Friday, October 9, 2009

We Have a Plan! … for Clifford and the $PRITE

With a great deal of help from friends and in particular, Mark Shelley, we now have a tangible plan for the Smart car bed and a means to load the car up on there.  Basically, this design lets us just drive it up and tie it down.

I had a few constraints:

  1. The deck needed to be 102” wide
  2. The car should be loadable from either side, driver or curb side of Clifford
  3. It should be a “drive-on” solution so no special mechanical, pneumatic or hydraulic dependencies to get it onboard.
  4. The design of the bed should be for ease of fabrication and only intended to be for carrying the Smart car.
  5. The bed should also allow for full and easy top side access to the truck chassis and parts for maintenance as well as future alterations should they be desired.
  6. The bed should be designed so that construction costs should be as low as possible and within reasonable reach of most HDTers.
  7. There should be ample protection for both the smart car and the trailer from damage caused by the truck’s tires throwing stuff into them or losing pieces of tread.
  8. Tie down of the smart car should be simple and easy to secure and very safe.

A few basics:

Clifford is a 2000 Volvo VNL64T770 with just under 600,000 miles. It has a Detroit S60 Engine and an Eaton 10 speed gen I Autoshift (with clutch pedal). It came from the US Express Fleet and was an owner/operator truck for a short time.

The wheel base is a little longer and I am keeping it tandem but dropping the outer tires on the forward axle. It has a full sliding 5th wheel hitch on it with an extension that allows it to be positioned nearly to the rear end of the square frame of the truck.


Truck Modifications to be made:

Only 1.  The frame will need to be extended to allow the commercial 5th wheel hitch to be positioned far enough back that the forward corners of the towed 5th wheel will not contact the side of the Smart car when it is loaded onboard.

I am considering putting an ET Jr. air ride 5th wheel hitch on it at some time to replace the commercial hitch.

Although I am using the ideas of others to load a Smart car crosswise on the bed of the truck, this design is significantly different than what many of these others have implemented, so far. It has no storage or skirting designed into it but should be fairly easy to add  some lockers in the future, should that be desired. Here are a few pictures of the designs of others that are carrying Smart cars on their trucks.


Bill and Joan - Their solution includes the Ramps I will use .

They also have a minimal transport bed to carry the car. The ramps store under the car in a special compartment built just for them but it was a very tight fit.  

They are the new Big Boy II folding ramps from Discount and are 12’ long with a 12 degree bend in the center to ease the break over angle where they attach to the bed. They are light enough at 54 lbs to be handled easily and strong enough (2000lbs) to handle the weight of the Smart car.




Virgil built a minimal bed, too. He has a movie of loading his Smart. He chose 16’ straight ramps

Each of these folks use a winch to load and unload but some occasionally unload by just driving the car off their truck and down the ramps.

Although when I asked the question, “Why load/unload a smart car from the driver’s side?” I did not get any answers that gave a concrete reason. Some said it was because of winching it up backwards and there is only 1 tow eye attachment in the front of a smart. Others said that if stuck on the side of the road in the truck, anything on the curb side would make offloading to that side impossible.

My thinking has been that the curb side makes more sense because the truck can be positioned in front of a driveway, along a curb or other places without having to be parked on the wrong side of the road. To me, it is also unlikely that in any condition where the truck may be disabled on the side of a road that it would be possible to deploy 12’ to 16’ of ramp out into the roadway to offload the car.

However, it really seems more natural to load and unload the car by driving it on or off of the truck and preferable to be able to do this ambidextrously.  Theoretically, one could drive on from the curb side and then drive forward off of the driver’s side of the truck.  The only difference would be whatever difficulty the location and storage method of the ramps might add to the process.

Driving on from the curb side allows better gearing for the climb up the ramps as well as placing the driver’s side door towards the rear of the truck. This makes it a lot easier to get in and out of the driver’s seat of the Smart.

I am convinced that driving the car on and off of the bed is not as big of an issue and some people think.  I watched Red Dog’s wife, CarolAnne, drive their Smart onto their truck bed with only 105” straight ramps so it has to be a lot easier to do it with 144” ramps with a slight angle at the middle. He solved the problem of the sharp breakover angle at the edge of the bed by lifting the rails the car sits on when loaded, with a triple chamber air bag. Inflated, it allows loading  and unloading without a winch. Once onboard, it is deflated to lower the car flat onto the truck bed and then tied down.




The solution:

The overall view should look like this:

NashVolvoFullBuild NashVolvoFullBuildExploded

The frame is at its current length and will have to be extended to move the hitch back on it.

The actual bed is made of 3 deck sections and 2 tire troughs for the wheels to rest in once loaded and tied down and 2 fender units under the bed.  Each of these segments are independently constructed and then mounted together to form the whole bed.

NashVolvoFullBuildTopViewofDeck  NashVolvoMidDeck 

Each of the decks are constructed by creating a welded frame of 2” x 2” Angle iron. Specs show this as 3/16” stock but it can be upgraded to 1/4” if desired.

The wheel troughs are also made of 2” x 2” angle iron in 3/16” material. These run the length of the trough on each outer edge and are bounded on the outside with a 2” x 2” 3/16” square tubular steel rib. A full length weld is recommended on each of these seams of bonding the angle iron to the square tubing. NashVolvoTroughTopViewNashVolvoTroughBottomView NashVolvoTroughCloseUpView NashVolvoTroughFloorPlate

The floor of the wheel trough is 3/16” diamond plate steel, also full length welded. Althought the actual trough width needs to be 13.3”, 12” wide plate stock is a more common size so it should reduce cost per foot. It rests on the flange of the angle iron trim.  However, a preferable alternative may be rough expanded steel mesh to make the trough bottom. It would drain better and probably have a little more traction. It should be of enough thickness to replace the strength of the diamond plate. 

Some explanation about this plate structure is necessary. The floor of each trough is made of 3  separate pieces.   This provides slots through the floor that accommodates the tie down straps that go up over the tires and are winched down with 3” webbed straps on load binder manual ratchet winches. The cutouts at the outer end of each of the plates at the ends of the trough is where the ramps attach to the edge of the smart bed. The ramps have a tang under the upper end of the ramp which drops down into these slots and then is pinned to keep them from jumping out unexpectedly.

 NashVolvoTroughFloorPlateEdgeCovers3/4” steel tubing is used as a cover to protect the tie down straps from the sharp edges of the trough floor plate, provide a place to hook the free end of the straps and also to stiffen it against the forces of the straps.

The fenders are made of 3/16” steel plate, bent with two 45 degree bends to  extend down behind the tires of the rear axle. They are full length welded to 2” x 2” x 3/16” angle iron along the long edges to reduce vibration and to strengthen them against possible impacts from flailing tread should a tire failure occur. This should adequately protect both the car and the RV being towed. They are fastened to the boxed frames of all of the components of the bed.

All of these components are mounted to two 3” x 5” sq tube 3/16” steel beams that run the length of the bed. They are attached to the truck’s 2 frame members with 6 U bolts. A single piece of 3/4” Oil Soaked Oak (preferably white oak) the width of the beam, separates the beams from the truck chassis frames. This acts as both a shock absorber and allows some gentle movement between these supporting steel structures. This plate is very important to the continued integrity of the bed mounting system to the truck frame.

The Ramps should stow easily between the car and the back of the truck cab but will need to be secured against theft.

I have present pictures of my truck with measurements for planning purposes and quick reference available on my SmugMug area.

There is a lot more information available including more pictures and websites with bed building albums showing the different ways that others have put their smart cars on the back of their RV tow trucks.

This is the way we are intending to do it.