I have an IRO model 19 (eccentric bottom bracket) and am currently running a 33 by 16 drivetrain. This gearing has proven a little too tall and I'd like to lower it a bit. I tried a 17 tooth rear cog but, couldn't tension it properly with either the existing chain or, a new, longer one. I discovered that I'd likely need a half link in the new chain. I would like to move to a larger cog while maintaining the functionality of the EBB adjustment (which I like very much) and not have to use a half link chain. I've heard about the "magic" gear combinations and don't really get it, I also don't want to go through multiple cog/chain combinations either. Can someone recommend a cog that would accomplish my goals? I seem to remember someone at IRO telling me that an 18t cog would work but, it's been a long time and can no longer get in touch with them to confirm.

Thanks,

You could just use a single half-link rather than an entire half-link chain. Why can't you adjust the bottom bracket?

Someone should come up with a handy, easy to use magic gear calculator for situations like this.

I can adjust the bottom bracket, it works fine. It's just that with 33x16 gearing and, a longer chain (since the existing chain is too short to work with the 17t cog) it doesn't adjust enough to tighten the chain sufficiently. I should point out that the bike has vertical rr. dropouts too. In order to use the 17t cog I would have to install a half link in the chain, I'd rather use a cog that allows me to stick with a traditional chain, even if I have to lengthen by a link or two.

In the previous response I meant 33x17, this is where I run into problems, with the existing 33x16 combo everything works as it should.

I'm too dumb to figure out Scrod's calculator or I'd tell you.

If you switch to a bigger cog, you need more chain. Unless you simultaneously switch to a smaller chainring. More teeth = longer chain.

edit- Actually I think I have no idea what you're asking. It seems like you're just diametrically opposed to using a half link, which is stupid.

I think we have a bad case of half-link aversion syndrome.

It makes me cross-eyed.

That's why I have to use this one.

And what, pray tell, does that have to do with determining a proper magic gear ?

Nothing, but the colors don't make me cross-eyed.

And, I get all the info that I need.

The gear fairy doesn't fly east of the Mississippi, and the batteries for the magic wand are on back-order. Why else do you think Scrod is CA bound??

Despite your skepticism with using a half link, a single half link will be far cheaper than any other option you could change, especially now that you have your desired cog. Just try it and see if you have any problems, if so you're only out a few bucks.

I too agree with giving the half link a try, just a single half link. It'd be a bugga to go to a lot of trouble and expense changing your gearing only to find you didn't go far enough. Try the half link, if the gearing works, then work out a more elegant solution (or stick with the half link)

Half-link chains are bad. They stretch out easily because a half link will stretch a fraction of a millimeter and this gets multiplied for each link so a chain can stretch quite a bit. However a chain with single half link will not stretch noticeably different than a chain without the half-link because the amount that a single half-link can stretch is tiny. I think people hear "half-link chains are bad" and they think that means "half-links are bad".

There is more than enough adjustability in the EBB to not need a half-link if you would rather not.

Put on the larger cog. Then see if the old chain is long enough with the EBB all the way in the back of the BB shell. If yes, then done. If no, then add another link. There is something like an inch of variability in an EBB like that, which is about four times the adjustability needed for any gear combo with the closest chain length.

So, I would play with the EBB a bit more before moving on to other solutions.

jim

A half link chain has the same number of pivots as a normal chain.

And a bend in each link that is prone to expansion.

I guess I am a little curious as to how significant this effect is and if it really makes a difference compared to other factors such as old sprockets, poor maintenance and so on. How many miles does someone's half link chain last compared to a normal one on the same setup?

Less.

Just accept it.

what is the best gear ratio for a smoother ride? and easier skidding?

Well, 58/14 seemed to work pretty smoothly for Tony Martin the other week, mind you, he's not human and he didn't do much skidding.

Now seriously, how on earth are we to comment on on a so-called "smooth ride" not knowing your physical strength and technical abilities and limitations, not to mention the type of riding that you do?

Chances are that you might find climbing Alto de LŽAngliru slightly more challenging than your daily commute wherefore different gear ratios may be required.

As for skidding, use a skid patch calgulator and bear in mind that a a low gear ratio generally makes skidding somewhat easier. But really, if you need to ask, use a brake.

+1, but with that said 42/16 or /17 is a good place to start IMO.