The Mule

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Mule01.jpg

Specifications

  • Frame: welded, mostly 40x20x2 mm steel
  • Steering pivot: 12 mm rod-end spherical plain bearings
  • Suspension: none
  • Gears: 3x6
  • Wheels: 26x1.75", road tread
  • Seat: plywood base, strings and foam
  • Purpose: long range heavy freighter

Construction

I spent most of the time thinking how to do it as simple and easy as possible, probably sucessfully. The frame consists of only two parts, front and rear. Dimensions were quite clear: wheelbase was limited by the height of hooks over floor in our bike storage room, BB-EOS was limited by length of my legs and the material was limited by what could be bought in our local shop and what our old welding machine could safely weld without burning through.

  • Dropouts: custom-made from 4 mm steel, the axle slots aim directly down. Convenient for mounting/unmounting the wheels, inconvenient for rear derailleur (must be unmounted as well and then it starts to fight, try to escape or bite my fingers).
  • Bottom bracket: taken from a donor frame, together with a piece of seat tube where the front derailleur is affixed.
  • Steering pivot: a 12 mm rod goes through two 4 mm steel plates welded parallelly on the rear end of the front frame, spaced apart some 130 mm or so to reduce bearing load and increase stiffness. The rod has threads at both ends and the inner bearing rings are bolted tightly. The threaded ends of the bearings are bolted into a piece of 30x30x3 mm square tube and tightened in a precise position where they show the least friction. Difficult to adjust, but doable and seems to need no more attention since then.
  • Handlebars: taken from an old touring bike, no modifications needed, just turned upside down and backwards. Bolted on the top of the front frame, between the mudguard and the pivot bearing (the only available place).
  • Seat: thick plywood base is bolted to the rear frame at three points: one at the top of the vertical 30x30 tube holding pivot bearings, two at the ends of a 20x20 cross-strut welded at an angle to the rear frame. Back rest is made of 3 mm clothes line (plastic-coated steel cable) winding zigzag through holes in the plywood and the strut located just over the rider's shoulders. This strut is held in place by one curved 20x20 vertical tube and two seat stays from the donor frame. The vertical tube was originally planned to be straight, but this is better - makes a lot of space under the seat. The mat is a polyurethane foam harvested from an old mattress (a temporary solution that is probably going to become permanent). Head rest is a T-shape welded from two stainless steel tubes, bolted into the vertical seat tube, with some soft foam duct-taped around the top bar. Good for stability (more contact between the body and the bike), bad for bumpy roads (gives you headaches if you forget to raise your head in time).
  • Cargo capacity: big underseat bag made of railroad-class waterproof fabric, and a rear rack made of 12x1 mm round tube. Both permanently fixed to the frame.
  • Mudguards: front aluminium, rear steel (difficult to get two identical sets of metal mudguards here). I left too little space under them, mud and snow build up quickly. The holding struts are welded to the frame, I didn't have the patience to bend their ends and drill bolt holes. Front mudguard is extended by some aluminium sticky tape to reduce dust and water getting out on me (it's enough if you can't see the tyre, you don't need to cover the whole wheel), rear one has sheet metal extensions at the front to keep the saddlebag away from the wheel.
  • Brakes: front one is direct-pull (V-type), mounted on the bottom of front frame (the only available place). Rear one is center-pull (cantilever), mounted on the bottom of rear frame, with the cable running between the two main beams. The sockets came from two scrap front forks.
  • Shifting: non-indexed control levers are located on the bottom side of the handlebars. Harder to reach, but these were the only remaining available spots (again). Front derailleur is not in optimal position, but it works. Rear derailleur needed some filing on its holder to fit my new dropouts (and some straightening, because it comes from the donor frame that probably underwent a lot of rough handling).
  • Wheels: first some 26x2" mountain tyres, then I cut off their side knobs, then finally switched to 26x1.75" road treads. Not much less suspension effect than the 2", but better rolling.
  • Trailer hitch: M8 bolt coming out on the left, just over the rear wheel axle. Universal joint is made of two small steel cubes on loosely threaded-in bolts, the trailer is a simple two-wheeled box.
  • Lights: homemade dynamo-powered LED system with 36 white LEDs at the front (modified handheld flashlight), 10 reds at the rear (modified standard bicycle taillight) and 9 yellows along the frame (just hot-glued in place).

