My Ebike – Dahon folding bike

This is an old post about a bike that I still use more than any other. I've changed the motor to a Xiongda 2-speed hub motor in response to overheating (see my post on overheating problems) on our long, steep climbs - here's my post about the Xiongda 2-speed motor. My other main bike is an electric cargo bike: here's my post about my Xtracycle with a Bafang BPM rear hub motor. 
This bike is the first I put an ebike kit on. It remains my favourite and most-used bike.

Making the bike

It started as an off-the-shelf Dahon Boardwalk, with 6-speed derailleur gears, that cost me about $500. As a plain folding bike the Boardwalk got me into much more frequent cycling than I’d done in years, as I could mix it with car transport to manage the mountains around us. I rode it as a plain bike for 2 or 3 years while I wondered about electric bikes.

I converted it to an ebike in March 2009, spending about $1800 (too much...) on an EVO kit. The supplied lithium “Philion” battery failed in the first few cycles and I struggled to get any service from the Australian supplier. Not a single piece of the original kit remains in use on this bike currently, though the (eventually replaced) battery is in current use on a friend’s bike and the motor is in working condition.

Overall

This bike works really well for me. The electric assist makes cycling a practical transport option in the steep mountains where I live – I did cycle before I had electric assist but it was often not an attractive prospect, it took a long time which was mostly spent puffing very hard, and I would arrive home ready for a rest instead of getting on with my work. Now I don’t hesitate to cycle to Mt Nebo (11km) or Samford (19km) even with 100s of metres altitude to climb each direction.

The folding bike is probably marginally less comfortable to ride than a well-fitted mountain bike, but this is more than made up for by the ease of multi-moding on trips. I frequently take my bike in cars (ours or friends’) or trains, and can fold my bike to take it on a peak hour train (where full-size bikes aren’t allowed). This way, my bike enables much more car-free travel than it carries on its own wheels. For example, I can ride down the mountain to Samford and do a big supermarket shop, then fold my bike and get a lift home in a car with someone already driving (luxury!).

The small wheels and low frame also make the bike easy to manage even when not folded, in a house or a train. I like the format of a 20” wheel bike.

Contrary to many people’s concerns, the small wheels don’t seem to make any noticeable difference to ease of riding. The bigger front chainring makes up for the smaller wheel diameter in pedalling rate. My friends and I often do hill rolling tests, starting at the top of a hill riding different bikes, and seeing which bike goes fastest. Small wheels don’t seem to have any significant independent effect on speed, compared to all the other variables such as weight of rider (seems to make for down-hill speed). I’m sure that tiny differences are important to racing cyclists, but I don’t think they’re significant for transport cycling.

Frame

The Dahon Boardwalk frame is steel (Chrome Moly I believe). To me this is highly desirable, as it enables easy modifications and repairs, and I can expect a long life. Aluminium bike frames break, sometimes just from normal use, and are not practically repairable or modifiable, so I try to steer clear of them.

Motor

The original motor was a Bafang SWXB 200w 20” motor. This worked faithfully for 7000km of mountain riding before the nylon gears failed (see my posting on the successful repair), at which time I replaced the motor with a Bafang (8Fun) SWXK 250w 20” motor. The new motor has a noticeable but small increase in power and speed over the SWXB. [Edit Feb 2015] The SWXK did 4000km without any trouble before being replaced in Feb 2015 with a Xiongda 2-speed hub motor so I could try it out - see http://bruceteakle.blogspot.com.au/p/blog-page_20.html

Battery

I use whichever battery I have spare, currently choosing from 3 different Lithium Iron Phosphate (LiFePO4) batteries, all with headway cylindrical cells. The battery box makes this flexibility easy. My current preferred battery when I make new bikes is the 36V 10Ah Headway pack from GreenBikeKit.com. This uses screw-ended Headway cells which are easy to replace, and has the BMS on the end of the cell pack which makes for a flat and robust pack. The Headway cells are specced for high currents, and have no trouble with the 15 or 16A peak currents in my low-powered bikes.

Battery box

The battery box is made from 4.5mm exterior plywood, with fibreglass and epoxy joints (like a sailing dinghy). This is strong and light, and can easily be made to any dimensions. I’ve tried various arrangements for placing and connecting the controller, and this is my current best idea. An aluminium box on the front of the battery box, fitting under the same lid, holds the controller in the bottom, and has space for the controller wires and connections above. I think this is better than previous iterations, with the connections in a separate jiffy box, or with the connections lying under the battery inside the box. I will see how well the controller stays cool inside the box under mountain-climbing conditions.

The Dahon’s original steel rear rack holds the battery box. The rack has been re-welded as joints have broken over time and hard riding. One leg has been bent to fit around the add-on disk brake caliper. I consider the small weight penalty of steel to be compensated for with the capacity to be repaired and modified.

Brakes

The Boardwalk originally had v-brakes front and rear, but over time it became clear that this was unsuitable for mountain riding. One day I had the rear tyre blow off the rim after a long steep descent down Mt Glorious, due to overheating from the rim brake. This wrecked the tyre and tube, did significant damage to the wheel rim and could have been really bad for me if it had occurred at higher speed on a steeper part of the slope. I was able to keep the rim in use with a bit of filing.

A few months later I noticed a strange sound when using the rear brakes. On inspection, I found that the rim sidewalls were so worn from the rim brakes that one side was worn through and starting to split off. I kept that wheel going by replacing the rim with the rim from the old front wheel, same spokes.

