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If you’ve been to or if you live in Southeast Asia, you’ll have seen a special type of motorcycle known as “underbones.”
But what is an underbone, and what makes them unique from a “regular” scooter?
Tune in to discover:
- The tell-tale signs of an underbone motorcycle
- Differences between an underbone and a scooter
Hello, and welcome to another episode of 30-minute motorcycling – a podcast for those riders who are at the beginning of their own Dual Wheel Journey, where you’ll discover something new about how your motorcycle, moped, or scooter works – in less than 30 minutes.
Have you ever been to the Philippines, Malaysia, Vietnam or any other Southeast Asian country? Maybe you even live there? Either way, you’ve probably seen a couple of so-called “underbone motorcycles” there.
But what is an underbone motorcycle, and how is it different from a regular scooter or a backbone design?
That’s what you’re about to find out in this episode.
So, let’s cut to the chase – what is an underbone motorcycle?
An underbone motorcycle or just “underbone” is a type of motorcycle whose frame is made from structural tubes, and often has plastic body panels.
This makes for a stable design that can technically fit as many as 3 people – not that I recommend it, but in Southeast Asia, it’s not uncommon to see 3 people or more riding on one of these underbones.
The most well-known example of an underbone motorcycle is the Honda Super Cub, but some other noteworthy underbone designs include the Honda Wave,
the SYM VF3i,
and the Suzuki FX125.
What’s particularly interesting about an underbone motorcycle is the transmission. Just like a regular motorcycle, it has a regular shifter that you operate with your foot.
But here’s where things get interesting – even though there’s a floor shifter, there’s no clutch lever.
That’s because the transmission is semi-automatic, which means that the transmission engages the clutch automatically when it’s time to change gears.
The gear change itself, however? That’s up to the rider.
Some other noteworthy characteristics of underbone motorcycles is that the engine is positioned between the rider’s feet, and the fuel tank is mounted under the seat, rather than in the front of the rider.
Aside from these two design differences, the drivetrain is nearly identical on both an underbone and a regular chain-drive motorcycle.
It sounds quite similar to a scooter, doesn’t it? But there are a few differences between a scooter and an underbone.
The biggest one is the transmission – while an underbone uses a semi-automatic transmission that automatically engages the clutch, scooters use a unique form of transmission called a “Continuously Variable Transmission” or “CVT” for short.
The CVT gearbox doesn’t have a clutch or individual gears, but rather a setup with two pulleys and a belt for one “long gear.”
If you’d like to hear more about the CVT transmission, check out episode 22 of the 30 Minute Motorcycling Podcast.
In addition to the transmission being different, scooters typically have their engines near the rear wheel.
And speaking of wheels, why do you think the engine for an underbone can be placed near the rider’s feet?
It’s because an underbone motorcycle has much larger wheels compared to a scooter.
As an example, the aforementioned Honda Super Cub has 17-inch wheels, while something like a Piaggio Vespa PX200E only has 10-inch wheels.
So that’s what separates an underbone from a scooter. But there’s also another common type called a “backbone” motorcycle that’s worth a brief mention.
As the name suggests, a backbone motorcycle has a frame that acts as its “spine” and holds the engine and every other crucial component in place.
They’re also much easier and cheaper to build compared to an underbone frame, although they’re not as robust.
As a result, the backbone design is limited to cheap motorcycles with small engines.
And that concludes this episode of the 30 Minute Motorcycling Podcast, where we talked more about underbone motorcycles and what makes them different from both scooters and backbone designs.
I hope you enjoyed listening, and above all, that you learned something new.
If you have a topic that you’d like me to talk about in a future episode, email me at firstname.lastname@example.org.
Until next time, keep your helmet on and your eyes on the road. Bye!