JC 911

Stupid newbie question - Hope someone can give a little insight on cassettes. I'm looking to pick up a Shimano Ultegra 9 speed cassette. These are the options that are available -

Size 6: 12-27: 12,13,14,15,17,19,21,24,27
Size 5: 12-25: 12,13,14,15,17,19,21,23,25
Size 4: 12-23: 12,13,14,15,16,17,19,21,23
Size 1: 11-21: 11,12,13,14,15,16,17,19,21
Size 2: 12-21: 12,13,14,15,16,17,18,19,21
Size 3: 11-23: 11,12,13,14,15,17,19,21,23
Compatibility: Shimano 9-spd
Weight: 210g
Material: Chrome-plated Chromoly


What is the deal with the sizes? I assume it has to do with the gears and the teeth. Any help explaing is much appreciated!

trin2du

The individual numbers you have listed are the number of teeth on the individual cogs. The lower the number the higher (harder) the gearing.

mxyzptlk

Is this off of a website? If so, "size" is probably just a default label they had to use.

bdcheung

The "Size X" is just categorical for the reselling company, I'll bet. There's no real "size" difference - all are compatible with your freehub body.

OCRider2000

As far as which to choose? You need to decide what is your prefered lowest gear. 21 is probably not low enough for most people who do hills. I ride a 12-23. The other question to ask is what is your prefered highest gear.

FormerBMX'er

Not to be smart arse, but if you have to ask then go with size 6

Dead Extra #2

slowandsteady

Sheldon brown's website will have a gear calculator. Just input those numbers and the number of teeth on your chain rings and you can figure out how much easier or harder those choices are.

superslomo

I would say avoid the cassettes that have an 11 tooth cog. You will rarely find yourself really NEEDING that super-high gear, especially if you are just getting into the habit of riding.

If it's hilly where you live/ride, go with a high count on the biggest cog (12-27, for example)... if it's not you can get on with a smaller big cog, which gives you tighter spacing between the gears.

bvfrompc

What you should do is go with a SRAM 12-26, if your new enough to ask these questions, you won't need to the tight gear ratios of an 11-21 or 11-23 or 12-21 or 12-23. I have been biking for a couple of years, had a 12-26 on my 9speed and now an 11-26 on my 10sp. I presume the SRAM 12-26 will be cheaper, same quality, and a nice mix of gears high and low.

slowandsteady

I would say that strength as a rider has nothing to do with knowledge of gears. I know quite a bit about bikes, but am very slow. I also know some people who would kick my arse three times over and are totally clueless about bikes.

Here is a link to the calculator. I like to use MPH at 90 RPM. If you know that the fastest you go on the hills where you live is 9 mph then you will need X gear, but if you fly up those hills at 15 mph, then you need Y gear. And if at any point you get off and walk you need the 12-27 and some interval training.

https://sheldonbrown.com/gears/

I did one for you assuming you have 700x23c tires and a crank length of 170mm(not that it matters) and a compact crank(50/36t) and the 11-23 cassette in back. As you can see below, the fastest you will go at 90 rpm is 32 mph and the slowest you can go at 90 rpm in your lowest gear is 11 mph.

23.0 32.0
21.1 29.3
19.5 27.1
18.1 25.1
16.9 23.5
15.8 22.0
14.9 20.7
13.3 18.5
12.1 16.8
11.0 15.3

FormerBMX'er

FWIW I run 12-26 on two of my roadies and 12-25 (10spd) on a third. Climbing to the top of Mt.Wachusett this past summer I would have loved a 12-27 to go with my 50-36 .

superslomo

I don't think anyone was implying that knowledge=fast or anything like it, but more that someone getting started, without the knowledge, probably needs to build up some strength and would appreciate the bigger bail-out cog and not have much use for the precise cadence setting ability of a closely spaced cassette.

I have a 9 speed touring cassette that goes 11-34... tighter spacing is necessary when dealing with regular road use while not loaded down.

cyccommute 

It depends on where you live and how daring you are. If you want to fly down hills at speeds that scare mortal men, an 52x11 top gear is almost required...especailly if you live at the foot of the Rockies

Alternatively, if you have compact gearing or touring gearing, an 11 tooth is almost required.

Psimet2001 

you know...it may not be the most flowery way of putting it, but there is some solid truth in here.