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Old 07-11-2017, 05:35 PM   #1
Johnny's Journey
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Question WTH set-up and tire pressure affect.

Took the 202 out for it's first outing to Zion from LA and back. This is how it was set up. (From a prior posting) > "So far so good. I left the dealer last week with the trailer only on the ball since the unit was empty except for fresh water fill (aft of rear axle). I already knew my ball needed to come up 1 but the truck for only being a 1/2 ton really surprised me. Only a 1 1/2" drop in the back with still a rake up out back and front only came up 1/2". That's right where things should be with WDH installed per instruction. Made my kind of afraid to use it. My brain had me thinking it would handle like a rear heavy trailer if I used it. But I installed it and it's doing well. I've got it dialed for now with 1" down in the back and front right back where it sit's unloaded. Also reduced fresh water to half tank and front pass thru is loaded with belongings." Back to the trip in question. While driving I was watching everything my truck could tell me. Various temps, rpm vs mph, so on and so forth and tire pressure's. Tire pressure caught my attention. The front tires were at a higher pressure than the rear. My truck never runs that way and I double checked it today unloaded. All four corner's were even by 1 lbs unloaded and loaded during the trip the front's were 5 lbs higher. Does it seem that I'm to front end to heavy and back end lite because I have the bars set to tight ? This was set @ 6 links which is easy to pull up with the bar and @ 7 links I can pull the lever by hand without the bar but it does have an affect even though it soft @ 7 links. And yes, I had the tongue and hitch raised 3'' higher when attaching the chains which takes tension off when placing them.
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Old 07-12-2017, 02:59 AM   #2
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Dialing in weight distribution can be a pain for sure. You should take another look at the hitch manufactures installation instructions as they will tell you how much the front and rear should move (measured) from unloaded height. Ideally with WD, you want to return the front to unloaded weight or as close as you can.

My recommendation would be to dial in the ride height of the trailer, once you get the WD bars in place, then go hit the truck scales. If you have time and attention, weigh the truck fully hitched and empty/unhooked. Bring that data back and plug it into one of the many tools available to calculate and present you with your realistic weight numbers (like this one).

As for tire temps, if you're using O2 and not Nitrogen, they're obviously going to rise from ambient temp when combined with heat and load. My toy hauler tires for example, will rise as much as 15 degrees rolling down the road supporting the 16k pounds of load. The most common rule of thumb for tire pressure when towing, is to air them all the way up to the "cold inflated maximum pressure" defined on the sidewall (or close to it). That will give you maximum load carrying capacity. If you have different tires from stock and/or custom wheel setup, make sure the wheels can support the maximum pressure of the tires cold.
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Old 07-12-2017, 03:29 AM   #3
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Ok, I'm curious. "Ideally with WD, you want to return the front to unloaded weight or as close as you can." If you aren't sending any weight to the front axle then where exactly would the weight be distributed to.....?
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Old 07-12-2017, 05:31 AM   #4
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Ok, I'm curious. "Ideally with WD, you want to return the front to unloaded weight or as close as you can." If you aren't sending any weight to the front axle then where exactly would the weight be distributed to.....?
I'm curious also and my question is a bit premature without some hard facts to back up my theory. As xcntrk mentioned above to answer the question I need to scale things. In order to get 100% accuracy I'll need to borrow the scales from my Son's work that they use to tune race car suspensions. That way I can see exactly the + and - that's happening at each axle.
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Old 07-12-2017, 08:53 AM   #5
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WD hitches do send weight forward, that's the whole point. What you're not considering is that with a bumper tow trailer, all the weight that is incurred from the tongue sits on the rearmost point of the truck. Like a pendulum, that weight gets loaded onto the rear axle sagging the rear suspension and lifting the front of the truck as weight from the front shifts to the rear. So as soon as you hook up your trailer (without weight distribution) the front end is considerably lighter that when weighed empty, with that weight having moved to the rear of the truck.

A weight distribution hitch will move some of that weight back towards the front. In my experience towing many bumper tow trailers with WD hitches and using different TV's, the very best I've ever been able to accomplish is to get the front axle weight back to the unloaded amount using WD. Actually seeing MORE weight in the front than what is measured empty is very unlikely with a bumper tow application (obviously 5th wheel is a different experience). I have numerous scale tickets and weight analysis to support this point.

