Cassette ratios explained?

[sonic909]

I need two cassettes for my bike.

One for my commuting/dirty wheels and one for my racey/clean wheels.

I am SO confused as to what i want and what i need... Its got to be 10 speed, but which range is right for me? i have googled and come up with a brain fry!

My choices in shimano land seem to be;

11-21
11-23
11-25
11-27
11-28
12-23
12-25
12-27

So... any advice from fellow agreeables?

[Keith]

The cassette is only half the story - what are you running "up front"? Double (say 53-39), Compact (50-34) or Triple (52-42-30)?

[Antloony]

[quote="Keith"]The cassette is only half the story - what are you running "up front"? Double (say 53-39), Compact (50-34) or Triple (52-42-30)?

[Hal]

Oooh I'm going to answer before mr

the two numbers are: small cog - big cog (you probably already know this)

small numbers give harder gears for speed / slow cadence

large numbers give easire gears for hills

bigger the difference between the two the larger the jump between gears, the wider range of gears you will have.

A tester may use 11-21 so that each gear is only one tooth different and a constant cadence can be maintained. But this may limit you range of gears over a range of terrain.

A grimper may want 12-27 for good climbing.

I would recomend assuming you have a standard 39,53
- for your race bike an 11-25 (or 11-27 if you don't like hills or are going to sportive country)
- for your commuter a 12-27

If you have a compact
- for your race bike an 11-23
- for the commuter a 12-27

(I ride sram 34-50 with 11-26 race/sportive, 32,42,52 with 12-25 training bike, 38-50 with 12-26 winter bike)

[sonic909]

[quote="Keith"]The cassette is only half the story - what are you running "up front"? Double (say 53-39), Compact (50-34) or Triple (52-42-30)?

[higg]

Anything you need to know and quite a lot more can be found here :

http://www.sheldonbrown.com/gears/

Just put in your gears and press the Calulate button.

You can get gear inches (if you want to sompare with the trackies) or mph at 80-90 rpm (to compare with roadies).



Aodan.

[Phil H]

If you're really hardcore, you'll get one of those 10 speed 11-17 cassettes.

[Maria David]

yep, sheldon brown is the gears bible - but I haven't adopted the religion very well so don't read it that much!

What you get is down to what you plan on doing, and also how fit you are/will be and whether you like pushing hard gears or spinning higher cadence.
Go for a wider range of gears for the commuting bike. 12 - 27 with a compact 34 50 will let you cope with anything.

If you are planning to do lots of cyclosportives especially on challenging hills around Kent, Surrey or even beyond (cornwall/yorkshire/north wales) and the european sportives those same ratios will do fine. (That's what I have.)

If you are planning on doing time trials and crit races a lower range is better and you don't need to have large cassettes at the rear. 11-23 will do with the classic 39, 53 chain ring at the front.
If you want to feel more secure, maybe cos you're worried about fitness (or just because you're cycling will vary alot) an 11 - 25 with a compact 34 50 could be a happy medium. Just bear in mind that in road races/time trials these ratios may have you adopting more of a spinning style of pedalling - not a bad thing at all, but you may or may not be into that.

[sonic909]

Some brilliant advice there guys... for some reason i didn't think of getting two different ones..!

I did see that sheldon site but it all got a bit deep!

[Alex S]

I ride with a lonely 50 on the front and 12-27 on the back.

If you have a 50-36 (unusual? its normally 50-34)

I find with 50 at the front and 12 at the back i dont quite reach the top gear I would personally like so go for one that starts with 11. and goes up to 23 or so for the nasty hills, you won't need anything higher than a 23.

[Alex S]

[quote]If you're really hardcore, you'll get one of those 10 speed 11-17 cassettes

[Dombo]

Simply divide the chainring teeth by the cassette cog teeth to give you the wheel revs per pedal turn.
You can then calculate the road speed at which you will spin out in each gear using 2πr where r is the radius of your wheel
Alternatively work out the circumference by rolling your bike along a flat surface and measuring one rev of the wheel.
As a weedy lightweight I tend to spin high revs and hardly ever use my big ring (52/39/30) unless going downhill.

[Andrew G]

It will depend on what you're comfortable with to suit your riding style etc as to what's best so to start with I'd get a couple of the cheaper cassettes (i.e. lower down the groupset food chain) with different ratios on them to see which you prefer.

I have different setups for different things. Cassettes are a doddle to change and take 5 minutes so you can always switch them for a different ride, like a sportive where you might want lower gears.

[Elliot M]

Just to note that if you're moving to a larger big sprocket you may need to add a link or two to your chain.

I think the usual rule of thumb is to wrap the unlinked chain round the big-big combo, bypassing the derailleur, see how many links you need, then add one links to account for the derailleur.

Otherwise there's a possibility that you shift into a gear that your chain isn't long enough to handle, everything locks up and you can't shift back again until you split the chain. Or the chain breaks. I've done both.

[Andrew G]

If you don't have too big difference then you should be okay if you only use the biggest sprocket when in the small ring for granny gear duty. Another option is to keep a chain with the sprocket and then they'll wear together and with a KMC quicklink changes are easily done when swapping the cassette.