MythBusting with Casey!
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- Опубликовано: 27 янв 2025
- An age old long battled debate in the towing industry is whether or not towing something on the sling allows you to tow more weight since the ram pushes down ahead of the rear axle. The same goes for whether or not an integrated wrecker tows better than an independent wrecker since it’s wheel lift is hooked to its boom. So I took my truck to the scales with my Jeep on the back to settle the debate once and for all.
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So why didn’t I weigh the front axle?? It’s very simple. If the rear axle weight doesn’t change, it’s flat out impossible for the front axle weight to change. The simple fact is that all the “experts” who tell people that they can tow more weight by using the sling are give flat out incorrect and dangerous advice, so it would be best if they simply shut up.
Why do I always fall for this click bait? 😁I am looking at lever length around the back axle as a pivot v the weight that is « going down » the crane arm and acting in the opposite direction. Load up one way..drive on and weigh the front wheels, back wheels and then the jeep..It is impossible for the sum of all three to change but front to rear axle can.
"Expert": But this test is flawed! Test must be done at the same time, air humidity, pressure, temperature, location and moon phase. All these variables can cause differences in measurements and it does not help that you are towing a Jeep with no black ice air freshener.
By the way, this was a joke for those who did not understand it.
@@ChannelJanis Yabut, some will still believe a difference in "moon phase", or humidity , will make a big difference because they read it on the internet. 🤣
Sorry I didn't see your comment when I was making mine with Google Translate haha
My favorite wheel lift myth "You shouldn't tow long distance behind a wheel lift. That causes rock chips and broken windshields "
So... this month we've had a roll in the hay, taken a daddy/daughter road trip, a solar canoe ride, treasure hunting with an underwater drone, and now it's a Lever Physics lesson with Casey.
I came here from Matt's Off Road Recovery and Rory's Irish and Trail Mater. This channel is always a welcome surprise to just another recovery video. Keep up the good work.
As a mechanical engineer, I can say that you are absolutely right, Casey! Good for you and nice video!
I love how you always go out and prove the debates of the towing industry. And you will go out of your way to show it. Great video
It's all about weight transfer, and some will never get it. Armchair experts will argue about your 50-800lbs differences. I don't care what kind of boom, sling or lift you design the same distance between axle and lift point will torque (weigh) equally.
P.S. weight doesn't change unless you add or take away something.
Load moment is the effect you are seeing on the scale.
One of the greatest mysteries to me was when I pulled my 7,000-pound camper. I would set the weight distributing hitch up to move the weight to the front axle of my tow rig. I'm pretty mechanically inclined but that always baffled me. I'm sure the guys who designed those wreckers knew what they were doing, maybe not as brilliant as Internet experts but smart none the less.
The torque bars are angled so lifting up on the rear, flat part, applies a twisting torque to the hitch head, causing more twisting force forcing the front end down. It works best with a framed vehicle vs a unibody.
What a weight distribution hitch does is remove some of the vertical articulation from the hitch point. In essence it uses tongue weight to pull down the front axle. It is a completely different scenario that this video.
I like the fact that you are so compassionate about your job. There are way to many keyboard warriors out there spreading way to much BS.
I think I can see what the "experts" were thinking. They thought it was the same as the gooseneck vs bumper hitch weight shift. They didn't take into account the leverage and direction of weight transfer on a tow bed. Great video as usual Casey and excellent demonstration.
I can kind of see that too. The other thing they're missing is the boom is also pulling up on the anchor pivot pins ahead of that ram. A gooseneck trailer is not pulling up on any part of the truck.
Impressive understanding of the physics. You had me re-thinking the lift point on the Jeep for a second. If you are interested, here's what I came up with. Note this is only a rough approximation -- not only because I'm guessing at the numbers, but also because the front axle is located back from the front of the vehicle and the and the center of gravity of the Jeep is probably not at the half way point.
