Ideas for larger-scale meal transport in an Interstate?

[InterBlog]

Originally Posted by slowmover

...

So, while axle load is likely okay, weight bias to port or starboard exaggerates steering in that direction. I can load a 53' flatbeds with [11] 4,400-lb pallets and tell if the steering is "off" when but two of those are 2" off centerline. What happens at 70-mph is serious stuff.

Get the individual wheel weights. (A Cat Scale is at +/- 40-lbs). Without the carrier and load, to start (as the conversion van won't be equal side to side). When satisfied, take a picture of the load when effects are minimized for future reference, and notes on details.

That said, the concern is hitch-carrier strength. And the fit to the hitch receiver. I bring this up as I see a great many of these cargo platforms in my 10,000-miles/month job. It's rare to see one not shaking or vibrating. Flopping.
... I'm saying I'd want the device built like a Navy destroyer. ...

I believe it would be a good test to have an observer in another vehicle look for other than steady motions. At 70-mph +. That there not be any movement -- at all -- separate from the movement of the Sprinter itself. ...
...
.

Great feedback... some of this was addressed on the threads in which other carrying challenges were debated (not food carrying specifically but the same issues have come up repeatedly when Sprinter owners desire to carry other large objects such as kayaks and dog pens).

A couple of summary comments, probably repeated elsewhere:

Our hitch carrier is absolutely built like a Navy destroyer. It was custom-designed by my engineer husband (LB_3). It does not move. I fully concur with you that most of these devices are utter crap - and they are dangerous crap to boot. But ours doesn't budge. It was built that way (see Part 2 of my hitch carrier blog series).

We have a local DIY welder who invested in his own CNC table, trying to scale up his own micro-business. We'd like to see more Class B-ers have access to this quality of carrier, plus I try to encourage the development of start-ups, being a micro-business owner myself. So we took our Interstate with its carrier to see this guy, to encourage him to offer something like this to the market (I told him I could probably bring him a few buyers). As I was demonstrating it, I hopped on top of it; I'm 133 pounds, but in the hop, I came down on it with a certain degree of F=m*a. The first words out of the welder's mouth were, "Holy s**t - it doesn't move!"


We leave the carrier in place full time (not our original intention) because my sensation is that the van drives more stably with it in place, either loaded or unloaded. Maybe that's some kind of placebo effect on my brain - I don't know. But I prefer the drive with it in place.

We've done CAT scaling, but only front to back in an official sense (where we got a weigh ticket). My memory is dim, but we did also do side to side, whereupon the scale owner pitched a roaring fit over the safety issue (what they perceived as a safety issue - it was a newer scale, with a concrete skirt that was flush to the main pad, so I believe it was actually quite safe). I can't find any record of side-to-side numbers in my file. My husband says he put them in an Air Forums thread somewhere (very difficult to search).

In general I find that 70 mph is too fast for our vehicle, unless road conditions are ideal, and I mean, absolutely ideal in terms of both pavement quality and wind speed and direction. I prefer 65 mph - it just "feels" right. We can do 70, but the time gains are not worth the added stress and fatigue of concentration.

[Pahaska]

Originally Posted by InterBlog

In general I find that 70 mph is too fast for our vehicle, unless road conditions are ideal, and I mean, absolutely ideal in terms of both pavement quality and wind speed and direction. I prefer 65 mph - it just "feels" right. We can do 70, but the time gains are not worth the added stress and fatigue of concentration.

Although my rig is much more recent and an extended 3500, I have the same perception that 70 mph can be a bit uncomfortable and 65 mph is the sweet spot where the rig just feels right in a wide variety of road and wind conditions.

[Boxster1971]

Originally Posted by Pahaska

Although my rig is much more recent and an extended 3500, I have the same perception that 70 mph can be a bit uncomfortable and 65 mph is the sweet spot where the rig just feels right in a wide variety of road and wind conditions.

+1 on 65 mph as a sweet spot for a loaded Interstate on Sprinter 3500 extended length. I've had mine up to 80 a few time, but 65 is best all around if conditions allow. One of my favorites is driving off the Interstates where I go 55-60 to stay legal and enjoy a less stressful trip.

