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Chain length and gear sizing beginner

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Chain length and gear sizing beginner

Old 06-08-19, 02:04 AM
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Alexi1speed
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Chain length and gear sizing beginner

Hi everyone!

Im new to fixed gear racing, and am running into an issue of my chain being either too long or too short depending on the gears I use.

A bit of a back story. I’ve always ridden the same gearing for years now, as it works great for my commuting and for longer rides. But now that I’ve wanted to start racing local Crit races, I have to finally leap out of my comfort zone and start changing my gearing for the different course conditions/ speeds/ etc.

So now I’ve been changing my chainring to a larger size (48T) to go faster for an up coming race. The issue is now my old chain no longer fits without my rear wheel being too far forward and being jammed into the seat tube. Due to this, I’ve bought a new chain to fit it, but I have the reverse issue of the new chain being too long when I switch back to the old chainring (46T) causing the rear wheel to have to sit at the very ends of the drop outs to get any tension.

Do I need to decrease the cog whenever i increase the chainring to keep the chain inches the same? Won’t that only keep the gearing at the same level and not change the speed?


Sorry for the long winded questions, I’ve got loads to learn!


Thanks so much,
Alexi
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Old 06-08-19, 06:56 AM
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Are you aware of chain tools/breakers? Or half-links?

If not, learn about them...

You are welcome
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Old 06-08-19, 08:08 AM
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Become friends with a gear inch chart. You increase your gearing by either adding teeth on the chainring, subtracting teeth from the rear cog, or both. Your gearing is really a matter of the difference in size between the chainring and rear cog, not the size of any one thing. Also, a difference of one tooth on the rear cog is usually equivalent to 3-4 teeth on the chainring, so you can make bigger changes that way without having to worry about chain length as much. Set the chain length such that your wheel is close to the seat tube with your largest (as in most total teeth) gear combination so that you'll have room to let it out when you make changes.

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Old 06-08-19, 12:47 PM
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Originally Posted by IAmSam View Post
Are you aware of chain tools/breakers? Or half-links?

If not, learn about them...

You are welcome

So I break or re link my bike chain every time I change the size of my gears? I feel like it would damage the chain if I have to do it multiple times over the course of a couple races, would it not?
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Old 06-08-19, 12:48 PM
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Also, people manufacture ENTIRE CHAINS made out of half-links.
This happened in the BMX world when the gear sizes got so small, a full size chain became inadequate.

Try searching "half link chain".
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Old 06-08-19, 12:58 PM
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Half links and constantly breaking your chain are completely unnecessary.
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Old 06-08-19, 04:05 PM
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If you have track ends (sometimes referred to as horizontal dropouts) then you can move the wheel forwards or backwards a bit. Too much movement and you will have problems with your brakes.

I find that I can change my sprocket by 1 or 2 teeth without it being a problem. A 14 tooth sprocket is 12.5% bigger gear than a 16t, or a 17% lower gear than a 12t. Either pairing should be different enough for most purposes. A flip flop hub with sprockets carefully chosen and 2 teeth apart in size gives you quite a range.

There is a physical limit to how much torque you can apply, but you can learn to spin faster. Therefore, if in doubt, choose a gear that will get you up the steepest hill on your route at a reasonable speed, and hope you can spin that fast on the steepest descent.

Yes, you can swap the chain ring as well. It is not a big job, but it is expensive to have a selection of chainrings as well as a selection of sprockets. Add 1t to the sprocket and take 1t off the chainring and you can keep the same chain length — this works within reason. Remember that a 1t difference on the chainring makes only a tiny % change to your gearing.

As for breaking your chain, it is not a major thing. Some people do that regularly just to clean their chain. The tool to do it is cheap and easily available. You an buy the pins or links cheaply, although personally I consider it unnecessary to use a new pin each time.
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Old 06-08-19, 04:54 PM
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Originally Posted by Mikefule View Post
If you have track ends (sometimes referred to as horizontal dropouts) then you can move the wheel forwards or backwards a bit. Too much movement and you will have problems with your brakes.

I find that I can change my sprocket by 1 or 2 teeth without it being a problem. A 14 tooth sprocket is 12.5% bigger gear than a 16t, or a 17% lower gear than a 12t. Either pairing should be different enough for most purposes. A flip flop hub with sprockets carefully chosen and 2 teeth apart in size gives you quite a range.

There is a physical limit to how much torque you can apply, but you can learn to spin faster. Therefore, if in doubt, choose a gear that will get you up the steepest hill on your route at a reasonable speed, and hope you can spin that fast on the steepest descent.

