Folding Bikes
On many rail carriers folding bikes with wheel diameters ≤20” (~400mm) are allowed to be brought on board as regular hand luggage. If the folding bike is small enough, it might even be possible to bring it as a carry-on on a plane.
There are many different kinds of folding bikes with more or less intricate folding methods. Each folding bike has advantages and disadvantages depending on what the designers were trying to achieve, so the right folding bike for you depends on what you want it to be able to do. For example, smaller tyre sizes results in smaller dimensions when the bike is folded at the cost of road comfort, more intricate folding mechanisms are often much more expensive but result in a more compact folded size, and different choices for technology (cassette vs. hub gears, chain vs. belt drive, suspension vs. rigid) all have their own sets of tradeoffs.
I ended up buying a second-hand, 30 year old, non-electric Brompton and would buy a new one in a heartbeat if mine broke. It’s very well-built, I love how small it folds (it can basically fit anywhere on a train), it’s surprisingly comfortable to ride despite the wheel size (except on rocky gravel, in which case I stand and let my body absorb the bumps), and I’ve been able to find replacement parts and maintain the bike without any problem, despite it being so old.
I would still be interested in trying out a Vello, Tern BYB, and Birdy though. They’re all very interesting and bring different tradeoffs compared to a Brompton.
If you specifically want an electric folding bike, take a look at the Brompton, Dahon Ei4, Vello and options from Decathlon (BTWIN).
This YouTube playlist by Radelbande (German) is also quite helpful.
General
In general, folding bicycles with cassette gears often have the derailleurs quite low to the ground which you risk damaging on very rough terrain or if you hit a curb while riding parallel to one. It’s usually not a problem, but something to consider nonetheless.
Also, the larger the tyre, the faster you’ll be able to go and the better the bike will be able to handle rougher terrain, but the larger the folded size will be. The speed difference isn’t really that big when talking about non-marathon situations, and bikes with small wheels often compensate by adding suspension or making their frames more compliant, but this is still noticeable.
Most folding bikes are made out of aluminium to save on weight and price, at the cost of longevity. Aluminium bicycles often have a lifespan of 10-15 years and are more prone to fatigue cracks whereas well-protected steel frames (i.e. not left to rust in the elements) can last upwards of 50 years or more. Additionally, a cheaply-made aluminium frame is less compliant and therefore offers a rougher ride than a cheaply-made steel frame, but well-made modern aluminium frames don’t suffer from this as much.
I don’t really care about disc vs. rim brakes, but some people might. For folding bikes meant to be used around the city I think it’s not really necessary and adds extra weight for little benefit, but I can see the advantages if you live somewhere with steep hills, and especially if you go very fast on an electric bike. It is also nice not to have to worry about rim wear, but I used a 90’s mountain bike with rim brakes for my entire childhood through university and never had to replace a rim due to brake surface wear.
Brompton
Link: https://de.brompton.com/
Pros
- Most elegant, well-thought-out, and smallest fold out of anything on this list.
- Large third-party accessories, parts market, community so it’s quite easy to heavily customise your bike.
- Stable design (bikes haven’t changed much in the last 30 years) so future upgrades will likely be backwards compatible to any bike you buy today.
- Bikes hold their value very well; steel frame and high quality components means people can keep these for decades.
- Electric option available and integrates well into the fold.
- Rack available so you can easily roll it around while folded, including bringing it into a store with a bag attached to the front and doing your shopping like that
- Very good customer service, specialist bike shops dotted around the world
Cons
- Can get quite expensive beyond the most basic model.
- First-party accessories are very expensive.
- 16” tires don’t handle rough terrain that well (still doable and helped by the rear suspension block, but not that comfortable).
- Gearing options are not great if you live in a very hilly place (can overcome this with the electric version) and the dual-gear system is a bit awkward.
- (Modern) rim brakes work quite well but still not as nice as disc brakes for going down steep hills in the rain.
Riese & Müller Birdy
Link: https://www.r-m.de/de/bikes/birdy/
Pros
- Probably the sportiest of the bikes I looked at. It has quite a bit of suspension for handling rough terrain.
- Very well-made and with a good fold given the size
- Comes with disc brakes
- Rear rack option is super handy for panniers which are often impossible to use on such small bikes
Cons
- 18” wheels are a decent compromise, but are uncommon so you have limited choice for tyres and wheels.
- Fold isn’t as small as a Brompton but still decent, would fit in a train luggage rack
- Quite expensive
BTWIN Fold Light 1 Second
Link: https://www.decathlon.de/p/klapprad-16-zoll-ultrakompakt-fold-light-1-second-aluminium/_/R-p-306555
Pros
- Clever folding and unfolding mechanism
- Inexpensive but not cheaply made
- Good service from Decathlon
- Integrated front bag carrying system similar to Brompton (can also go “shopping cart” mode)
Cons
- Doesn’t seem to be available anymore :(
- 16” wheels does not handle rough terrain that well
- Doesn’t fold that small despite its small wheels
- Braking is a bit mushy because of the one-sided forks
Note
Decathlon (the company behind BTWIN) makes other models of folding bike including pretty cost-effective electric folding options. Often their folding bikes use simple folding methods so the bikes can’t get very small, but they use easily replaceable parts and it won’t feel like you need to sell a kidney to buy one.
Dahon Curl i8/Ei4
Link: https://dahon.com/bikes/curl-i8/
Link: https://www.bikepro.de/p/dahon-curl-ei4-16-racing-red
Pros
- Good mix between price and performance
- Folds almost as small as a Brompton
Cons
- Parts not as high quality as on a Brompton (aluminium frame, cheaper gearing system, etc.)
- 16” wheels and seemingly no suspension will make for a rough ride
- Looks a bit weird tbh
Note
Dahon also makes plenty of inexpensive but good folding bikes that use the “classical” folding method (i.e. basically just a hinge clamp in the middle that folds the bike in half). They’re good and the price makes it a lot easier to just leave it locked up somewhere, but they don’t fold down all that small.
The Dahon Mariner D8 is one of their best-rated folding bikes.
Kwiggle
Link: https://www.kwigglebike.com/shop
Pros
- The absolute tiniest folding bike, you can fit it in a backpack
- Easy to take anywhere with you
- Super cool
Cons
- Definitely a bit awkward to ride at first
- Does not handle rough terrain… basically at all
- Limited gearing
Tern BYB
Link: https://www.ternbicycles.com/de/bikes/471/byb
Pros
- Very small footprint given its 20” wheels
- Luggage block compatible with Brompton, opens up that whole world of accessories
- Rear rack can take small panniers
- Lots of accessory attachment points
- Easy to roll around when folded
Cons
- Unfolding likely to get your hands dirty from reaching in to undo the fold
- Folding and unfolding is a bit of an awkward process
Vello Bike
Link: https://vello.bike/
YouTube Channel (German) by someone who owns one: https://www.youtube.com/@martinsbike
Pros
- Probably the most tech packed into a folding bike form factor that you’ll be able to find
- Extremely compact electric model because battery and motor are built into the hub
- Belt driven options for lower maintenance and noise
- 20” tyres and rear suspension block soften the impact of rough terrain
Cons
- Can get very expensive
- Fold is not that great, a bit awkward with the handlebars
- Electric motor controlled only by an app over Bluetooth (at least the app isn’t proprietary as far as I know)
- Not as easy to roll around when folded