Compact 12-25 v 12-27

Lightbox

So I followed the Fat Cyclist's instructions, and somehow convinced myself and the missus that a new bike was an essential purchase, even though the fridge hasn't worked properly for over a year, and consequently a Bianchi 928 Carbon Ultegra C2C now hangs on display in the garage, and has already winged its way around the 100 ml Lancs Valley Loop charity ride, and Rourkie's Cat & Fiddle on Sunday..

Having spent the last 20 months on a Ribble triple with Campag Mirage 9 spd ratios of 53/42/30 and 12/25, and a committed user of the granny ring to spin my way up the steeper bits of Lancashire, I am now finding my way around a compact Ultegra 10 spd of 50/34 and 12/25, and finding that low ratio of 1.36 a little hard to push round on the more testing climbs I encounter - something like the Nick O'Pendle or Waddington Fell in Bowland for example.

My question is this - would I notice much difference by changing the rear cassette to 12-27, giving a low ratio of 1.26, a little nearer to the 1.2 I have available on the Ribble? Or should I take the advice of my younger and fitter brothers, and simply train harder, eat less cake, and drink less grog?

maddog 2

go for it

it's only the top two sprockets that are different

on the 12-25 it's 23, 25
on the 12-27 it's 24, 27

Just give you a tad more at the bottom end.

richa

Previously you had gears...
30~21 = 37.5 in
30~23 = 34.3 in
30~25 = 31.5 in

Options...
34~23 = 38.8 in
34~25 = 35.7 in
34~27 = 33.1 in

A 27 cog is an 8% increase over 25. Thus on a steep climb it would change your cadence from, say, 75 to 81.

It depends how often you were required to use your lowest 2 gears.

Lightbox wrote:

My question is this - would I notice much difference by changing the rear cassette to 12-27... Or should I..simply train harder, eat less cake, and drink less grog?

I would suggest a bit of both. Get a 27 cog and get fitter.

John.T

Yes you will find it better. The problem with the 12/25 cassette is the gaps between the 21, 23 and 25 cogs are too small in percentage terms. the 12/27 gives a more even spread of gears and reduces the bottom gear from 36" to 33". A drop of 8%. This is only 1.5" higher than your 30/25 with the triple.

Lightbox

Thanks for all the helpful responses, which confirm my gut feeling that changing to a 12-27 will help me negotiate the lumpy stuff.

Now to the fridge problem - any ideas why ice forms at the top, but it gets warm at the bottom? I could probably live with it for another year, but it's getting difficult to keep beer cool.

John.T

Beer to top of course.

maddog 2

separate beer fridge!

richardjallen

When the fridge is iced up it does not work as well as when its just been defrosted. It also needs some space behind it for the convection fins to dissipate the heat that is being taken out from the inside. Keep it away from heat sources as well or it will be working overtime instead of chilling. That's pretty basic stuff though and I don't know any more than that. My fridge is an under the counter one with freezer in the top but its crap and does not come close to freezing anything. Not even an ice cube.

SteveR_100Milers

Definitiely a 12-27 for anything hilly, otherwise you might as well become all hard and ditch the compact completely...

OllyBianchi

I've just changed my Campag 10 speed from a 12-25 to 13-29 with a compact on the front, which gives me a lowest gear the same as the triple on my wife's bike.
Most of my riding is in North Wales and I just got fed up of planning a long ride then hitting soime stupid 25% ramp after 10 miles and blowing up - I usually ride with a high cadence and I'm not too good at pushing round a gear slowly.
Only been out a couple of times but I think it's a good decision.

calvjones

Agree with Olly that the 13-29 Campag cassette is a good way to go for low gearing (and it works fine with my standard Veloce Mech, tho mine is a 9 speed). You do find, even with 53-39 tho that there are not many big gears for the flat bits between the hills...

Lightbox

Thanks again - SteveR, I don't think there's any chance of me getting all hard, which is why the triple has been such a life-saver up to now - by the sound of it, 12-27 is the way to go for me, I have been managing without the lowest of the low ratios on the triple, so I don't think I need to go completely like-for-like with a 13-29.

Out of curiosity, and pardon my ignorance if this is obvious to everyone but me, but would the Campag 13-29 cassette be compatible with my Ultegra?

magliaceleste

The answer to that question is that a Campag cassette only fits a wheel with a Campag freehub since the splines on the Campag cassette are different to Shimano's. So it depends on the wheel you're using.

Also I think that the Campag cassette spacing is also slightly different, although I suspect that wouldn't actually stop it working.

reyserf

Lightbox wrote:

Thanks for all the helpful responses, which confirm my gut feeling that changing to a 12-27 will help me negotiate the lumpy stuff.

Now to the fridge problem - any ideas why ice forms at the top, but it gets warm at the bottom? I could probably live with it for another year, but it's getting difficult to keep beer cool.

Sounds like it's short of gas or perversly the heater could be stuffed. Either way get a new fridge, cool beer is important.