Picking the right Fixed Cog

doctorkoh

Hi, if there is a thread on this already, I apologize; a link would be appreciated!

I'm currently in the middle of converting an old road bike into a fixed gear and am in need of help in picking the right fixed cog. I just don't understand what some of the numbers stand for. For example:
http://www.amazon.com/Avenir-Fixed-Gear ... xgy__img_c

What does the "(1/2 X 3/32)" mean?

I am getting a 27" wheel if that is important in answering this question.

LeighB

½ x 3/32 is (narrow) derailleur chain, ½ x 1/8 is (wider) single speed chain.
Its up to you which one you choose but you need to put the same size sprocket/chain combination.
I built a fixed winter trainer and used 3/32 components and it was fine.

Chiggy

doctorkoh wrote:

Hi, if there is a thread on this already, I apologize; a link would be appreciated!

I'm currently in the middle of converting an old road bike into a fixed gear and am in need of help in picking the right fixed cog. I just don't understand what some of the numbers stand for. For example:
http://www.amazon.com/Avenir-Fixed-Gear ... xgy__img_c

What does the "(1/2 X 3/32)" mean?

I am getting a 27" wheel if that is important in answering this question.

It's 'self appraisal' time.

First, what is your 'natural' cadence. ie the pedaling speed you feel most comfortable?
Second, what average speed do you think you could keep up on an unhindered one hour ride at about 1/2 your max exertion power.

Calc a gear ratio which satisfies both these criteria.

Monty Dog

How many teeth are on the chainring that's driving the rear wheel? Other factors include how hilly is the area you're riding in and your relative fitness.

amaferanga

LeighB wrote:

½ x 3/32 is (narrow) derailleur chain, ½ x 1/8 is (wider) single speed chain.
Its up to you which one you choose but you need to put the same size sprocket/chain combination.
I built a fixed winter trainer and used 3/32 components and it was fine.

1/8 chain works on 3/32 rings, but not the other way round.

Mark Elvin

It appears there are two seperate issues being confused here.

1. Gear ratio

2. Chain/sprocket width.

Chiggy

Mark Elvin wrote:

It appears there are two seperate issues being confused here.

1. Gear ratio

2. Chain/sprocket width.

He doesn't want to buy the correct width and then find he's bought the wrong number of teeth.

If it were me, I'd bung for both the 16 and 18.

52 x 18 is 78".

amaferanga

If its for general riding and there are hills around then something around 70" would be a good start. Better to be spinny on the descents than grinding up even slight inclines.

I have 42-16 which is around a 69" gear and I find it just right for Sheffield and (some) Peak District hills.

John.T

The 1/2 bit means it is for 1/2" pitch chain which nearly all are.
The 3/32 is 3/32" which is the internal width of the chain. Current deraileur chains are this size. Just use any cheap chain. 7 or 8sp are probably best as they are a little more robust.
What size you get does as mentioned depend on how high a gear you want / can manage. I use 42/17 which means that at 90 rpm I am doing 17.5 mph and can still get up the hills. I can get to 30 mph but that is all I can manage safely. Like all single speed set ups it is a compromise.

Butterd2

1) On chain width, if you are building from scratch go 1/8th, it's stronger plus it is designed for SS/FG so no ramps on the chainrings and the chains are also different as they do not need to have sideways flex as your chainline will always be straight. This makes it less likely you will throw a chain, which is a good thing especially if you are Fixed.

2) On ratio I started 46/18 (fixed) and have now gone to 48/18 which gives me 72". From what I read this is a typical ratio and works well for me. I can cruise at 20mph but can just about heave it up a hill when I have to. Coming down hill I would like to be able to go faster but that is the compromise you have to make.

cougie

42*17 works for me. I can spin happily on that for hours, and still get up any hill in the area. Its the coming down hill where I struggle, but thats fixed for you.

cougie

42*17 works for me. I can spin happily on that for hours, and still get up any hill in the area. Its the coming down hill where I struggle, but thats fixed for you.

bigpikle

personal choice based on strength and fitness - you'll probably end up changing. I got a nice Andel 44t chainset and 18t sprocket IIRC but then changed sprocket to a 17t as fitness came on a bit. Its reasonably hilly here so any more would have been too tough for climbing much.

Bar Shaker

Butterd2 wrote:

Coming down hill I would like to be able to go faster but that is the compromise you have to make.

What is the upside of this compromise?

Have you considered a bike with several gears?

These gears could even be selected by pressing a small lever, rather than by adding or removing chain links.

Its only a thought.