this.

The method mentioned above to calculate estimated new axle and pin weight assumes that the load per foot is uniform for the trailer.

probably close with the trailer empty, but i would recommend the weights for the tanks be figured separately by weighing when empty, then with one tank full, then two full, etc.

that will give you information to calculate the center of gravity for each tank, which would need to be added to the weight per foot method mentioned above.  That would get a somewhat close answer.

[mptjelgin]

Again, if the OP has scaled weights "wheel for wheel" (as he stated previously) and some indication of the current pin weight it would be very simple to calculate the current CG of the trailer, at least in the as-weighed condition. Determining the change in pin weight for variation in axle locations would be pretty straightforward. 

Now if there are a bunch of scenarios like one tank full, others empty vs. all tanks full that will complicate things. 

OP - If you'd like to send me your weights and measurements from pin to axle(s) I'll give you a hand. 

[adept99]

Ok Mark;

I have the weigh sheet from Trey & Susan. It has the Wheel-for-Wheel weights and the current pin weight. (and about any other weight you might reasonably need). I'll have to go measure the axle to pin distances. I will also get the center of the motorcycles and the washer/dryer. The smart rides behind the sleeper on the truck. We occasionally take only the smart or only the motorcycles, in which case which ever it is rides in the trailer. 

I will have to do some additional exploring to see the frame at the aft end. Will probably need to box the frame rail in the rear area and possibly add add gussets at the step up at the front of the trailer. I don't think the door or leveling system will be an issue with the addition of some longer hydraulic hoses. My local dealer can remove the fender well cut-outs and the side panels. Most of that should be reusable. Steps may present the biggest issue.

So, if having read this preliminary stuff. if you're still game. send me a PM with a phone # and email and we'll proceed.

Paul

 

 

[rickeieio]

9 hours ago, spindrift said:

LOL...just a little photo shop?

Nope, it's sitting abut 15 miles from our house, and hasn't moved in the 5 years since that photo was snapped.  It's only about 50' off the highway, and you can hardly see it through the weeds.

[noteven]

Rick - are there run off scars in the ditches and crops both ways from the RV Weight Police ditchin 'er after catching sight of this combination?

[rickeieio]

I came past it again last evening. Weeds as high as the roof of the truck, but mostly mowed around it.

It's along a two lane state route, just south of Batesville, Indiana.

 

[Dollytrolley]

On 8/20/2017 at 4:28 PM, adept99 said:

Cut right to the chase. We're getting some waggle out of our trailer. With the Smart loaded and both motorcycles loaded, you don't notice it too much. Take the Smart off the truck and things get sloppy quickly. I've talked to Trey & Susan and had them weigh the rig, wheel for wheel. Bottom line is that we're really light at the pin and heavy at the tail. We're already a tad overweight so just adding weight isn't really a good answer either. Most of the heavy stuff can't really be moved, like motorcycles and washers and dryers.

SO.....

Has anyone else tried moving the rear axle mount(s) further to the rear?? Yes, I understand I need to verify the design load and a wad of other issues. First among them would be determining the distance needed to move. Any "Nuts...Didn't think of that" items??

Paul 

 

Paul.

I don't want to sound presidential however.........I have been unfairly charged with being a truck / trailer Weight & Balance nerd just because I cobbled-together a live data spreadsheet to calculate actual truck / trailer combo loading's in real time.........it's darn unfair being a Wt &Bal nerd, but at least the president has a airplane with good leg room.......

 

I would be happy to email you my truck / trailer live data spreadsheet and you can have a ton-of--fun moving axles, hitches, smart cars , scooters, and gold bars to various locations and in the bat of a eye the spreadsheet will give you axle loads, pin loads and C G locations ...........

 

Now some floks may think that I am a nerd but actually folks that know me might tell you that I tend to be somewhat lazy with way too much "stuff" on my "too-do-list" so that is why I cobbled up the Wt & Bal spreadsheet........sorta true but in reality the real reason is that our RV combo tends to be configured pretty odd with fairly long distances (arms) to highly variable mass (load) points so I use the spreadsheet to keep some order to the rig(s) balance profile........better balance, better trips, just what a lazy person wants.

 

Now I have no formal education in vehicle dynamics however I was the "lab-rat" that had to test various "vehicles" that were configured by some very "big-brain-engineers" that I spent way too many years watching them trying to keep the "lab-rat" alive. So where am I going with this babbling.........well perhaps before getting out the smoke wrench and cutting a bunch of axles out of your rig........perhaps it might be wise to stand way back and take a wide angle view of your entire rig......

MANY factors compose your vehicle dynamics and longitudinal-Weight & Balance is just one of many factors, you likely could benefit from considering Vertical C G , and a huge factor is suspension including tire configurations.......often tires can solve or add to unstable tows.....

For the most part RV trailer suspensions are simply crap and MUCH can be done to improve the handling of trailers with better suspension.

If you would like to try the Wt & Bal spreadsheet simply send me a email at   mmcdan3189@aol.com and I will send the spreadsheet file via return email. If you want to chat try my cell (520) 891-3695.

 

Drive on...........(Better vehicle dynamics......better trip)

[lockmup68]

is the trailer level when hooked up? if front is high, will shift weight to the back. Even two inches high will make a difference in towing.

[adept99]

Well, just got back from the sawbones' office. We're gonna do a total reverse shoulder replacement on Sept 6th, which will put me out of commission about 8 weeks before I can drive at all, and about 6 months before  I can do something like relocate the axle positions on the trailer.

Thought I'd like to thank the folks (mptjelgin, CrazyCooter, and DollyTrolly) that responded with formulas and calculations to help me figure out how far to move the axles.  Looks like this can be done without running into the door, steps, or leveling cylinders. Skirt will need to be "adjusted". 

