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Jim Shepherd





Thoughts and Concerns About Towing Large Trailers

With a Bus Conversion/Motorhome

Updated 1/17/11 with updated links

Over the years, I have made many posts of various bus conversion bulletin boards, expressing my concerns about towing large trailers with many types of busses.  I have pasted parts of three of my replies that will give you some thoughts about my concerns:

Post 1:

There have been many threads on towing trailers behind buses on this board. As most of you know, I have committed to writing an article for George and Sue Myers on the subject (even apologized to them at Bussin 2005 for being so tardy). (Editorial Note:  George and Sue no longer publish their bulletin - I still hope to get this information into a format that can be published)

The article will address some of the issues involved and hopefully let the reader make a better decision. I can’t begin to go into all of the details here, but the following are some brief thoughts.

In general, buses were never designed to pull a trailer. Most do not have strong frame rails like a truck. Instead, the trailer hitch must attach to the engine cradle system. I won’t go into all of the problems that can occur there.

There are two major force components when we pull something: horizontal and vertical. Pulling a toad is basically a horizontal load and an engine cradle in sound condition with a well designed hitch can handle any reasonable sized toad. It is when a vertical load is introduced that problems can occur. Reinforced engine cradles combined with good hitch design and equalizer hitches can handle reasonable sized trailers. Bear in mind that equalizer hitches can introduce their own frame issues and care must be exercised in how the hitch is attached to the engine cradle.

Post 2:

The big issue is the structure of the bus. Any trailer hitch design will attach to the engine cradle system on most busses. The cradle was not designed for some of the large loads that trailers can impose on them. This can be made worse by corrosion and fatigue which can reduce the ability to handle large loads.

There are two kinds of load: horizontal (straight pull as in a tow bar and toad). The second is vertical load. In my opinion, most engine cradles that have not been compromised by corrosion will handle reasonable horizontal loads/pulls (i.e. most any size toad). It is the vertical loads that are a concern. Any trailer should have at least 10% of its weight imposed on the trailer hitch. Thus a 5,000 pound trailer will impose at least 500 pounds on the hitch minimum. That is a lot of load on the engine cradle structure.

Some folks use equalizer hitches to take some of the load off the trailer hitch. That works to some degree, but puts some different loads into the system that can cause problems if the hitch is not properly designed.

Lots of folks tow large trailers and have had no problem. Having said that, there are also folks who have reported frame problems. In my opinion, you are really pushing the limit, if you have a trailer that weighs more than 5,000 pounds.

Larger trailers can be used with auxiliary trailer tongue dollies or specially designed trailers. As a part of gathering information for an article I am writing, I have described some of those systems on my web site:


You mention GVWR. That is for the bus only and the trailer would not normally count against that rating. The rating that includes trailers is GVCWR where the “C” is combined which includes the bus and trailer. Since buses were not designed to pull trailers, they do not have a GVCWR. The main issue with the weight rating is to make sure that no axle is overloaded (each axle will have a rating) and the trailer impact on the brakes. If no auxiliary brake are used, you should not exceed the GVWR which is a real challenge with some conversions.

There are some other issues that might come into the pictures. Overall length can be a concern in some states on some highways. Having enough power and gearing can also be a concern.

Post 3: 

To build on Tom’s excellent post, you can also apply the term “engine cradle” to many/most non-transit busses.

Most commercial motorhomes, as well as school bus and truck conversions have a true frame system (two “C” channels running the length of the vehicle). However, most over-the-road buses do not have that type of frame. Some are monocoque (body stressed design such as GMC and early MCI) and some are tube frame (Eagle, Prevost, and recent MCI). In either type of construction, the engine is supported by a structure that can be called a cradle. In most cases that is a tube structure tied into the rest of the bus structure. It is designed to support the engine and make installation/removal a simple process. In the “T” configuration, where the engine runs for and aft, the cradle usually has two rails on which the engine mounts rest. Once the bumper is removed, the engine/transmission can easily be slid out the rear of the bus.

While it is not a part of the subject of this thread, you will often see me expressing a concern, in various threads on the bulletin boards, about pulling large trailers with busses which have engine cradles (as opposed to “C” channel frames). Engine cradles were designed to support the engine and mount the bumper, but they were not designed to support large vertical loads on a trailer hitch. Lots of folks get by with no problems, but it still is a concern to me.



As a part of researching the article, I have been looking for devices or trailers that minimize the weight on the hitch (a significant concern for bus application which were never designed to withstand large vertical tongue/hitch loads).  I am listing the results of this research. 