Anyway, say your Jeep is 160 inches long and weighs 4000 pounds. If you could extend the wheel lift to just the middle of the jeep, you could pick up the whole Jeep (all 4000 pounds). When you lift the back of the Jeep with the sling, you are lifting right at the very end of the jeep so you are picking up around 50% of the weight (2000 pounds). If the Jeep is 160 inches long, the mid point is at 80 inches. So moving the lift point 80 inches changes the lifting load by 2000 pounds. Dividing 2000 lbs by 80 in gives 25 lbs per inch. Surprise, surprise, this roughly agrees with your experimental results at 5:57 where the block was around 2 inches forward and the weight on the truck was 50 lbs more.
Somebody gets it
now the tough part: convince Casey
@@Wannes_ Um, did you think I was being sarcastic? I wasn't. Are you being sarcastic? I'm not sure. In any case, to be clear, Casey explained it very well. I agree with him 100%. I was just adding some numbers to his observations.
@@andrewsnow7386 and 25lb/inch when adjusted to the axle pick he did first at ~18" further under the jeep (~37" tire dia / 2) = ~450# extra weight lifted, the effect of which would be larger since the moment arm length acting on the truck end increased by that same distance as well. Hence, this is seen in the increased rear axle weight of ~800# in his first measurement.
Unfortunately, the inclusion of the first wheel lift(axle) numbers at the beginning is throwing everyone off and has riled up all the dissenters. Since that setup is not an apples to apples comparison to his original point of wheel lift vs sling and which attachment method transfers weight "better"; those without an established understanding of the physics in play are arguing over the 800# difference. "But where did the 800# go....?"
Another way to explain could have been to have the Jeep sling towed on the first weigh in and then lifted with the wheel lift at bumper secondly. Numbers would have been the same as shown in the video, proving the point that the attachment method is irrelevant. Although I'm sure some would still argue that without the front weight numbers, they are not convinced. However, as pointed out in the comments already and Casey's second video, if the rear bumper is lifted to the same height each time then the Jeep front axle has to weigh the same.
(Same Jeep Axle + Same Tow Truck Rear = Same Tow Truck Front) --> which also equals no difference in weight transfer based on lifting method - his original point
Also seems that the debate evolved a bit from, "The sling places more front axle weight due to the ram/boom being attached ahead of the rear axle" to a more generic "wheel lift(axle) vs sling lift" debate in the comments. This is not an apples to apples comparison though when compared in their typical usage & the different lift point (axle vs bumper) is not taken into account. Some arguing for "sling tows more" are forgetting that the wheel lift(axle) has to pick up much more weight (being under vs at the end) and at a farther distance from the tow vehicle as well.
While the mode of attachment has no bearing on the weight the rear axle sees (at the same distance), I would argue that a heavier vehicle could be pulled by the tow truck using the sling or wheel lift attached at the bumper vs attempting to lift the same vehicle by the wheels. So in a way, all of those arguing "sling tows more" are inadvertently correct, but not for the reasons they think.
Nice physics lesson. We want to thank our Professor of Recoveries for delivering our lesson for the day.
Knowledge is King
8:30 Truck-lite head lights. Got the heated ones for my Jeep. There is a great RUclips review of them and others. These were one of the best and recommended. The “failed” ones got taken to a skeet shooting range... entertaining. I got heated ones as I live in snow country and didn’t want to have to scrape them off.
Thank you Casey for helping those who were not sure
Thanks for the weight demonstration. I'm a bit of a nerd when it comes to headlights, and I hope "one day" comes soon for your sake.
Nice practical application of physics. Structural engineer here. I enjoyed and 99.99% agree with your argument. The weight on the rear axle from the lifted load is a function of the lifted weight and the perpendicular (or horizontal in this case) distance of the lifted weight from the center of the axle. Love the videos and your desire to stamp out ignorance and never stop learning! Keep it up, buddy!
You're absolutely right, great demonstration. It has everything to do with fulcrum point (rear axle) distance to the pick point of what's being lifted.
I towed in the 70s and 80s when I worked at an automotive shop. I couldn't tell much difference in weight distribution between sling and wheel lift and certainly never worried about it.
