If you like strange bikes, you would like my Fixed/free 1-speed/2-speed/3-speed mountain bikes. They have a truly weird drive train!
These bikes are equipped with "flip-flop" (reversible) hubs, which are threaded for a freewheel on one side, and a fixed sprocket on the other.
This, in itself is not that unusual; many fixed-gear fans keep a slightly larger single-speed freewheel on the opposite side. This provides a freewheeling gear slightly lower than their fixed gear. If they find themselves getting overtired, or if they just want to go on a longer ride than they feel comfortable with on the fixed, this gives them a gear that is a bit easier to climb with, and that also allows them to coast down hills.
My Hercules has a 165 mm Shimano 105 crankset, with 52/42 Biopace chainrings. It has a 52/18 fixed gear, which is what I use most of the time. If I flip the rear wheel around, I have a 52/20 freewheel gear, good for longer or hillier road rides.
The most unusual feature of this bike, however is that it has a 2-speed freewheel, with a 30 tooth sprocket as well as the 20. The crankset has a 42 as well as the 52, and I can change gears manually, much as the speeds are changed on a drill press. The 42/30 gear is the off-road combination, and makes a pretty good general purpose gear for the local singletrack.
Front Rear Gain
Inches Meters Fixed 52 18 5.46 75 6.01 Freewheel 52 20 4.92 68 5.41 Freewheel 42 30 2.14 36 2.91
This system is very light, very efficient mechanically, and very reliable. I highly recommend it to fixed-gear fans who may have an older mtb frame gathering dust. Ideally, you need a bike with horizontal dropouts, so you can adjust the chain tension when you change from one combination to another. Some bikes that have semi-vertical dropouts can be used, but you may have to have the same road gear on both sides.
The freewheel is an old discarded Sun Tour "Perfect" 5 speed unit, with 3 of the sprockets removed and replaced with spare spacers.
My first experiments along this line were on a 50 or 60 year old Hercules three-speed frame. It had been crudely re-painted by the previous owner, so I covered the frame (and Zéfal pump) with wood-grain contact paper. It looks like a wooden bike, makes a great conversation piece...
This bike has been through a lot of changes. Before I converted to the drive-train described above, the Hercules was my first derailer-geared off-road bike. In the late 1970s I adapted it into an early mountain bike. It started out as a 12 speed, then an 18 speed after I bought my first triple crankset, then a 21 speed. The 21-speed configuration featured a 52/47/34 triple, with a 7-speed 12-38 freewheel (that freewheel was a whole story in itself...)
At that time, I didn't have the facilities to install cantilever brake bosses, so I made home-made "drop bolts" out of aluminum stock. (See: Home Made Drop Bolts for details on this.)
The frame has relaxed geometry, 68 degree angles and a long wheelbase. It is quite comfortable, and in some ways I prefer it to modern mountain bikes. It has a low (by mtb standards) bottom bracket, which means I have to pay attention to where my cranks are in tight off-road situations, but the low bb also makes it less scary to attempt to ride marginal sections, since I am low enough down to be able to get a foot down if I can't make it.
The Hercules turned out to be so much fun to ride that I am searched for something a bit more up-to-date, eventually coming up with an early '90's Bianchi Osprey, which I have given a similar treatment to.
This bike has truly vertical dropouts, but I wanted to set it up with a flip-flop hub: fixed gear on one side, two-speed freewheel on the other. The vertical dropouts don't allow chain tension adjustment because the axle is a snug fit in the slot. I solved this by cutting the axle off short, so that it does not extend past the cone locknuts. Only the quick-release skewer goes through the dropouts. Since the skewer is thinner than the axle, this allows some front-to-back adjustment. So far, I've had no problems with this unorthodox rig, but I carry a spare skewer, just in case.
The Osprey has 42/34 chainwheels, a 14 tooth fixed sprocket and a 15/23 freewheel. I may add a third freewheel gear, since the cranks are set up for a triple...
Front Rear Gain
Inches Meters Fixed 42 14 5.65 75 6.01 Freewheel 42 15 5.28 68 5.41 Freewheel 34 23 2.79 36 2.91
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