SERIOUSLY!< lets talk about weight

[jponder]

We got alot of info from a post started by Mike Ellis entitled "over GVWR?: Slow down.



I't kinda turned into, somewhat, a physics lesson and people got a little carried away like Me. The fact of the matter is the physics of pulling heavy is relevant. I personally think that the energy a rig has on level ground at a certain weight is relevant as it will give us an idea of the time to stop the rig. We have hashed alot about Kinetic Energy and it is easy to see that a rig with lower Kinetic energy will be stopped easier than one with a higher Kinetic energy. That is the Basis of the Idea that I have that speed kills not weight.



Zari enters into the equation with Potential Energy and that is a Killer. That is why they have runaway lanes in heavy mountain terrain. I emailed JC and Mike Ellis with waht I PM'd Thomas and Zari with and it follows





I need some help here. I thought I would try to do some kind of unified eq that would take weight and speed and also the force of gravity due to grade. I dont even have a dogone scientific calculater anymore! If you had a standard right triangle of sides a,b and c a being the rise and b being the run and c the hypoteneus and you wanted the force of gravity due to grade wouldnt it be Force = weight(sin(arctan(a/b)). Try it!



I am trying to do an equation that people could use by looking at a grade sign on the road. We can get a/b easily from grade. Let me know if you see an easier way or if that is right



I need the force of a rig on a grade using weight and Grade. Dont worry about speed for now.



I think that equation will give you the force of the vehicle in Lbs but I cant check it. I cant find a calculater that can do arc tan or any other trig functions at the Moment. Once I know that Force = weight(sin(arctan(a/b)) is correct I can continue

John Ponder

 

[Prairie Dog]

Shouldn't you be out changing your oil or waxing your truck or something?



Oops, sorry, you did say "seriously" didn't you.

 

[jponder]

At his point I am tired and I am missing something in the calcs. It is not clear to me how to tie weight into something usable with grade. I've been banging on this for a couple of hours and I just cant get it but I bet there is someone who can. Throw that initial equation in the trash, its useless. I think I got close with the laws of Cosine and using vectors but I am tired. It is not something that fell out easily.



I probably need to normalize the vectors or something but I am tired and I give up. I am humiliated, in 1985 I could have done these calcs in 1 minut and now I cant. Oh well go get them guys. there are alot of people who can do them in one sec

 

[merryman]

I never could do the calculations:{ . But then I never could figure out what numbers to stand them up against anyway.

We use the GVW, and GVWR, but after Sales kickes them up as high as they can, the warranty guys kick them back down as low as they can get them and then the DEQ guys diddle them around to deal with smoke and particulate cut off points, the weight cut off points for "truck" license fees in different states etc etc, wonder if they even talk to engineering??



Vaughn

 

[zari]

PM? Humm...

Guess have to go check. Are you talking about the projection of the weight vector (straight down) onto the slope? That would be what's "pulling" you down the hill. It's



Slope Weight Component = Weight x sinus (Slope Angle).



So a 20,000lbs rig on a 6 degree slope (not %, since percentage of slope is defined as 100 x (Vertical Distance, VD) / (Horizontal Distance, HD), so my 6 degree slope example corresponds to a 10. 5% slope [%slope = 100 x tan (Slope Angle)]) will be 'pulled' downhill by approximately 2091lbs. Is this what you're looking for?



Alain

 

[RustyJC]

John,



An e-mail with an Excel spreadsheet is on the way. As you'll see, up to 20% - 30% grades, just taking the %grade x gross combined weight to calculate the additional force due to gravity acting on the vehicle tracks very closely with the trigonometric calculations (assuming we've finally agreed that % grade is defined as rise/run).



Rusty

 

[Peter Campbell]

for small angles Sin(X) = X when X is expressed the proper way- in radians

 

[2ndgen2500]

when trying to decide applied force, there is the force perp to the grade, and the force downward, aplied and normal.

 

[dresslered]

I'm an engineer also, and would like to discuss weight issues as well. However, you can pull any equation out of your books and apply it any way you want. Do we want to be serious or not? Are you going to hand the officer a spread sheet and expect to get out of that ticket? The fact of the matter is that there is a stamp on the side of the truck which states very clearly the GVWR!



I confess, I exceed the limits with a completely empty camper--but just wait until I load it up with my provisions! And, tell me, what truck was even designed to carry a Bigfoot 3000, a large Lance, or any of the other bigger slide-in campers? I would think, that if any knowledgable officer ever saw the words "Bigfoot 3000" written on the side of a slide-in camper, he should know that he's got a violation at hand. I could give you all the equations in the world, until I was blue in the face, explaining why I was safer than someone pulling a 5th wheel (or driving a shopping cart as Costco for that matter). The fact is, that I am knowingly exceeding my rated limits. What are the true alternatives? Will I be stopped in Canada, and if so, what are my consequences? I don't want to pull a trailer so should I just go the route of Earthroamer? I love my setup, it handles fantastic, but this 11,000-lb rating sucks! :{

 

[RustyJC]

Originally posted by dresslered

I'm an engineer also, and would like to discuss weight issues as well. However, you can pull any equation out of your books and apply it any way you want. Do we want to be serious or not? Are you going to hand the officer a spread sheet and expect to get out of that ticket? The fact of the matter is that there is a stamp on the side of the truck which states very clearly the GVWR!

David,



With all respect, I didn't send John the spreadsheet with the idea that it would be waved in any officer's face. I put it together strictly to define the additional force acting to accelerate (on a downgrade) or retard (on an upgrade) a rig as a function of % grade. All it does it produce a number. What someone does with the number is up to them.



Rusty

 

[jponder]

Originally posted by RustyJC

David,



With all respect, I didn't send John the spreadsheet with the idea that it would be waved in any officer's face. I put it together strictly to define the additional force acting to accelerate (on a downgrade) or retard (on an upgrade) a rig as a function of % grade. All it does it produce a number. What someone does with the number is up to them.



Rusty

Thanks all,

Zari> Yes I am talking about the Vector that will pull you down the hill. I think your equation will work for small angles but I think the solution might not have any trig functions. I dont know my head is still hurting from monday night.



JC> Thanks for the spreadsheet and I am embarrased to tell you that I dont have Excell but I will forward it to work where I can open it. You mentioned The geometric calcs and the variance from the trig functions. I want to see how you calculated some stuff and maybe that will help me see the light.



Dress> I envy you for having that Bigfoot all I can say is one day, For now I will just stare at them when I se one going down the road and dream. With two kids in College and car notes I just dream of the Day I can afford one

 

[zari]

Ha!

dresslerd - I agree. I think these are really two separate issues.



One is that speed <b>and</b> weight play <em>both</em> a very important role in driving/towing safely. My energy conservation response in the previous thread was more a 'tongue in cheek' kind of response, not to justify driving/towing overweight. As I stated there, I will say again that, while speed (especially slowing down at higher weights) is a big factor in driving/towing safely, so is the weight itself - purely from a theoretical/mathematical point of view, and from a practical one (over 2,000lbs "pulling" on you when you're driving down a 10% slope at 20,000lbs gross weight should make you think! "I don't need no stinking engine break!" Yeah right... )



The second issue is legality (your point). If you drive/tow over any of your G*WRs, you are taking a risk - hopefully a well-understood, calculated risk. If anything should happen, you<em>will</em> have trouble with your insiurance, with your warranty, and with the officer



jponder: The projection of the weight vector parallel to the slope, as given in my post above works for *ALL* slopes.



Alain.