[Protagonist]

When I'm towing my Honda toad, I try not to exceed 60mph. The Honda owner's manual says not to exceed 65mph while flat-towing it, and maintaining 60mph leaves me a small buffer for the inevitable gravity-assist acceleration on a downhill slope.

I've gotten so used to towing my Honda (over 20,000 miles towed so far!) that I routinely drive my Interstate at 60mph even when not towing my Honda. Fuel economy is improved at the lower speed.

When I'm driving my Honda instead of towing it, I'll still do whatever the posted speed limit happens to be. I'm not always poking along at 10 miles below the limit!

But I now have matching bumper stickers on both my Interstate and my Honda for the benefit of those who think I drive too slow:

[LB_3]

We weighed the van last May. I can't remember if that was with or without the hitch carrier.

LF: 1800# RF: 1780#
LR: 2220# RR: 2320#

Since then we've removed the Lifeline battery from the passenger seat and installed the Lithium batteries just front of the left rear axel.

[slowmover]

Originally Posted by LB_3

We weighed the van last May. I can't remember if that was with or without the hitch carrier.

LF: 1800# RF: 1780#
LR: 2220# RR: 2320#

Since then we've removed the Lifeline battery from the passenger seat and installed the Lithium batteries just front of the left rear axel.

I wondered how far off it would be side to side. I was imagining loading the carrier towards the heavy side (in ignorance), and carrier flop helped exaggerate that force. Bye bye traction on Drive Axle on the wrong day at the wrong time, etc.

Had a very old driver (retired; started 1939) tell me twenty years ago that, "you drive the truck up to 70-mph, but after 70, it drives you". You all have found the same. It turns into real work. Peripheral vision is WAAAY down as the need for braking distance really jumps.

For those interested in time versus distance, use Average MPH. Total engine run time over a distance. Chances are that on any 3-400/mile day that ACTUAL time is closer than hypothetical.

That sail area (with a tractor trailer) becomes a devil to manage at high speeds. Many aren't up to it.

The drag created by that non-aero rear on a Sprinter is a long tail. Disturbance of that tail is enough to reach forward at times. Kinda strange, huh? The sail area is itself enough work.

The hitch carrier "could" be the basis for an aero tail. While mpg would be improved, it would be the handling improvement that really counted.

No more OT. I'm learning from you all about how to pack an ice chest. Thx

.

[InterBlog]

Our carrier itself weighs 57 pounds (by design, despite being built like a brick outhouse). Add chains, locks, and peripherals for another 5+ pounds.

The Yeti this time will weigh about 75 pounds on the up-trip. The empty gas can next to it, with its bracket, weighs maybe 15 pounds. (Of course the hitch bracket is heavier than the can itself.)

Driver side is thus effectively heavier from that source by about 125-ish pounds (half the weight of the hitch carrier itself is toward the curb side, actually more than that, because the thing's unloaded center of gravity is toward the curb on account of the solid floor on curb side vs. open floor on driver side).

That's the rough weight equivalent of one rather small butt sitting on the driver side couch at the very rear, which I sometimes like to do, because I like to watch the world go by out the big back windows. When I'm sitting back there, I'm not more than a foot from the Yeti, because we snugged it as close to the back door as we could.

Common sense has suggested to me that this kind of weight difference can't cause a very significant issue. If a small human being sitting in the back of the van can cause the stability to change based on whether they've parked their butt on the curb side or the driver side couch (our van has longitudinal jack-knife couches), then we've got bigger problems with the vehicle than what the hitch carrier might impart.

This is my instinctive sense, at least. Perhaps there are factors I haven't considered.

[Protagonist]

Originally Posted by slowmover

I wondered how far off it would be side to side. I was imagining loading the carrier towards the heavy side (in ignorance), and carrier flop helped exaggerate that force. Bye bye traction on Drive Axle on the wrong day at the wrong time, etc.