I think a well designed rig will do just that..But there are definitely some bad designs out there
Couldn't you just sense the eyes of all the armchair towing masters glazing over when you started throwing real physics at them? Great video, Casey!!
I really wish you took front axle weights from truck in each configuration to show its effect on steering tire loads. Which to me is the most important part of this debate. And i appreciate your taking this on. Its important.
The argument for that is the rear axle is the pivot, so its load will barely change as you move the towed vehicle further from the axle. But the weight seen at other end of the lever, ie front axle will change significantly more as you change the length of your lever arm.......
You are 100% wrong. If the front axle gets lighter, something else has to get heavier. And that something else would be the rear axle, which didn't change in weight
@@CaseyLaDelle It should be split between the towed vehicles axle and the rear axle of the tow truck. As light as I imagine the rear of your jeep to be, I don't think the roadside scale is likely to be able to show the difference on your rear axle. Measuring the weights of all three axles would have provided definite proof either way.
Great practical demonstration of physics. Love your passion!
Casey...
There is always going to be... know it all people... to drive you crazy...
Some people just have to think they are right... even when they aren't right...
They have to put you down... and criticize....to make themselves seam better than you... "There Jealous"
Try and let it go... It doesn't matter what other's say about you... and your technics...
You are Awesome and very thorough in everything you do...
You explain yourself and make RUclips very entertaining...
Keep up the good work Casey
Love the videos Casey, keep them coming Bud! Maybe a full truck tour soon? Love to see how you set up your boxes.
I like watching your videos. They’re not a waste of time like a lot of other stuff on you tube.
It's nice to learn something new everyday. 😁
the only difference would be due to the Hight of the boom above the centerline of the rear axel acting as a lever during hard braking there would be some additional weight transfer to the front axel for the duration of the brake application. the wheel lift exerts all the forward push close to the centerline of the axel where as the boom lift transfers forward momentum at the top of the bed and at the top of the boom. the wheel lift is the better choice.
Fun with Physics!
Thanks for the edumacation Casey. 👍
your explanation is correct, however.. the example using the jeep is very lightweight & doesn't matter which hookup is used, more importantly... it also has a VERY short departure angle/rear set axle so it's easy to either sling or WL with similar results... a regular vehicle would have a much longer overhang to reach with a WL... if the towed vehicle has a long overhang before the rear axle such as a big truck... the WL must be extended creating a longer lever from the Fulcrum (rear axle pivot point) as well as sometimes, a wheel lift simply cannot reach far enough to grab the wheels & still be able to turn without hitting the tailboard. The weight of the vehicle is the same either way, but the long reach changes leverage for steer axle weight, making it light on the steer axle. that same long overhang vehicle can be slung, using chains to do the long reach to the rear axle or frame etc & keep the lifting point close to the tail of the wrecker keeping the lever between lifting point & the rear axle (fulcrum) and retaining as much steer weight as possible. The sling advantage isn't so much weight transfer on the wrecker chassis, it's about ability to tow heavier stuff with long overhang & keep it closer to the wrecker body/rear axle. The vast majority of towers don't even know how to sling anymore. when they do, they often hook it wrong making the straps support the load instead of rigging the chains to. The rubber sling itself isn't meant to support the load. many never even heard of or have seen one let alone used one...It's a lost art... Great video Casey
Both Casey and Woody are correct.... But I want to add, you also need to take into consideration the weight capacities of each component. An average wheel lift from the era of Casey's wrecker was probably rated at 3500 pounds of lift, and maybe 5000 pounds of tow. (pull) That boom is probably rated between 8 - 10 TONS, (yes, I said tons) which is 4 - 6 times stronger (roughly) than that spindly wheel lift. If you're going to tow something heavy, regardless if the weight on the front end of the wrecker is the same or not, why WOULDN'T you use the sling??? I 'd rather have a 1-ton dually pickup (for example) hanging off the sling and chains, than having that same 1-ton dually pickup scooped into the wheel lift. And I guarantee anyone who argues that with me has never towed a 1-ton pickup behind a light duty wrecker to begin with, and certainly has never towed one with a sling. Because if they have, they would be in total agreement with me. Good video, Casey!