Yes, you can swap the chain ring as well. It is not a big job, but it is expensive to have a selection of chainrings as well as a selection of sprockets. Add 1t to the sprocket and take 1t off the chainring and you can keep the same chain length — this works within reason. Remember that a 1t difference on the chainring makes only a tiny % change to your gearing.

As for breaking your chain, it is not a major thing. Some people do that regularly just to clean their chain. The tool to do it is cheap and easily available. You an buy the pins or links cheaply, although personally I consider it unnecessary to use a new pin each time.
Wow, thank you so much for the big response @Mikefule , this is extremely helpful! I think the key will be to try and keep my gear selection within a constant range (48x15 or 46x17) in order to have some range depending on how technical the race course is, and not having to alter the chain length between race heats if the gearing isn’t quite right to from previous heats.
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Old 06-13-19, 09:22 AM
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Trackies are used to swapping chainrings as well as cogs in order to modify gearing at the event, in order to leave the same chain on the bike.

My fixed-gear is also my winter bike, and I swap gearing every fall and summer along with my studded (and not-studded) tires. 45/16 in the summer, 42/18 in the winter, same chain.
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Old 06-14-19, 01:24 AM
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Read through This thread. Lots of great advice. I had this same question a few months back and ended up solving it with a half link.

Seeing as you're only going up and down 2 teeth (same as me) a half link might also work in your case. Unfortunately though if you want to change your gear ratio significantly you're most likely gonna need to either have multiple chains of different lengths or one chain that you constantly add or subtract links from. (That is unless you really plan things out well with different sets of corresponding cogs and chainrings)

Last edited by PeopleAreIdiots; 06-14-19 at 01:27 AM.
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Old 06-14-19, 07:46 AM
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I'll never understand why y'all are so obsessed with half links. There's no reason a bike with reasonably long drop-outs can't easily accommodate a 2 tooth gear change.
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Old 06-14-19, 07:53 AM
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Originally Posted by seau grateau View Post
I'll never understand why y'all are so obsessed with half links. There's no reason a bike with reasonably long drop-outs can't easily accommodate a 2 tooth gear change.
Chainstay length and tire size play a big part in how much fore and aft adjustment on that reasonably long drop-out you actually have.
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Old 06-14-19, 08:18 AM
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Originally Posted by seamuis View Post
Chainstay length and tire size play a big part in how much fore and aft adjustment on that reasonably long drop-out you actually have.
Fair point, but if chainstay length is a limiting factor your bike was designed by idiots.
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Old 06-14-19, 09:34 AM
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Originally Posted by seau grateau View Post
Fair point, but if chainstay length is a limiting factor your bike was designed by idiots.
@PeopleAreIdiots's Wabi, for example?
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Old 06-14-19, 10:42 AM
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Originally Posted by ThermionicScott View Post
@PeopleAreIdiots's Wabi, for example?
Bingo.

No shade intended btw -- it's a nice looking bike. It's just a ridiculous design ****-up on Wabi's part.

Last edited by seau grateau; 06-14-19 at 10:53 AM.
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Old 06-14-19, 11:21 AM
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I am almost certain you can do everything you want with one chain. (I don't know your bike and the length of your track ends or dropouts.) Think both the gear inches you want (seau grateau's post above) and "total number of teeth". Say you want to ride a 72" gear around town, show up at the crit and re-gear to an 93" gear.

So: first, get yourself a wheel built on a double-sided track hub, fix gear cogs on both sides. (Miche and others). Now a 45-17 will give you 71.5", plenty close enough to 72". 45+17 = 62 (total number of teeth). A 48-14 (again 62 total number of teeth) will give you a 92.6" gear. So you show up, change chainrings, flip the wheel and race. Repeat to ride home. Odds are good that you can go 1 tooth either side of the perfect total number and stay in the sweet area of your track end or dropout.

I am a huge fan of double sided track hubs. I have two road fix gears running them. On one of those bikes, the dropout is so long I can run anything between 12 teeth and 23. The other is an ancient road bike with 1970s Campy dropouts. I have it set up to do roughly what I am suggesting for you, but with 3 gear inch possibilities and fast gear changes. 2 minutes at hill tops and bottoms. 3 chainrings. 2 cogs on one side of the hub (21 and 17) and the usual one on the other. Each cog lines up with its respective chainring. The three gears can be 38-21 = 49", 44-17 =70" and 46-14 = 96". (59, 60 and 61 total teeth works out nicely.) (I don't recommend doing this unless you have a machine shop at you disposal and/or engineering/CAD skills and/or most of a grand to burn, but done right it is really fun!)