This is more of a concern for T1N Interstates than for NCV3 Interstates. The more modern vans have improved stability control systems, that work by differential braking. As a given wheel loses traction, brakes are selectively applied to that wheel, even if you never touch the brake pedal. That braking increases friction at that wheel, which tends to help the van resist movement in directions that it's not supposed to go.

"Carrier Flop" has next to no effect on vehicle stability. The load moves so little in any direction that there's hardly any effect on the vehicle's center of gravity.

The weight distribution is limited by two factors: (1) gross axle weights; and (2) tire load capacity. As long as the front/rear distribution is within acceptable limits, stability is not affected. As long as no tire is overloaded, stability is not affected. Because the van is still within the parameters of the stability control systems.

The factors that affect stability more than any others are: (1) wind; and (2) centrifugal force. In simplest terms I can manage, the center of gravity of the van is always somewhere inside the footprint of the wheelbase, until the van is acted upon by an outside force.

Wind force can be converted to a pound equivalent, by virtue of pounds per square foot of wind force times square feet of surface. I won't quote ASCE 7 for how to compute wind forces, but it can be done. The force of wind acting horizontally can move the effective center of gravity outside the footprint of the wheelbase, leading to rollover. If the load isn't balanced side-to-side, it can take less wind to push the center of gravity to the already-heavier side than to push it the other way.

Centrifugal forces can be converted to a pound-equivalent in the same way. The tighter a turn and the faster the van is moving, the higher the centrifugal force, and the more likely rollover will occur. Again, rollover toward the heavy side is easier to induce than rollover to the lighter side if the weight distribution isn't centered.

Vertical weight distribution can have an even greater effect than horizontal weight distribution. The higher the center of gravity, the less the van has to lean over before the center of gravity goes outside the footprint of the wheelbase. Sprinters are less sensitive to this than some vans because the width of the van at the roof is narrower than at the floor, so the van has to lean even farther before stability is lost than other models. The issue of vertical weight distribution is the reason why a high-roof Sprinter has an allowable roof load of 300 pounds, but a low-roof Sprinter has an allowable roof load of 600 pounds.

Also, the stiffer the suspension, the less likely the van will lean in the first place, because it takes more effort to lift one side and lower the other. Thus a stiffer suspension adds to stability as well, all other things being equal.

Between live loads inside the van and live loads outside the van that detract from stability, and forces resisting unwanted movement of the CG and increasing stability, there are way too many factors for a non-engineer to calculate. Suffice to say, keep the weight distribution within allowable limits front/rear and left/right and as low as possible, slow down when winds pick up, and don't try to whip around turns like the van's a sports car, and the van's stability will not be a problem.

[slowmover]

Okay. But this weight is leveraged behind the rear axle. Pendulum effect. Might want to read up on extended body passenger van rollovers a few years back. The " why" is that the actual weight is multiplied against Drive Axle traction. It's a lever, not the same as cargo weight between the axles.

Were we dead serious, this hitch carrier would be fitted with a slimp wheel.

To say the last on my part, it's reasonable to want to minimize effect. To argue there isn't one in the first place is not where we want to go. A really well built device and items secured against movement is the whole of it, right?

[Protagonist]

Originally Posted by slowmover

To argue there isn't one in the first place is not where we want to go. A really well built device and items secured against movement is the whole of it, right?

Not saying that there's no effect. "Carrier flop" I took to mean that the carrier is a loose fit in the hitch receiver, and wobbles a bit. It flops slightly to one side or the other based on loading and vehicle motion— unless you add shims to prevent that wobbling motion once the carrier is secured in the receiver. That's something I noticed when I used a hitch-mounted carrier, and I used plastic wedge-shaped shims to more tightly secure the carrier in place so it wouldn't flop.

But that's completely different from the moment arm caused by the load on the carrier being outside of the wheelbase footprint. Carrier flop has no significant effect on vehicle stability because the range of motion is so small even on the end of the moment arm. But a 400-pound load on the hitch does have an effect, whether the carrier flops around or not. It moves the vehicle's center of gravity slightly to the rear. Even on a T1N Interstate, the load on the hitch-mounted carrier is still only about 5% of the vehicle's gross weight, so the effect is minimal— but there is an effect.