@@SlipFitGarage Great point... plus, with the sling, you're not limited by wheel size. Wheel lift arms have a hard time with large tires. Slings don't even need tires.. :)
@@woody4u247 👍
Great video, will admit im not a tow truck driver operator, it all makes sense, just like when you had to put in the fame braces on the black truck and was mentioning all the why and what for, it makes sense
Absolutely! same two axles with same loads!
that was so rad Casey! I like how you explain stuff, makes total sense to me. Can't help this round but coming out to help on a future cleanup is on my radar! Keep up the rad videos Casey! Such a rad channel!
Does the blinker fluid need to be full. ??? Or do you need to adjust your muffler bearing ??
in my 15 years of towing I only used the Sling for a few things. mainly wrecks, and the time's where the vehicle was more the the capacity of the wheel lift. and you are 100% on the fact of it matters how far out the load is from the back of the truck
I see your point about the weight being the same whether lifting at the bumper with the sling or lifting at the bumper with the wheel lift.
I had to think a little about the problem before I understood the heavier weight when lifting at the wheels with the wheel lift. What I came up with was that, when lifting at the wheels rather than at the bumper, you are lifting more of the towed vehicle's weight. You are taking more weight off the wheels of the towed vehicle that are still on the ground. I suspect that this difference only becomes important when you are trying to haul bigger weights than either system is designed for.
I like your style. No BS.
Back in the 70s through to the 90s where I worked had 2 wreckers a sling and a wheel lift there was many times I had to tow the same vehicle twice and not always with the same wrecker and from what I could tell there was no difference so personally as long as you get the job done safely what difference does it matter and from what I've seen in Casey's videos he hasn't done anything wrong or over loaded the wrecker, weight transfer is exactly what it is period. Casey loved how you demonstrated weight transfer and loading in the exact same spot gives you the same numbers but keyboard warriors are going to be keyboard warriors. Awesome job Casey and as always be safe 👍
This reminds me of the question of what is heavier, a ton of feathers or a ton of steel? Weight change is the matter of inches of change on distance to the rear axle. The farther back from the rear axle, less weight on the front axle. Closer to rear axle, more weight. Rear axle in this case is a pivot point on lever action. Just my two cents.
Those Ford headlamps on that model truck were beyond horrible. I swear that a flashlight shines further and brighter. Maybe a sponsor will send you some to give a review on!. Thanks and have a good day Casey 👍
A dear friend of mine had a towing company and salvage yard. He taught me EXACTLY what you said in this video. Plus LOGICAL THINKING also says that weight just in front, on OR behind the rear axle will put weight ON the rear axle and NOT on the front like the "WANNA BE TOW OPERATORS" state. I have helped load both sling tow trucks(like yours Casey) and recovery bed trucks. Both are TOTALLY different for loading and for weight distribution.
Great video! You are totally correct. Next you can really confuse some people by asking what happens when you are moving down the road and apply the brakes on your truck. Weight up high above your rear axle will add more weight to your front wheels while braking.....more food for thought....
The way to measure if the weight is spread out more over the truck is to weigh the front axle, both while lift both ways. That will tell you if there is more or less weight on the front. More weight means it is spread out more, less weight means it is heavier on the rear axle. You are also towing a JEEP from the rear which has about 6 inches past the rear tire. if you are towing a car the towed vehicle would have to be much further away for the car to clear the tow truck in the turns.
After years of towing I agree with you Casey 💯%.Thanks for all your post 4 the people🏆
I have the same issue with my headlights on my 2001. Looks about the same on camera. The former owner of our wrecker broke the sling some how, so I don't have one at this time. I only have used them for convenance. If a car or truck has a missing wheel or was too far back for my wheel lift, or so damaged that it doesn't matter. Good visuals. Makes it easier to understand.
Awesome info Casey..... didn't know anything about towing with a tow truck. Thanks for sharing!
