Over GVWR? Slow Down

[jponder]

I dont know if thats right Mike. Give me a general formula for the force of a weight on a grade and I could tell you. Up unto this point we have been using the work done by a brake , yes the work energy theoreom works great for that but the load induced by gravity and the difference in loads well I still dont know. I would be willing to bet that speed will be negligible on a 1 mile descent even if the speed changes a good bit. You have alot of energy to burn on a descent like that



Did you think any about calcs for grades?



I can get close but I am missing something... . Have you thought any about it?

 

[jponder]

Re: Re: Wow...

Did I mention that I'm a physicist by education ? [/B]



No offence meant zari. I am way outta' my league here.



Sorry guys, my head hurts. I am removing my subscription to this thread [/B][/QUOTE]



Sticks> dont worry about the relativity stuff. I doesnt apply here

all you need to know is

F=MA

g= 32 ft/sec*sec

Change in K. E = work done



oh yeah and of cours 1/2MV*V = Kinetic energy with those you can solve almost anything.

EXCEPT a general equation for force of a load induced by Grade and that will come shortly

 

[RustyJC]

Originally posted by jponder

Plus RustyJC has marked himself forever as a GP AND he owes me . 50 cents, I anint paying the extra postage to send him the 2 quarters. He is a marked Man forever

Be it known to all that John is a man of his word! Got the $7. 00 in yesterday's mail. Thanks, John.



Rusty

 

[Hohn]

YES A techie thread!!!



I LOVE this stuff! I can't believe I let some of them happen without me playing the poser.....



A lot of what matters when towing is TIME. How much TIME does it take to dissipate all that energy?



Ponder this: if you changed the atmospheric pressure in your office my 2 psi over the course of a minute, you would probably never even notice. If this change happened in a picosecond, you would probably go deaf if not be killed. (never mind that it never could happen because air moves slowly and all that)



So, the brakes can only dissipate so much energy so fast. Since we are dealing with energy over time, maybe POWER would be an appropriate descriptor to use?



So we could increase braking power by simply shedding heat faster, or increasing the amount of energy the brakes can store as a TER. Thus, we have the thicker rotors, vented brakes, etc.



But let's get back to our braking as energy theme. Say we have one guy cruising at 70 with 20K# out back. Our guy pulling 30K pounds has the same energy when he is travelling at 57. 15mph.



TRUE, it would take the same amount of energy to STOP these two vehicles. But what about simply slowing down to 20 mph? Obviously, our man with the 30K load has a lot more energy than our guy with the 20K load when both are going 20mph. Since the guy pulling 30K has a lot more KE, that means he must have had to dissipate much LESS KE than the guy with 20K pounds to get down to 20mph.



All that to say this: The guy who is overweight (30K pounds in this example) can slow down from 57. 15mph to 20 mph faster than the guy who is legally going 70mph with 20K pounds.



Conclusive proof that the linear increase with weight is FAR LESS significant than the exponential increase with velocity!!!



More proof that weight isn't the issue-- speed is.



HOHN

 

[jponder]

Originally posted by RustyJC

Be it known to all that John is a man of his word! Got the $7. 00 in yesterday's mail. Thanks, John.



Rusty

I could have bought a scientific calculator with that money :{

 

[jponder]

Originally posted by Hohn

YES A techie thread!!!



I LOVE this stuff! I can't believe I let some of them happen without me playing the poser.....



A lot of what matters when towing is TIME. How much TIME does it take to dissipate all that energy?



Ponder this: if you changed the atmospheric pressure in your office my 2 psi over the course of a minute, you would probably never even notice. If this change happened in a picosecond, you would probably go deaf if not be killed. (never mind that it never could happen because air moves slowly and all that)



So, the brakes can only dissipate so much energy so fast. Since we are dealing with energy over time, maybe POWER would be an appropriate descriptor to use?



So we could increase braking power by simply shedding heat faster, or increasing the amount of energy the brakes can store as a TER. Thus, we have the thicker rotors, vented brakes, etc.



But let's get back to our braking as energy theme. Say we have one guy cruising at 70 with 20K# out back. Our guy pulling 30K pounds has the same energy when he is travelling at 57. 15mph.



TRUE, it would take the same amount of energy to STOP these two vehicles. But what about simply slowing down to 20 mph? Obviously, our man with the 30K load has a lot more energy than our guy with the 20K load when both are going 20mph. Since the guy pulling 30K has a lot more KE, that means he must have had to dissipate much LESS KE than the guy with 20K pounds to get down to 20mph.



