Jack Mayer Posted April 1, 2016 Report Share Posted April 1, 2016 The 16.7% pin situation Henry speaks of was never really resolved. It was only masked by changing to a super-pickup (from an HDT) which allowed the dynamics to be more "hidden". But the situation still exists. And it could cause an issue in the future in less than "ideal" conditions. While that situation was somewhat "unusual" because of the large weights involved, the same thing exists - to a lesser extent - with lighter overall weights that are out of balance on the low end. Jack & Danielle Mayer #60376 Lifetime Member Living on the road since 2000PLEASE no PM's. Email me. jackdanmayer AT gmail 2016 DRV Houston 44' 5er (we still have it) 2022 New Horizons 43' 5er 2016 Itasca 27N 28' motorhome 2019 Volvo 860, D13 455/1850, 236" wb, I-Shift, battery-based APU No truck at the moment - we use one of our demo units 2016 smart Passion, piggyback on the truck -------------------------------------------------------------------------See our website for info on New Horizons 5th wheels, HDTs as tow vehicles, communications on the road, and use of solar powerwww.jackdanmayer.com Principal in RVH Lifestyles. RVH-Lifestyles.com Link to comment Share on other sites More sharing options...
RickS Posted April 1, 2016 Report Share Posted April 1, 2016 You would think that a design of a toyhauler would be biased toward a heavier pin weight when empty to compensate for the max load capacity of the garage. Once loaded reducing some pin weight from the teeter-totter effect while still leaving a safe pin weight. But, I am no RV designer....... Maybe, someone should make these types of conversations available to those designers. Rick & Carey,Excel W41GKE Wild Cargo Toyhauler Volvo 730, D13, I-shift, 500/1850Brabus Smart Car Link to comment Share on other sites More sharing options...
phoenix2013 Posted April 3, 2016 Author Report Share Posted April 3, 2016 Once we have confirmed numbers we can give you a better answer. But in general, on an MDT or HDT (that can take the weight) I consider around 23-25% pin weight to be ideal. Anything under 18% is pushing the bottom end to me. That is MY OPINION, based on experience. RVIA says 16% is the low end of 5th wheel pin weight. For what it is worth. My personal opinion pulling such light pinned trailers is that they are OK in ideal conditions, but they can be a "handful" as soon as anything changes from the "ideal". Again, MY opinion, only. And it does vary somewhat based on WHAT you are pulling them with. Jack, it's a big website, any specific section where it could have been mentioned? Or was it another of their sources. Link to comment Share on other sites More sharing options...
Alie&Jim's Carrilite Posted April 3, 2016 Report Share Posted April 3, 2016 You would think that a design of a toyhauler would be biased toward a heavier pin weight when empty to compensate for the max load capacity of the garage. Once loaded reducing some pin weight from the teeter-totter effect while still leaving a safe pin weight. But, I am no RV designer....... Maybe, someone should make these types of conversations available to those designers. It makes sense if you think about it.... How many times have you seen a large toy hauler- triple axle- being pulled by a SRW truck? By keeping the pin weights in the light end - low %, they have a larger market to sell to. 2500-3000lbs of pin will make any LGT seem or feel ok until something goes wrong like a bridge bump or the spacing of the concrete that sets up the bump and bounce dynamics. Alie & Jim + 8 paws 2017 DRV Memphis BART- 1998 Volvo 610 Lil'ole 6cyl Cummins Link to comment Share on other sites More sharing options...
