Monday, June 13, 2011

Why tire carrier hinge kits using a trailer axle spindle break, crack, or snap

A quick search on the internet will provide you with some examples of broken spindles that have been installed in a swing out or swing away tire carrier application. There are many ideas, suggestions, etc. out there on why this happens; however, I thought it would be beneficial to provide our answers.

Why would we have the answers? Most of the fabricators commenting on the occurrence of the broken spindles either have a ‘friend’ or ‘brother-in-law’ that is a mechanical engineer or rocket scientist or some other reason of why they are a 110% right in their reasoning. We however have a full-time mechanical engineer on site with training in metallurgy. Although I personally have an MBA, I have a background in engineering with training in metallurgy as well. We also have our spindles tested by a metallurgical testing service in Utah to provide sound results. That being said, we have sold and used these spindles since 2002 and as such have a sound understanding of why they fail and what you as a fabricator, installer, or designer/engineer can do to prevent it.

** It’s also important to note that out of the one thousand plus spindles we have sold, we have only had one customer report of a failure. The failure was due to improper design, load, and bracing.

First off, let’s debunk a common misconception.

“Trailer axle stubs (spindles) don’t break on the trailer when you weld them, so why can’t you weld them on your tire carrier? Your sleeve design is smoke and mirrors.”

A spindle installed in a trailer application is welded directly onto the axle tube at the base of the spindle with the remaining 5 +/- inches exposed for mounting. The tire is then mounted with the bearings etc. onto that remaining 5 +/- inches of the spindle. All the pressure put on the spindle from the trailer is concentrated onto that area of 5 or so inches. Because the length is so short, the amount of bend stress inflicted on the spindle is greatly reduced.

Now imagine that you removed the tire from the spindle and then installed a 48” long extension tube onto the spindle. At the spindle end, you still use the bearings etc. and tightly secure it to the spindle. At the other end, you install the tire. Now drive around town with a load in your trailer and see what happens to the spindle. The bend stress is greatly increased on the spindle due to the extension of the tubing. All the force is now exerted onto the base of the spindle where it’s welded to the axle housing. There is much more flex, vibration, and movement in the spindle due to the extension. As such, its chances of failure are increased. The welding becomes much more critical in this example as opposed to the standard trailer setup.

For this reason, you can’t compare a trailer to a tire carrier as the application is different as well as the stress inflicted on the spindle.

How do you resolve this issue?

Because the spindle welding is far more critical in the tire carrier application, we eliminate the process at the base of it. Most all spindles that you will find that have fractured have failed at or near the base area of the spindle. This is also were they are commonly welded into the bumper.

A common welding error is excessive heat which causes the area to become brittle. The second most common welding error is quick cooling. After a hot weld, many people will throw wet rags on the area, spray it down, or dunk it in a cooling tank to quicken the cooling process. In this critical application, it also weakens the area and makes it more brittle. For those of you not using our sleeve design and wish to weld it anyways, make sure the area is welded at the correct temperature for the material thickness. After welding, provide a slow and even cool down for the entire area. This can easily be accomplished by laying thick leather over the weld area to keep it hot and insulated.

Competition 4x4 however uses a sleeve design to eliminate the need for welding at the base of the spindle. The sleeve also offers the option of a standard height for setting up your tire carrier using the provided drilled hole and roll pin.

The sleeve on our standard 1000 lb. spindle kits in single shear and dual shear applications have an outside diameter of 1-5/8” while the 1750 lb. spindles have a 2-1/4” OD. The sleeve gets tack welded into the bumper with the spindle inside of it. Once the correct height setup is determined, you can then fully weld the sleeve to the bumper top and bottom (with the spindle still inside of the sleeve at the desired height). The inside diameter of the sleeve will shrink and pressure fit onto the spindle. For added measure, we recommend putting two light tack welds on the bottom of the spindle to the bottom of the sleeve.

You can view full installation instructions on the sleeve and tire carrier hinge kit on our site at:

The use of the sleeve therefore eliminates fatigue and fracture of tire carrier spindles due to welding.

The spindle can still be fatigued if the tire carriers overall design is poor or has excessive weight. The next most common reason for failure is that of a poorly designed latch that allows side-to-side and forward-to-back movement. Competition 4x4 is currently working on finalizing some latch designs to be laser cut that will box in the latch end of the tire carrier to eliminate movement in all areas. This will eliminate the flex suffered by the spindle from poorly designed latches.

Lastly, the excessive weight from some tire carriers is just too much. Many designs have an over the tire rack/cooler area, two Jerry cans, and a hi-lift jack etc. This is a lot of weight in addition to your wheel and tire. In order to provide the strongest solution, we offer our tire carrier hinge kits in a dual shear design. We have a ‘Z’ shaped bracket for our standard upright tire carrier hinges that tie in the top of the spindle and bolt the whole assembly to the bumper. This reduces all the flex that would be suffered by the spindle and transfers the load to the bracket.

We also have dual shear designs for mounting onto the face of a bumper or any other angle. We also have designs that use a 1” bolt instead of a conventional spindle setup.

Competition 4x4 is committed to providing solutions to all tire carrier systems. We have more tire carrier hinge kit designs that any other one manufacture. All our kits are CNC machined and laser cut to provide the best quality and performance. We are constantly improving and adding new designs and solutions to our product mix.

You can view all our tire carrier hinge kit options on our website HERE!