12/25 vs 12/27 vs 11/25

mclarent

I need a new cassette for my new wheels (keeping the old ones for the turbo).

Just wanted to get peoples opinion - should I get a 25 or a 27? I'm assuming the 25 will provide smoother changes in the smaller gears, but as mainly a social / sportive rider with cat 4 ambitions, will I really notice the difference? Also leaves me wondering, if I'm getting a 25, why not get a 11 rather than a 12? Not likely to get up too many big hills where I live (east London), though I do a few rides out with short sharp ascents...

redddraggon

I like my 11-25, but the 21-23-25 jumps are too small really, I'd much prefer a 11-26 with 21-23-26. If you haven't got any big hills I can't see you needing a 11t sprocket, or really needing the 27t sprocket. However if you ever go anyway needing a smaller gear you might be glad you've got the 27t.

On my winter bike I've only 50-13 as my biggest gear, and it doesn't get used that often.

So I reckon you're probably best off getting the 12-27. You could always get a 11-23 if you were to start racing.

Monty Dog

Also depends on what chainrings you're running. I'd say the 11-25 - if you're race fit, you'll get up most climbs and you'll need the 11 if you've got a 50 tooth chainring. The 27 sprocket would be OK for hilly sportives but pretty redundant for racing.

mclarent

Thanks for the comments - the wheels I've bought are just for winter training really, 2nd hand pair of open pro's on 105 hubs. I'm on a 50/34 (compact) crank, so sounds like the best bet is a 11/25...

maddog 2

it's only the bottom two sprockets that are different

12-25 is 21,23,25

12-27 is 21,24,27

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

I'd say for general road work, on hilly routes, the 12-27 has benefits and very little downsides over 12-25. It'll be a tad heavier but does give you a better low end for proper steep stuff, on the 34 ring, without really influencing the 50 ring shifting.

JimmyK

I use an eight speed Shimano 13 - 26 rear cassette and I just love it, great for climbing and all the speed I need.

Jimmy

willbevan

I would second maddog2... get a 12-27..

I have several casssetes mind you depending on what im doing..

12-27 for general road riding, training, long distance stuff

If im racing, well time trialling its different...

Depending on the wheels a 11-21 or 11-23 (campag 8 speed) on a disk
or a 11-23 , 10 speed on a powertap

peanut

for a compact like yours I'd go with a 12-25 or 11-27
most standard chainsets now are 53t and 39t which with a 12-27t cassette gives a lowest gear of approx 39"
A 50t x34t chainring with 12t-27t would give approx 34" which should be more than ample for any hill unless you are touring with a tent & gear etc.
I wouldn't recommend 13t up with a 50 chainring myself you'd soon spin out on a long downhill unless you want to spin like a demented gyroscope. stick to 12t up
So my recommendation would be 12-27t
As a guide I am unfit and weigh nearly 18 stone and its hilly round here in Somerset .I have 53x39t with 12t-27t and I can manage most hills I come across not sure about Porlock though :roll:

salsarider79

You've not said if your running 8, 9 or 10speed.
I ran a 12-27 on my Tarmac with a 39/52 chainset. I used the 27t once in the time I had the bike, and that was as an expierment to see what it was like. To be fair, unless you are going anywhere hilly, I'd not bother with a 12-27.

p.s. 52/12 got me to about 33mph on the flat.

peanut

salsarider79 wrote:

You've not said if your running 8, 9 or 10speed.
I ran a 12-27 on my Tarmac with a 39/52 chainset. I used the 27t once in the time I had the bike, and that was as an expierment to see what it was like. To be fair, unless you are going anywhere hilly, I'd not bother with a 12-27.

p.s. 52/12 got me to about 33mph on the flat.

you need to condider age weight fitness diabilities loads of things . Imagine picking up 2x 56lb bags of cement one under each arm then riding up Bathwick hill without a granny gear :shock: Then you'll have some idea of what I face every time I go out for a ride

mclarent

thanks for the advice, I ordered a 12/25 Ultegra in the end - mainly cos it was half price on SBR!!