How Much Safety Margin to Allow...If Any?
Hi Everyone, We have a 2011 Ford Expedition 4x4 with the Heavy Duty Trailer Tow package. A few relevant specs: Axle = 3.31 Max Loaded Trailer Wt = 8,900lbs GCWR = 15,000lbs GAWR Front = 3,70...
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Tow ratings are not safety ratings per say. ONLY performance stds. IE what Larry is mentioning. I've towed 150-200% of a rigs tow rating with no issues from a safety standpoint. Meanwhile, a trailer that was 1/3 the max rating was loaded incorrectly, started to fishtail sway, and dang near took me off the road! This latter incident is what I would call a safety issue. This is solved with proper loading etc.
But as noted by Larry, Frontal area is NOT a forced factor in ratings much. Meanwhile weight is. BUT, a rig at 15K lbs with 70sqft of frontal area, needs about 105hp to go 60 mph. Meanwhile, same rig with 90sqft needs 135hp. Same hp as a 25K rig with 70sqft! These numbers can also vary by plus/minus 30% depending upon the total aerodynamics of the rig too.
I've had a rig rated to 16K gcwr, but it could not go up a 20% grade at 12K. Meanwhile, the rig with a gcwr literally 100 lbs LESS than its 8600 gvwr, went up the hill with at 12K. The latter had better low end grunt gears vs the one with over double the HP and 1/3 more torque!
In 30 yrs of towing, I have found safety is the human factor, along with tow ratings, but one better know what the spec is the engineer that specs the tow rating is using vs my needs! That engineer usually has a lower expectation on some things than I do.
marty
But as noted by Larry, Frontal area is NOT a forced factor in ratings much. Meanwhile weight is. BUT, a rig at 15K lbs with 70sqft of frontal area, needs about 105hp to go 60 mph. Meanwhile, same rig with 90sqft needs 135hp. Same hp as a 25K rig with 70sqft! These numbers can also vary by plus/minus 30% depending upon the total aerodynamics of the rig too.
I've had a rig rated to 16K gcwr, but it could not go up a 20% grade at 12K. Meanwhile, the rig with a gcwr literally 100 lbs LESS than its 8600 gvwr, went up the hill with at 12K. The latter had better low end grunt gears vs the one with over double the HP and 1/3 more torque!
In 30 yrs of towing, I have found safety is the human factor, along with tow ratings, but one better know what the spec is the engineer that specs the tow rating is using vs my needs! That engineer usually has a lower expectation on some things than I do.
marty