I liked learning this, but the most impressive thing is you can use scales after hours to check your rig weight.
Back in the day I ran a single axle heavy, because a single axle axle moved the pivot point closer to the tailboard. A tandem axle has it's pivot point in-between the rear axles. Although when air suspension came along, that made calculations a bit different, especially if you put a manual pressure control in the cab for the rear axle. But yeah you are right on the money Casey. I find it amazing how many tow operators seem to never have mastered the seesaw in kindergarten and are now grown men who still don't understand the seesaw
I love my times learning with Casey. You approach things in a very similar way that i have my entire life. Thank you for sharing knowledge that is fun and useful. I appreciate you. Hope the clean up has more people than they know what to do with. Peace Out.
Very interesting video. For those of us that know squat about the subject, your research is very good.
great job, very interesting. thanks for explaining!
Great information for anybody in the towing Business
Like you said, pretty basic physics with a bit of civil engineering thrown in. Good old triangle supports and lever arms.
An interesting test would be to show that the further away from the tow truck the more weight is transferred to your tow truck, and less to the front wheels. Put the front wheels only on the scale and extend the wheel lit out to show the difference in weight on the front steering wheels of your tow truck, and also do the same thing with all four wheels of the tow truck on the scale.
Cool thanks 👍
As a former tow operator I get what you are saying because when I did tow it was with a truck just like yours and you're absolutely correct
You are 100% correct. I have been a registered professional mechanical engineer since 1975. An engineer would convince him/herself by drawing a "free body diagram" to analyze the loading. The main difference that the truck will see between the two methods is the internal stresses in the framework. If you really want to get into the weeds, there may be some difference in direction and point of application of the intertial loads of towing (accelerating or decelerating). Your underlying premise is sound - and you proved it.
That was pretty cool Casey thanks for the Lesson.
I always thought what did change between the truck bar/ sling and the underlift was the capacity. Winch capacity being greater then the hydraulic rams capacity. And also clearance issues. You can gain clearance with a sling style. I wàs also taught that braking weight transfer was better with a sling. Which is why we used a truck bar instead of a wheel lift or frame forks for the bigger loads.
My dad was a tow truck driver for 10 years. He always told me that it doesn't matter wether it's a wheel lift or a sling. All the sling is really there to do is to haul a wrecked up vehicle that either can't get into the wheel lift or is way too broken to be hauled via wheel lift.
Really good info Casey, having recently acquired a couple of square body wreckers for our new tow operation, this was cool to see.
Morning, nicely done
Definition of expert = X an unknown element + spurt " a drip under pressure " = expert
I personally prefer getting advice from a craftsman or in your case a master craftsman 🤙🖖
I like how you show the transfer of weight on the 2 hook-ups. Would it also depend on how high the rear of the towed vehicle is as well, transferring the weight also to the front wheels on the towed vehicle? To me it looked like the sling held it higher. Just asking.
Yes the weight pushes down on the ram which is in front of the axle but the top of the ram is a pivot point which means that same weight is pulling up on the front/bottom of that boom which moves the fulcrum to at least the end of the boom if not a little further back.
No it’s not. The boom, ram, and all its components are a rigid structure. The rear axle is the fulcrum. If you believe anything different, you are wrong and there’s simply no two ways about that.
Good job Casey like your videos. God bless you and your family all the time.
Yes, new headlights and off road lights too. Stay safe.
One contributor to your slight weight difference would be that as you are lifting the load with the sling, you would also need to position all components of the hydraulic arm at the same positions, just not touch the load, as they were when they were being used to lift the load. Where the center of mass of that hydraulic arm is positioned relative to the rear axle changes depending on how extended the arm is at the time. You should be able to see this this affect while sitting on the scales and running the hydraulic arm in and out, even unloaded.
