Changing from a Campag 12/25 to 13/29

Peak Times

I am a heavy weight rider 110k with a new bike fitted with Campag Mirage, and with a Miche 12/25 cassette. As we are surrounded by some of the best cols in the Pyrenees I am toying with the idea of changing cassettes to help me with the climbs.

My options seems to be either a 13/26 or a 13/29 the latter of which I guess will make a big difference. My question is whether or not switching to a 13/26 from a 12/25 will make a noticeable difference and if I do opt for the 13/29 is there a down side to bear in mind?

ColinJ

Peak Times wrote:

I am a heavy weight rider 110k with a new bike fitted with Campag Mirage, and with a Miche 12/25 cassette. As we are surrounded by some of the best cols in the Pyrenees I am toying with the idea of changing cassettes to help me with the climbs.

My options seems to be either a 13/26 or a 13/29 the latter of which I guess will make a big difference. My question is whether or not switching to a 13/26 from a 12/25 will make a noticeable difference and if I do opt for the 13/29 is there a down side to bear in mind?

I have a 13/29 on my Cannondale and get on pretty well with it. Obviously the ratios are not quite as tight as on a 13/26 but with 10 sprockets there aren't any huge steps. A 26 tooth sprocket would be about 3.8% easier than a 25 and I wouldn't bother changing cassette for that. The 29 is 13.8% easier which is well worth having if you need it (which you probably do or you wouldn't be asking !).

redddraggon

You might need to change the chain length - I've got a 13-29 sitting in my toolbox, and I know that one of the chains on one of my bikes definitely is too short for it, but the other is fine.

If you can go big-big on the ratios and the rear mech is still "bending the chain" you'll probably have enough chain for the cassette swap.

ColinJ

redddraggon wrote:

You might need to change the chain length - I've got a 13-29 sitting in my toolbox, and I know that one of the chains on one of my bikes definitely is too short for it, but the other is fine.

Oh yes, that's true!

Also - I think that I have a medium length rear derailleur, but I'm not sure if a standard one would have done the job?

OllyBianchi

I changed my Campag Mirage/Xenon equipped bike from 12-25 to 13-29 last year and it was one of the easiest bits of bike work I've ever done - cassette slipped on and off easily and I didn't even have to adjust the indexing to make it work.
Much of our riding is in North Wales and the tiny bottom gear is really useful - since the steepest hills we ride on have a surface not much better than the Plan Des Corones - being able to sit and spin is much better than being out of the saddle round here...

redddraggon

ColinJ wrote:

redddraggon wrote:

You might need to change the chain length - I've got a 13-29 sitting in my toolbox, and I know that one of the chains on one of my bikes definitely is too short for it, but the other is fine.

Oh yes, that's true!

Also - I think that I have a medium length rear derailleur, but I'm not sure if a standard one would have done the job?

I think it would, if you were careful with the chain length I'm sure it'd be fine with a short cage- if you can just go big-big 53-29 (50-29) I'm sure it'd be able to take up the slack in 39-13, maybe it would in 34-13 but less likely . The directions are normally pretty conservative so it probably would be feasible - I think people on here have done it.

Medium caged deraillers are fine with the 13-29.

redddraggon

OllyBianchi wrote:

Much of our riding is in North Wales and the tiny bottom gear is really useful - since the steepest hills we ride on have a surface not much better than the Plan Des Corones - being able to sit and spin is much better than being out of the saddle round here...

Where abouts?

OllyBianchi

We live in the middle of Chester and one of our regular routes is out along the cyclepath to Shotton then up to the hills behind Northrop. I think we're going to do Worlds End/Horseshoe this weekend.

Of course if we head into Cheshire there is some nasty stuff in the Peckforton Hills too, narrow, twisty, steep and potholed.

redddraggon

OllyBianchi wrote:

We live in the middle of Chester and one of our regular routes is out along the cyclepath to Shotton then up to the hills behind Northrop. I think we're going to do Worlds End/Horseshoe this weekend.

Of course if we head into Cheshire there is some nasty stuff in the Peckforton Hills too, narrow, twisty, steep and potholed.

I've thought of North Wales more like a hilly Paris-Roubaix, rather than Plan de Corones.

I roughly always go through Kinnerton, to Llandegla, Ruthin, Bofari.

il_principe

Not sure there's a lot of going from 12/25 to 13/36 go for the 29 as long as your rear cage is not short then you'll be fine. I'm going from an 11/23 to a 13/26 for the Etape, just pray I don't have to re-index cos try as I might I'm rubbish at indexing properly.

Peak Times

Many thanks for all the feedback so far. One question (I am new to this) is how can you tell whether your rear derailleur is short, or medium?

redddraggon

Peak Times wrote:

Many thanks for all the feedback so far. One question (I am new to this) is how can you tell whether your rear derailleur is short, or medium?

What's the rough distance between pulleys? About 1in it's a short about 2in and it's medium.*

*disclaimer - only rough distances

JamesB

You can use the short Campy derailleur with a 29 - I do!! BUT avoid at all costs trying to run big / big, it is mechanically inefficient if nothing else; I found that if I had enough chain length to run big / big then the short cage mech wouldn`t take up enough slack to enable running the 34 / 14 or 13 combination so I now run a shorter chain and run all cogs with the 34 ring and just the top 7 with the big ring (which is a 46 PMP ring on Campy Centaur)
I have also `fettled` a block to set up a 12 -29 system (basically 12 -15 straight thro`, then a jump to 17 - 29 set), but teh 15 / 17 change isn`t the smoothest as the cog ramps don`t line up. I used it OK though in GFC and plan to use this on Raid Pyrenean later this year, gives a good low gear and a reasonable gear for the downhills

Happy fettling!!