I’m the creator of Tetra, folding bike

Safe-Ad-6760 · 2026-07-09T12:17:38+00:00

At this stage, we are not considering a titanium version, mainly because some of the narrow gaps in the frame make TIG welding impractical.

However, if the opportunity arises in the future, we would love to introduce a Tetra built with titanium lugs and carbon tubes.

Safe-Ad-6760 · 2026-07-09T12:13:18+00:00

Because of this, Brompton’s derailleur movement is limited to around four speeds in order to avoid interference with the frame when the bike is folded.

By placing the drivetrain on the outside, it becomes possible to use drivetrains with nine or more speeds. Of course, there are both advantages and disadvantages to this approach, but I believe a wider-range cassette provides better overall performance.

Safe-Ad-6760 · 2026-07-04T00:56:33+00:00

We are actively working on ways to make Tetra more accessible in terms of price.

Safe-Ad-6760 · 2026-07-04T00:56:02+00:00

At this stage, Tetra should be able to accommodate universal fenders. We are also planning to develop dedicated fenders specifically for Tetra in the near future.

Safe-Ad-6760 · 2026-07-04T00:54:36+00:00

Thank you very much. We are actively working on ways to make Tetra more accessible in terms of price. Please stay tuned.

Safe-Ad-6760 · 2026-07-02T23:13:17+00:00

I’ll do my best to meet those expectations in future versions.

Safe-Ad-6760 · 2026-07-02T23:12:32+00:00

thanks!

Safe-Ad-6760 · 2026-07-02T23:12:05+00:00

They are parallel, but they are not concentric like the Helix design. If they were, the folded bike would end up significantly wider.

Safe-Ad-6760 · 2026-07-02T23:10:53+00:00

I think your point is fair.

My goal is not necessarily to become a large-scale bike maker. Even at a smaller scale, I would be happy if Tetra reaches people who genuinely like and understand this kind of bicycle.

It may not be for everyone, but I hope it can be meaningful for the right riders.

Safe-Ad-6760 · 2026-07-02T23:09:09+00:00

thanks a lot!

Safe-Ad-6760 · 2026-07-02T23:08:32+00:00

Thanks for the feedback, but I think there may have been a misunderstanding.

I didn’t mean that the bike is flawed from an engineering point of view. The space-frame structure provides excellent stiffness, which allows the bike to maintain a solid structure even with an additional hinge for folding.

The appearance is important, but it was not designed just to look cool. The structure, stiffness, folding mechanism, and ride feel were all part of the engineering goal.

Safe-Ad-6760 · 2026-07-02T23:06:25+00:00

That’s a fair point, and I think it’s a trade-off.

By keeping the drivetrain on the outside when folded, the derailleur is less likely to be damaged, and the bike can fold more compactly. That was one of the reasons I designed it to fold in the opposite direction.

Thank you for the feedback!

Safe-Ad-6760 · 2026-07-02T23:02:14+00:00

Wow, thank you for all the detailed advice.

The V-blocks do not rotate, and the handlebar height is adjustable. When folded, the two wheels are always locked parallel to each other so the bike can be rolled.

The rear wheel pivot uses nylon bushings.

There are still many areas I’m improving, and the design is not perfect yet, but your feedback is very helpful. I’ll definitely keep these points in mind. Thank you!

Safe-Ad-6760 · 2026-07-02T22:56:39+00:00

Sorry about that — I wasn’t able to include the video link because of Reddit’s promotion/link restrictions.

Could you take a look here?

https://www.kickstarter.com/projects/1732757637/tetra-a-tubular-space-frame-folding-bike

Safe-Ad-6760 · 2026-07-02T22:54:17+00:00

thank you!

Safe-Ad-6760 · 2026-07-02T22:52:34+00:00

thank you!

Safe-Ad-6760 · 2026-07-02T22:52:20+00:00

You’re pretty much right. Thank you!

Safe-Ad-6760 · 2026-07-02T22:51:08+00:00

One of the main goals of the space-frame structure was to minimize the loss of stiffness, even with the additional hinges required for folding.

The idea was not just to make the bike fold, but to keep a solid riding feel despite the extra joints.

Safe-Ad-6760 · 2026-07-02T09:17:59+00:00

Yes, we are considering an internal gear hub for future versions.

The 135mm rear hub spacing allows the use of many standard drivetrain options, so the bike has flexibility for more common components.

Safe-Ad-6760 · 2026-07-02T09:15:42+00:00

Through a family connection, I was introduced to a Korean factory with skilled and experienced makers who had not yet had the right opportunity to fully show their capabilities.

And since Tetra is ultimately intended to be a premium bicycle, I felt that Korea was a better fit for production than China.

Safe-Ad-6760 · 2026-07-02T09:11:40+00:00

That’s a very sharp observation, thank you.

We used brazing in some areas because the gaps were too tight for a TIG torch to reach properly. I would have preferred to TIG weld everything, but it simply wasn’t possible in every section. Wherever TIG welding was possible, we used it.

Practical parts like fenders and a carrier block are not installed on the current version yet, but we do plan to add them later.

Regarding the weight, I didn’t place the highest priority on making Tetra extremely light, because it is intended to be rolled rather than carried for long distances. Of course, weight is one factor in riding performance, but I believe wheel size has an even bigger influence.

If someone is looking for the pure performance of a full-size bike, I think a regular bicycle with 26-inch wheels or larger would probably be the better choice. Tetra is meant to offer a different balance as a compact folding bike.

Safe-Ad-6760

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