Riding

First rides were just walking on my hands while sitting on the bike. Then it slowly changed to staying upright for a few metres, having no influence on direction. Then going in the general direction I wanted to go and finally staying on the right side of the road and making turns at will. This took about 60 km of practicing on grass fields and park roads. Then I ventured on an 18 km trip on public roads (they were mostly empty - it was a lazy Sunday morning), taking 12 kg of cargo on the way back. Speed is still rather low (downhill top speed 30 km/h because I'm afraid to go any faster, average about 18), but I'm sure it is going to improve.

150 km: first real (c)rash test happened. Feeling quite sure on the bike, I let it go downhill without braking to see how fast it can go. At 40 km/h the steering response became faster than my stabilizing skills and the bike started to oscillate left and right, finally laying me down on the tarmac. Nothing serious, just a lot of road rash on me and some scraped surfaces on the bike. Still more practice needed.

300 km: I feel quite confident now, riding on normal roads. Still no heavy urban traffic, though. Downhill speeds up to 39 km/h with no more stability problems except the lack of confidence. Uphill speeds quite low due to the weight.
First night test was a fail. I still haven't installed normal lights, so I took just a forehead lamp (quite bright one) and a red rear blinky. The blinky was OK, but the headlight didn't make the road any brighter at all because my legs glared me. Overtaking cars did shed some light on where I was going, but those in the opposite direction were making me completely blind - sitting so low, I look directly into their headlights. Making a note: the new lights must outshine them.

700 km: proper lights installed. Enough to see the road and make me visible, but cars still dazzle me. So do my feet passing near my front light. Taller bikes are better for night riding. Day riding definitely feels safer, 40 km/h on the flat is no longer a problem, I even did 50 downhill (with a heavy trailer behind). At last, average cruising speed reaches 26 km/h - that's 2 km/h more than my upright road bike!

800 km: finally decided the bike is severely undergeared for the speeds I can achieve now. Switching the 14..28-tooth threaded 5-sprocket cluster for a 11..28 7-sprocket cassette (actually only 6 usable sprockets due to insufficient derailleur range; I swapped the two biggest ones to keep the full range). New splined hub is too wide for the original front "fork", so I've had to cut and re-weld it to a wider shape. Forgot to watch the geometry, so the fork twisted and had to be cut and re-welded on the other side too. That made it too tight for the 2" mountain tyre, so I had to switch to 1.75". Mirror installed on left hand so I can glance back before turns (vital thing!).

1000 km: underseat bag has been installed, so the bike finally has some decent cargo capacity. It even improved the aerodynamics a bit.

2000 km: platform pedals switched to SPD, so I don't have to stop pedaling and brace for impact on every little bump. The iterative process of upgrades to the bike seems to slowly approach an end. Average speeds on not-too-hilly trips exceed 28 km/h, top downhill speed was almost 70 km/h without any fear (smooth straight road, good visibility, no traffic in sight). Stability is no longer an issue, although the control routines running somewhere in the background of my brain still consume more runtime than on an upright.

3000 km: learning process is finally complete, now I feel like I could easily fall asleep on the bike :-). No problem to reach into the underseat bag for a snack, unpack and eat it and have a drink from a normal screw-top bottle - all while riding. Came handy during a 24-hour bike marathon I've attended (over 400 km, whew!). Little mirror installed on my glasses - very good thing, much better than the previous hand solution.

3600 km: the rod end bearings in the steering pivot start to drag, probably due to all the dust that got inside. After another 100 km the drag made balancing near impossible. I cleaned and re-lubricated the bearings and swapped them so that their less-worn halves are loaded now. And covered them with leather gaskets to prevent more dirt ingress.

6000 km: steering pivot started to drag again. Nothing serious this time, lubrication fixed it.

6916.7 km: I passed the bike to a new owner. My absolute speed record was 73 km/h, last years of riding were without a single crash. Performance on smooth and flat roads was very good, but I needed something that can also handle hills, potholes and loose terrain.


Strong spots

  • Simple, strong and stiff. It survived my sometimes rough riding without any problems.
  • Lots of cargo space, good behavior with a trailer.
  • Definitely faster than standard upright road bike and less susceptible to winds.
  • Comfort.
  • Instant conversation starter :-).

Weak spots

  • Low riding position => can't look over cars, can't look behind, glare from oncoming cars at night.
  • Quite heavy (22 kg).
  • No space left for a stand or steering stop => difficult handling and parking.
  • Not even close to maintenance-free, but that is a matter of my implementation, not the design.
  • Poor offroad performance. Front wheel slippage is a killer.
  • Used to make my leg tendons and knees hurt after long rides (250 km in two days), but that seems to be solved by switching to SPD pedals. Shorter cranks than 170 mm also helped me a lot, but that was done on another bike.