Project 2: Part 1: Adult-sized folding bike

A little bit of freedom in my trunk!


3 minute read

This is part ONE of a new project to build a folding bike.

A folding bicycle

I have always wanted to be able to ride my bike anywhere I had space and time. Usually, when I have the time and space I don’t have my bike with me. What if I always had a spare bike in my truck, ready to jump out like one of those Transformer Robots on my command. That would be a goal worth working toward. My google search results produced bike-ish objects with long necks and baby tires. I was looking for a full-size bike. I found a bike by a company named Montague. They designed a bike for military paratroopers. This full side mountain bike folds in half right at the seat post. Perfect!!

Something about the design, that struck me as futuristic yet classic. This bike felt familiar to me, somehow. Then moments later, it hit me. This design reminds me of the Mantra Mountain bike by the now-defunct Klein Bicycle Corp. Introduced in 1996, the Mantra Pro mountain bike was one of those $4000 mountain bikes that I would never be able to afford. That makes this selection even better. The next issue to consider is the fact that I do not want a mountain bike. I do not want a suspension fork, nor flat handlebars. My ideal folding bike would be a single speed or a 1x. Powered by my list of quirks, I searched the internet for a frame of the same design.

The Boston by Montague is the perfect frame. It has horizontal drop-outs and fits a 700c tire. Unfortunately, the starting price of just the frame is twice the price of my entire budget for this bike ($350). There are many “look-alikes” of the folding Klien frame. Some of the frames have the same locking mechanism as the Montague, others have a hinge and latch.

I ordered the frame from the mass online China based retailer AliExpress. This is my first time using the site. I must admit, Amazon has spoiled me rotten. Waiting 14 to 35 days for a package to arrive feels like a lifetime.

The frame I purchased had the official description “BMX folding frame 26 / 27.5 /29 inch folding mountain bike frame portable Hummer folding frame” the brand name is “RONGDEXIN”.

The frame has the following features:

  • can fit a 26, 27.5 or 29 inch wheel
  • vertical dropouts
  • mount for rear disk brake
  • no posts for v-brake
  • made from Aluminum alloy
  • comes with a headset, no fork
  • I picked the green color frame
  • unknown hub spacing (assuming 130mm for a mountain bike)
  • Weight: 2.5KG
  • 68mm bottom bracket
  • 27.2 seat tube diameter
  • 44mm head tube inside diameter


I hope to spend no more than $375 to build this bicycle. There are my expenses so far:

Item Cost
Folding Bicycle frame $160
Origin 8 crank (bought used) $29
34T Chainring $20
MTB forks $50
SHIMANO DEORE FH-M475 Rear Bike Hub QR 32 Hole 6 Bolt Disc Black Alloy $30
rear rim and spokes (existing) $0
front wheel (existing) $0
Mechanical Disc Brake kit $45
Bicycle Seat Post $15
Bicycle Saddle $30
Handle bars
Handlebar stem and spacers
handlebar grips