from Rookie’s keyboard
Hello, friends
Yesterday, I got an interesting e-mail asking about the logic behind the dual top tubes found on some commuting bicycles. I decided to make an entire post about this phenomenon. Thank you, Rick, for giving me the idea.
Let’s go.
At first glance, a second top tube is an unnecessary feature. But it has many reasons to exist such as:
Reinforcement
The extra top tube instantly boosts the overall strength of the frame. That said, the design makes more sense on larger frames as long top tubes experience more stress, to begin with.
It doesn’t take a 170IQ brain to understand that a longer pipe is easier to bend in the middle than a shorter one because its body serves as extra leverage. Longer frames suffer from the same issue.
Greater Stiffness
The supplementary top tube makes the main frame triangle smaller and therefore stiffens the entire frame.
The default belief is that stiffer frames are more efficient and responsive as there’s less energy loss and delay upon input from the rider.
Toughness
Two top tubes are more common for areas where people rely on their bicycles for all sorts of transportation. (Think of the crazy images of people transporting an entire store on their bikes.)
And since the“higher” top tube often has to support bulky cargo or serve as a seat for passengers, it can be damaged from daily overuse.
The second top tube acts as a supplementary “level of defense” and greatly lowers the likelihood of catastrophic failure that may render the bike unusable.
In areas where the bicycle is the main vehicle, a single top tube is seen as a liability because the bikes are often loaded with 120 lbs or more.
And don’t forget that those bicycles are made of steel. Steel is super tough, but it’s also subject to corrosion (rust). And when the main top tube is constantly in contact with external objects, the layer of paint can get damaged. Once exposed to air and moisture, bare steel rusts and can eventually corrode to the point of no return.
Battle-Tested
The dual top tube design is anything but new – it goes back to the late 1800s.
The original motivation behind the double top tube was to minimize frame damage during an accident – a common occurrence at the time due to the poor braking capabilities of the bikes and the unpaved roads. Back in those days, even the cheapest V-brake would feel like something made in the laboratory of a genius.
Marketing
During the early days of double top tubes, companies were often installing an advertising placard between the two top tubes.
Looks
Some bicycles have a second top tube for appearance rather than strength.
Carrying The Bike Is Easier
A second top tube makes bicycle carrying on the shoulder easier for two reasons:
- The second top tube does not have brake and gear cables digging into your shoulder.
- The upper top tube can be used as a handle to stabilize the bike. Here’s how – slide your arm through the main triangle ( he lower top tube is resting on your shoulder); hold the the upper top tube to stabilize the bike.
Did you know that? Early motorcycles relied on a dual top tube too. The second top tube was there to reinforce the frame and provide a stable location for the fuel tank.
Downsides?
Dual top tube frames have the following shortcomings:
Additional weight. The second top tube increases the overall weight of the frame.
Reduced space. The presence of a second top tube takes up space that could be utilized for a frame bag, U-lock, or water bottles.
Outdated design. Double top tubes have a vintage appearance that may not appeal to everyone. If you prefer a contemporary look for your bike, opt for a single top tube.
Twin Top Tubes/Splitting Top Tubes
The double top tube has a variation known as a twin or splitting top tube. In this case, two top tubes split out of the head tube.
This frame architecture is found on retro BMX bicycles and mountain bikes.
The purposes of this design are:
- Increased rigidity and durability
Certain bikes with robust twin-top tubes are specifically built for freeriding and are capable of withstanding long travel forks and a lot of abuse.
- Visual appeal
Sometimes twin tubes are used primarily for aesthetic reasons, providing a unique and modern appearance.
A major drawback of twin top tubes is that the upper section of the bike becomes noticeably wider, particularly around the saddle, making it common for riders to bump their knees against one of the top tubes.
And there you have it, friends. Another informational post on a niche topic.
I hope you like it.
Until next time,
Rookie.
P.S. I am waiting for your e-mails.
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