It also affects wind loading by providing extra surface area to catch the wind, and moves the center of effort for wind loads farther to the rear. But not enough to cause the van's stability control computer chips to have an aneurysm trying to compute how to differentially brake the wheels to maintain traction and stability. Otherwise every time you loaded the carrier the dashboard idiot lights would light up like it was Christmas to tell you the stability systems are having hiccups.

And a load on the carrier causes an increased range of motion for the rear suspension out of proportion to the actual weight involved due to the moment arm of being located so far behind the rear wheels.

I'm not saying that weight on a hitch-mounted carrier has no effect. I'm saying that the effect that it has is still within the design parameters of the van's suspension and its various traction and stability control systems. Just like learning to pull a trailer, you have to learn to drive with a load on the carrier, so that you can gain a feel for how to compensate for the differences in handling.

Anyway, I think that for vehicle stability the best type of hitch-mounted carrier would actually be a single-wheel trailer, like this:

[InterBlog]

My husband will be the first to confirm that I am a cranky wench when the universe fails to unfold as I believe it should. I am not one to minimize any complaint or critique for the sake of saving face, so if something sucks, I'm going to tell the entire world whether they want to hear it or not.

Five hundred twenty four miles today with those two mmmmmmassive blocks of ice hanging off my tail, and I swear the rig has never driven better. And I hit construction madness, lateral wind shear from severe thunderstorms with the NWS siren squawking out of my radio - you name it; you know that the freeway never holds back where drama is concerned, LOL. I don't know what the physics is supposed to say about this hitch contraption, but I can tell you that it works.
:-)

[OTRA15]

Originally Posted by Protagonist

. . .
. . . And a load on the carrier causes an increased range of motion for the rear suspension out of proportion to the actual weight involved due to the moment arm of being located so far behind the rear wheels.
. . .
Anyway, I think that for vehicle stability the best type of hitch-mounted carrier would actually be a single-wheel trailer, like this:
. . .

Aren't the two statements above somewhat in conflict? Imagine putting the maximum load allowable on the rear of that single-wheeled carrier, way behind the truck's rear axle and its center of gravity.

Say a 500 pound generator, for instance.

With the moment arm being so long, won't some new sway type issues be "generated" ? Lightly sprung pickups are already pretty squirrely anyway with the suspension set to mimic a passenger car in some ways . . .

I know this pickup scenario devolves a bit from the AI rear carrier discussion, but that single wheeled carrier just scares me, at the thought of how carelessly it could be loaded.

Thanks,

Peter

[Protagonist]

Originally Posted by OTRA15

Aren't the two statements above somewhat in conflict? Imagine putting the maximum load allowable on the rear of that single-wheeled carrier, way behind the truck's rear axle and its center of gravity.

Say a 500 pound generator, for instance.

With the moment arm being so long, won't some new sway type issues be "generated" ? Lightly sprung pickups are already pretty squirrely anyway with the suspension set to mimic a passenger car in some ways . . .

I know this pickup scenario devolves a bit from the AI rear carrier discussion, but that single wheeled carrier just scares me, at the thought of how carelessly it could be loaded.

Here's what you're missing. A more traditional cargo tray is cantilevered, and not free to move in any axis, not vertically and not horizontally. The connection between the single-wheel cargo tray is free to rotate in one axis, vertically, but not horizontally. And a trailer tongue fits on a hitch ball to provide two axes of movement, vertical and side-to-side. Actually, the ball joint of a trailer tongue has limited motion in the third axis as well, rotation in a longitudinal axis, but that's not pertinent to this discussion.

The connection at the hitch for a single-wheel carrier is hinged so that it can pivot up and down as you cross a dip or a rise. Your moment arm is only as long as the hitch, not as long as the carrier, because you can't transfer moment of inertia across a hinge. That means the single-wheel carrier will always have a shorter moment arm than a cantilevered cargo tray, not a longer one.

The hitch connection on a single-wheel carrier is rigid from side to side And because it's only hinged up and down, but not side to side, the single-wheel carrier doesn't induce sway like a conventional trailer would. The carrier increases tail-swing as if the vehicle's overhang was that much longer, just like a cargo tray, but that's it.

