3-wheeled motorcycles are the new trend—but are they a good investment?

For Polaris Industries, there's an unexpected reason for optimism: pavement.

While the Minnesota-based company (and the industry at large) continues to struggle with its trademark off-road vehicles, motorcycle sales are growing — and so are the number of wheels.

By now you've probably seen a Polaris Slingshot cruising around your town. It's unique, kind of like the Batmobile mated with a dune buggy. It has two wheels up front, one in the rear, and side-by-side passenger seats within a partially exposed cockpit.

Basically, the Slingshot mixes some of the stability of a car with some of the freedom of a motorcycle, which is why some states aren't exactly sure how to classify it.

Slingshot classifies itself as a three-wheeled motorcycle.

Slingshot, a go-cart by Polaris.
Myung J. Chun | Los Angeles Times | Getty Images
Slingshot, a go-cart by Polaris.

It doesn't have airbags or meet automotive safety standards, so most states agree: It's a motorcycle.

However, in some states they call the Slingshot an "auto-cycle." In South Carolina, it's a "passenger vehicle," and in North Dakota, they simply call it "unconventional."

It's not just semantics. Different vehicle classifications require different types of licenses and additional personal safety equipment.

Polaris isn't alone when it comes to tapping into this market of three-wheeled motorcycles.

Canada-based Bombardier Recreational Products (BRP) also has a popular three-wheeler in the Can-Am Spyder, and then there's the T-Rex series by Campagna, another Canadian company.

A 1932 Morgan Supersports three-wheeler as shown on CNBC's "Jay Leno's Garage."
Source: CNBC
A 1932 Morgan Supersports three-wheeler as shown on CNBC's "Jay Leno's Garage."

Although there's growing excitement within the industry, three-wheelers are nothing new. In fact, since 1909, the Morgan Motor Company in the U.K. has been making them from the get-go.

Comedian and car enthusiast Jay Leno even has one, a 1932 Morgan Supersports.

Is it a good investment? In the above video from CNBC's "Jay Leno's Garage," Leno and automotive valuation expert Donald Osborne discuss how his iconic Morgan has appreciated over time compared to two other non-four-wheeled vehicles — a 1983 Ducati 900SS (two wheels) and a 1977 Pinzgauer 712K (six wheels).

Each week, Jay Leno shares his thoughts about hot topics in the auto industry. Tune in to "Jay Leno's Garage" Wednesdays at 10 p.m. ET/PT on CNBC.