confused about chainrings and cogs
 

I know that either increasing the chainring size or decreasing the cog size will increase the gear ratio and gain ratio.

Is either way particulary better for some reason?
other than the fact that it's more expensive to get a new chainring.

Is it possible to have a chainring that is TOO big?
or a cog that is TOO small?

let me know if this is too confusing and I'll try explaining it better.

i'm running 46/16 right now and its not good enough. i just want to be able to ride fast. like keep up with cars fast.

nice

46/16 is a pretty nice gear ratio for all around terrain. but consider from your location (bay area), im not sure if you want to go with a higher ratio considering all the hills you have. learn to spin faster.

go up to a 48t chainring, with a 16 cog it isnt too hard! if it is you can always put a 17 if the 16 is too hard, like you i like to go fast, and hate spinning!!!

lol

If you plan on to making up any of the hills in the Bay area, go as low as you can handle.

If you want to go faster, spin faster, easy as that.

Changing a cog will be cheaper than changing a chainring, and it will be easier to switch out. Also realize that changing a cog will affect your GI by about 3 times more than a chainring (if you're adding or subtracting the same amount of teeth to either).

The first thing you need to do is determine your optimal gear ratio/gear inches. There's a calculator on the Sheldon Brown site to help you with that.

Once you know your optimal gear ratio, calculate your variance window, i.e. how much adjustability you want. For instance, your optimal is 72 GI, and maybe you want a range of 66 - 76.

Then figure out what combination will give you the range you're looking for. Also look for what's generally available. Generally speaking, chainrings will be 42, 44, 46, 48, 49 teeth while cogs will go from 15-19 teeth. There are some companies that make cogs up to 22 teeth or so, but your choices become significantly limited.

As a side note, Sheldon Brown does mention that larger chainrings & cogs will put less strain and wear on the chain.

Changing the tooth count on the cog makes a bigger difference than changing the tooth count on the chainring.

If I were starting from scratch, I'd select a chainring with a prime number tooth count (e.g. 43 or 47) and pick a cog to give the gearing I want. The prime number tooth count means you always get the maximum number of skid patches regardless of what cog you use in back.

Learn to spin.

It takes work, but in the end you will ride faster and have more fun.

I'm going to take advantage of this thread to get some help with this too. I'm running 48/16 but I just moved from a relatively flat place to a town with some fairly large hills. Should I go up on the cog size or down on the chainring size?

How many teeth less before its a noticeable change?

1 cog tooth change = 3 chainring teeth change. I would change the cog, more of a change and generally the cheaper way to go. To me 48/16 is already a very high gear ratio for the road, and I run no more than a 48/18 or 46/17 in an area with rolling hills and some wind.

I've moved by 2's so far. 15-17-19 and I've found that each change has been fairly significant, as in if I did a smaller change I may not really feel a difference. On my Jamis I have a 19/17 Fixed/Fixed rear hub. I ride 19 on my commute, and most night rides, I find it's actually a bit faster then my 17 for most practical riding, I have a tendency to beat a lot of people to the top of hills without a standing effort, it's only on the straight away sprints that I can really feel the spinny-ness of the 19t. I take that as my need to increase my cadence, rather then my gearing(also my stamina.) Over all i'd say go up to 19 if you have a lot of rolling hills, I seriously enjoy riding a lot more when I can take hills, up and down without destroying myself on each one.

I just want to point out an observation...

If the home mechanic was looking to chance his cog or change his chainring, one must buy additional tools to change the cog (lockring remover, chain whip) VS the chainring which can be taken off with an Allen wrench... So if it is a one time one bike sort of thing, its actually relatively cheaper to change the chainring than it is to change the cog (assuming you find a good deal on a chainring).

Problem is, you need to change a large number of teeth on a chainring to affect a significant change in gearing. This often requires also changing the number of links in the chain, which requires having a chain tool. Also, the cost of your typical good quality chainring is sufficiently higher than a good cog to afford a cog and lockring tool, which everyone with a FG should own anyways. In addition, you usually need a tool to restrain the chainring nuts on the back of the crank spider as well as a hex (allen) wrench to remove / install the chainring bolts.

With a 46x16 and 700x23 tires you should be able to ride over 30mph and average 26mph.

How fast is your traffic and how long are your rides?

Everything you have pointed out is correct.

However, my point is:

To change a cog, one needs at least a lockring removal tool ($15-$30) and some grease (~$5), utilizing the rotafix to remove and re-apply the cog, VS to change a chainring, one only needs an allen wrench (I have sucessfully gotten my chainring bolts off and on without the use of the dedicated tool. Though for the record, I do own the tool, and have needed it as well.

The price of the Cog and the price of the Chainring are subject to many different factors, but there are cheap enough Chainrings that make it more financially beneficial to change the Chainring than to change the Cog.

Has anyone used the Surly Dingle Two-speed Fixed-gear Sprockets:

http://www.sheldonbrown.com/harris/f...ets.html#surly

Two cogs in one essentially. Is the only drawback weight?

Seems like a good option for different kinds of rides.

You also have to compromise on chainline. But only nerds worry about chainline.





Has anyone used Campagnolo 11 speed freewheel cassettes?
Eleven cogs in one essentially. Is the only drawback weight?
Seems like a good option for different kinds of rides.

Assuming you have enough room in the drop out to tension the chain, would the chainline be any more compromised than on a geared bike?

If you take your chainring bolts off and on without the appropriate tool on both sides then you are doing it wrong even if it seems to work, and it's a good way to torque those bolts improperly as well as a good way to chew up your parts, since the nut will slip as you tighten the assembly. Am I wrong?

I can not answer your question exactly, but I can say that the proper tool that is suppose to slide into the slot with a peg in the middle only connects for me on one side...it works, but I found using it to not be a necessity

If you're gonna ride fixed you might just want to invest in the tools to tighten the cog and lockring, to me they're necessary tools.