How much is the different centre of gravity effected, between carrying low on the wheel lift to high on the boom? Does that effect the ride of the tow truck much?
i have fun watching you playing and having fun hahaha im glad you got that old tow truck heck of a toy for sure :)
Thanks for the comparison and I never really thought of it like it. I honestly trust you
I'm glad u explained how the wheel lift and the boom works cuz anyone that wants to get n to towing would understand the way it all goes together
the wheel lift may be behind the truck rear axle, but what affects the weight distribution is where the wheel lift attaches to the bed or frame of the truck ...
if someone were to 'home brew' a truck wheel lift, i'd have to see where those connecting points were before guessing whether or not their arrangement would be better or worse than the old style boom lift
Yes head lights would be a good idea 💡
Well done Casey. Spot on as usual.
Another one you should have tried. The " experts " keep saying to raise your boom if it's heavy while on the sling. Possible pt 2 for this video play with boom height. If these " experts" have paid attention in Wreckmaster it was hammered like you said its the amount of weight picked with the over hang determined the front axle weight.
My wife just saw your headlights and thinks you should get them today.
OK,You are wonderful!
Don't forget too that the boom is a big lever itself. Yes it's pushing down on the ram, but it's also pulling up on the anchor pins by the headache rack. It's a lever on a bigger lever system. The weight is still pulling down behind the back axle. Gravity doesn't change directions.
And yes, I watched this one AFTER your shorter video.
It's all about fulcrum point and lever length. Scales don't lie.
I’ve been telling people this for years and folks tell me I don’t know what I’m talking about. Nicely done
Interesting , Thank You .
Casey, I lived in K.Falls from 62 to 1980,4x4 always during that time, love your channel.
I have to say... The comments on moon phase are wrong... Oregon's moon's phases are different from the rest of the country.
Just Saying...😎😎
Picking up further back will make a difference on the weight still on the wheels of the towed vehicle. Also the load is a tension load on a cable install of a sheer load on the bolts holding the wheel lift. If you are near capacity, I wonder if either of those could be enough to be helpful.
What about the stress on the boom tower that’s bolted to the bed? And the winches that are bolted to the tower?? And the tiny little pins that are holding the winch gears in place??
Good morning Casey, for lighting a small LED light bar installed above the front bumper. Will add add the look of daylight up front.
Exactly, Casey! Cantilevered weight remains the same no matter where it pivots.
Cool video. Yet the video began with the question of weight transfer to the front axle. It would have been interesting had you done both ways picked up with your front axle on the scale to see the effect differential between the two ways to lift and tow. Yes it made a slight difference to the rear axle load. But the myth in question was steering axle load differential??? Keep up the interesting videos
Thanks, awesome
the old timers are right, if you hooked your jeep up exactly like you would tow it down the road for each system, one system will have more weight on the rear axle then the other no matter how little the difference, your not going to tow with the wheel lift on your rear bumper with a block, that's why they say you get a little more weight on one over the other! love the vids Casey i hope you keep them coming
The higher you lift the rear end of the jeep the more weight you transfer to the front wheels of the jeep. Weighing all three axles simultaneously while keeping jeep angle the same with both lifts is the only way to know the difference.
I am glad you did this test.
People overthink about stuff 😕
The correct explanation is that if the mounting point you use is fixed relatively to the rest of the truck, it doesn't matter how you apply the load to the truck and the "path" the load should follow, the only thing that matters is the point where you apply the load (in this case, the distance of the towed vehicle's attaching point from the truck's rear axle). Again, the structure must be fixed and not have pivoting arms or whatever
Hey bummed I cannot make the Cleanup but I will clean up some crap in the desert in keeping with the spirit. Totally dig that you nerd out on this shit. 😁
By this logic it shouldn't matter if the car is on the wheel lift or on the bed of a flatbed according to you the front wheel won't go up any farther. In practice that is flat out not true. I can't tell you how many times I've driven f550s especially in the winter even with one on the bed as soon as you put one on the wheel lift that front tire goes up and you lose your steering and braking.
That is easily one of the dumbest arguments I’ve ever heard.
