J2807 falr

[Dustyhd]

Continued from another thread;
“J2807 has brought about change to the latest trucks. My goal on the 4th gen Ram is to keep steer weight as close as possible to the unloaded steer weight. My understanding & experience is this generally retains the best COG as well as the full braking power/traction. Towing this makes for a stable truck/suspension and trailer.”

Contrary to what many believe using a WD to restore unloaded steer weight doesn’t return its COG. The lever of the WD will increase the downward force(weight) on the front steer axle but it physically moves very little mass back forward that it lost due to the addition of TW. This is the very reason they recommend a lower FALR now. Higher amounts of WD reduces the vertical load on the tires which in turn reduces its ability to grip and control the inertia from the mass that still exists rearward. Adding TW to any vehicle reduces understeer, using any amount of WD will reduce it further. The ideal balance is to use as little TW required to maintain sway performance so the amount of WD required is less. An example. My current TT is just shy of 8k loaded and I can tow it comfortably at 60mph with 12% TW, no WD or sway control, and no loss of steering compliance.

[jrm1493]

I think I'm general you are correct but with a half ton you might need some weight dist to avoid going over your rear axle limit, esp with a heavier trailer. But most likely less than full return, probably about 50%, although I believe Ford is only recommending 25%. I would go by whatever ram recommends. But definitely not equal drop or even 100% return.

[jrm1493]

I've also been looking at the Andersen hitch recently as it's sway control is basically independent of weight distribution... While I think friction sway control won't fix a true loading issue it can't hurt. I don't own it yet but the design to me seems Taylor made for j2807.

[VernDiesel]

Never been a math major or claim to be the smartest guy in the room but do always seek to better understand. Ok you say using WD doesn't return much of its COG as it physically moves very little mass back forward. Got it. Although anything has to be better than nothing. Also how does putting more weight on the steer tires as proven by the scales reduce the verticle load on the tires and reduce their ability to grip the road? I mean having more weight on the drive and allowing the steer axle to be lighter than unloaded weight doesn't improve your COG, stability, or steer traction to my understanding and especially not to my experience with semi truck bowave or doing any kind of emergency swerve around with the trailer.

The ideal balance is to use as little TW as required to maintain (trailer) sway so the amount of WD required is less. Agreed. I generally shoot for 12.0% as it seems to work best with my truck at least to my normal 65 mph tow speed. As jrm notes keeping under drive axle limits also comes into play. Also interesting that Andersen is the only WDH that has sway control independent of WD. fwiw I use the Andersen WDH.

[Dustyhd]

“Also how does putting more weight on the steer tires as proven by the scales reduce the verticle load on the tires and reduce their ability to grip the road?“
Sorry for the confusion, I was referring to the rear tires.

“ I mean having more weight on the drive and allowing the steer axle to be lighter than unloaded weight doesn't improve your COG, stability, or steer traction to my understanding and especially not to my experience with semi truck bowave or doing any kind of emergency swerve around with the trailer.”
This is a lot to cover technically and beyond what I care to type, but I’ll try to address as basically as possible.

Minimizing TW along with TV mass/distribution and wheelbase is what controls TV COG location. As the TV COG moves towards the rear axle, yaw stability is reduced just like when the trailer COG moves rear towards its axles. WD won’t change this.

Steering traction as you described I think is really understeer/oversteer. It is quantified as understeer gradient which is essentially the change in steering response between the unloaded TV and then with TW applied. WD applied may make the front feel better but it also in turn reduces rear cornering ability, again there’s a balance and practical limit each way.
To really get a handle on it you need to understand how loading effects a tires cornering stiffness/slip angles. Adding WD reduces rear tire cornering stiffness and that reduces its ability to withstand the inertial forces of tongue mass that’s still right where it was put.

[jrm1493]

I think Dusty gave a good explanation... probably the key thing to understand is that WDH does not move the c.g. at all, which is the point about which the vehicle rotates. All WDH does is change the vertical load on the rear and front axle (increase it in the front, and reduce it at the rear). It thereby improves the grip of the front, and reduces it at the rear. BUT, since the c.g. stays further aft with WDH use, the steering authority is dramatically improved (more grip + longer moment arm over which to act). Sounds great, but you also lose both grip and moment arm at the TV rear axle, and that sets you up for a bad situation if overdone, because you don't ever want your rear axle to lose grip before the front or trailer axles... that would be basically impossible to control.

