406 · custom design · experimental · folding bicycle · hand built · portable · small wheel · trail

Portable bike # 14

Still rideable with your standard touring tires, but it gets more challenging down the trail.

Having ridden portable bike #13 for about 6 years, I came to the point where I needed to make a new one from scratch. The event that was a catalyst for this was my ride on the OC&E trail I did last year. The largest tires the bike fits are 50mm (2.0). It just wasn’t a large enough footprint to ride on the surfaces I encountered on the trail. A bigger tire would make the gravely and loose sections easier to negotiate. So I figured I would make a new one with bigger tire clearance; having signed up for the Oregon outback ride (although I cannot make the group ride this year).  It will be easier to take Amtrak with this bike, just fold it up and put it in the luggage area as I board the train.

The new fork would be an inch taller. The rear triangle would need extra space. The new design would increase the folded size slightly, but it would allow for the fattest tires out there for the BMX size- 20×2.4 (or 406-62). Outfitted with narrower 406-50 schwalbe big apple tires, the folded size would be 28x11x21 (that includes racks and fenders) on the new bike.   With the super-fat 20×2.35 BMX tires installed the folded bike gets about a half inch wider and taller, but the same width. It still meets the 62″ length/height/width requirements for airline baggage and Greyhound bus, with 2″ to spare.

Demolition 20.2.35 tire on a CR18 rim with a 74mm Phil Wood 32 hole front hub. The new fork (not yet finished) offers plenty of clearance.


2.0 wide Schwalbe big apple tire on left; 2.35 inch Demolition Machete tire on right. A significantly bigger cushion of air.  A bigger apple.



Side view comparison. 2.0 on left, 2.35 on right.


A fat tire like that is probably better if installed on a wide rim. On this narrow Sun CR18 (23mm wide) rim it has a rounder profile and at lower pressures it may cause the bike to feel squirrelly in turns if at low pressure (the sidewalls would be better supported  on 50mm wide rims). But with my 28 hole Schmidt generator hub (they do not make a 36 hole in the 74mm width) my choice of rims is limited. I may map out a spoking pattern so I can use a wider 36 hole rim, skipping every 3rd and 4th hole, and using a variety of spoke lengths. I built such a wheel and the blog post is here.

I will also stiffen up the main boom structure connecting the seat tube to the forks/handlebars. Existing tubes were butted (9/6/9) and I thought it was a bit flexy when riding a heavy front load while speeding downhill. There will be other refinements as well.

jigging up the fork. I ended up giving it a 20 mm offset.


Bike plan drawn up life size on a piece of drywall.

After making the fork, I drew up a plan for the frame. 72 degree head and seat tubes. Bottom bracket height 10.5 inches with the smallest tires I intend to run (40mm)

making some smaller parts. This is the lower clamp. 1 1/4 .058 tube with the tangs; 1 3/8 clamp silver brazed around it, and slotted. There is no way you can over tighten this thing.
Above, seat tube/bottom bracket, with extension for swing arm. Below upper boom tube connected to  head tube extending below, rust covered. And the clamps, awaiting to be brazed on.
Clamps are silver brazed on. I am holding a mitered tube the will mate with the lower clamp and be brazed on to the seat tube.  It’s a beefy 1 1/8 .049 piece., like the one installed in the upper clamp. Mitering took 20 minutes using a grinding wheel and a file. It is spot on; the angle when held up against the seat tube is perfect, and there are no gaps or crescents of light when viewed against a light background to assess the miter.


The boom tube was a bit off when all was brazed. The head tube was about 1 degree off  compared to the seat tube. They should be exactly parallel.  Here  I am cold setting it in a makeshift way. It helps to have a lot of spare steel tubes around to use a leverage. The cinder block the boom tube is inside is part of my very heavy work bench. Although I had a lot of mechanical advantage here, it took a surprising amount of force to straighten it out. This part is probably overbuilt. I may use 1″ x .035 tubes for the next one.


Everything lines up…


just about to braze the seat tube area.

Flat tables and fancy machinery is not necessary for building steel bikes, unless you are a pro who does it for a living. To check for parallel, I sight tubes lined up against the daylight coming in the window, just like Norman Taylor did when making Jack Taylor frames in the 80s. There is a great BBC documentary, part of which is devoted to the Taylors and their frame building.


