Dose the weight on tongue go up from leverage?

[sdasaro]

Pretty much that's the question. I have a 2013 Winne View 24J, v6 turbo diesel. Would like to have some sort of toad so the bride and I can leave the campgrounds on occasion. I really don't want to pull anything because I can get into most shopping centers with no problem and I believe that would change drastically if even a tow dolly was added. The tongue weight limit is 500 lbs. The scooter I am considering is under 300 lbs. I would guestimate the ramp and platform of the receiver hitch mount carrier to weigh in at about 60 lbs. The MC salesman suggested that it would be more than the sum of it's parts because it stands about 18 in. behind the hitch and thus would exert leverage on the hitch. Tom over at Winni said the 500 lbs is vertical weight on the hitch but didn't think a 350 lb. payload would be a problem. Any experience greatly appreciated.

Regards

Capt.

 

[Lowell]

The weight of the scooter is still 300 lbs. If the length of the support bracket is 18", then you will only be putting 450 ft-lbs of torque on the hitch.  It should handle that easily.

 

[sdasaro]

Tx Lowell. How did u derive that leveraged weight? I would like to know.
Regards
Capt.

 

[Gary RV_Wizard]

This is always a tough thing to assess. The receiver was designed to handle 500 lbs of downward pressure (weight) right at the end of the receiver, where a hitch ball usually goes. Since a ball mount is normally quite close, the moment of force (weight x distance) is about the same as the weight. As you move the weight further away, the force applied to the receiver increases (gets multiplied by a longer distance). This is a twisting or torque effect that can break welded joints or bolts, and also stresses the receiver mounts (where it attaches to the frame).  The engineer who designed the receiver doesn't know how well or poorly it is attached to the vehicle, so his rating is kind of guess work, based on assumptions about a reasonable quality attachment. For that reason, it is almost surely conservative.

Superficially, then, if you increase the distance by 3x, you triple the force being applied, so your 300 lb scooter indeed has an increased effect. Whether that actually overstresses the receiver is harder to say, since the engineers didn't test or calculate for that kind of load.

 

[driftless shifter]

E-Trailer says hitch tongue weight is reduced by 50% when using any extender. Seems like a CYA response as there are some pretty long extenders available and the 50% applies across the board. Think about using a cheater bar on a wrench to break loose a stubborn bolt. A two foot cheater may require you to stand on it and bounce your weight to break the bolt free. a five foot cheater may only take moderate effort with one hand. Bring the whole thing, including the motorhome to a welder that repairs heavy equipment and trucks. ask what he thinks. He may say you good, he may suggest welding in some gussets or braces.

Bill

 

[grashley]

Lowell's response is the definition of torque = distance X force, or 1.5 ft X 300# = 450 ft-pound of torque.  If you were only 0.1 ft from the receiver, the TORQUE is 30 ft-lbs.  Torque is a rotational force.

The weight applied to the end of the receiver will also increase with distance, as Gary said.  It is also more difficult to estimate.  If the 300# is applied directly at the receiver, then 300# is applied.  If the force is applied a foot away, or 1 X 300, certainly the force is greater than 300#!

Bill really offered the definitive suggestion.  Take it to a welding shop for evaluation.  Some hitches are very firmly attached, and can carry a heavy load.  Others are barely held in place well enough to support their own weight.  The welding shop can both evaluate and upgrade as needed.

 

[Gary RV_Wizard]

If the 300# is applied directly at the receiver, then 300# is applied.  If the force is applied a foot away, or 1 X 300, certainly the force is greater than 300#!

Yeah, but the component of that force in the straight-down direction is still only 300#. Technically the weight rating of the receiver itself hasn't been exceeded, but the torque (force x distance) can still rip the receiver off the RV, or maybe even twist the receiver itself. That's where the risk comes in.

The receiver manufacturer doesn't provide detailed torque specs, so all this arithmetic isn't real helpful except as a caution. The receiver spec doesn't say "500 lbs at no more than x inches from the lip of the tube", so we have no idea how to multiply for distance. Best we can say is, "the further away the weight is, the worse the torque gets". That translates to "keep it as close as possible so you don't have trouble".

Given that a ball mount typically places the weight several inches behind the receiver, I think that 300 lbs at 2 feet is probably ok on a 500 lb receiver, but [personally speaking] I would not want to exceed that.

 

[grashley]

Thanks Gary.  Those Physics classes were a looooong time ago.

 

[driftless shifter]

Hitch ratings,  in my opinion, are likely under estimated for a fudge factor and liability. A 350# limit in my mind is a soft figure. will something catastrophic happen you happen to end up with a 400# hitch weight? Probably not. THese hitches take up a large load when, say, you go over the kind of dip on a highway that compresses your suspension and makes you go oof in you seat. I imagine the tongue weight on hitch increases immensely at the same time. Now think about 250# me bouncing on the end of an 18 " breaker bar to break a frozen bolt free. An 18 " extension on a hitch with a 350# scooter and 60# rack bouncing on the end of a breaker bar and what kind of twisting force is being applied. It's way different from 350# tongue weight bouncing up and down right at the receiver. It's the lever twisting the receiver that the welder has to analyze. Heck on a cheap hitch the mouth of the receiver may even flare.

Bill

 

[sdasaro]

Tx guys for the physics class. You really went the extra mile for me and I appreciate it. The scooter, a Honda PCX 150 is only 289# but I will buy a light weight aluminum ramp and rail combo @ under 50# and try to keep weight a far inboard as track width will allow. I can also reduce weight by carrying only 1 gal. of fuel in scooter tank as it gets about 100 mpg. 2.5 gals. @ 8 PPG is figured into the 289#. I can understand the principal tx to you and will approach it with caution.
Happy motoring and a fun but safe 4th. to y'all
Capt

 

[Gary RV_Wizard]

Good luck, Capt!