Regarding single speed bicycle assembly
I need a bike that I’m comfortable with for getting around London. My Claud Butler steel mixte frame is in good condition and I’ve always wanted to learn more about bikes, so I’ve started to replace the heaviest and most problematic bits myself. Over time, the project evolved in to a single speed conversion. The notes below are an overview of the work and research I’ve done thus far. Expect misused terminology ahead, bumps in the road, etc.
The old wheels had to go first. The fat steel rims were heavy, and the shiny chrome was terrible for braking. Wet weather made them even worse, and there’s no avoiding rain in the UK. The wheels were hands-down the major reason I wasn’t comfortable on the bike. When I started looking for a replacement set of road wheels however, I quickly realised I’d have to make some decisions about the gearing. The project got a whole lot more daunting.
After a lot of hemming and hawing and a lot of advice from the bike-savvy people in my life, I decided to make it a single speed. It will be easier for me to maintain, which is appealing, and London is pretty flat so gears aren’t strictly required. The bike will be a little lighter as well. I need all the help I can get with the weight since I’ll be carrying it up and down a narrow and steep set of stairs. And who knows, maybe the ride will be closer to my experience as a little kid riding a simple single speed coaster-brake bike all over the place. Minus the carefree attitude and southern California sun.
Crucially, my bike doesn’t have a vertical dropout. It’s worth noting that the dropout is the first thing to check when considering converting a bike to single speed.
First, I removed the down tube shifters and gears. They were just clamped on, not brazed, so it was a simple task. Then the search was on for a new set of wheels. SB has 27” clinchers on his steel road bike and he has offered me a set of tires and tubes, so I knew I wanted to get the same sort of wheels. As a side note, though I’ve adjusted to a lot of British spelling since 2010, it will always be a “tire” to me.
I ran in to difficulty finding a rear wheel that would fit the rear spacing. The 116mm spacing seems very weird in comparison to guidance on fork/dropout spacing I’ve seen, and the narrowest rear wheel I could generally find was 120mm. Even that was kind of hard to find, particularly within my low budget. I did come across some used wheels occasionally on Pedal Pedlar, but they were usually tubular. I also came across the Shroom Components Classic Wheelset, currently for sale online at Brick Lane Bikes. This set was highly recommended on an online forum and fit the bill measurement-wise.
Then SB happened to come across some suitable wheels on sale at Condor. Not a matching set, but better quality than the Shroom set overall and a similar total price. After a quick chat with one of the mechanics about fitting the 120mm rear wheel in to the 116mm spacing – “not a problem” – the wheels were purchased. As advised, they fit totally fine.
Next up was the gearing. The rear wheel has a threaded flip-flop hub, so I needed to get a single speed freewheel. Until very recently, I knew nothing about gear ratios except that the wrong one could seriously influence my overall satisfaction with the bike. After some searching around, I found an excellent “gear ratios for dummies”-type article written by the folks at Surly bikes. I also found lots of great forum threads on LFGSS with personal opinions and thoughts about the right ratio depending upon strength/experience/topography.
My understanding of gear ratio is FAR from comprehensive – it’s clearly a complicated subject – but I did learn a few things. A) The lower the ratio, the less resistance and “easier” it is to pedal, B) It’s probably best to go odd:odd or even:even when it comes to the overall tooth count on the chainwheel and rear cog, and C) Larger chainwheels and cogs will last longer since the wear is more spread out. As a semi-inexperienced, lightweight cyclist living in a fairly flat place, I decided to go with 2.3:1.
After choosing the gear ratio, I needed to do a little math to get the cog tooth count. Trouble is, I’m not quite sure which crankset I’ll be using. The original Suntour crankset is heavy and has three un-removable chainwheels. I wouldn’t be able to move any of them much, if at all, to get the right chain alignment. If I know nothing else at this point, I know that chain alignment is paramount with a single speed setup. At least that’s what countless YouTube videos seem to emphasise.
Since I’m hoping to use a nice hand-me-down crankset from SB’s steel British Eagle road bike (which, in turn, used to be his dad’s), I used the tooth count from that chainwheel (39) to figure out what I needed for the freewheel (17). Now: 1/8” or 3/32”?
I saw those fractions popping up on different cycle shop websites and had not a clue what they meant. Turns out that it has to do with the width between the plates on a single chain link (as opposed to the length of the link, which should be 1/2”). The chainwheel and rear cog need to match up with that measurement so that the whole mechanism runs smoothly and efficiently. Advice that I found ranged from “NEVER mix sizes, you’ll break both your bike and your body” to “Eh, go for it, it works for me”. The majority opinion seems to be “Of course you should match up the chainwheel, rear cog, and chain; it makes sense, and why risk it?”. This video illustrates why the chain width should match the teeth on the chainwheel in particular.
I’m still not sure exactly how to take that measurement though. Is it just the width of the rollers? The distance between the inner side of the plates themselves? The exterior of the plates? At any rate, it sounds like 3/32” is far more common since it’s what multi-speed bikes use. 1/8” chains are frequently used on BMX bikes since they’re wider (thus a bit more heavy) and perhaps sturdier. Since both SB’s bike and mine were multi-speeds, I think (hope) I’m safe in assuming that the front cog requires a 3/32” chain.
I ended up purchasing a 3/32” 17T Sturmey Archer freewheel. It’s heavy and not a top-notch part, but it’s cheap and should do the job for now. I’ll wait until I’m sure about the gear ratio to get a nicer/lighter freewheel. Someone suggested fitting different freewheels on each side of a flip-flop hub if unsure of of the “right” gear ratio, so I could give that a try I suppose.
The next task is to get the whole mechanism in place and adjusted, ideally with the hand-me-down crankset. I expect the braking to be much better with the new wheels but won’t know for sure until I’ve gone for a spin. I found an interesting tip suggesting leather face brake pads for wet weather. I think the ride will be fine without that sort of thing, but useful to know it exists. In fact, that might have worked well with the old steel rims.
The brakes need to be adjusted for the narrower rims, but that should be simple enough. Famous last words, no doubt. It’s still got the original Weinmann brakes, and I’ve done a few adjustments to them in the past. At the front, the sidepull brake started rubbing randomly on one side of the rim. I was “that guy” with the super squeaky wheels. In the end, it was a simple problem with a simple fix, the tension on the cables to each brake arm was uneven. This guy had a similar problem with his sidepull Weinmann brake. I was lucky enough to have enough excess in the cable to let it out a sufficient amount without replacing the cable.
Down the line, I’d love to replace the shockingly heavy steel riser handlebars. That upgrade will surely be the start of a whole new research wormhole on the pros and cons of handlebar types, brake lever positioning, etc.