Bicycle gears

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poleo
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Bicycle gears

Post by poleo » Sat Aug 27, 2016 2:37 pm

To the bike wise on the forum,

I've started cycling to work, which is about 8 km one way, and it's great. This forum helped me in gettings started too - when I was wondering shit shit shit what bike should I get, I read a post that just said "any" and also "don't pay much for it". So I did, and got one for a fistful of dollars, or kroner as I'm in Norway.

Thing is though, the bike is fine and all, but the gears are kind of messed up. The mechanical part is ok, I'm going to get my head around that very soon, get some tools and start maintaining it properly.

The main question though is that I find that the gears "run out", i.e. I will be coming down a fairly gentle slope, and I'll wish to give some power in order to go faster/gain momentum before a hill or whatever, and then there are no higher gears. This is a so called hybrid bike, and has 21 purported gears.

What do I do about this? Can I somehow adjust the mechanicals, add or subtract something, change the mechanism, or do I start saving up for some sort of super bike? How do I need to think about this problem?

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Ego
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Re: Bicycle gears

Post by Ego » Sat Aug 27, 2016 2:47 pm

Are you shifting both the front and back gears? A big ring in front and small ring in back will allow you to pedal at faster speeds.

Or watch this...
https://www.youtube.com/watch?v=J4ok96KDfpE

Toska2
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Re: Bicycle gears

Post by Toska2 » Sat Aug 27, 2016 4:45 pm

Coast and pedal harder on flat & inclines. Relax, 8 km is short enough that 20 km/h vs 24 km/h is only 5 minutes.

Save money and get winter tires / knobbies and cycle longer in the year. You'll need those low gears then.

poleo
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Re: Bicycle gears

Post by poleo » Sat Aug 27, 2016 5:56 pm

Yeah, I'm shifting both.

It's not so much about saving time, as it's about wanting to get the most out of the piece of equipment. However, Toska2, I do get your point and I think it's a good one.

Toska2
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Re: Bicycle gears

Post by Toska2 » Sat Aug 27, 2016 7:22 pm

In that case, a good bike lock. ;)

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vexed87
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Re: Bicycle gears

Post by vexed87 » Sun Aug 28, 2016 4:55 am

Here's a good place to learn more:
http://sheldonbrown.com/bicycleGears.html

How many cogs are on the rear cassette, and how many on the chain rings?

My road bike has 10 speed cassette with 11-26 teeth, and a double chainring up front with 35-50 teeth. The easiest thing to squeeze out a little extra speed would be find a cassette with less teeth on the smallest cog. You'd need to shorten your chain too to maintain proper chain tension. Depending on the crankset, you may also be able to add a larger chainring up front too, it depends whether you can take off just one chainring. If so you may need a longer chain, which means buying a new one and cutting to size. There are calculators online for determining appropriate chain length.

You'll need the cassette lockring tool to remove the cassette, a chain whip to stop the free hub spinning and apply leverage with the lockring and a chain length tool to resize chains. The cost of of the tools might outweigh the cost of a trip to the bike shop to get them to fit new gear, but at least you can do your own maintenance in future if you decide to.

jacob
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Re: Bicycle gears

Post by jacob » Sun Aug 28, 2016 9:22 am

Presuming that you understand how the gears work(*), the modern philosophy of pedalling is to use a high cadence, typically around 80-100 rpm. New riders will often naturally gravitate towards 60 rmp which doesn't make for speed desiring even lower cadences for high speed. So I'm guessing that's what happening? The better you get, the higher the cadence before you spin out.

Example: Suppose your highest gear is 46x12 and you're running 700c tires, then at 100rpm, you'll be going 48km/h ... is that not fast enough?

http://www.bikecalc.com/speed_at_cadence

(*) Not trying to be facetious here. I've run into people who didn't understand how a coaster brake works, so just covering all bases.

poleo
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Re: Bicycle gears

Post by poleo » Sun Aug 28, 2016 1:07 pm

@Vexed87: There are 7 cogs on the rear and 3 up front. I will investigate the things you have said, I very much enjoy maintenance and tinkering, so your tips are very interesting.

