Please Explain the Gear Notation

[gregboyd]

I'm fairly new to this and I am having some trouble understanding what people mean when they write 53X13 or similar. I have gathered that 53 is the big ring and 39 is the small ring. I also think this is the number of teeth on the front chain ring. Maybe the second number is the teeth on the gears in the rear block? If I am right so far then what is the "normal" notation for a standard bike (assuming two rings up front).

I have also notice this notation used in spinning DVDs and it would help me out if I could understand what gear they meant.

(I could just count the teeth on my rear block, but I'm not sure I understand it well enough to make the assumption that those numbers are talking about the teeth)

Thank you very much.

 

[larry barr]

Originally posted by gregboyd
I'm fairly new to this and I am having some trouble understanding what people mean when they write 53X13 or similar. I have gathered that 53 is the big ring and 39 is the small ring. I also think this is the number of teeth on the front chain ring. Maybe the second number is the teeth on the gears in the rear block? If I am right so far then what is the "normal" notation for a standard bike (assuming two rings up front).

I have also notice this notation used in spinning DVDs and it would help me out if I could understand what gear they meant.

(I could just count the teeth on my rear block, but I'm not sure I understand it well enough to make the assumption that those numbers are talking about the teeth)

Thank you very much.

Yes, generally the standard configuration for the front chainrings is 53 for the big ring and 39 for the small and the numbers are the number of teeth. The rear cassette comes in many configurations and can depend on whether you are running an 8,9 or 10 in the back. For instance, I run a campy 10 and my rear rear cassette is an 11-25. Thus the smallest cog has 11 teeth and the largest has 25. For me, the 13 is the 3rd smallest. You should be able to look at your front chainrings and rear cassette and see numbers imprinted, which will give you the teeth count. Hope this helps.

 

[gregboyd]

So if I have SRAM PG-950, 12-26 as a rear block, then the smallest gear in the back has 12 teeth and the largest has 26. The are 9 total gears in the rear block. "12" is written on the smallest one, but I don't see any writing on the others. I may be missing it, but the others do not seem to be marked.

Is there a way to tell what the count is for each gear without actually counting the teeth?

 

[larry barr]

Not that familiar with the SRAM cassette, you could contact the company or the store where you got the bike. If you bought the cassette separately the box would have the individual count. otherwise you would have to count. Generally, it would increase by one up until the 15, not sure where they make the change to finish with a 26 instead of a 25.

 

[dhk]

Originally posted by gregboyd
So if I have SRAM PG-950, 12-26 as a rear block, then the smallest gear in the back has 12 teeth and the largest has 26. The are 9 total gears in the rear block. "12" is written on the smallest one, but I don't see any writing on the others. I may be missing it, but the others do not seem to be marked.

Is there a way to tell what the count is for each gear without actually counting the teeth?

You've probably got 12-13-14-15-17-19-21-23-26. But, why not just count the teeth....only takes a few minutes to be sure.

 

[edd]

Originally posted by dhk
You've probably got 12-13-14-15-17-19-21-23-26. But, why not just count the teeth....only takes a few minutes to be sure.

easy way to count cassette teeth is to mark one tooth with a black marker and be sure not to count it twice.

Gears are also referred to in "penny fathing speak" that is you calculate the chain ring / cassette cog / wheel size ( ie 600 or 700 ) and you get a size equal to the diameter of a large wheel..

is a good way of checking ratios to see if you have a useful spread

http://home.i1.net/~dwolfe/gerz/howto1.html

 

[Fixey]

A gear chart.....available from your LBS is helpful. Be aware that gear ratio's can be writen 2 ways, for example a 46 front chainwheel with a 15 rear sprocket can be writen as 82.8 or as 6.610

the first is easier to work out....front chainwheel (53) times rear wheel (in inches, 27 is the excepted normal (or 26))
divided by sproket eg 46 x 27 / 15 = 82.8
second way involves Pi and I have forgoten the formula