Community Forums

travelinJ · 08-24-2018, 06:28 PM

I've been towing a Demco Kar Kaddy 460 SS with a 40' gas Class A. The hitch height is 22". Demco specifies 18" to the top of the ball. My problem is to set the ball height correctly I was dragging the hitch and dolly going in and out of storage and in campgrounds.
I just purchased a 4" drop Curt hitch with a 2" ball. Nothing drags now but the top of the ball is at 21.5". The Kar Kaddy tows the sedan straight without issue.

The sedan and Dolly are of moderate weight at 3820 lbs. All the weights are within the RVs chassis spec. Drive axle is at max, steer axle is 980 lbs below max, and gross weight is 560 lbs below max. I am going to lower the 'traveling' fresh water level to address drive axle weight.

What am I missing here. King pin angle is somewhat different, toe will be adjusted for the new king pin angle.

What ball height do people use on their car Dollys? On the highway I see all levels of balls, some clearly incorrect due to the rake of the neck of the dolly.

At 21.5" ball height the Dolly stills sits relatively level. Tire pans are approximately level which, besides alignment and king pin angle, is a primary concern.

Thoughts? Any suspension or chassis engineers out there?

Joe

twinboat · 08-24-2018, 07:04 PM

My tow dolly specifies 18" to the top of the ball mount, not the top of the ball.

Your 21.5" height, to the top of the ball, is about the same as mine.

Are you sure they say top of the ball ?

Mr_D · 08-24-2018, 07:08 PM

My KK-460 also specified 18". By playing with the drop on the hitch and long shank ball I got within 1/2".

travelinJ · 08-25-2018, 06:10 AM

According to where you look in the instructions there are at least two references to Ball height.

For hook up the instructions specify

"Secure ball coupler to 2” (5,000 lb. capacity) towing
vehicle ball only. Make sure that the hitch and the hitch
ball are in good condition and not rusted, loose or stripped.
Recommended ball height is 18” to the top of the ball.
Make sure hitch is locked down and secured with safety clip.
Criss-cross safety chains under tongue and secure to towing
vehicle frame."

To set the Toe the wording is slightly different:

"Have the tongue in a “hooked-up” position with the ball coupler 18” off the ground. Jack up the axle just enough to allow you to take the wheels off and put blocks under the axle."

I tried the adjustable hitch but the trailer and hitch would drag on driveway aprons, large road dips and speed bumps.

c92vette · 08-26-2018, 06:56 PM

There are a couple of things to consider with ball height. First is ground clearance of all parts of the dolly. Second is reaction to movement.

Your statement: "At 21.5" ball height the Dolly stills sits relatively level. Tire pans are approximately level which, besides alignment and king pin angle, is a primary concern." is correct.

What the manufacturer takes into consideration is the movement of the hitch during acceleration and stoppage which is why they "recommend" the height to be 18". When applying the brakes on the tow vehicle the front lowers and the rear rises. Therefore the hitch area rises and may cause the rear of the dolly to lower to an extreme if the ball is located to high. Plus if the dolly has surge brakes the tongue angle may be as such that the piston applying hydraulic pressure may not move as it is in a bind. The manufacturer takes into account all types of installations from pickup truck or cars to large motorhomes. Each one reacts differently during braking situations. I expect their recommended height is based on best use installations.

Also the reaction of the towed vehicle on the dolly must be considered. If the dolly tongue is too high the tow vehicle can place to much load on the tires of the dolly during a stop. Consequently if the tongue is too low the towed vehicle can remove pressure on the tires limiting braking action of the dolly. If the dolly is level there is minimal change in load on the dolly tires during all movements and the dolly works as advertised.

Try to get the dolly tongue as level as possible without dragging the hitch on the ground. If the best you can do is 21.5" so be it. I expect the dolly will perform well in this set up.