All that to say this: The guy who is overweight (30K pounds in this example) can slow down from 57. 15mph to 20 mph faster than the guy who is legally going 70mph with 20K pounds.



Conclusive proof that the linear increase with weight is FAR LESS significant than the exponential increase with velocity!!!



More proof that weight isn't the issue-- speed is.



HOHN

Welcome HOG Brother, pico second eh, hehehehehe. You are DEFINATELY speaking HOG language. I think we should use your change in air pressure as a tool to Question suspected Bin Laden people. Put them in a capsule at normal pressure and surround it with another capsule and suck the air out. Have numerous wastegates in the first capsule that you can open. Have a big meter that show the outer capsule's pressure. The first capsule is just big enough to squeeze them into and the second is the size of a gymnasium. Have a glass of water in the outer chamber right in front of a window that they can see and start the Vacume. When the water starts to boil at room temp ask them if they have any Idea of what their blood is going to do when you open the gates to evacuate their capsule, better YET have Chris Rock talking Smack to them as they watch the meter drop and then see the water start to go to GAS!



You might want to back off the pressure and just blow all the fillings out their mouth the first time.



I'm sorry but my son is in Afghanistan and I just wish we werent so NICE and gavem what they give.



You are correct on your analysis of energy. I'm against the use of Power though, I'd rather stick to energy where we can easily use the Work energy theoreom.



If yall need any other sadistic methods of torture let me know

 

[DLeno]

Boy I wish i had encountered this thread earlier, as I routinely think of 312. 5 slug trailers. While we all learned to live and breathe SI units, its takes but a single extra brain CPU cycle to think English and divide force (pounds) by acceleration (32 ft/s^2) and get mass (slugs).



While not so routine, I have certainly encountered GPs who scurry away like roaches when exposed to the light of Newtonian physics. Only I usually refer to them as worshipers who refuse to think.



This thread is a hoot and i only regret not seeing it earlier. Cant claim to be a certifiable HOG though, and I'm not a GP, so I don't know what you guys would call me



BTW, since physics is welcome here, may I presume to ask this teaser: how much total (constant) stopping force (in pounds) does it take to bring a 20,000 lb combo rig to a complete stop from 60 mph on level ground in 20 seconds, and at what rate (in watts) must energy be dissipated during that time to accomplish this?

 

[DLeno]

ok, in case anyone is interested:



I takes 2750 lbs of total constant stopping force to bring 20,000 lb combo to 60-0 stop in 20 seconds.



doing so requries dissipating 6. 5 MJoules of energy at the rate of 440 horsepower or 328 MW.



Important conversions:



1 HP is 746 watts

1 watt is 1 Joule per second

1 slug is 14. 59 kg

 

[OTRPU]

I don't know none of this stuff, all I do know is I slid for what seemed to be forever. Finally got it stopped, bout a foot from the problem. What I learnt was I can't stop fast so I go slower. And I do this 10 hours a day bout every day. Those that do it less prolly know more. . . but do they know better?



Tow Safe,

Steve J.

 

[snowracer69]

Hey y'all,



I just wanted to post in this thread to say:



I UNDERSTAND THIS STUFF!!!!



Ok, that's all! I'm just glad that the past 2. 5 years of school hasn't been a total waste, cause I actually get what you're talking about here. 'Course, I'm better w/ the aerodynamics of the pickups falling off the cliff for 1/4 mile then the whole dissipation of heat from the brakes, but I understand that stuff well enough too.



Here's a website some of you physics/enginerd guys might enjoy. Maybe it's cause I'm young, but I relate to most of the jokes on this site WAAAYYYY too much! Ah well, at least I'm good breading material! Varmint Al's page



Josh

 

[DLeno]

whats interesting for me to see is the apparent contradiction between GVWR statements and the actual truck hardware. But we gotta remember that:



GVWR is the mfg linkage to compliance with Federal safety standards. NHTSA does not enforce HOW the mfg arrives at the GVWR number itself.



GVWR MAY or MAY NOT represent the vehicles design limits, in my opinion. Indeed, there is evidence of some lawyer and/or marketing manipulation thing going on, if you ask me.



the mfg can declare any arbitrary GVWR they want to, as long as the vehicle can be shown, upon demand, to meet the federal safety standards when loaded accordingly. This creates every opportunity for the mfg to play games with 1 ton versus 3/4 ton ratings for marketing purposes.



The great mystery around what the weak point is that determines GVWR is becasue nobody wants to take the liability. suppose, for example, that a 3500 SRW GVWR (9900) is limited by wheels and tires (this may or may not be true I don't know). you won't find anyone willing to re-plate your truck to a higher GVWR by putting on different wheels!