Just a thought but would rotational torque play any part in loading or unloading the wheels with either setup? Thinking of the tractor pulls when the sled moves up the change in weight/ torque on the hitch lifts the front off the road. Even if the pick point is before the back axel, if it’s trying to rotate, using the back axel, could it still lift the front? Love the myth busters format, and agreed, the front lights need improvement, is it the bulbs, reflectors or glass? I had to change out the headlights on my Mazda as the reflector dulled, they looked really bright to look at them but no projection
Great video, keep them comeing, you are the man.
So when used as he did and as is common under the wheels the wheel lift added more weight which is multiplied when the suspension is stroked. and the other guys are wrong?
Depends on the truck.
1974 F350 with a Holms 440 and some unknown aftermarket add on wheel lift and an 87 F350 with a Nomar Hotshot wrecker. The 87 was better about it but both of them had more front axle weight on the sling. I can't tell you distance from the wheels to the towed vehicle but both were in a normal "go down the road" position for that setup. And that may be the birth of that "myth", but there's no way I could wheel lift a full size truck but I could sling it all day long. In fact, on the 74 if you hit a bump the front end half the time would hang in the air uncomfortably long. I learned how to tow a modern car on a sling with that truck using a 4x4 on the front core support. Took a lot of fidgeting but it worked.
IMO the only way to truly test is to get a front axle weight. Get all the weights.
Also a tower here, I was always told the sling just lets you pick up more weight. 10,000lb boom rating vs a 6000lb wheel-lift rating. So thats why you tow the heavier stuff with the sling. Is that what you understand too? Nothing having to do with your weight on the ground.
I love the lessons, keep teaching.
Either way, the fulcrum point is the rear axle. That's where the weight will be anyway. The only thing that really matters is which method gets the particular job done better.
Casey, you're a great soul, and I love your channel, but my Cal Tech ACM grad says you should weigh the front axle. He tutors college level physics and says there will be a difference. Physics doesn't lie. Keep up the great work!
A bumper lift will put less load on the tow truck, overall, than a wheel lift. Where has that extra load gone? It goes to the casualty's rolling axle. A thing to consider when lift towing a loaded goods truck as it could overload the truck's rolling axle if it has been lifted at the bumper. Also it could bend the chassis if the lift point is a long way from the casualty's axle, as on a bus or coach (or one of your giant RV things).
It is only physics and maths, and understanding how levers work.
Just to confirm, I fully agree with Casey that the front axle load on the tow truck doesn't change when the same load is on the slings, or the underlift. In the case of Jeeps and the like, the axle centre to bumper is small and so any variation in the load on the tow truck is negligible, so changing from underlift to slings won't be significant. Likewise sling lift on the bumper and underlift on the bumper doesn't make any difference.
However, if Casey was to tow an RV with the underlift on the axle, and then change to slings on the bumper then the long overhang on the RV will change things. The under lift will need to bear a greater load at the axle, then the slings would from the bumper. It is like lifting a wheelbarrow at the back of the bucket vs lifting it at the ends of the handles. The reduced load with a bumper lift would then change the tow truck front and rear axle weights and put more load on the RV's rolling axle.
I am not sure I understood everything you were saying but what you said made good sense. I choose not to take physics class in High School, I was told it may not go so well. I did take Advance Biology class and did well. I did not even bother about taking Physics in College but did take Psychology Statistics. A lot of this is Mechanical know how and I am just beginning to understand that aspect in life. My brother and my father were better at that then I was.
Dang leverage. Doesn't also help with the center of gravity if you use the wheel lift and not the boom? The weight is being lifted at frame height instead of boom height?
Physics doesn't lie. When I worked for a company where lifting was involved, we had an expert come in to show how to lift safely. Two key points, lift with your legs not your back, and, the part that relates to this, when you carry something, position it such that the weight is as close to your body as you can. The expert said that the difference to your back, in carrying something with your arms extended vs arms close to you, is 100 hundred times more load on your spine. It should be obvious to a tow truck operator that the further out you extend the boom, the greater likely hood you are going to lift your front tires, given the same amount of weight. Something you demonstrated so well.