@jacob: No worries, I appreciate the need for clarity. I like to think that I understand how the gears work, though from your reasoning here there is definitely more to learn. I'll try and find the actual dimensions of my bike and play around with the numbers and the calculator. I'm very much a beginner, and not particularly fit (yet?) either, so I'm still soaking up any old bicycle related info... However, I suspect Northern European unfit might be slightly different from US unfit, though that's a different matter. I guess I'm getting some sort of rpm measuring gadget?

poleo
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Re: Bicycle gears

Post by poleo » Sun Aug 28, 2016 1:27 pm

I just watched this guy who is apparently doing 90 rpm. On those flat parts I was describing I often get to that kind of cadence, and that's when I "run out" of gears (fast) and just have to coast a lot. Many more rpms than that and it starts feeling like a Mickey Mouse thing pretty quickly... No 48 km/h by increasing cadence in other words.

jacob
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Re: Bicycle gears

Post by jacob » Sun Aug 28, 2016 1:52 pm

So what's your maximum gear ratio?

Fumbl
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Re: Bicycle gears

Post by Fumbl » Sun Aug 28, 2016 3:23 pm

Hi! Sorry for writing this before my introduction, I'm still working on that.

In my opinion, the easiest way to increase the total "gear" ratio would be to replace the rear tire (only the tire) with a bigger one. It's easy because it doesn't need special tools. But it's limited by how big a tire the bike's frame has room for.

Clarification: I mean a broader tire. It still has to fit the rim. 28" on 26" obviously doesn't work, but 60-559 instead of 47-559 could be possible and adds 26mm of diameter. That increases the ratio by about 4%.

henrik
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Re: Bicycle gears

Post by henrik » Mon Aug 29, 2016 3:13 pm

poleo wrote:I just watched this guy who is apparently doing 90 rpm.
OT, sorry: watching someone pedalling (or running) without going anywhere just hurts my brain:)

tommytebco
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Re: Bicycle gears

Post by tommytebco » Mon Aug 29, 2016 4:28 pm

http://sheldonbrown.com/gloss_g.html#gearinch
http://www.sheldonbrown.com/gear-calc.html
a couple of reference pages I have used in the past. From memory, poleo is looking for something over 100 gear inches for his downhill speeding. a 42 tooth crank ring and a 10 tooth driven sprocket is equal to 109 gear inches. (If my math is correct)

Also from memory, somewhere around 40 or 50 gear inches allows climbing fairly steep hills comfortably. mountain bikes typically have a lowest gear of 22 to 25 gear inches.

( gear inch represents the diameter of an imaginary wheel corresponding to 1 full turn of the crank.Think of the old big wheel bikes)

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C40
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Re: Bicycle gears

Post by C40 » Mon Aug 29, 2016 6:28 pm

Don't bother with a bigger tire. That would barely help or not at all, or is a bad idea anyways for other reasons.

The simplest way to get what you want is to replace some or all of the rear cogs (those gears are called cogs. The front gears are called rings)

You can't get a different cassette (full set of 7 cogs) that are smaller - for example, changing from a 14-28 to an 11-25 would get you around (14/11-1)*100 percent more speed in the smallest cog at the same pedaling rpm. You could also just replace a couple of cogs and not the entire cassette, if you have a source for them. If doing this, it is generally a good idea to check that youre buying a cassette or cog that is meant for your drivetrain (basically, the same brand).

That said, consider these:
- get used to pedaling up to about 120 rpm. Once youre used to cycling a lot and pedaling quickly, that can still be comfortable.
- your bike may not be meant to go all that fast. IDK what kind you have though. Make sure your brakes work well.
- do you REALLY need to go faster?

poleo
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Re: Bicycle gears

Post by poleo » Tue Aug 30, 2016 9:07 am

@jacob, I'll find out my ratio as soon as I'm back from travelling.

@henrik, lol.

@tommytebco, this will be included in my further research and accumulation of knowledge.

@C40, the answer to your last question is of course no. What I do like though, is mastering the equipment I own and thus utilizing it to the full. So in that respect this is perhaps more of an academic inquiry than a strictly practical problem.

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