But all that aside, the OP should go weigh his rig empty, then weigh it with the trailer and WD to see for himself
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Old 07-12-2017, 08:54 AM   #6
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Originally Posted by Johnny's Journey View Post
I'm curious also and my question is a bit premature without some hard facts to back up my theory. As xcntrk mentioned above to answer the question I need to scale things. In order to get 100% accuracy I'll need to borrow the scales from my Son's work that they use to tune race car suspensions. That way I can see exactly the + and - that's happening at each axle.
Depending on your location, running across the CAT scales might be easier. It's cheap, $20 bucks for your first weigh and I think that includes 1 additional re-weigh. All you do is drive over them.
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Old 07-12-2017, 09:22 AM   #7
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I agree, CAT scales are easy to use. First weight is $11, Second one is $2 additional, and third one is another $2....for a total of $15. Three weights should give you every bit of info you need about the truck and the trailer.

First weight is truck and trailer with WDH used just like when you travel.
Second weight (do not move off of the scale), loosen up the WDH completely so that it is no longer is in use. You don't need to remove it, just loosen it up. Push the button and tell the operator you need a second weight...or re-weigh. Once completed drive of the scale and drop the trailer.
Third weight....truck only this time...no trailer.

Hook back up and drive home with your three scale tickets, then go to this website and follow the procedure for tow behind trailer calculations. Do the worksheet first, that way you have the numbers you need handy for the calculation step.....

http://fifthwheelst.com
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Old 07-12-2017, 09:32 AM   #8
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Front end weight using WD:

Here’s an example of what I’m talking about using real scale numbers and analysis. Here you can see that the TV (an F150) has an empty steer axle weight of 3700#. When the TT is hooked up to the bumper hitch (no WD) the steer axle has lightened to 3420# with 280# of the trucks own weight having shifted from the front to the rear, due to the rear sag (pendulum effect). So now the rear end is supporting both the 780# of tongue weight incurred by the trailer AND the 280# of weight that has shifted from the front.

Now apply WD to that configuration and you can see that the steer axle is almost returned to its unloaded weight with the WD system pushing 240# back to the front of the truck using the magic of leverage (which I won’t get into here). You’ll also notice the WD system has distributed 200# of the tongue weight back into the trailer as well.

…and that, is a perfect example of how you want to restore the front-end to the unloaded axle weight as a target for WD setup.
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Old 07-12-2017, 04:29 PM   #9
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Quote:
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Here’s an example of what I’m talking about using real scale numbers and analysis.
Nice spread sheet, Thanks. Dumb question. How can or how does a Cat Scale tell me front and rear axle weight of the tow vehicle? Or do I do it by placing one axle at a time on the scale which would be impossible because trailer is attached. This is why I mentioned earlier about using four corner scale's. It's free to me to use and I can do all the tweaking I want without having to tie up a public scale and come up with a neat spread sheet like above. I'm no stranger to physic's and cause and affect's. To further the theory of too much spring bar tension came today in the form of examining the receiver and the shank. It's pulling up very hard per the gouging marks left behind on the top of the shank closest to the ball and the bottom of the shank furthest away from the ball. Now back to science. I can also try driving at 7 links vs 6 links and see what happens with tire pressure. Science is fun, one just needs to be willing to experiment. "What I cannot create, I do not understand" Richard Feynman
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Old 07-13-2017, 05:28 AM   #10
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CAT scales have three platforms - one for the front axle, one for the rear axle(s) and one for the trailer axles.
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Old 07-13-2017, 06:23 AM   #11
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^I've even seen some that have 4-platforms. I guess for "pup" axle tractor trailers. Just put an axle on each pad and you're good to go. Each pad with weight on it will show up on the scale ticket.
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Old 07-13-2017, 03:34 PM   #12
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CAT scales have three platforms - one for the front axle, one for the rear axle(s) and one for the trailer axles.
Excellent
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Old 07-13-2017, 03:35 PM   #13
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^I've even seen some that have 4-platforms. I guess for "pup" axle tractor trailers. Just put an axle on each pad and you're good to go. Each pad with weight on it will show up on the scale ticket.
Dumb questions do pay off
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