I'm not advocating not using WDH, I use one myself, but I think that most are probably over-adjusted, in order to give a better "feel" which in fact is more steering authority, but it comes at the cost of a loss of rear axle grip and combination vehicle stability "at the limit". When I first got my trailer the dealer set it up for about 120% return, and it felt pretty good and responsive... now that I'm down to around 50% (GM recommendation), it is definitely not as responsive, but it also feels much more damped, less lively, which I like. I think on long trips its less tiring this way because it just seems to want to go straight...

[VernDiesel]

Sorry I should have figured out you meant drive tires that does make more sense. Reason I first thought of steer tires is because the wrecks you see on the highway and in Youtube videos is that of people with too little or no WD and very little weight on the steer. They are usually the "white knuckle rides" often with trailer sway and what you see end up backwards upside down it the ditch the first time they have to try to swerve around somebody.

Yes good understandable explanation. "again there’s a balance and practical limit each way." Agreed the whole exercise is more about determining what this is using or within MFG specs for a given vehicle. At least that is how I see it.

"Adding WD reduces drive tire cornering stiffness and that reduces its ability to withstand the inertial forces of tongue mass that’s still right where it was put." Yeah because you are transfering weight off the drives even though its still more weight on them than when the truck is unloaded just that I think as you are pointing out that this is more than overcome by the additional push against them from tongue and trailer weight. The same push that wears your drive tires out faster than when there is no TW / trailer weight. Curious as to your thoughts on this. Started towing with the P275/60/20s. Have two sets of stock rims. Have tried 265/60/20 E loads and the 275/55/20 XL loads that manufacturers including Ram have now went to. Both far better than stock tires with say common 6 to 900 pound TW. To my surprise the slightly shorter lower profile XLs seem to feel better than the stiffer heavier but taller E loads. Both wear well with proper for the load inflation. That said lol I have not pushed a corner to the point that the trailer breaks the drives loose.

Back to the whole exercise is about more concretely determining what generally is the best guidline using or within MFG specs. Agreed lightest TW necessary to maintain trailer sway control. Seems with relatively new half tons this is safe with 12.0% as a goal or more broadly the 10 to 15% range. Steer weight I still have a hard time coming to terms with suggesting less than close as you can get to unloaded steer weight assuming good drive tires. Because I haven't seen much evidence of wrecks being caused by lack of drive traction especially with now common 4wd. But then generally other than someone describing it how would you see evidence of this in a typical non in-climate weather loss of control TT accident. How would you guys recommend Joe lunchbox with 5 year old half ton and a new larger TT set his rig up for stability & family safety?

[Dustyhd]

I’ve been using less than 50% FALR for over 15 years so it has nothing to do with the age of the truck, it’s basic physics. They should still try to follow the new formula if they can but many don’t understand the reasoning behind it let alone execute it. The reality is that due to design and/or loading many won’t be able to reduce they’re TW to say 12% or less and still maintain a reasonable sway damping ratio at highway speeds. If I were starting at the beginning and selecting a TV and trailer, the addition of TW of the loaded trailer shouldn’t remove more than 10% of the TV unladen front axle weight.

[jrm1493]

I think a lot of the wrecks are probably due to improper loading of the trailer and/or overloaded TV band aided by friction sway control, with loss of control caused by large change in wind load or emergency swerve due to driver inattentiveness, driver induced oscillation, or other cars doing stupid things around the trailer.

But, I think ultimately in order to swap ends or flip, the TV rear axle is going to have to break loose... If only the front broke loose you'd just plow straight ahead, without jackknifing or flipping. Of course going into a turn too fast with an understeer bias might cause you to leave the road and flip but an attentive driver should have been ready for a turn and entered at a reasonable speed.

It seems that j2807 is intended to maintain adequate understeer bias and natural sway damping (by planting rear axle more firmly) and therefore minimize the possibility of jackknife/flip. It probably does reduce ultimate cornering limit, but that's not necessarily a bad thing as most drivers have never driven a vehicle on the edge, certainly not with a trailer attached. In the end you only have a certain amount of grip to play with and in most cases it's probably better employed in straight ahead max braking than in swerving.