Dollytrolley Posted April 3, 2016 Report Share Posted April 3, 2016 The 16.7% pin situation Henry speaks of was never really resolved. It was only masked by changing to a super-pickup (from an HDT) which allowed the dynamics to be more "hidden". But the situation still exists. And it could cause an issue in the future in less than "ideal" conditions. While that situation was somewhat "unusual" because of the large weights involved, the same thing exists - to a lesser extent - with lighter overall weights that are out of balance on the low end. You would think that a design of a toyhauler would be biased toward a heavier pin weight when empty to compensate for the max load capacity of the garage. Once loaded reducing some pin weight from the teeter-totter effect while still leaving a safe pin weight. But, I am no RV designer....... Maybe, someone should make these types of conversations available to those designers. Jack, it's a big website, any specific section where it could have been mentioned? Or was it another of their sources. It pains me to watch the hand-wringing and wild-A$$-Guessing going on regarding the marginal pin weights and the rather clueless attempts to make changes about how much and where "consumable-loads" and cargo-loads should or could be shifted to help or hinder the RV safety and stability. OK what I am about to say WILL get me flamed so be it....... "Everyone" seems comfortable with individual wheel position weights..........and this is good.....to a point.......AND THAT point is that now you have defined a "BASELINE-WEIGHT & BALANCE"!! NOW get out the flame-throwers........Once you have obtained a "BASELINE-WEIGHT & BALANCE" life starts to become complicated because the "DEVIL IS IN THE DETAILS".........ANY and I mean ANY change to shifting loads in your RV has now changed your "BASELINE-WEIGHT & BALANCE"...........yes children taking a shower , flush the toilet, take the Hog out of the garage....or put a Equine in the garage and all of a sudden your "BASELINE-WEIGHT & BALANCE" is invalid.....kuput....nadaaa,......it's just a bunch of bad numbers on a sheet of paper.....oh sure you could "Guesstimate" the mass (weight) change and you might get close but the change to the CG location (Balance) has proven to be HUGELY in error from what I have observed here on the forum and out on the road. The "BASELINE-WEIGHT & BALANCE" IS A VITAL........BASELINE........Thats it .....Just a BASELINE ......it's a starting point only!! Once you have a "BASELINE-WEIGHT & BALANCE" your RV's day to day Weight & Balance just to need some fairly SIMPLE accounting for mass (weight) and CG (Balance) changes that occur over time in order to MAINTAIN a reasonable awareness of the RV's actual Weight and Balance for a given point in time. OK I feel the flames and heat but my skin is Rhino-thick so it's just part of the fun ........so folks will say BIG deal I am retired and I don't want to become a RV-Weight & Balance-accountant and of course that is your choice .....and some folks say "so what if I do keep my day to day RV Weight & Balance current what do I gain? Well the gain is that with the REAL and CURRENT RV Weight & Balance you can then Quickly calculate moves of mass (weight) to different locations in such a manner to optimize the RV safety and handling...... Many folks seem afraid of the "advanced math" involved in the Weight & Balance accounting.........NOT so ......it is third grade addition, subtraction, multiplication ..........and that hard one Division...........and of course all of these "math" functions all ready in the live data spreadsheet so all you have to do is measure back from the front axle of your truck to the various load centers and from the hitch pin on your trailer back to the load centers then add the various weights and the spreadsheet calculates everything LIVE...... This is NOT Rocket science!! I have some input of the Percentage of pin weight that is 'kosher'....... but...... of course folks will need to refuel the flame throwers before I make that posting..... Flame me I have my nomex speedo on Drive on........(What are your real ........numbers??) 97 Freightshaker Century Cummins M11-370 / 1350 /10 spd / 3:08 /tandem/ 20ft Garage/ 30 ft Curtis Dune toybox with a removable horse-haul-module to transport Dolly-The-Painthorse to horse camps and trail heads all over the Western U S Link to comment Share on other sites More sharing options...