I run all my fix gears with 1/8" chain. I really like the $20 Izumi chains. Not the quietest, but very hard to throw off and very forgiving of too much slack. Last a good long times. For the same reasons I like the Eur-Asian 1/8" cogs. (I also notice both of these are popular at the velodrome with racers on budgets.)

Ben
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Old 06-14-19, 11:31 AM
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Originally Posted by seau grateau View Post
I'll never understand why y'all are so obsessed with half links. There's no reason a bike with reasonably long drop-outs can't easily accommodate a 2 tooth gear change.
I use 1/2 links when needed on both my fix gears. One has a very long dropout but to run both a 12 and a 23 or 24 requires getting the chain length just right. The other has a short horizontal dropout (long by road standards but still ...). I see absolutely no drawback to 1/2 links other than they cost several dollars and usually don't match the chain color. For 1/8" chain, I consider them like washers for bolts and nuts, When appropriate I use them. No obsession here -they are just another tool.

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Old 06-14-19, 11:35 AM
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Originally Posted by seau grateau View Post
Fair point, but if chainstay length is a limiting factor your bike was designed by idiots.
Or the bike is doing things that weren't envisioned when the bike was designed. I never dreamed I'd be running 35c tires and fix gear on my Peter Mooney when I ordered it 41 years ago to ride very rough gravel. I did spec horizontal dropouts so I "could" run fix gear if I ever wanted to but never dreamed I would.

Guess that makes me an idiot. Funny, I thought I was being smart.

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Old 06-14-19, 11:50 AM
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Originally Posted by 79pmooney View Post
Or the bike is doing things that weren't envisioned when the bike was designed. I never dreamed I'd be running 35c tires and fix gear on my Peter Mooney when I ordered it 41 years ago to ride very rough gravel. I did spec horizontal dropouts so I "could" run fix gear if I ever wanted to but never dreamed I would.

Guess that makes me an idiot. Funny, I thought I was being smart.

Ben
Was referring to Wabi frames where half the length of the dropouts are unusable even with skinny tires but OK.
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Old 06-14-19, 01:24 PM
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Originally Posted by ThermionicScott View Post
@PeopleAreIdiots's Wabi, for example?
Originally Posted by seau grateau View Post
Bingo.

No shade intended btw -- it's a nice looking bike. It's just a ridiculous design ****-up on Wabi's part.
Yeesh, tough crowd haha.
I've been toying with the idea of an NJS frame with a wound up track fork for a future build. I'm sure you guys would be all over that one

Also, whats wrong with half links? $2 and problem solved. I'm struggling to see the issue here.
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Old 06-14-19, 01:50 PM
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Originally Posted by PeopleAreIdiots View Post
I've been toying with the idea of an NJS frame with a wound up track fork for a future build. I'm sure you guys would be all over that one
1" threadless? I'm down. (I have a weird fetish for Cinelli stems)
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Old 06-14-19, 01:51 PM
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Originally Posted by seau grateau View Post
Fair point, but if chainstay length is a limiting factor your bike was designed by idiots.
Or you’re doing a conversion on a frame that wasn’t designed specifically for the tires you want to run? maybe it’s a road frame with very short stays designed for the use of very skinny tires, maybe has no dimples on the inside of the stays? Petty common for 70s era road frames, which are very popular choices for conversion. You could easily enough say, use a different frame, but none the less, there are in fact reasons why you could have little room for adjustment and it’s not a ‘frame designed by idiots’. But you’re welcome to your foolish opinion, I guess.
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Old 06-14-19, 01:54 PM
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Originally Posted by seau grateau View Post
Was referring to Wabi frames where half the length of the dropouts are unusable even with skinny tires but OK.
So you have one singular example, of this ‘stupidity’, but put out a rather broad criticism so that two separate people completely misunderstood exactly what your were referring to? You should have just said wabi dropouts are poorly designed.
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Old 06-14-19, 01:56 PM
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Ok.
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Old 06-14-19, 02:19 PM
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Originally Posted by seau grateau View Post
1" threadless? I'm down. (I have a weird fetish for Cinelli stems)
Cant decide if I go threadless and then spec it like a modern track bike or do threaded and go full fixie with a leather saddle and risers

More of a day dream than an actual plan. And I have a wound up fetish so no judgements here
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