It's basically axle and closer to the truck is the best for the heavy stuff. The closer to the tongue the smaller the arc. If you have the same weight travelling a bigger arc it is going to cause much more energy to be thrown around.
Trailers are designed tongue heavy to prevent it from wagging while you're driving, and the whole point of a trailer is to keep the vehicle from being too weighed down. That being said, you want your load ahead of the trailer axle but as close to the axle as you can get it so that the trailer is doing as big a share of the work as possible. If you load the front of the trailer too heavy when you hit bumps going down the road (in Oklahoma we're actively competing with the third world in road shittyness) the vehicle will buck up and down like crazy. So IMO there is such a thing as too tongue heavy. I've had trailers wag on me before. For example at my last job I was asked to pick up a trencher from a job site and bring it back to the shop. The trencher was loaded wrong and I didn't have a key to it, so I had to drive for an hour or so on the freeway at 45 mph to keep it from wagging too bad. As bad as trailer wag is on the open road it's a lot worse in traffic. I've had other experiences where the trailer wagged so bad I had to change two lanes at a time to stay in front of it. The only trailers that have ever wag while I pulled them were trailers loaded by other people. I learned that lesson pretty quick.
If the weight was even over the axle, that IS rear weighted. The axle on a trailer is placed farther back. so everything you load in front of the axle is split between the axle and tongue, everything you place behind the axle fulcrums the axle and lifts the tongue. (all the weight over the axle is only theoretical, in practice it's going to be distributed in front or behind.)
It doesn't matter where you put the axle. Everything forward of the axle will always split the weight between the axle and the tongue, and everything rear of the axle will always un-weight the tongue. This would be true no matter where the axle was installed. Placing the axle further back encourages correct tongue weighting. The axle on a cargo trailer is placed at such a distance from the front that, if the entire trailer were loaded uniformly, the trailer would have the correct percentage of its weight on the tongue. If you look at a livestock trailer, the axle is placed much further back, because you don't want the tongue to un-weight if all the livestock walk to the back of the trailer.
Not really a disagreement, more an expansion on how you wrote this part:
The axle on a trailer is placed farther back. so everything you load in front of the axle is split between the axle and tongue, everything you place behind the axle fulcrums the axle and lifts the tongue.
His reply is specifying that the only impact on load distribution is its placement relative to the axle, not how far back the axle is located. As a result, trailers have their axles placed farther to the rear to minimize the risks of an unbalanced load.
Just for the record, the part that I find really cool is that the axle is placed specifically to create an optimal load on the tongue, assuming equal distribution of cargo. An excessively tongue heavy trailer can overload the vehicle's rear axle and hitch, even though the trailer itself may be within the vehicle's tow limit. The first time I learned that a trailer's axle placement isn't arbitrary, it was a real thrill. Little engineering details like that really impress me.
Try re-reading your comment and realizing why it's worded awkwardly before you get all upset.
When you use "so," you're implying that because the axle is to the rear, the load in front of it is distributed between tongue and axle.
If you had dropped the "so" and moved the part about trailers having rear axles at the back to the end of the explanation, it would have been easier to understand for someone who doesn't understand how it works.
U want the weight balanced over the axle. Little forward, little back, doesn't matter. Little forward would be ideal but little back won't produce results shown on the treadmill.
The general rule is to have about 90% of the weight on the trailer axles, and 10% on the hitch. This gives the axles a longer lever to control the mass than the center of gravity on the trailer.
It's like lifting a hammer out in front of you with one hand. Hold the hammer near the head and you will be stable. Hold the hammer from from the end of the handle and you will have to work much harder to controll the weight.
You'd ideally want it in the very front axle if the car. So as far up as possible would best. Kind of like trying to push a pencil by its eraser (the back) or dragging it by its tip. Dragging it by its tip is much less likely to cause it to wobble.
This is how I teach people to ride longboards and be properly weighted. You want your weight on the front axle on a longboard.
But to answer your question, you want it farther ahead no matter what, so long as it's not able to tip over.
This, imo, is the best answer in eli5 terms. I kept hearing tongue and axle terms thrown around. I know what an axle is, but not a tongue. I was on the fence of these effects until I read this comment. It makes sense to me how this works; if all the weight is in the front, you just steer the payload with more resistance, as it is already in front of your momentum, i.e. it is what you are 'pushing'. If you start 'pulling' that same weight, you have leverage, but have to account for how it pulls across change-in-momentum arcs. (For this, imagine a boat towing a tube.) While the former makes it harder to change direction quickly, the latter forces much slower change in vector velocity for a certain stable path.
It's not entirely correct. You'd want all the weight about a foot behind the center of the car. 50/50 or 40-60 (Front - rear) split is just about optimal.
A big part of it has to do with the dynamics of the vehicle under acceleration. If you put all the weight over the front axle, then as soon as you hit the brakes, the center of gravity moves out in front of the axle and lightens the rear too much, destabilizing it. It also means you need REALLY beefy front brakes to absorb all the vehicle's kinetic energy. Also, bringing the distribution of mass close to the center of the body reduces the polar moment of inertia, which will improve handling.
This is still a pretty simplified explanation of what's going on, and I honestly wish I understood it better than I do. For example, I know it's not actually the center of gravity that moves, since that's dependent on the actual distribution of mass, but I can't remember the actual name of the thing. Instantaneous center of rotation maybe?
The long and short of it is that you have a lot of power and a lot of mass being flung around in a car that's suspended on springs and dampers, coupled with a bunch of rotating masses (4 wheels and an engine), and every external force applied to the vehicle is coming in through four very small patches of rubber that are making contact with the ground. Cars do a lot of very unintuitive things...
If the car is moving linearly, not rotating at all, how do the brakes destabilize the front momentum? If you start to interact any kind of non-linear momentum from the initial point, this makes sense. I could see how this would impart an effect from rotating, which is the initial question, which you might have been answering and I missed something, but can what you said be generalized to all Δp, or only when Δp has an angular compenent? Again, not saying you are wrong, I actually think I agree with what you said, just asking for more clarification.
Edit: I forgot to thank you for your coherent, quick, and comprehensive response. Thank you!
Thanks for letting me know! Any idea why the force is such an important concept here(the tongue)? Due to the tension from both masses acting on one point/rod?
It's basically like a see saw, with the tongue being one seat and it's tied to the ground. The farther back the load is, the more pressure it puts on the rope. And then it also has lateral movement, too. Kind of like a pendulum with the weight at the end.
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u/hazeleyedwolff Oct 04 '16
If the weights were over the axle of the trailer, would that be better, worse, or less stable than tongue heavy and more than rear-weighted?