My truck is rated to pull about 8,000lbs. Without pulling any trailer, I can go 70mph and I'll get ~19mpg. I've pulled about 7,000lbs with it on a flatbed trailer, and the truck pulled it just fine, shifted as it should in tow mode and my mileage dropped to ~14mpg @ 70mph.
Recently I was going to pull my company's enclosed box trailer to a job in Louisiana. I didn't think it would be a problem since the trailer was nearly empty (trailer + a few items inside = ~4,000lbs) but my truck did a terrible job of pulling it. I got 50mi. down the road and called for a hot shot driver to take it the rest of the way because I was afraid I would damage my truck. I couldn't get above 8mpg, and that was keeping the speed under 60mph. The truck would shift between 3rd and 4th gear over and over, RPM going up to 3,500 just to maintain 55mph.
recap:
no trailer, 0lbs, 70mph, 19mpg, perfect performance
flatbed, 7,000lbs, 70mph, 14mpg, perfect performance
box trailer, 4,000lbs, 55mph, 8mpg, poor/potentially destructive performance
Obviously the problem was wind drag. Dragging the flat front of the box trailer through the air was like dragging a braking parachute same as a dragster race car does. Even though the box trailer was much lighter, it was much harder to pull through the air.
I cannot find any reference to drag in the documentation for my truck, or online, which strikes me as odd since my experience indicates that it is more important than trailer weight. Everything I can find about towing, talks only about trailer weight. My truck is rated to pull 8,000lbs, and on a flatbed trailer, I have no doubt it could pull that; probably even double that, if the load were say a 16,000lb sphere of solid iron on a tiny trailer that didn't have any appreciable wind drag. But put that sphere inside a box trailer, and I'm dead in the water.
If I were to install a load cell in my trailer hitch and feather my accelerator to keep the readout always below 8,000lbs*, I theorize that I could probably pull massive amounts of weight, with very slow acceleration and limited highway speed (assuming the trailer had brakes capable of stopping its own load). I theorize that on flat roads, I could probably pull even more still. I theorize that the manufacturer's towing capacity rating is just a "shoot from the hip" guesstimate and really isn't real-life applicable.
So why is wind drag and incline excluded from manufacturer's documentation and why does nobody talk about it? Aside from retrofitting my trailer hitch with a load cell, how can I calculate the load my truck is actually able to pull, given the frontal area of the trailer?
*EDIT: I wouldn't keep the readout below 8,000lbs, that would be much too high; like pulling an 8,000lb trailer straight up off the ground. I would need to find/calculate the proper readout that matches what the pull force is for a trailer that weighs 8,000lbs. But then we're back to "what kind of trailer?" a flatbed with no drag? a box trailer? what?
Recently I was going to pull my company's enclosed box trailer to a job in Louisiana. I didn't think it would be a problem since the trailer was nearly empty (trailer + a few items inside = ~4,000lbs) but my truck did a terrible job of pulling it. I got 50mi. down the road and called for a hot shot driver to take it the rest of the way because I was afraid I would damage my truck. I couldn't get above 8mpg, and that was keeping the speed under 60mph. The truck would shift between 3rd and 4th gear over and over, RPM going up to 3,500 just to maintain 55mph.
recap:
no trailer, 0lbs, 70mph, 19mpg, perfect performance
flatbed, 7,000lbs, 70mph, 14mpg, perfect performance
box trailer, 4,000lbs, 55mph, 8mpg, poor/potentially destructive performance
Obviously the problem was wind drag. Dragging the flat front of the box trailer through the air was like dragging a braking parachute same as a dragster race car does. Even though the box trailer was much lighter, it was much harder to pull through the air.
I cannot find any reference to drag in the documentation for my truck, or online, which strikes me as odd since my experience indicates that it is more important than trailer weight. Everything I can find about towing, talks only about trailer weight. My truck is rated to pull 8,000lbs, and on a flatbed trailer, I have no doubt it could pull that; probably even double that, if the load were say a 16,000lb sphere of solid iron on a tiny trailer that didn't have any appreciable wind drag. But put that sphere inside a box trailer, and I'm dead in the water.
If I were to install a load cell in my trailer hitch and feather my accelerator to keep the readout always below 8,000lbs*, I theorize that I could probably pull massive amounts of weight, with very slow acceleration and limited highway speed (assuming the trailer had brakes capable of stopping its own load). I theorize that on flat roads, I could probably pull even more still. I theorize that the manufacturer's towing capacity rating is just a "shoot from the hip" guesstimate and really isn't real-life applicable.
So why is wind drag and incline excluded from manufacturer's documentation and why does nobody talk about it? Aside from retrofitting my trailer hitch with a load cell, how can I calculate the load my truck is actually able to pull, given the frontal area of the trailer?
*EDIT: I wouldn't keep the readout below 8,000lbs, that would be much too high; like pulling an 8,000lb trailer straight up off the ground. I would need to find/calculate the proper readout that matches what the pull force is for a trailer that weighs 8,000lbs. But then we're back to "what kind of trailer?" a flatbed with no drag? a box trailer? what?
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