Time To Look at Curved and Straight Frame Tubing With a Critical Eye

This post compares the advantages and disadvantages of curved and straight bicycle tubing.

The Advantages of Curved Tubing

  • Shorter Chainstays

Some aggressive road and track bikes have a curved seat tube allowing the frame to accept regular size tires while having shorter than normal chainstays. If the seat tube isn’t curved, the user won’t even be able to install a tire of the same size.

The goal of shorter chainstays in this case is to shorten the distance between the cranks and the cassette and thus make the power transfer more efficient.

That said, 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 that case, 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.

For more information on the differences between short and long chainstays, consider reading the dedicated post.

  • Fork Clearance

Some modern MTBs come with a curved downtube. The purpose of this engineering 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 may get in contact with the frame.

  • Unisex Look

Classic bicycles with horizontal top tubes and straight tubing look masculine. To reach a larger audience, some producers rely on round tubing because it makes the bike less “edgy”.

  • Modern Appearance

Sloping top tubes and curves are the norm for new school frames. Some people like the modern look and go for it.

Others hate it and wish that the industry would revert to the old days.

  • Compliance

In theory, curved tubes are more compliant and thus capable of offering a smoother ride. Hence why some frames have curved seat stays meant to reduce the vibrations reaching the rider through the rear tire.

The effectiveness of this measure is questionable because there are many variables at play besides the shape of the tubes.

The Disadvantages of Curved Tubing

  • Limited Seat Post Insertion

Curved seat tubes limit the length of the seat post that can be inserted into the seat tube.

This will be a problem 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 easily prevented by getting a shorter seat post that doesn’t reach the curve of the seat tube.

In the second case, 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 allowing you to lower the seat post all the way down when doing stunts.

  • Extra Weight

The shortest distance between two points is a straight line. Thus, a curved tube is longer than an equivalent straight tube. The extra length comes with extra weight. Of course, the difference isn’t substantial and matters only when trying to build the lightest possible bike.

  • Extra Steps To Manufacture

Curved tubes require one extra step 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.

The Advantages of Straight Tubes

  • Classic look

Straight tubes preserve the classic appearance of a bicycle. People 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.

  • Potentially Stronger

Technically, every bend introduces a weak spot. Hence why 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 things are equal, however, straight tubes win.

  • Stiffer

Technically, 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. Thus, one cannot conclude that a straight tube is stiffer than a curved one by default.

The Disadvantages of Straight Tubes

  • Reduced clearance

The main downside of straight tubes is that they offer less clearance for the same length. Thus, one has to compensate by making the rest of the tubing longer.

FAQ: What are the differences between curved and straight forks?

You can read a dedicated article on this subject here.

Summary: What You Need To Know

The advantages of straight tubes are:

  • Classic look
  • Can be combined with longer seat posts
  • Potentially Stiffer and Stronger

The cons of straight tubes are:

  • Reduced tire and fork clearance

The advantages of curved tubes:

  • Extra tire clearance allowing engineers to design a frame with short chainstays
  • Modern/alternative look
  • Compliance

The cons of curved tubes are:

  • Limited seat post insertion
  • Extra manufacturing steps
  • Potentially weaker and flexier

It will be inaccurate to conclude that one type of tubing is superior to the other since the final outcome is highly dependent on the overall design, the used materials, 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.

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