Cassette question - ratios

by Spud   March 1, 2012  

I have a 12-25 cassette and a 53/39 chainset on my (relatively) new road bike, I've entered te C2C in a day with a mate at the end of June so need to train a lot. Question is would going to a 12-27 make much difference when climbing? Ride goes up Hardknott and Wrynose, so I suspect I'll do some walking anyway.

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Not sure if this will help but I have 53/39 and swapped my 25/12 for a 28/12. Easier on hills a bit but not as easy as a compact set up obviously.

posted by Nevetsyarg [74 posts]
1st March 2012 - 10:27


I've no idea of your level of fitness but unless you have legs of steel, cavernous lungs and weigh about 8 stone, you'll probably struggle up Wrynose and Hardknott. I have heard of people on the Fred Whitton using mountain bike cassettes.

To answer your question; a 27 will made a noticeable difference but I'd go with a 28 or 30 (if your rear mech can take it). I cant' recall too many places where a 53-11 gearing would be useful (unless you're racing) so 12 as a smallest cog would be fine.

Good luck and I hope you enjoy it. Are you doing it to raise money or just for the challenge?


posted by arrieredupeleton [587 posts]
1st March 2012 - 11:41

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I did a C2C last year. Hardknott is a fantastic challenge, unfortunately I couildn't make it up on a 34/28 compact set up, but as has been said, depends hugely on your levels of fitness.
Will definitely be returning one day to conquer it however!!

posted by MickeyBlueEyes [21 posts]
1st March 2012 - 22:50

1 Like

And if you want a proper bailout gear, Shimano's new Tiagra 12-30 cassette works fine with a standard cage Ultegra rear derailleur. You'll probably need a longer chain though.

posted by msw [126 posts]
1st March 2012 - 23:57


i used a 50/34 compact and 11-32 cassette for hardknott and wrynose on the fred whitton. needed all the gears to get up 'em

swapping 25 for 27 will make a noticable difference. I don't know many people who'd get up hardknott on a 39/25, and i certainly wouldn't make it on 39/27.

tiagra 30T is a good option if your mech will handle it. technically most road rear mechs are 27/28T max, but then there's a long list of stuff shimano says you shouldn't do that works just fine Smile

Dave Atkinson's picture

posted by Dave Atkinson [7857 posts]
2nd March 2012 - 8:58


I'm running SRAM so not sure about compatibility of the mech/ cassettes etc. fairly new to road bikes. I'm not expecting to ride all of it and given it's a short way into a long ride I'm not bothered about walking! I have chance for a trial run early June too.

posted by Spud [47 posts]
2nd March 2012 - 10:07


Apex rear mech will take a 32T Smile

still on the 3rd switch-back of Bwlch !

posted by therevokid [926 posts]
2nd March 2012 - 10:14


The only way I could contemplate getting up there is attaching the back wheel to the chainrings and the pedals to the cassette. Can go vertical with 12/53 set up!!!! Thinking

Seriously 34/28 would be my attempt ratio .. and wear my road shoes that are easier to walk in!

posted by Bobbys boys [81 posts]
2nd March 2012 - 11:00


Get an apex rear mech and a 11/12-32 cassette. Just done that myself, £32 for the cassette from chain reaction, picked up the mech brand new £39 off ebay.

"I can't believe I ate the whole thing..."

Cooks's picture

posted by Cooks [525 posts]
2nd March 2012 - 22:43


Could not agree more with first 5 comments, and have thought about last comments as well for one bike (upgrade to apex).

Ultimately, its hard to imagine needing those gears until you are there, but on a long ride, with no glycogen left in the thighs for big gears, for everyone except 8 stone pros as one of above comments said, you will need more gear inches!

Firstly, practically, I take it you are 9 speed shimano, no? so apex is a shift too far? (forgive pun)

if you can get a 12-30 tiagra as above, and it will fit. then do, or 12-27 as a bare minumim.

Other options:

can you swap a 28/29/30 cog from somewhere else? I once did this the other way round, where the casette was 13-x and needed speed - put an 11 in there and took the biggest gear out? some people are doing this with MTB as well, when moving to a double up front, there is a company that makes a 9 speed 36T and you just remove your fastest cog (in mtb that is 11/12 depending on cassette)

I did a search on CRC for road chainrings and the compact rings are not that expensive and add up to around the same as a non standard cassette? however it may depend on your mech and how it is mounted as to whether you can change?

bear in mind the road inches and cost / ease of doing as its easy to get carried away. the best options should be lower inches for least work and least money:

at the moment you have 45" or 45 gear inches (lowest crank / biggest cassette * 29 wheel inches).

The 27 cassette will give you 42 road inches, which is much better, although not great.

assuming you can get and fit a 12-30, then you are in 37 road inches; more like it. You should not need a longer chain as long as you stick to the small chainring with that gear, if you want to use all gears you will need a new chain as above comment.

so, the other options are to change the chainrings, assuming mech can handle it, anyone?

34/ existing 25 rear gives you 39.5 road inches, which is better than a 12-27 cassette. you will need to change both chainrings as the maximum difference is 14 to 16 cogs between chainrings. If you do chainrings and 12-27 you will have every combo of gears you will ever need, and assuming the front mech will take it, the easiest path Smile

having said that, 12-27 will def help, and should not need any fettling; the others will need some playing with / special orders. If you can get the 12-30 and it fits, that would be great. if not consider chainrings as well. hope this helps.

roadie come mountain biker come single speeder and back again

posted by cborrman [84 posts]
5th March 2012 - 10:39


Thanks for all the info and advice guys. It's my first road bike (Planet x RT-57) and is running SRAM Red so I think I'll have to check with P-X what will work on it. I think that I can't put smaller rings on the chainset (although the SRAM aero ring isn't very aesthetically pleasing Wink ) so that's out, so looks like a change of cassette is the way to go. And I am more than prepared to walk where I have to.

posted by Spud [47 posts]
5th March 2012 - 10:57


aha, why did you not say: sram-red is the nuts!

I am running sram red on my specialized tarmac and 11-28 with 54/39 has got me up most things, even after 70km in my legs

The OEM sram red mechs are good for 28T as you can see here:

you can get a much better geared 11-28 here for £55:

this will give you better top speed as well as better climbing gears, I would say you are good to go with this upgrade and zero fettling Smile

roadie come mountain biker come single speeder and back again

posted by cborrman [84 posts]
5th March 2012 - 12:45


Ta, gotta be worth a punt and then just MTFU and train harder! Big Grin

posted by Spud [47 posts]
5th March 2012 - 13:11

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oh, yes, doh! train harder... buy better seems so much easier *sigh*

roadie come mountain biker come single speeder and back again

posted by cborrman [84 posts]
5th March 2012 - 13:50


cborrman wrote:
oh, yes, doh! train harder... buy better seems so much easier *sigh*

That's because it is!

Training (as opposed to a ride) is hard work and you can't expect much to happen in a couple of weeks, so it takes willpower to persevere.

The Apex mech & 32T cassette looks a good idea, though bear in mind you will probably need a longer chain too. Spud, I hope you find a way to get those lower gears and enjoy the C2C. Let us know how you got on.

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posted by Simon E [2421 posts]
5th March 2012 - 22:36