I'm lowering my gearing for the winter. Is there any reason to switch the cog over the chainring, or does it matter at all which is switched?

cogs are cheaper

+$

switch whatever is cheaper. if you need 130/110 you can get old road stuff fairly cheap or parts bin it.. 144 you might be better off getting a new cog..

It's easier to replace a cog than a chainring. Also, to obtain the same change in gearing ratio, you would need to have more difference in chainring teeth than sprocket teeth. This difference is relevant if, for example, increasing the sprocket by 1 tooth is all you need. Then you might get away without having to break the chain and attach a link.

EDIT: to clarify the last statement: say you have 46/16. You want to gear down for the winter and you would be satisfied with

46/17

or

43/16

They both give about the same gearing, but one will result in just one tooth difference, most probably allowing you to not touch the chain. The other requires 3 teeth of difference, and your dropouts probably won't have enough room to accomodate the extra chain.

I think it's far easier to take off 5 low torque bolts than deal with the cog and lockring. Also doesn't removing and installing cogs often increase wear on the threads, leading to an eventual stripping of the threads entirely? Slightly different tooth profiles or imperfections make their mark on the threads.

It wouldn't be fun to remove your cog only to realize that the hub is stripped.

Replacing chain rings is easier.

Also, chain rings are often made of aluminum, as opposed to stainless steel (like cogs). Aluminum wears faster than steel, so it makes sense to replace the chain ring with some regularity.

Yeah, so last night my hub stripped on the way to work. I think I'm going to go with disc conversions from now on

That being said, I would rather change the cog than the ring.

-Rob.

I always keep an assortment of cogs on hand, not that I change them often. After years of tinkering you start to accumulate cogs and rings. But it's a lot easier to deal with cogs than chain rings though....

cog before chainring, just make sure you drop the money on a good quality cog! chainrings have a lot more work in the installation.

On the flip side, you may find that your current ratio is too high and adding one tooth on the cog gives a ratio that is too low. Because 1 cog tooth equals about 3-5 chainring teeth, you have finer control of the gearing if you swap the chainring. Also chainrings are easier to swap than cogs, unless your cog is not on tight enough to begin with.

You have a disk brake hub setup? Did you modify a normal cog or did you buy a prefab?

Yeah replacing a cog on a disk brake mount hub would be probably the easiest of all!

i disagree, rotafixing is about the easiest thing ever and works to get a cog on and off pretty easily. I think easier than getting equal tension of 5 bolts and dealing with reinstalling cranks. Plus all you need is a lockring tool and your bike for rotafixing. Although you're point on fine tuning gearing is 100% on.

The replacement wheels will be flip-flop 29er wheels from bike island. Eventually, I would like to replace them with disc 29er wheels so I don't have to worry about this ever again. I seriously doubt I will ever generate enough force to shear six 4mm bolts.

As for the cog, I'm running it on my Monocog 29er now, and ran the same cog on a SS 26er before that. I bought an $8, 18t Shimanno BMX cog and drilled it. Just use a bit designed for drilling harder steel. Your hardware store should know what you're talking about.

And while I'm thinking about it ... I don't know of any 120mm disc hubs, but you could put a 100mm front disc hub on a 120mm axle with some spacers ... Its been done before. Might be less of a hassle and more reliable.

-Rob.

Think it would be cheapest of all to get two 29er front wheels and drill a cog? Are 29er rims exceptionally wider than road rims? My hub is partially stripped so I need to plan for the future.

When looking for wheels for my fixed cross bike I was told that on a 17mm rim (track wheels), I could run up to a 32c tire without worry of rolling or pinchflatting. On the 29er wheels, IIRC, I could run down to a 28. I wanted to run 38c's so I went 29er.

So long as you were looking for a larger tire, a 29er wheel should work fine.

-Rob.

A lot more work? As in removing 5 bolts, putting a new ring in, and re-tightening the 5 bolts?

chainring much faster and much more expensive.

ok, the answer is........



's faster to switch out a cog if you know how to do it

Thanks all. Cost wasn't an issue as I have various chainrings and cogs. Ended up for now going to 42/16 from 42/14. My chainring bolts are too long and I have washers taking up the space so switching the chainring to a smaller one wasn't going to work, chain hits the washer and my cranks have different bcd so no swapping from the shimano to the campy. Since I was fixing the bike already I decided to change the crank, chain and front wheel as well for winter. What I can do when my wife is away. Now the worlds second ugliest fg bike is ready for the winter, more or less.

i change the chainring. 48/19 and 42/17 are both about 65 gear inches, what i like to ride in the city. with the 42 tooth chainring, when i feel like riding the freewheel side i only have a 1 tooth difference (16t freewheel) as opposed to a 3 tooth difference(about 10 gear inch difference) if i just change the cog.

so, getting a $40 chainring is cheaper and more versatile for me than buying a $30 cog and a $25 freewheel.

I wrote my original answer assuming that the person who asked, had made the ratio calculation already and found that +1 tooth on the sprocket or -n on the chainring was appropriate for his needs. I modeled my answer around that assumption.

After reading the comments written later on, this is what I conclude:


Striping of threads on hub as an argument against replacing the sprocket: this is a good point, but marginal in my experience. I have threaded plenty of sprockets and freewheels on an off and think the danger is minimal.

Replacing chainring because "it's usually made of aluminum so it lasts much less than sprockets made of steel". Well, this is not necessarily the case. If you use Rocket Rings, then sure, your chainring is due for replacement after 2000 miles. But with chainrings that are not made of butter, the lifetime is quite high, due to the fact that force is distributed on more teeth than on the sprocket. Chainrings are usually considered the part that wears the slowest. And if you have a steel chainring like I do on one of my singlespeeds, it will outlast a steel sprocket. Besides, we don't know what material chainring does the OP have.

As someone said: rotafixing off the sprocket is about the simplest thing in the world. Adjusting a chainring correctly is simple, too, but it requires much more work. Sheldon Brown has detailed instructions how this is done.