I improved the braking situation by making a disk brake mount from mild steel, and brazing it onto the frame – a much easier task than I expected. The inside face of the mount is in the same plane as the inside face of the dropout. I use a cheap disk brake caliper from BMSBattery.com, which takes Shimano pads and works very well under a lot of hard use. The only problem I find with them (I use them on a few bikes) is that the pad adjusting screw seems to rattle out and not hold adjustment. A simple solution under trial currently is some teflon plumbing tape on the thread of the adjustment screw. I buy Clarke’s disk brake pads from Chain Reaction, which last 600 - 1000km per pair, whether sintered metal or organic. This shows what hard conditions they work under: every ride I do ends in a 500m steep downhill dirt road down to our house, and rides down from the mountain to the valley require lots of hard steep braking as 15%+ slopes end in tight corners.

Gears

I love the Shimano Alfine8 speed rear hub. This gives me just the right range of gears for the steep slopes I have to climb, and the 8 speeds are so easy, pushing buttons up and down. With electric assist you don’t need as wide a range of gears, and I think the Alfine’s 305% range might be unnecessary for people riding on normal hills. I use the standard 20t Alfine sprocket on the back and a 52 tooth chainring on the front, which seem to be perfect for a 20” wheel.

The hub gear gives chains a long life. My current chain is coming up to 4000km, and tests fine with a chain-stretch guage. In contrast, chains on my derailleur-geared electric Xtracycle seem to last about 1500km.

I’ve modified an old derailleur to tension the chain, as the rear dropouts are vertical. This works fine. My friend Bradley recently installed an Alfine on a frame with vertical dropouts, and bought an Alfine chain tensioner instead of using an old derailleur. The genuine Alfine tensioner was hopeless – used as per instructions with an Alfine hub, the idler wheel flops around at the limit of the sliding left-right adjustment.

This Dahon Boardwalk originally had 6-speed derailleur gears. These didn’t give enough range for mountain riding, and it wasn’t easy to add front gears due to the folding frame. They’d probably be fine for normal terrain, but I love hub gears…

Forks

As the Dahon original front wheel had a narrow folding bike hub (about 75mm over locknuts), the Bafang hub with standard 100mm over-locknut width would not fit straight in. I investigated options for using or modifying other forks, but couldn’t find anything that fit (the original forks had a 1 1/8” threaded steerer – bigger than most forks). I ended up heating the original forks in the charcoal forge and bending them out to 100mm between dropouts. This worked fine, but I did need to re-braze the dropouts after bending them.

Widening the forks also widened the space between the V-brake studs, and necessitated adjustment of the brake pad washers to move the pads inboard. This has some disadvantages: can be difficult to get it well set up, and if not set up well there is an increased risk of the pads contacting the tyre, especially with the fatter tyres (which I like to soften the ride on rough or rocky roads).

In 2011 one of the kids crashed my bike into a post and bent the forks. This time I bent them cold, and was surprised how soft they felt. The bike has done 2000km since (with the usual heavy loads) and the forks have gone fine. 

I have attached a steering damper to the back of the forks, to make the bike more stable when parked - you know how often the front wheel turns and lets your bike fall on the ground, especially when heavily loaded? The damper consists of a lever bolted to the back of the forks through the mudguard hole (lever adapted from an old steel front reflector mount), some short bungy cords with hook ends, and a long zip-tie holding the bungy cords to the frame. I've attached steering dampers to all my daily use bikes, and it saves a lot of fallen-down bikes.  

Wheels

I laced up the rear wheel onto a Shimano Alfine hub. The rim is a 20” Sun Ringle Rhyno Lite: strong and wide profile, suiting larger tyres, rough roads and heavy loads, cheaply available from Chainreactioncycles.com.

With a big diameter hub and a 20” rim, the spoke length is very short and not available from normal suppliers (I usually buy plain guage Swiss spokes from Chainreactioncycles). I have a Hozan spoke threader (from Ceeway: www.framebuilding.com) and thus was able to cut to length 2mm dia stainless steel spokes (salvaged from an old wheel) and thread them myself.

I use the “spocalc” spreadsheet from the Sheldon Brown website to calculate spoke length. Lately I’ve preferred to use SpocalcExpress, which leads to less risk of reading the wrong section of the page (however you do need to do two spreadsheets for wheels with significant dishing, like rear derailleur gear wheels).

The front wheel uses 2.3mm heavy guage spokes and a Chinese double walled rim from Greenbikekit.com, which I laced myself (to make a significant saving on shipping compared to buying them already built). These rims are reasonable in quality, though a bit narrower and probably lighter than I’d prefer. However being able to buy spokes of the right length from stock and the very low cost of spokes and rims makes this a satisfactory compromise for me.

After trying a few tyre types, I have settled on Shwalbe Marathon Plus 1.75” tyres for this bike. They are extremely durable (current rear tyre has done 4000km and still looks new) and extremely resistant to punctures (one puncture in the rear tyre in 4000km, and that was a screw or nail straight in). And they’re cheap from Chainreaction.

Racks and panniers

I’ve made and installed a front pannier rack on this bike, which carries two Ortlieb front roller panniers (from thetouringstore.com) very well. I’m comfortable with heavy weights in the front panniers (up to around 10 kg) as they help balance a bike which tends to be very light in the front. The rack is simply welded from 6mm mild steel round bar – not the lightest material but there is so little of it this is not a problem.

I occasionally put rear panniers on but this is not currently convenient. I’m wondering about adding a rack to the battery box lid to make it easy to carry panniers.