Thanks again;

Paul

 

[Dollytrolley]

On 8/20/2017 at 4:28 PM, adept99 said:

Cut right to the chase. We're getting some waggle out of our trailer. With the Smart loaded and both motorcycles loaded, you don't notice it too much. Take the Smart off the truck and things get sloppy quickly. I've talked to Trey & Susan and had them weigh the rig, wheel for wheel. Bottom line is that we're really light at the pin and heavy at the tail. We're already a tad overweight so just adding weight isn't really a good answer either. Most of the heavy stuff can't really be moved, like motorcycles and washers and dryers.

SO.....

Has anyone else tried moving the rear axle mount(s) further to the rear?? Yes, I understand I need to verify the design load and a wad of other issues. First among them would be determining the distance needed to move. Any "Nuts...Didn't think of that" items??

Paul 

 

Paul,

IF you re-read your original post above you might ask yourself............why does the trailer behave better when I have the Smart car loaded on the truck ?  ?  ?

Think about that for a moment ..........loading the Smart car on the bed of the truck has "diddly-squat" (Engineering term) to do with your trailer hitch pin weight......zip, none.....nadaa

The term that would likely be used by vehicle-dynamics-geeks would be .........damping......

[ In engineering, the damping ratio is a dimensionless measure describing how oscillations in a system decay after a disturbance. Many systems exhibit oscillatory behavior when they are disturbed from their position of static equilibrium. A mass suspended from a spring, for example, might, if pulled and released, bounce up and down. On each bounce, the system is trying to return to its equilibrium position, but overshoots it. Sometimes losses (e.g. frictional) damp the system and can cause the oscillations to gradually decay in amplitude towards zero or attenuate. The damping ratio is a measure of describing how rapidly the oscillations decay from one bounce to the next.

The damping ratio is a system parameter, denoted by ζ (zeta), that can vary from undamped (ζ=0), underdamped (ζ<1) through critically damped (ζ=1) to overdamped (ζ>1).]

So in non-engineering terms what does all that gobbly-gook mean.........well it means that by loading the Smart car mass (load / weight) onto the truck you have INCREASED the trucks ability to stabilize the "natural oscillations" inherent in the trailer that you have.

Increasing trailer hitch pin weight is a "URBAN-LEGEND" here on the forum........heavy pin weights are NOT 100% cure for unstable tows.

Listen to your truck....it is trying to tell something......listen and stand back and study what is really happening.

IF you have to get out the torch and welders and forklifts and charge off and make some "blind-changes".......perhaps you just might go back out to the truck bone-yard and throw a chain around the old power-divider-axle and change the old rig from single to tandem ......again........tandem adds a HUGE ratio of DAMPING to a rig.

What you are proposing to do to your trailer is not easy-peasy to do correctly.......

Now that I have likely ticked-off many of the forum members that read this post perhaps I offer a more subdued suggestion(s)

Suggestion #1:

Perhaps Paul you might try to have another forum member singled HDT tow your trailer and see if perhaps your unloaded truck may need some tire or suspension work done to provide better damping when the Smart is off loaded.

Suggestion #2:

Perhaps Paul you might try to have another forum member tandem HDT tow your trailer and see if perhaps your unloaded truck may need a tandem axle to provide better damping when the Smart is off loaded.

Likely adding the tandem back to the truck might be less cost and headache than "molesting" the typical "gawd-forsaken" "structure" that almost all RV trailers are composed from.........

Ok folks flame away..........

 

Drive on.............(try to damp-down your........ oscillations s  s   s     s     s.........)

[rickeieio]

6 minutes ago, Dollytrolley said:

Suggestion #2:

Perhaps Paul you might try to have another forum member tandem HDT tow your trailer and see if perhaps your unloaded truck may need a tandem axle to provide better damping when the Smart is off loaded.

Some dumb ol' farm boy suggested just that, a coupla weeks ago.  I offered to "swap" trailers on the way home from North Carolina, cuz following him was soiling MY shorts.

Looks like we might get to play with RV Dynamics" while Paul is healing.

[Sculptor]

Rick, you didn't even call while you were here?

 

 

[Dollytrolley]

1 minute ago, rickeieio said:

Some dumb ol' farm boy suggested just that, a coupla weeks ago.  I offered to "swap" trailers on the way home from North Carolina, cuz following him was soiling MY shorts.

Looks like we might get to play with RV Dynamics" while Paul is healing.

OK Ricko-oh-ho............

Farm-boy-tows don't count........shucks everybody knows that the side mirrors on the old corn-binder got broke when the frozen sillage slid out the back of the dump last hard freeze and broke the glass out of all the mirrors when the front wheels hit the frozen ground........and if you bit the tip of your tongue off that's what ya get for driving around the farm with your mouth open .........

Likely your right Rick-oh..........and of course not looking in the mirrors helps prove your right........

 

Drive on..........(Don't dump the truck with your mouth ......open)

 

[WLee]

On the subject of the shoulder. I had the Delta reverse sholder replacement about 2-1/2 years ago on my right shoulder  and no regrets! The only drawbacks are scratching you back, (or butt),limited amount of weight I can pu over my head, getting off the floor from a laying position.

  The pain level is a little rough for about 2 weeks. I will have the Left replaced as soon as I get a few more thing done around the house.

Good luck!!

[rickeieio]

11 hours ago, Sculptor said:

Rick, you didn't even call while you were here?

We were in Marion, riding the roads running up and down along the BRP.  Are you close to there?

Watching Paul that week, it was painful to see him use his left hand to assist his right arm.  He even used the left ot get his right to the handlebars.  I hope I never get that old........