 

[CFAR]

All I have to add to this discussion is one simple fact,



The way my truck steers, from the factory scares the HILL out of me, now put 10k behind it.....

 

[jponder]

Originally posted by DLeno

ok, in case anyone is interested:



I takes 2750 lbs of total constant stopping force to bring 20,000 lb combo to 60-0 stop in 20 seconds.



doing so requries dissipating 6. 5 MJoules of energy at the rate of 440 horsepower or 328 MW.



Important conversions:



1 HP is 746 watts

1 watt is 1 Joule per second

1 slug is 14. 59 kg

This thread did accomplish one thing. SPEED KILLS NOT WEIGHT

 

[Crowhurst]

Hmm... . Hohn said "Conclusive proof that the linear increase with weight is FAR LESS significant than the exponential increase with velocity!!! " That was on 20th August, and it's been bugging me ever since. This ole man can't die happy without suggesting that this is a terminological inexactitude.

An exponential function involves the constant "e" raised to a power which is a variable. Kinetic energy is the other way round- a variable raised to a constant power (i. e 2). In lay terms, an exponential function changes vastly more rapidly than a squared one. If Hohn was correct, we would all have to drive a lot slower! Now I'll go back to my knitting. Sorry, guys Nick.

 

[DLeno]

love the precision crowhurst!



note however that the term "exponential increase" is often used differently than the term "exponential function", and is often applied more generally to polynomial terms of the form kx^n where the exponent, n, is a constant and greater than 1. In this case, the term "increase" is a term describing how quickly such a term (with order greater than 1) increases in value, compared to a term of the same form when n = 1 (linear). Since any individual term in a polynomial can be expressed as a function we see that the term "exponential increase" in this case refers not to increases in the exponent, but increases in the value of the function f(x) = x ^n.



But yes, you are right that the the term "exponential function" is itself unambiguous and refers to very specific functions of the form ke^x, where the exponent, x, is the independant variable.



Since the kinetic energy function is of the form, f(x)=kx^2 it is appropriate to describe this polynomial function as as increasing "exponentially" even though clearly (as you point out) it is not an "exponential function".

 

[Crowhurst]

Dleno, you are quite correct, unfortunately. This sliding away from precise meanings is a great loss to our beautiful language. Let's take another example. You and I both know that "decimation", was a technique used by Roman Generals to encourage their legionnaires to greater efforts, or to punish them for past inadequacies. To do so, the Generals would kill 1 in 10 of their own legionnaires. (No wonder they eventually lost the Roman Empire!) To decimate is directly derived from the Latin "to take 1 in 10". Sloppy usage and lack of knowledge has led to this now being used to mean "killing a high proportion of". Even the Oxford English Dictionary has surrendered to this travesty. And now even my kids are teaching my grandkids to call me a Boring Old F--t. Nick.

 

[Dean Upson]

Originally posted by Crowhurst

To decimate is directly derived from the Latin "to take 1 in 10". Sloppy usage and lack of knowledge has led to this now being used to mean "killing a high proportion of". Even the Oxford English Dictionary has surrendered to this travesty. And now even my kids are teaching my grandkids to call me a Boring Old F--t. Nick.

I believe our Russian friends picked up on that concept during the battle of Stalingrad That type of action tends to get the troops attention.



Dean

 

[jponder]

I miss threads like this. They are a whole lot more fun than the political forum

 

[klenger]

Trouble maker



I personally would enjoy a thread like "Is it OK to drive 80 MPH when I am towing 2000 lbs overweight with my (opt 1: 6 speed manual) (opt 2: 47RE auto DTT modified) transmission using Amsoil with extended drain intervals with my (opt1: SWB) (opt2: LWB) truck on my way to a camping spot in the boondocks where I plan to dump my gray water on the ground and stay at Wal Mart overnight on the way back? While on this trip I plan to stop at the Bill Clinton library and museum.



Did I miss anything?

 

[RustyJC]

Originally posted by klenger

Trouble maker



I personally would enjoy a thread like "Is it OK to drive 80 MPH when I am towing 2000 lbs overweight with my (opt 1: 6 speed manual) (opt 2: 47RE auto DTT modified) transmission using Amsoil with extended drain intervals with my (opt1: SWB) (opt2: LWB) truck on my way to a camping spot in the boondocks where I plan to dump my gray water on the ground and stay at Wal Mart overnight on the way back? While on this trip I plan to stop at the Bill Clinton library and museum.



Did I miss anything?

Yep. Am I using a K&N, AFE or BHAF air filter? Do I have a GearVendors or U. S. Gear overdrive? Which exhaust brake?



Rusty