The single-wheel carrier would take a bit of getting used to, but it's actually more forgiving and safer than a cantilevered cargo tray or box.

[OTRA15]

Originally Posted by Protagonist

. . .
. . . The carrier increases tail-swing as if the vehicle's overhang was that much longer, just like a cargo tray, but that's it.
. . .

This is the main concern I had, the lateral side-to-side sway forces generated by a large load on the back of this new carrier. Sorry not to be clearer about this. Of course, the up and down loads are ameliorated considerably.

With the lateral motion's moment arm being increased in length about 4'+/- would not the square of that increase [with 500 pounds at the end] be pretty significant? With a quick evasive action to miss a child in the road etc., I bet the front steering wheels could actually lose their grip, with the cart steering the horse IMO.

Thanks and sorry for not framing the questions better.

Peter

[Protagonist]

Originally Posted by OTRA15

With the lateral motion's moment arm being increased in length about 4'+/- would not the square of that increase [with 500 pounds at the end] be pretty significant? With a quick evasive action to miss a child in the road etc., I bet the front steering wheels could actually lose their grip, with the cart steering the horse IMO.

That does depend a lot on the actual axle weights of the vehicle to which the carrier is attached (with the caster wheel as a third axle), as well as the wheelbase length.

I haven't crunched the numbers. Now that I'm retired, I try not to crunch numbers if I don't have to because I don't want my retirement to be too much like work. But my engineering intuition says that on a long-wheelbase, heavy GVWR Interstate, a single-wheel carrier will not affect stability even as much as a traditional cargo tray, for similar loads properly balanced— though on the single-wheel carrier the load would have to be balanced front-to-back as well as side-to-side.

Any vehicle improperly loaded is inherently unsafe. That's no reason to distrust the design just because some lamebrain could load the single-wheel carrier improperly. That same lamebrain could improperly load a pickup bed even if nothing was attached to the hitch receiver at all, and cause handling problems as well.

[BurntAsphalt]

These detailed discussions done with the utmost decorum confirm why this is the one of the best forums on the net. Following Rivet Masters Yoda and Obi-Wan discussing "The Force" is about as good as it gets!


Do or Do Not...There is no try!

[Protagonist]

Originally Posted by BurntAsphalt

These detailed discussions done with the utmost decorum confirm why this is the one of the best forums on the net. Following Rivet Masters Yoda and Obi-Wan discussing "The Force" is about as good as it gets!

As long as Jar-Jar doesn't toss in his two cents worth!

[InterBlog]

Has anyone seen the roads in Pennsylvania?! OMG, I'd rather die than tow anything here, including a wheel-supported hitch extension. When my rig is propelled upward with a force exceeding 1G, and when our stomachs end up in our mouths upon the inevitable free falls, something instinctive in me wants the rig to be one cohesive unit.

I asked a store clerk why diesel was $2.999 in PA when it was $2.169 in TX. He said, "That's because of the Governor's road tax." I asked, "So he's actually going to fix the roads?" Clerk replied emphatically, "We don't believe so, no."

[Boxster1971]

Originally Posted by InterBlog

Has anyone seen the roads in Pennsylvania?! OMG, I'd rather die than tow anything here, including a wheel-supported hitch extension. When my rig is propelled upward with a force exceeding 1G, and when our stomachs end up in our mouths upon the inevitable free falls, something instinctive in me wants the rig to be one cohesive unit.

I asked a store clerk why diesel was $2.999 in PA when it was $2.169 in TX. He said, "That's because of the Governor's road tax." I asked, "So he's actually going to fix the roads?" Clerk replied emphatically, "We don't believe so, no."

Agree - just went through Pennsylvania and paid the $3/gallon. But avoided the terrible PA turnpike and stayed south on I-68 on our way to Minnesota.

[InterBlog]

Beginning of Day 5, daytime high temperatures in travel area = 90 to 101 degrees. I feel bad for those folks in Alabama with the non-working a/c (other thread).