Attention: TDR Forum Junkies 
Mike Ellis
TDR MEMBER
I have had several e-mails from various folks over the last several months asking about the old thread on GVWR and the HOGs out there. I finally took a couple of minutes to convert my graph in Excel over to jpeg, am posting it here so people can see the relationships and maybe understand a bit better what we were talking about.
For those who didn't see the old thread, and are wondering "What the heck does this graph show me?", it all boils down to the fact that when you stop your truck your brakes have to soak up the kinetic energy of your motion. KE = 0. 5*m*v^2, so if you are heavier or faster your brakes have to work harder to stop. You can always lower the braking work required simply by slowing down a bit.
The graphs shows the comparative energies for a truck that weighs 6,800 pounds empty but has a 10,500 pound GVWR (hmmm suspiciously like my '97 1-ton Dodge
). The blue curve shows the energy of the empty truck. The pink curve shows the energy for the same truck loaded to GVWR. Notice that the energy of the truck at GVWR (10,500 lbs) at 65 mph is almost the same as that of the empty truck moving 80 mph.
Quite simply, if you are loaded to GVWR and driving 65 mph, in a stopping situation your brakes have to work as hard as they would if you were running at 80 mph (!) empty. OK, no surprise there, we all know that running heavy translates to a longer stopping distance, although some might be surprised at how significant the difference can be.
But suppose you are one of the guys who likes to speed, even when loaded all the way up to your max GVWR. If you push up to 80 mph on the Interstate like all the rest of the traffic around you, now your brake system has to do the same job as if you were travelling 100 mph in the empty scenario - that makes for a LONG stop, and if you are like most drivers you probably aren't allowing enough distance to the car in front of you at that speed to stop in a panic situation.
So the common sense message that everybody "knows" but ignores anyway, is: If you are loaded heavy, SLOW DOWN. Check the other curves on the graph, they show the energies for the same truck but overloaded by 1000, 2000, and 3000 pounds over GVWR. It shows that to keep the braking energy roughly the same as the truck loaded to GVWR, you should be slowing down even more.
If you are in mountainous terrain or just trying to stop on a downhill, being overloaded hurts you some more because you now have additional potential energy (m*h*gravity) to deal with. So on a downhill, slow down even more.
Moral of the story: Watch your weight, watch your speed, use common sense, and give yourself plenty of room to stop. If you are going downhill, give yourself more! (grin)
For those who didn't see the old thread, and are wondering "What the heck does this graph show me?", it all boils down to the fact that when you stop your truck your brakes have to soak up the kinetic energy of your motion. KE = 0. 5*m*v^2, so if you are heavier or faster your brakes have to work harder to stop. You can always lower the braking work required simply by slowing down a bit.
The graphs shows the comparative energies for a truck that weighs 6,800 pounds empty but has a 10,500 pound GVWR (hmmm suspiciously like my '97 1-ton Dodge
). The blue curve shows the energy of the empty truck. The pink curve shows the energy for the same truck loaded to GVWR. Notice that the energy of the truck at GVWR (10,500 lbs) at 65 mph is almost the same as that of the empty truck moving 80 mph. Quite simply, if you are loaded to GVWR and driving 65 mph, in a stopping situation your brakes have to work as hard as they would if you were running at 80 mph (!) empty. OK, no surprise there, we all know that running heavy translates to a longer stopping distance, although some might be surprised at how significant the difference can be.
But suppose you are one of the guys who likes to speed, even when loaded all the way up to your max GVWR. If you push up to 80 mph on the Interstate like all the rest of the traffic around you, now your brake system has to do the same job as if you were travelling 100 mph in the empty scenario - that makes for a LONG stop, and if you are like most drivers you probably aren't allowing enough distance to the car in front of you at that speed to stop in a panic situation.
So the common sense message that everybody "knows" but ignores anyway, is: If you are loaded heavy, SLOW DOWN. Check the other curves on the graph, they show the energies for the same truck but overloaded by 1000, 2000, and 3000 pounds over GVWR. It shows that to keep the braking energy roughly the same as the truck loaded to GVWR, you should be slowing down even more.
If you are in mountainous terrain or just trying to stop on a downhill, being overloaded hurts you some more because you now have additional potential energy (m*h*gravity) to deal with. So on a downhill, slow down even more.
Moral of the story: Watch your weight, watch your speed, use common sense, and give yourself plenty of room to stop. If you are going downhill, give yourself more! (grin)