Rear dropouts about to be brazed on the chainstays.  The wheel is used in the jigging. This way I am assured that things will be aligned. The tacking heats the dropouts a lot. When I first used this wheel the bearing grease melted out and rubber seals melted. So I use it just for jigging during frame making.
After tacking the dropouts, I take the wheel out and finish the brazing.
main hinge area here


Lots of clearance with these 2.35″ tires. Whether the chain clears the tire when in the biggest cassette cog is to be seen. (postscript: the chain does clear the tire).


angles distorted by phone camera. Or the photographer. Head and seat tube are parallel.


I am checking frame angles with this Very Straight Board the bike is on. I used an iPhone with a level app. After zeroing the board, I found the headtube and seat tube to be 71.8 each, with the bottom bracket height at 10 5/8 inches with 50mm tires. I can still use 40 mm tires with this bike, but smaller tires than that could cause pedal strike in corners. It can use tire widths from 40 to 63mm. The trail measurement with 25mm fork offset looks like 50mm.  My main criteria for good handling is when a slow uphill with weight on the front is easy to manage. Because that’s how I spend most of my time.



measuring frame angles..


seatstays, or the equivalent, are installed now
A tube is needed to connect the seat and chainstays. It doesn’t need to be very big.

I spent an hour working on this 1/2″ tube. Bent it with heat to match the tire curve. It was an eighth of an inch too short though, to my chagrin. So I made another one, with greater concentration on the task at hand.

new curved connecting tube in place
disc brake supporting tubes in place before brazing
A disc brake mount dropout for a bike like this does not exist. So I put something together. First I clamped the brake onto the rotor of this wheel, by tightening the brake adjustment wheels. The brake is centered  and the pads are aligned to the curve of the rotor. The black mounting bar the brake is clamped to has adjustability relative to the brake. I made sure it was centered; and tightened in a neutral position. I had made a couple of T shaped steel tubing pieces that the brake mount bolts go thru. They are in place and ready for brazing. You can see a sheet of aluminum behind them which will protect the rotor and hub from the brazing flame.
after tacking. Now I remove the wheel to finish brazing


Brazing is finished.
What a messy workbench. This is how I set up brazing the cantilever bosses on the fork.


Frame and fork components displayed here. Still need to braze on the front rack, front derailleur, and finish numerous small brazed-on details related to the folding of the bike. I have a feeling I will be painting this one with a brush and rustoleum.
setting up for brazing a small supporting tube onto the fork crown


Making a set-screw attachment for the front fender struts.


The bike is rideable and I couldn’t wait to try it. The first thing I noticed was the larger amount of trail in this geometry compared to my last bike (which had 42mm of trail as I recall). It rides easily hands-off. I notice it dives into corners a bit, and that taking corners at speed is easier with this bike than the last. The self-centering effect of a lot of geometric trail is something I have been missing. I  also find it needs less correction when going slowly uphills. I hit the nail on the head this time with the design. 72 degree head angle (actually 71.8) with 25mm fork offset. I measured the trail to be about 50mm. Big wheel bikes tend to have trail figures in the 50 to 60mm range. Should a small wheel bike have less trail to achieve good handling characteristics? I don’t know, but I find that this combination works very well. The bigger tires add some “pneumatic” trail perhaps, but there is a major change in how this bike handles compared to the last.


front fender and rack installed. It took a whole day to do this.


I made wood fenders in the past, but would break one or 2 a year. They just don’t hold up, especially with a folding bike. I needed aluminum strip 2″ wide and 1/16″ thick for the fenders. Seems this is not available, but I found an angle strip at home depot that was 2×2″x8′ and of the thickness I wanted. I cut the strips from that with the sawzall. Bent them around a pail, and began the laborious process of fitting them. The fender struts slide into a small tube brazed to each fork blade. A set-screw holds them in place. If a stick becomes lodged in the spokes of the front wheel and pulls the fender strut- causing the fender to be forced against the tire- a crash could result. This design makes it likely that the fender strut will be pulled out so the fender will not jam against the tire.


still need front derailleur and rear fender/rack setup


Front dérailleur needs to be more rearward because of the smaller wheel.
setting up to braze on small connector pieces


The front bag is an experimental thing made out of a discarded Weber barbecue cover. It’s been on a few short tours already and about a year of commuting. It is involuted and folded at the back. It unfurls to become a bag that you can put the folded bike into.
The bag is really more like a soft basket. It is double thickness in the involuted mode and is quite substantial. Weighs about 1.5lb. It can hold an enormous amount of stuff while providing easy access when riding.