Hewhoknowslittle Posted April 4, 2016 Report Share Posted April 4, 2016 It pains me to watch the hand-wringing and wild-A$$-Guessing going on regarding the marginal pin weights and the rather clueless attempts to make changes about how much and where "consumable-loads" and cargo-loads should or could be shifted to help or hinder the RV safety and stability. OK what I am about to say WILL get me flamed so be it....... "Everyone" seems comfortable with individual wheel position weights..........and this is good.....to a point.......AND THAT point is that now you have defined a "BASELINE-WEIGHT & BALANCE"!! NOW get out the flame-throwers........Once you have obtained a "BASELINE-WEIGHT & BALANCE" life starts to become complicated because the "DEVIL IS IN THE DETAILS".........ANY and I mean ANY change to shifting loads in your RV has now changed your "BASELINE-WEIGHT & BALANCE"...........yes children taking a shower , flush the toilet, take the Hog out of the garage....or put a Equine in the garage and all of a sudden your "BASELINE-WEIGHT & BALANCE" is invalid.....kuput....nadaaa,......it's just a bunch of bad numbers on a sheet of paper.....oh sure you could "Guesstimate" the mass (weight) change and you might get close but the change to the CG location (Balance) has proven to be HUGELY in error from what I have observed here on the forum and out on the road. The "BASELINE-WEIGHT & BALANCE" IS A VITAL........BASELINE........Thats it .....Just a BASELINE ......it's a starting point only!! Once you have a "BASELINE-WEIGHT & BALANCE" your RV's day to day Weight & Balance just to need some fairly SIMPLE accounting for mass (weight) and CG (Balance) changes that occur over time in order to MAINTAIN a reasonable awareness of the RV's actual Weight and Balance for a given point in time. OK I feel the flames and heat but my skin is Rhino-thick so it's just part of the fun ........so folks will say BIG deal I am retired and I don't want to become a RV-Weight & Balance-accountant and of course that is your choice .....and some folks say "so what if I do keep my day to day RV Weight & Balance current what do I gain? Well the gain is that with the REAL and CURRENT RV Weight & Balance you can then Quickly calculate moves of mass (weight) to different locations in such a manner to optimize the RV safety and handling...... Many folks seem afraid of the "advanced math" involved in the Weight & Balance accounting.........NOT so ......it is third grade addition, subtraction, multiplication ..........and that hard one Division...........and of course all of these "math" functions all ready in the live data spreadsheet so all you have to do is measure back from the front axle of your truck to the various load centers and from the hitch pin on your trailer back to the load centers then add the various weights and the spreadsheet calculates everything LIVE...... This is NOT Rocket science!! I have some input of the Percentage of pin weight that is 'kosher'....... but...... of course folks will need to refuel the flame throwers before I make that posting..... Flame me I have my nomex speedo on Drive on........(What are your real ........numbers??) Great post Dolly, This is the reason I am getting my rig weighed at the ECR and will post my weights. I have a 610 Volvo with a steel bed and a 43 foot DRV Atlanta that I am sure is pin light. The tail does wag at high speed, keep her under 65 and all is well, but I like to run at posted speeds at my young age. Roger Link to comment Share on other sites More sharing options...
phoenix2013 Posted April 7, 2016 Author Report Share Posted April 7, 2016 OK, no project that I have known comes off 100% right off out of the gate. Although (after decades) I claim membership in the 95 percenters club, here's the 5% that I need to solve. I have a solution but I want to give you guys a shot at it. The problem. Looking more carefully at the response characteristics of this particular bump I noticed that it is pretty flat for a considerable height differential before it accelerates I have built in a preload compression into the system. The hitch at the design height settles to within 2 inches down from the upper stops, therefore it can compress the bump 2 inches within that travel. In addition the bump projects 1.58 inches down below the upper surface of the platform, therefore it is already pre-compressed by that height when the hitch inflates and settles at the design height. Looking at the graph at 1.6" pre-compression the bump only produces about 100 pounds of resistance (or 200 for two of them). In the scheme of pin weights this seems somewhat pitiful in my mind. At full travel to the stops (3.6 inches, 1.6 inches of pre-compression plus 2 inches of travel to the stops) according to the graph we are still only at 500 pounds of force (or 1,000 pounds for two of them). I also don't expect things to go all the way to the stop (except on really, really bad roads) in normal operation. So I think I would like to see a bit more of response and "aggressiveness" out of this bump. I miss those engineering design reviews where one's ideas are open to praise, criticism, or "improvements". I already have a solution which I will implement and try on the prototype to do this, but I also wanted to give you "geniuses" a chance to contribute. Let the engineering begin! Oh, there is also another "little problem" that has to do with the field installation, for which I have solution, but lets deal with one thing at a time. Link to comment Share on other sites More sharing options...
