from Rookie’s keyboard,
Hello, friends
It’s time to dissect another cycling topic. I am dedicating this evening’s post to tube shape.
There are two main options – straight (the classic choice) and curved (the snob/alternative variant).
My preference is for straight as I like classic things. But don’t worry. I will still try to be as objective as possible.
Let’s start with curved tubing.
“Curves” have the following strong points:
- Shorter Chainstays (the main motivator)
Many aggressive road and track bikes have a curved seat tube. This architecture allows the frame to accept regular size tires while having shorter than normal chainstays.
If the seat tube isn’t curved, the rear tire will have to be smaller – and that’s big no in the world of road cycling.
The shorter chainstays reduce the distance between the cranks and the cassette and thus make the power transfer more efficient. At least, that’s what the manual says.
Curved seat tubes are not limited solely to road and track frames. There are freestyle, hardtails and dirt jump frames that have curved seat tubes too.
In the case of stunt bikes, the goal of the shorter chainstays is to make it easier to lift the front wheel while still allowing the frame to accommodate wider tires.
- Fork Clearance
Many MTBs have a curved downtube. The goal is to create clearance for long travel suspension forks.
When the fork compresses, the front tire gets closer to the frame. If there isn’t enough clearance, the wheel will hit the frame.
- Unisex Look
Classic bicycles with horizontal top tubes and straight tubing look masculine. To reach a larger audience, some producers rely on curved tubing because it makes the bike less “edgy”.
- Up-to-Date Appearance
Sloping top tubes and curves are the norm for new school frames. Some people like the modern look and go for it.
Others like me hate it and wish that the industry would revert to the old days.
- Compliance (theoretical)
Curved tubes are allegedly more compliant and offer a smoother ride. Hence some frames have curved seat stays meant to reduce the rear vibrations.
Let’s be real. The effectiveness of this measure is questionable.
The Downsides of “Curvy” Bikes
- Very Limited Seat Post Insertion
Curved seat tubes limit the length of the seat post that can be inserted into the seat tube.
This creates issues for shorter riders who have to lower the seat post substantially and for those who purposefully install an extra-long seat post to make a jump bike easier to pedal when not doing stunts.
The first problem is prevented by getting a shorter seat post that doesn’t reach the curve of the seat tube.
In the second scenario, the only options are to accept that a jump bike is not designed for comfortable seated pedaling or to use a frame with a straight seat tube.
- Weight
The shortest distance between two points is a straight line.
A curved tube is therefore longer than an equivalent straight tube.
The extra length comes with extra weight.
The difference is minimal and doesn’t matter.
- More Difficult To Produce
Curved tubes require extra steps during production. From the outside, this may seem like a small issue, but 1 step becomes a million steps when you’re mass-producing a component.
Why I Like Them Straight
- Classic look
Straight tubes preserve the classic appearance of a bicycle. People like me who are after retro lines are likely to find straight tubes more aesthetically pleasing.
- Compatible with Long Seat Posts
A straight seat tube allows the use of longer seat posts making the bike more versatile. If the frame doesn’t have bottle cage mounts on the seat tube, it will be able to accept even longer seat posts.
- Maybe Stronger
Every bend introduces a weak spot. Hence people say that straight tubes are stronger. In practice, however, the overall strength of a frame depends on many factors such as design, used materials, craftsmanship…etc.
A well-built frame with curved tubes will be many times stronger than a poorly manufactured model with straight tubes.
When all variables are equal, however, straight tubes win.
- Stiffer
A straight tube has the potential to be stiffer than a bent one. That said, the overall stiffness of a tube depends on a number of properties such as material, length, quality…etc.
Final words
With the risk of sounding boring, I have to admit that it will be inaccurate to conclude that one type of tubing is superior to the other since the final outcome is dependent on the overall design, the used materials, the geometry and the quality of the production.
When all parameters are equal, the choice between curved and straight tubes boils down to personal preference rather than game-changing performance.
In other words, fellas.
Allow yourself to be free.
Until next time,
Rookie
Leave a Reply