Trailer Toad 




Update 1/17/11:  The description below was written several years ago.  A review of the updated website suggest that they have a 3500 HD unit for $3195.  It appears that the smaller units are no longer available.

This is a recently marketed product that has been under development for quite a while.  It is covered by US Patent 6,820,887.  There are two versions.  The first has 8 inch tires and is rated for 2,000 pounds tongue weight (priced at $2695) and the second has 10 inch tires and is rated at 3,000 pounds tongue weight (priced at $2895). 

The unit was developed by Bob Riggle (owner of the patent) who is a drag racing driver/owner famous for his "Hemi Under Glass" exhibition car.

The axle is pivoted (small amount of rotation) and the unit is mounted to the bus/motorhome via a direct connection (no pivot).  The unit comes with the equalizer bars and an extra tire with cover. 

The marketing folks say that it backs up well for short distances without any change to the unit (wheels are not castered), while longer backing can be easily accomplished by locking the back-up arm.

I talked to Rick at Penn Glass Fenders (1-814-344-8110 ext.4) and he said it has been tested behind motorhomes with large overhangs and the unique solid mount system with the pivot axle tracks very well.

I have briefly reviewed the patent and I am impressed with the design of this unit. 



Tuff Tow Trailer Dolly



This device has been used by the racing industry for years.  It has been installed on OEM trailers.  There has been concern expressed over the tire size and the ability to handle large vertical movements that occur with buses and motorhomes with large rear overhangs.  The manufacturer has been asked to respond to those concerns.  I will post the response when I receive it.



Easy Tow

Note, this link (http://www.dallasmotorsports.com/) is still active, but it appears that they no longer carry this item.  A search of the internet would suggest that it is no longer available.  I will continue to list it, as do-it-yourself folks might want to consider the concept.




The Easy Tow is a complete system with articulated drawbar (with air bags) as well as an air bag suspended set of castored wheels.  It is essentially a custom built unit.  It is designed for a tongue weight of  up to 3,500 pounds.  It uses two Goodyear 13 inch trailer tires. 

They have been installed on some custom built Champion stacker trailers - mostly for racing teams.  I did not ask about price, but the person I talked to said “it ain’t cheap”. 

They went with the articulated draw bar design to handle large movement of the rear of a motorhome when going through dips – they felt that the suspension of the dolly wheels could not handle the full travel required for these applications. 

One interesting design feature is that they dump the air bag for the wheels and add air to the draw bar so that dolly wheels are raised off the ground for backing up.  This puts the full load of the trailer tongue on the bus for a short period of time. 

This dolly would probably not be a practical retrofit, but would be a great solution for a person building their own trailer or ordering a large trailer.




As was the case with Easy Tow, the manufacturer of this product seems to be out of business.  A search of the internet would suggest that it is no longer available.  I will continue to list it, as do-it-yourself folks might want to consider the concept.



The Hitch Buddy unit is primarily aimed at the goose neck/fifth wheel market. They do show a tag hitched to it. The likelihood of a bus or motorhome towing a goose neck trailer is not high. If it were used for a tag trailer, it would be an extra piece of equipment to find a place to store in a campground. Also, it adds to the overall length in a tag application and that could be a real issue in some states.

I downloaded the video and was surprised to see that the unit would allow backing up. I am not sure how they do that, but it apparently is possible. Both the Tuff Tow and Dallas Motorsports unit allow backing up.



Special Designed Trailers

Competitive Trailers (no web site   phone:  562-634-2006)

Note: as of 1/17/11, this phone number seems to be current.



This company makes various size stacker trailers under the name "Bus Companion".  It has wide spread axles (much like the old hay wagons), with the front axle being self-steering.  The front axle has built-in castor which is hydraulically reversed when the tow vehicle is placed in reverse.  A good friend has one and is very impressed with how it handles on the road and backing up.  The price is not for the faint of heart (over $50K), but it is the perfect answer for someone who wants to take all of his toys with him.


German Semi Trailer with pivoting front axle

Front view of front axle suspension

Rear view of front axle suspension


We were in Germany in March of 2005 and saw many semi size trucks pulling trailers like the one shown above (photos are thumbnail and can be enlarged by clicking on the photo).  Tag type trailers used in the US have a separate fifth wheel type dolly, while these trailers have the pivoting front axle mounted to the trailer.  The axle itself is suspended by a trailing arm and air bag suspension.  This type of trailer design would not put any vertical load on the hitch and would be very easy to hook up.  I would suspect that it would not be as easy to back up as a normal tag trailer.  It would be relatively easy to design and fabricate a scaled down version of this trailer for use behind a bus.