I've been experimenting with the idea of single-speeding a bike. According to what I've read and seen, the cassette/little freewheel's cog and the single freewheel gear need to be in the same spot by adding spacers or realigning everything. But why must this be so precisely aligned when a geared bike may shift the chain several centimetres from side to side without any problems?
Why do single-speed bikes seem to have such a problem with chainline but multi-geared bikes don't?
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Yeah. You definitely joined the wrong forum if you were expecting this to be a BICYCLE forum.
Later, Doug
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The account was created July of last year and has two posts. I was giving the user the benefit of doubt.
Later, Doug
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To answer the question, it's because for a multi gear bike, the derailuer keeps the chain running onto the selected rear cog. The cogs themselves are also shaped to work acceptably well when the chain is a bit mis-aligned. On a single speed bike, there's nothing guiding the chain onto the cog except alignment, and the teeth are taller and thicker so if you miss by just a little the chain will run up onto the tips of the teeth and off to one side, and then you throw the chain. The upside is the single speed drive line is more efficient.
Belt drives face similar alignment challenges, but are even MORE finicky. The sacrifice some efficiency because the belt flexes instead of being composed of articulated segments.
To bring it back to motorcycles, a motorcycle chain and cogs / sprocket has the same design features as the single speed bike, and is also very efficient. The other options all give up a little bit of (or even a decent chunk of) power to various sorts of friction, but are usually less demanding in terms of maintenance and may handle adverse conditions and abuse better.
Belt drives face similar alignment challenges, but are even MORE finicky. The sacrifice some efficiency because the belt flexes instead of being composed of articulated segments.
To bring it back to motorcycles, a motorcycle chain and cogs / sprocket has the same design features as the single speed bike, and is also very efficient. The other options all give up a little bit of (or even a decent chunk of) power to various sorts of friction, but are usually less demanding in terms of maintenance and may handle adverse conditions and abuse better.
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Man I hate to respond to a potential bot… but
track/single speed chains don’t allow for misalignment. Many are 1/8” wide, some are 3/32” wide. But road chains are usually narrower and are meant to be able to bend more.
converting to a single speed:
Most track bikes/track bike wheels use a 120mm spacing. If you’re converting a former road bike, most frames are either a 126mm (older bike into the 90’s) or a 130mm frame. A steel 126mm frame can be “cold set” or just bolted up okay. A 130 is a big gap, and you’d need spacers.
if you’re using a former road wheel with a threaded cassette, then throwing a single speed freewheel isn’t going to line up. The wheel is dished for having a wide cassette body (meaning the rim is offset to the side). You’re better off buying an actual track wheel, rather than trying to convert an old road wheel.
As far as lining up a chainline, your cranks should be track cranks. Or you need to buy the correct width bottom bracket to line up with the single speed gear.
considering how cheap single speed and low end track bikes are these days. You’re better off buying a track bike. If you’re dead set on converting a bike, buy an actual track crank and bottom bracket, and a track wheel. It’ll make life considerably easier.
track/single speed chains don’t allow for misalignment. Many are 1/8” wide, some are 3/32” wide. But road chains are usually narrower and are meant to be able to bend more.
converting to a single speed:
Most track bikes/track bike wheels use a 120mm spacing. If you’re converting a former road bike, most frames are either a 126mm (older bike into the 90’s) or a 130mm frame. A steel 126mm frame can be “cold set” or just bolted up okay. A 130 is a big gap, and you’d need spacers.
if you’re using a former road wheel with a threaded cassette, then throwing a single speed freewheel isn’t going to line up. The wheel is dished for having a wide cassette body (meaning the rim is offset to the side). You’re better off buying an actual track wheel, rather than trying to convert an old road wheel.
As far as lining up a chainline, your cranks should be track cranks. Or you need to buy the correct width bottom bracket to line up with the single speed gear.
considering how cheap single speed and low end track bikes are these days. You’re better off buying a track bike. If you’re dead set on converting a bike, buy an actual track crank and bottom bracket, and a track wheel. It’ll make life considerably easier.
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If its got two wheels, I'll ride it. Over the years I've built a fixie from an old steel road frame using a track crank and bottom bracket, and to sort the aforementioned alignment issues with the 1/8 chain, I ran the front chain ring on the inside of the spider instead of the outer. Full of success I hacked a decent hardtail mtb into a single speed, using a 3/32 chain and the original front chain ring, and an original single sproket at the back (split out of the 9spd cassette), using spacers out of old cassettes to get the chain line right. It ran Ok for a season or so, but as the chain wore it tended to throw off, and I got bored of putting it back on halfway round a trail. The point being, it can be done, but unless you run 1/8 chain and SS rings and sprockets, or a jockey wheel, it'll probably be a pain to live with. In essence It'll be easier to build, and it'll run for longer if you do it properly...
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