Just when I thought I had a decent grasp on the math involved in towing....

[Olde School]

I had no idea the loads of towing could increase so much in various situations.
Watch this from about 6 minutes on.
MY POST IS NOT INTENDED TO BE ABOUT CYBERTRUCKS!!!

 

[Max123]

Ugh - using math to mislead people

The video goes fast, but if you slow down and actually take in some of his assumptions:

1) (7:05) He uses 1G braking force to arrive at his load transfer calculation. Let that sink in 1G... A BMW M3 on performance tires can achieve 1G 60mph-0mph deceleration. An empty F350 can brake at about 0.5G. Not sure what a loaded truck can reasonably panic stop at with a 11,000lbs load - but it is not 1G. Any math after that point is off by a factor of at least x2-x4 because of that little assumption he just casually slips in there.

2) In his trailer braking force diagram he sets the centre of mass (11,000lbs) at 3ft above the hitch and 3ft back from the hitch. Stop and think about that again for a second. In what universe have you ever seen a trailer like that? If you had an 11,000 lbs boat / trailer you would likely be towing it on a something like a 25ft trailer and the axle would be at about 20ft from the hitch. To achieve a 10% tongue weight at static load, the centre of mass would be about 3-4ft in front of the trailer axle and about 16-17ft back from the hitch. Re-do that calculation using 17ft as the distance between hitch and CoM and the downward load at the hitch (F2) is... 1941lbs (again, at 1G braking).

Bad math.

People who build financial or mathematical models have a saying: garbage in, garbage out.

(edit - just looked at some trailer websites - total trailer length on 10,000lbs - gross weight is around 32ft. So its even less - not sure where the axle would be, 24-25ft back?).

 

[Pineapple Express]

Ugh - using math to mislead people

The video goes fast, but if you slow down and actually take in some of his assumptions:

1) (7:05) He uses 1G braking force to arrive at his load transfer calculation. Let that sink in 1G... A BMW M3 on performance tires can going 60mph-0mph can achieve 1G. deceleration. An empty F350 can brake at about 0.5G. Not sure what a loaded truck can reasonably panic stop at with a 11,000lbs load - but it is not 1G. Any math after that point is off by a factor of at least x2-x4 because of that little assumption he just casually slips in there.

2) In his trailer braking force diagram he sets the centre of mass (11,000lbs) at 3ft above the hitch and 3ft back from the hitch. Stop and think about that again for a second. In what universe have you ever seen a trailer like that? If you had an 11,000 lbs boat / trailer you would likely be towing it on a something like a 25ft trailer and the axle would be at about 20ft from the hitch. To achieve a 10% tongue weight at static load, the centre of mass would be about 3-4ft in front of the trailer axle and about 16-17ft back from the hitch. Re-do that calculation using 17ft as the distance between hitch and CoM and the downward load at the hitch (F2) is... 1941lbs (again, at 1G braking).

Bad math.

People who build financial or mathematical models have a saying: garbage in, garbage out.

(edit - just looked at some trailer websites - total trailer length on 10,000lbs - gross weight is around 32ft. So its even less - not sure where the axle would be, 24-25ft back?).

Thanks for your analysis. I haven't watched this whole video but I have watched this particular YouTuber (Engineering Explained) over the years and sometimes his videos seem OK, and other times his videos are based on some very poor/misleading assumptions (my opinion) and as such I've given up on watching his videos.

 

[macro]

The relevant bit. Steel typically deforms before failure giving you warning of bad things to come. Cast aluminum not so much.

 

[Max123]

Just to give you guys an idea of what 1G braking looks like - that's going from 60-0 in about 125ft.

The relevant bit. Steel typically deforms before failure giving you warning of bad things to come. Cast aluminum not so much.

I totally agree with that. Aluminium is also susceptible to metal fatigue based on a finite number of stress cycles so undoubtedly a steel frame offers a ton of advantages (excluding corrosion risk).

I don't have a problem with the premise that a cybertruck might not be a great tow vehicle - for a lot of different reasons. I just absolutely hate people creating fake or misleading scenarios in service of a point.

First they beat it up with an excavator, then they white-board a bunch of bad math. What gives? Just say you don't like it because it looks stupid and keeps breaking.

 

[Squire]

Ugh - using math to mislead people

The video goes fast, but if you slow down and actually take in some of his assumptions:

1) (7:05) He uses 1G braking force to arrive at his load transfer calculation. Let that sink in 1G... A BMW M3 on performance tires can going 60mph-0mph can achieve 1G. deceleration. An empty F350 can brake at about 0.5G. Not sure what a loaded truck can reasonably panic stop at with a 11,000lbs load - but it is not 1G. Any math after that point is off by a factor of at least x2-x4 because of that little assumption he just casually slips in there.

2) In his trailer braking force diagram he sets the centre of mass (11,000lbs) at 3ft above the hitch and 3ft back from the hitch. Stop and think about that again for a second. In what universe have you ever seen a trailer like that? If you had an 11,000 lbs boat / trailer you would likely be towing it on a something like a 25ft trailer and the axle would be at about 20ft from the hitch. To achieve a 10% tongue weight at static load, the centre of mass would be about 3-4ft in front of the trailer axle and about 16-17ft back from the hitch. Re-do that calculation using 17ft as the distance between hitch and CoM and the downward load at the hitch (F2) is... 1941lbs (again, at 1G braking).

Bad math.

People who build financial or mathematical models have a saying: garbage in, garbage out.

(edit - just looked at some trailer websites - total trailer length on 10,000lbs - gross weight is around 32ft. So its even less - not sure where the axle would be, 24-25ft back?).

I made pretty much the same observations especially around the 3’x3’x1G bit. His example did have me mentally replace the variables in the formula to my specific boat and trailer setup which definitely eased the mind over the magnitude of possible sudden downward pressure on the hitch.

 

[Olde School]

Appreciating the replies! Well written.
All in all, my take away holds for me - there are more factors to trailering than I had ever been aware of. So, to push any of the known boundaries is not a good idea.