Sunday, October 9, 2011

Homebrewed Components - Choosing a Chainring and Cog Combo

For my post on choosing a rear cog go here: choosing a cog

I'm in the market for a new cog and chainring for my singlespeed. Homebrewed Components seems to be a preferred designer and manufacturer of cogs and rings by many singlespeeders, and is mentioned quite a bit in the forums.

Dan Wilcox is the man behind Homebrewed. He explains how the business started:

After being a Machinist/Engineer for my whole working life, i decided to start up my own machine shop. Granted, doing it in the height of the economic recession was probably not the best of ideas, but i figured what does not kill me will only make me stronger. Also, i figured it would keep me from making a bunch of useless crap that has flooded the markets partially causing this predicament we’re in.
At first, i started making parts for other companies and building tooling for people i had worked for in the past. That was going OK, but it wasn't really what i wanted to do with my capabilities. Also, i take pride in what i do, and if I’m going to make something, i want my name on it, not someone else’s. 
Now here’s where i started thinking… what do i like to do the most? Well, that would be creating things and mountain biking. How can i put those 2 together? Well duh, make bike parts! At first it was just going to be a hobby to cure some boredom in between the normal work. I started making chain tensioners using part of a design that i had made a few years ago. The only modifications i did to it were basically a little material removal to lighten them up. I posted them up on a web forum and got some decent feedback along with a few orders.

Read the full post at the Homebrewed Components blog.

I'm currently running a 2:1 ratio, and feel I could do better with a fraction more, maybe 2.1:1 or 2.2:1. This will make my flats a bit faster and the hills harder. Coming from a 32 - 18, I was on a 1.78:1 ratio. So a jump up to 2:1 was 22 tenths.

Using this 22 tenths figure as a benchmark, I don't think I could handle another jump of 22 tenths considering the terrain where I live (it's not very hilly but the few hills we have would be very hard for me at 2.22:1 I think.

Let's take a look at the combinations Dan from Homebrewed offers. This is a grid between the aluminum chainrings he has which are compatible with 104 BCD (for Shimano) and his aluminum standard cogs.
Ratios between Homebrewed Al chainrings and Al cogs

The red cells are ratios I don't think I can handle. The greens are even less viable as they're even easier than what I'm running now. And the orange cells are what I'm on now.

So my best options are those in the white, above 2.0 and below 2.22. I think 2.21, 2.20, and 2.19 are probably just about the same or indistinguishable from 2.22, so I'll avoid those. I think 2.12 or 2.13 would be best.

Starting from the bottom of the chart, 2.12 at 36-17 is good, as it affords more chainwrap than the other options, but it doesn't leave me with many options if 2.12 is too hard or too easy - the neighboring cells are 2.0 and 2.25.

The next choice is 35-17 producing a ratio of 2.06, which probably isn't quite aggressive enough. 35-16 sounds just right, and if it is too hard, I can keep the 35 and easily move to a 17 cog.

The problem with 34-16, is I can only move down to a 2.0 if the 2.13 is too hard.

A 33 chainring give me almost exactly the same ratios as a 35, but being smaller would be a hair lighter - but I'd lose some chainwrap.

32-15 is the same as 34-16, including the neighboring options.

A 31 ring looks good, as I can get 2.21 with a 14 or if that's too hard, 2.07 with a 15.

I wonder just how critical chainwrap is. I suppose there's only one way to find out, and that's test it myself by buying a 31-14 and 15.

Last, I wonder why Homebrewed has so many other ratios that very few singlespeeders would ever want. I'd imagine the 31-24 combo would be far too slow to ride on the road and not practical unless you lived in a super hilly area.


Update, 11 Oct, 11

As I was about to place my order, I noticed a note regarding the 31T chainring. It says:

This is enough for me to not order the 31, not knowing the extent to the modifications or why it may not fit.

Thus, I'll go with a 33 and a 15 and 16 for almost identical ratios to the 31 with a 14 and 15.


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