Thursday, September 4, 2014

Drews city bike, a two speed mini-velo: portable #15

Time for another bike! I wanted something I could hand over to the coat-check person at the museum. Or take into the movie theater with me.

Portable bike #15


a 2 speed mini-velo

Folds up in 60 to 90 seconds.


Goes from a bike to bike in bag in a few minutes. Weighs 22lbs.


This is a stripped down and lighter version of my 20" wheel folder. My last folder is a wonderful beast of a bike. While it just meets the 62 inch max requirements for length/width/height for bus and airplane transport, it's 34 lbs and rather biggish. It's a bike designed for heavy duty use, or around-the-world travel. Handing that heavy bagged bike over to the hat-check girl is asking for a lot.

A mini-velo is a full sized bike with wheels smaller than the usual. This bike is 22lbs and 58" length/width/height added up when it's bagged (vs 62" for the other folder), I could bring it inside with me to a restaurant, movie house, or a museum, and expect it to be regarded like any other piece of luggage. Taking it on a bus or a plane would be just as easy. If I am concerned it could get rough handling during airline travel, I could put cardboard scraps between the bag and the bike. But it's unlikely to get damaged even if it gets dropped on the tarmac, because of the way it's clamped together- it protects itself.

The Brompton (when enveloped in it's cover) is the most appropriate of the commercially available bikes to hand off to a coat-check person. Some consider it to be the standard to which all other folding bikes are compared. The reader should consider a bike like that for the purpose.

I wanted a lighter/faster/more durable bike than the Brompton. I recently retired a 16" wheel bike I made many years ago. It disassembled and went into a canvas sack. It took too long to assemble (8 minutes) and I found I was not using it anymore. I used some parts from it to make the new one...

My 16" wheel bike that disassembled into a small pile that goes into a 22x12x16" bag. Took 8 minutes or so to perform this task. All the tubes had sleeved joints. What is left of this bike is now in my bike frame bone-pile.  RIP. The massive walnut tree behind it lives on for now.


This new bike uses the same 20" (406) wheel format as my last folder, and the same folding principals illustrated in this post, but is as light and small as possible when folded. And it folds and bags rather speedily; in 2 or 3 minutes from rideable bike to bike in a bag, or vice versa. There has not been a restaurant that cared about my bagged bike next to me, or under the table, yet. I have walked into the theatre with the bike in the bag and put it in the seat next to me a couple of times. Wouldn't try this on first run features though. The coat check lady at the art museum took it. I told her how much it weighed and showed her the carrying strap. No problem for this lady in her 70s to lug it over the counter. 

Folding bikes need to be bagged in many situations. You never know how someone will react when the item you carry could be identified as a bicycle. And bikes get dirty from riding on the streets. Things just go better when it it's bagged.

I spent quite a bit of time making the bag. It is carefully tailored to fit the folded bike. It slips over the top of the bike and zips shut at the bottom. Made out of nylon pack cloth. It needs to look good.

Bag slips over the whole thing

Zips up at bottom. A frame tube extends out of the top of the bag. This can be used as a handle for carrying it. There is also a shoulder strap.
Takes me a relaxed 3 minutes to go from ready to ride bike to bike in a bag. I have done it in 2 minutes when I 'm focused and trying to do it quick. 





Taking this on a bus is easy. It is 19.5 inches wide when folded. I can put it in my lap as the bus fills. The chair space on a bus is about 20" wide. At 22lbs it is not too much of a burden on my lap.

Two chainrings; 52 and 39 tooth. One 14 tooth freewheel cog. A Rohloff chain tensioner (looks like a derailleur) takes up the chain slack. I use my fingers or push it over with my heel to shift the chain up or down on the chainrings, when a hill is just too long and steep.


This bike needs to be a minimalist: light and small as possible when bagged. No built in lights and fenders unfortunately. I used the smaller and lighter 42mm folding tires (Schwalbe marathon supreme 406-42). Got rid of the derailleurs and shifters. It's really a one speed, with a smaller chainring so I can manually down-shift it when I encounter a long, steep hill. To shift to the lower gear requires using my fingers and getting them dirty, so I only do it when really necessary.

I wanted to minimize the $$ I put into it. As a city bike, it is more likely to get stolen. I won't always be bagging it to go into a store or other place of business, so there is always a risk of theft. Another technique to reduce it's chance of being pinched is to make it look crappy. For me, that's easy to do. 

Some details:

The bike folds up like my previous bikes. Kicking the rear wheel under  brakes the rear wheel and allows me to lean it against anything without risk of it falling over. And it just looks too weird to steal. 

Rear brake tucks into a tight space under the chain stays. This is the only place it would fit. I can't use a disc brake with the DX hub.

Pedals are MKS quick-release. They disengage from the crankarm quickly, similar to an air compressor fitting. Only the left pedal needs to be removed when bagging. I need toe clips and straps on this bike so I can pull up hard on the hills. 


The seat extender post. A 26.8 mm seat post fits into it. I made it as short as possible and used as little material I thought I could get away with.

Old stem I made for some earlier project was shortened and re-brazed to fit this bike. A coin was brazed to the top of the stem tube.


Rear hub is a 10 year old Shimano DX singlespeed freewheel, 120mm spaced. It came from the 16" wheel bike.  Designed for BMX use, 36 spoke holes. I don't think they make these anymore. There is a 14 tooth cog there. That, with the 52 tooth chainring, makes a 69.5" gear. Perfect for almost everything. 

Since the wheel flips down, I need something to take up some chain slack and keep it in place. This chain tensioner is from an early Rholoff hub kit. It is not a derailleur, and not designed to shift the chain sideways.

In a Safeway grocery store with the bike under the basket. Where a large sack of dog food may normally go.
The smaller 20" wheel format makes it easy to carry stuff, because of all the space that exists under the handlebars. A nylon tote bag straddles the brake hoods. I shortened the straps so it sits about 2" above the front wheel. Because of triangulation, it does not move at all when rocking back and forth while climbing a hill, or going over broken pavement. Carries lots of stuff and comes on and off in 2 seconds. I cannot imagine an improved version of a "handlebar bag" for this bike.





THE END