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dlduck · 05-19-2015, 03:59 PM

Does anyone know how much drop down I need from the receptacle going into the RV for towing on a dolly with a 2006 National Dolphin 36 ft V-10 gas model?

mhbell · 05-19-2015, 04:49 PM

This would depend on the hitch height of the tow dolly. With the tow dolly hitch level in the horizonal position measure from the front of the hitch to the ground. Now measure from the Hitch receiver on the motor home to the ground. if the distance is greater then the difference is how much of a drop you would need. For example if the hitch height is 15 inches and the receiver height is 19 inches, then you would need a drop of 4 inches. You can get adjustable ones to fit the receiver that will allow you to raise or lower the ball for the hitch to be level.

Gary RVRoamer · 05-19-2015, 04:49 PM

It's not critical with a dolly, just avoid a really steep angle on the dolly tongue. You can measure your dolly tongue height by simply holding it level and using a tape measure. Then guesstimate the different between that and the coach receiver.

It's primarily 4-down towbars where level towing is critical.

twinboat · 05-19-2015, 05:16 PM

Look up the dolly manufactures specs. They will list a hitch height, that you want to be near.

If the hitch is to high, dollys with attached ramps can drag, going into parking lots.

If mounted to low, the ramps could hit the car.

My Stiel Tow dolly, instructions gave me a hitch height spec. and I set it there, 6000 miles ago, with no problems.

I would think the hitch height, would be critical, with steering dollys. It would change the steering geometry.

My Class C hitch is low, so I used a 2 inch drop, upside down, to raise the ball, to the spec. height.

Brockx · 05-19-2015, 05:21 PM

Hitch height is also critical on tow dollys with surge brakes. Acme dollys with surge brakes require 14 to 16 inches from the bottom of the dolly hitch to ground for best operation.

edit: My Acme is a 2012 the current Acme FAQ is "14 inches is ideal".

ShapeShifter · 05-20-2015, 10:03 AM

Quote:

Originally Posted by Gary RVRoamer

It's not critical with a dolly, just avoid a really steep angle on the dolly tongue.

[...]

It's primarily 4-down towbars where level towing is critical.

I respectfully disagree. The dolly's coupler, the "cup" portion that goes over the hitch ball, should be close to level. That will prevent problems with the lever action trying to force the hitch off of the ball, or the edge of the coupler contacting the ball mount.

With 4-down tow bars, there is no such restriction because there is no ball and coupler -- the tow bar mounts directly into the hitch receiver. The concerns about the coupler/ball angle don't apply since those items don't exist for a tow bar. However, the tow bar has its own geometry requirements that dictate the level range.

The reasons are different, but both a tow bar and a dolly require hitch points of the correct height. Here is a good discussion about how to measure the required ball height (the dolly is the same as a trailer for this discussion): eTrailer: Choosing the Correct Ball Mount