Changing gears on a single speed bike

January 19, 2013 2:05 AM

My new single speed is a bit too easy to ride. What are my options to make the gear harder? Specifically, what should I ask a bike shop to change and how much should it cost?

My bike was stolen (boo!) so I bought a new one (yay!). I like everything about it except that it's a bit too easy to ride. I think it means the gear is too low but while I like bike riding, I'm a newbie when it comes to terminology so I'm not sure exactly what I'm describing. My previous bike and my new one are both single speed because I prefer it that way but my old one was a better ride for me since it was geared slightly harder.

What can I replace on my new one to give it a similar gearing? Do I want a bigger front sprocket or a smaller rear one? What should I experiment with first?

posted by Silentgoldfish to sports, hobbies, & recreation (8 answers total)

Do I want a bigger front sprocket or a smaller rear one?

Either will work, but changing the rear sprocket is cheaper.
posted by jon1270 at 2:28 AM on January 19

Not only is a rear sprocket cheaper than a front one, it also means the chain can be shortered, and you don't need to buy a longer one. So I'm seconding what jon1270 said.

I don't understand 'too easy to ride', though. Cycling is a means of transportation, shouldn't that be as easy as possible?
If you're using it as a way to get exercise, which I guess is an option, try cycling faster or farther or both?
posted by Too-Ticky at 3:42 AM on January 19

I guess I mean I have a low top speed - I reach a point where there's nothing to pedal against and I'm coasting too easily for my liking.
posted by Silentgoldfish at 3:45 AM on January 19

Fair enough... apparently you use your bicycle in a different way than I use mine. :-)
The advice stands: a smaller rear sprocket should help.
posted by Too-Ticky at 5:33 AM on January 19

Also, since you wanted to know exactly what to ask for, you're technically looking for a new freewheel, not a cog (though any good bike store will figure out what you mean). Very specifically, you want a single-speed freewheel.

Freewheels contain the ratcheting mechanism which allows you to coast. Cogs don't, and are what you would want if your fixed-gear bike was too easy to pedal. "Sprocket" is a non-specific term for a wheel that engages a chain, and can (kind of sloppily) apply to both, but is more commonly used to talk about a fixed cog.

Since the freewheel/ratchet mechanism sits inside the teeth, freewheels have a minimum size of 16 teeth. I think there might be a 15-tooth out there somewhere, but your bike shop may not stock it. BMX freewheels go as low as 12 or 13 but that's a whole new world of weird miniature part sizes and they won't fit on your bike anyway. If you want to get fancy, there are two-speed freewheels out there, but they're expensive. You shift them by loosening the rear axle bolts and manually shifting the chain.

You can count the teeth on your current freewheel to see how many sizes you can go down. If you already have a smallish freewheel, your only recourse may be to increase the size of the front chainring. If you're feeling really motivated, you can calculate the gear-inches of different freewheel and front chainring combinations to see how they compare--once you start messing with the front chainring it can get confusing.

While this is a matter of personal preference, I would recommend against overdoing it (with, for instance, the smallest freewheel in stock, unless you have an unusually small front chainring). Ideally, you should be "spinning" rather than "pushing" unless you're going uphill or into the wind--a too-low gear is bad for your knees. The bike shop should be able to recommend a freewheel that's the appropriate size.
posted by pullayup at 6:57 AM on January 19 [1 favorite]

How to figure out what size sprocket you need:

Hop on a nice multispeed bike with a similar crank length as yours at the bike shop and find a setting you like. Once you find a difficulty you're happy with, count the front and rear sprocket teeth on the test bike in that gear and note the tire size.

Next calculate the gear inches: GI = rear tire diameter x (front teeth / rear teeth).

Plug that answer into this equation: Rear Teeth = rear tire diameter * (front teeth / GI).

Try to get as close as you can to this number of teeth. If you can't get close, you might need to change out both the front and back gears to get a good gear ratio for you.
posted by zug at 7:06 AM on January 19 [2 favorites]

You want to replace the freewheel (the rear sprocket) if possible, because that's the cheapest and fastest way to get a higher gear ratio.

By the way, when you say the gear is too easy, I'm guessing you mean that you can't spin the pedals fast enough to achieve the speed you'd like. Do you have any idea how many rpm you can comfortably sustain? I ask because a lot of casual cyclists, especially on singlespeeds, tend to prefer a low-rpm, high-torque pedalling style that's actually quite inefficient and harmful to the knees. The standard for racers is 90 rpm; Lance Armstrong famously spins at 110 rpm; even triathletes tend to stay above 70 rpm. If you're anywhere in that range, go ahead and change your gearing, but its worth counting your strokes for a minute or two next time just to make sure you wouldn't be better served by learning to pedal faster.

Note that even if you only replace the freewheel, there's a good chance the shop will insist on replacing the chain as well. This is because over time a chain and freewheel can adjust to each other---the chain slightly reshapes the teeth on the freewheel, and the freewheel slightly increases the pitch on the chain. When you move a worn chain onto a new freewheel, it can cause accelerated wear on the freewheel. When you're a racer whose chains cost twenty dollars and whose "freewheels" (actually a different technology) costs hundreds, this is a no-brainer. When you're a casual rider whose chains cost five dollars and whose freewheels cost fifteen, the case is less clear, but many shops will insist on it as a matter of good practice.
posted by d. z. wang at 9:12 AM on January 19

Thanks guys, went in to the shop, asked for a new freewheel and in 20 mins that's what I had, not only does the bike ride exactly how I want it to now, they didn't charge me! So I'm happy.

I went from 20 teeth to 16 teeth.
posted by Silentgoldfish at 7:00 PM on January 19