Why Do Plastic Wheels Break on My Model T Go Kart?

Back in the late sixties, early seventies the Model T Go Karts started to come out with plastic wheels. I am unsure of the actual make up, but my guess is that they are glass filled nylon or PEEK. My guess is based on my experience as a longtime mechanical engineer with a wide range of plastics experience. There are tell tail signs that the wheels are at least a nylon or PEEK, based on the fill patterns on the wheels.

However, it doesn’t really matter what they are made of, they are plastic and will degrade over time, especially if they are kept outdoors.

With the plastic wheels there are two types of failure:
1.) Mechanical Failure due to over-inflation and or rough terrain riding.
2.) UV Damage Failure – due to weakened plastic structure from UV degradation.

Broken Plastic Model T Go Kart Wheel

Broken Plastic wheel with UV degradation. Note the faded condition of the wheel. Also observe the broken spoke and rim. Owner complained of failure occurring during parade.

Very often the end user will try to pump up the tires beyond the 15 to 20 psi recommended and end up either popping a tire off the rim, or actually fracturing the rim.

There are some unique design features to the plastic rims that were developed over time to combat fracture mechanics. The rims were gusseted on later plastic rims to combat the rims from breaking. From my plastics experience, adding those gussets will aid in the plastic flow in the mold and lessen the stress risers in the plastic injection molded parts. As a result many from the factory rims had these gussets and give the go kart a signature mark.
There are also other features on the plastic rims that give the rim an authentic look, such as the raised simulated tire clamp areas. These features are unique to the rims and are not present on other types of replacement rims. (As a collector, or you trying to retain resale value of the cart, this is an important consideration. As of this writing the go karts routinely are fetching $2500 when they are in good condition.)

UV damage is a subtle or discrete material degrader. It is not readily apparent whether the rim is subject to degradation. It is not uncommon for normal looking rims to break, as well as faded units. However, as a general rule, if the wheel is faded, it has been subject to the sun, which faded it.
The sun, as we all know, emits UV (or Ultraviolet Radiation). This radiation rips through the plastic at an atomic level and can dissociate the bonds in the material, weakening it. The reason the plastic rims turn white, or fade out, is that the UV radiation has penetrated into the material and altered the coloring agents in the material. As a side note, plastics that are black tend to absorb the radiation preventing it from diving in further. So surface damage may occur over time on blackened rims.

The UV radiation problem can manifest itself as chalkiness on the plastic, or even powdery-ness when scratched. Another manifestation is brittleness.
The plastic rims don’t just break at the rims section either, the ribs themselves can break or crack. These are subject to pretty high loads, especially when cornering, so it is not uncommon for the wheels to break at the hub or midway on the spokes.

As a general rule, the plastic rims are not salvageable as the UV damage and the possible cornering loads are pretty extreme.

People are selling plastic rims, and I guess that is their purgative, however, know what you are getting and beware of the dangers of possible breakage.

Aluminum rim with same details as original plastic rims

Observe the level of detail that is on the aluminum rim which is identical to the original plastic rims. For example the webbing between the spokes and the wheel clamp ridges added every other rib. These are authentic details that enhance overall retail value.

There is light at the end of the tunnel though. At the GoKartGuru.com we have invested in designing and developing aluminum rims that are made out of durable C319 aluminum. This is the kind of aluminum used in casting cylinder heads on engines. It is tough and reliable. Compared to plastic it is almost 4 to 5 times as strong. For example the C319 aluminum is 27000 PSI tensile strength, where as nylon is 5800-14000 psi. And even if the rim is made out of PEEK (which is another high strength injectable plastic) its yield strength is (9430-17400 psi).

Additionally, the aluminum will not corrode and is not affected by UV radiation at all.

The downside to aluminum is that it is slightly heavier than plastic, 5.4 pounds versus 1.5 pounds. Additionally they require painting, if you want to match the initial red rim look. Other wise end users do like the aluminum sheen look also.

If you are interested in looking at our aluminum wheels be sure to check out our Aluminum Wheel page. Keep in mind when you order more, you get a discount, versus ordering one at a time.

And finally, our rims are different than other aluminum rims on the market. There is an aluminum rim that has a square or diamond shaped spoke design to it. First this rim is made in China. Second it is not authentic. Third it does not have the same look as the original rims in that it does not have the gussets and clamp features the originals have. And finally they do not have the proper bolt pattern, they have four bolts versus the six bolt pattern.

These are important considerations especially if you are trying to retain retail value and keep the go kart sound mechanically.

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