The back of the bag is folded and strapped. At the bottom it bunches around the headtube. The upper strap goes around the handlebar stem.
Bike is in the bag here at a greyhound bus station. Next to it are 2 grocery sacks full of camping stuff that I will take on board with me. The tent, toolbag, and a few other items are in the bike bag as well.


From arrival at the bus station to all bagged up like this takes an easy 10 minutes. If rushed I could probably bag everything up in 5 minutes.


Bag unfurled and ready to drop the folded/clamped together bike into. It takes a just a couple of minutes to fold it up.
I remove the left pedal and put it in the crank arm backwards, before I put it in the bag


bike is inside bag


Move along, nothing to see here. Just another boring piece of luggage. Telling a transit authority that a bicycle is in that bag is  just asking for trouble. If they ask I say it’s “bike parts”.

Bikepacking with a folder. The bigger tires make a huge difference, rocky and gravelled roads are much more rideable and pleasant. I lower the PSI to 20 and it’s full speed ahead. Huge front bag holds food, stove, and misc items. One gallon of water in 2 bottles straddles the top-tube. Sleeping bag and clothes in dry sack on top of rack. Tent and inflatable pad in burgundy bag underneath. Tools in blue bag above crankset.


Camping spot I like near Larch Mt, in the Mt Hood natl forest.
New rack is 5″ wide and very long. Inner tubes work really well to tie stuff down. 4 posts pointing down near each corner provide a place to lash the tube to. Rear light is in a protected spot.



A new rack was needed. It offers more space and stability for the camping stuff. The rack is not removed during the fold or bagging. Still 60 linear inches, total. Still meets max size requirements of 62″.
Fort Rock was the end of the line for us due to time constraints and commitments.


On the OC&E. When herding cattle, always wear a helmet
I had fenders and Tim did not. When following the cattle, abundant soupy poop would come out of the agitated bovines. Never was I more thankful for my fenders. Poor Tim got splattered.


ready to head out from Klamath Falls
Tim riding the Pugsley on the OC&E with 2.4 Maxxis tires. They rode over almost everything without issue.


Our first campsite along Five Mile Creek during the oregon outback ride.

A few mixed photos from our trip above. We left the route at fort rock because of prior commitments. I will return to finish the route soon, probably from north to south, and will use the folder again. While there were some short sections that made me pine for a fatbike, overall the folder did perform admirably with the 20×2.35 tires. Its a good size tire for all around mixed riding on road or trail and it was a huge improvement over the 2.0 tires I used last year.

Returning to Portland the quick way, we took McKenzie pass over the cascades. It was closed to motor vehicles but was  opened for bikes/peds.  It was an awesome ride.


Addendum: Crooked river to the finish

I took the cobreeze bus from Portland out to Bend to ride another section of the outback ride. While the drivers are nice, the business office is not and I do not recommend them. Being able to bag the bike and get on the bus made the trip very easy. The driver had no idea there was a bike in the bag; it was just another piece of luggage.

From Bend, I rode 30 miles to the Crooked river; here descending towards Prineville reservoir.


My first camp at trout creek, in the Ochoco mts.


a bough shelter somebody made, near my camp


following the dirt roads and double-tracks towards Ashville


Gravel roads after Shankio; riding by wheat fields as far as the eye can see. Imagine a lot of headwinds as well.


Another camp in a cemetery near Grass Valley. There was a lot of wind so I didn’t bother using a tent.


Along Old Moody road, after finishing the ride at the Deschutes river. A U shaped valley overlooking the Columbia river.


I rode all the way back home to Portland thru the columbia gorge.


My last campground near Wyeth. Wild camping near a tiny hidden cemetery.  Cemeteries can make good spots for camping if you do not fear the spirits.

I am looking forward to finishing the last 60 miles of the route I have not ridden thru the Deschutes forest sometime this year.



3 thoughts on “Portable bike # 14

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