Mastercraft Posted April 8, 2016 Report Share Posted April 8, 2016 Ok, I'll bite. In the engineering world, the temptation is to develop a solution before the requirements are fully understood or solidified. I have had systems engineering types come to me well into the development cycle and say "now....how does that work again?" yet, here I go ........ If we make a simplistic model of the original unsnubbed system, the force vs displacement relationship has three segments, a linear region in the 0 to 5" travel, with the force going to negative infinity at 0" (topped out) and pos infinity (bottomed out). The snubbed system is about the same except at the 3" sled position, the snubber f=kX personality is summed with the air spring personality....so, the linear region now has a bit of a second order hook to it for sled positions in the 0 to 2" range (ignoring the preload for simplicity). It seems that no damping was added to the snubbed system, so the Q could remain quite high.....maybe at a different frequency. It is likely that the frequency the system will Q up on (start the large displacement floating) will be driven higher, indicating a stiffer system (counter to the ET design intent). The approach may help some applications but is likely to have limited wide success considering the many variations and contributing factors that result in a "floater". Ok, so what would add damping, have adjustability features, not too high cost, and be field retrofittable w/o a mobile machine shop and welding equipment? Maybe a COTS shock absorber. The drag racing crowd uses dual adjustable units that are available in various travel lengths. You can set the damping rate for extend a retract individually. One could set these up to have a lesser effect for air spring compression (maintaining the light touch of the ET hitch) and a greater effect on air spring extension (reducing the systems ability to self excite). There are a bunch of manufactures for these shocks and they come in various stroke lengths, some near 6". Check out Summit Racing, Jeggs, etc http://www.strangeengineering.net/make-and-model/ford/shocks-struts-springs/bolt-in-shocks-struts/79-93-mustang-alum-double-adj-shock-ea.html Henry - you are the master of fun projects. I always enjoy reading about your development process. Rich 2009 Volvo 780 D16 535hp 1850 ft-lbs I shift 3.36 Thermo King Tripac APU DIY Bed and Frame Extension ET Hitch, Stellar EC2000, EcoGen 6K 2002 F350 CC Dually w/ Lance 1181 2012 Mini Cooper S 2007 Teton Royal Freedom " The only place you will find success before work is the dictionary " Link to comment Share on other sites More sharing options...
Star Dreamer Posted April 10, 2016 Report Share Posted April 10, 2016 Looks like you need to increase the preload to about 2-1/2" but at full compression you could max out the bump, so you may want to go just a little bit less. Dave 2005 Freightliner Century S/T, Singled, Air ride ET Jr. hitch 2019 46'+ Dune Sport Man Cave custom 5th wheel toy hauler Owner of the 1978 Custom Van "Star Dreamer" which might be seen at a local car show near you! Check out http://www.hhrvresource.com/ for much more info on HDT's. Link to comment Share on other sites More sharing options...
NoDirectionHome Posted April 20, 2016 Report Share Posted April 20, 2016 This might be a simpler answer to what you're trying to solve: http://www.hendrickson-intl.com/CMSPages/GetFile.aspx?guid=9ac18176-0c81-498d-8545-a260e44a94ea "There are No Experts, Do the Math!" 2014 Freightliner Cascadia DD16 600hp 1850ft-lb 18spd 3.31 260"wb SpaceCraft S-470 SKP #131740 Link to comment Share on other sites More sharing options...
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