UKC

Morning all. I'm after some information regarding changing my cassette on my new road bike.
I have recently bought a new Specialized Allez (16 speed) with a 11-32 cassette. I know this is marketed to have a wide range of gears et but i am quickly finding out that the gaps/ratio between cogs is to big. I would like to change the cassette to close up the ratio and found a Shimano cassette 12-25 (8 speed) that might do it?
My question is will I be able to make the straight swap and keep my current rear mech or will this need to be swapped to a short cage.? Im planning on keeping my 8 speed shifters if possible.

Many thanks.
Adam

In reply to adamholden:

I'm going to be no help at all but when I saw your thread title I read it as "Changing my cassette radio" and I wondered whether you had n mind one of these new-fangled CD players or the super-modern Minidisks.

In reply to adamholden:
I swapped an 8 speed from a 23 biggest cog (too sporty for my liking with 53/39 up front) to a 28 biggest cog with no new parts required, so the other way round oughn't to present a problem.

In reply to adamholden:

You can keep the Rear derailleur. You only need to swap when you have a short one and you go up to a 32

In reply to adamholden:

Where do you ride ?
If your plans include Yorkshire or Cumbria I'd stick with the 11-32 !

In reply to Chris the Tall:

I live at the top of Scotland, which know sounds hilly but near the coast where I am is flatter than the West/Central etc. The main reason I want to replace the Cassette is due to the large jump in cadence/effort between each cog, i find it either spins out or is to hard.
Cheers for your reply anyway.

In reply to adamholden:

Fair enough, mine is 2x11 which would make a slight difference. Plus I guess I'm the sort of rider who stays in the same gear for too long, then changes two or three at a time. I'm a bit like that in the car too - drives my wife mad...

In reply to adamholden:

Should be fine, I went the other way and had to buy a long cage mech.

Incidentally, I had used my bike a for a few years in Finland with not so many hills, and had even done cyclocross races on it which included some short killer climbs, and found 25 ok. Soon as I moved to Sheffield I wanted a lower gear so got a 32. But it sounds like you might do well with 25 if where you are isn't particularly hilly.

In reply to adamholden:

sounds like an excuse to buy a new bike

In reply to adamholden:

Global cycle network have a YouTube video explaining how to work it out. I think if you go to a smaller cassette it's not a problem.

In reply to adamholden:

I think you're in danger of swapping one problem for a worse one. 32 down to 25 is a huge change.

Have a look at Sheldon Brown's Gear calculator, but in essence your lowest grinding up hills/battling into the wind gear (assuming a 34 small ring) will go from 28 inches to 36. (i.e. 36 inches travelled for every turn of the pedals). At the other end, assuming a 50 tooth large ring, you will go from 120 down to 110.

It would be worth finding out exactly what size each cassette sprocket size is and putting it into Sheldon's calculator to see exactly what you're going to get.

You may well find that you end up sitting uncomfortably on the larger gears for the large ring and the smaller ones for the little ring.

Moving down to 28 from 32 would be less of a shock.

In reply to adamholden:
Changing the cassette and nothing else should work.

nniff makes a very good point, 32->25 means you have lost your two lowest gears (32 and 28 teeth probably) which is pretty drastic.

How about 11-28 or even better 12-28 if that exists?

Your current ratios will be the same as or roughly the same as...

https://www.rosebikes.co.uk/article/shimano-cs-hg51-8-speed-cassette/aid:52...

11-28 (11-13-15-17-19-21-24-28)
11-30 (11-13-15-17-20-23-26-30)
11-32 (11-13-15-18-21-24-28-32)

In reply to adamholden:

PS - if you put your actual sprocket sizes into Sheldon's calculator it will also show you the percentage changes between them, which will give you some insight into the problem you are experiencing. You then need to check that the step that you experience in practice will be fixed by the change that you are proposing. Most changes are about 15%, but some are 20%. The 20% is probably where your problem is, but if those gears aren't the ones where you're really noticing the problem in practice then changing it won't fix it. The other thing to do is to see where gears are duplicated (ie which gear inches feature on both the large and small rings, so that you can build up a proper picture of what your gearing really looks like. For example, the step you experience when you're riding on the large ring might be filled by a gear on the smaller ring and if you know that, you can make the appropriate change. PITA, but that's one reason for having 11 sprocket cassettes.