cassette size
 

I've been using a cassette size of 11 - 34 for a while now. I do some climbing here in central PA, but nothing too extreme. I did some work for a friend recently and in exchange he gave me a 12 - 25 cassette. Will I notice a huge difference? I have a triple crank, but I rarely use the small chain ring unless I'm doing a really long, steep climb.

Yes, like chasm54 (where did his post go?) said, it sounds good. Some riders will use the small chainring and 34 cog on steeper hills, but if you don't need that low a gear, the 12-25's closer cog sizes will be good.

I was thinking the chain might be too long, but the small chainring-small cog combination won't be any different than the current 11-34. It'll work fine.

That's a question that only you can really answer.

If it was my bike I'd stick on the new cassette and ride with it for awhile. You may find you like it better, you may decide to go back to your old cassette, and you may decide to try something in between. There's more to it than just the highest and lowest gear combinations, when and where you happen to be when you make front chainring shifts has a lot to do with the ride-ability of the bike. If you find yourself having to shift into the granny ring in the middle of a long steep uphill, you might not like the new gear combination.

Your lowest gear will increase by nearly 33%. If you only use the granny ring for long steep climbs you may find the increase in gearing is more than you're comfortable with. Having gears spaced closer together is a good thing but when your low gear increases substantially you may find it makes the difference between getting to the top of the hill and getting off and walking the hill.

I use a compact with 50/34 and 12/27 or 30 if it is going to be extra hilly. That is on two bikes but for the bike with a triple I run 50/39/30 and 12/25 cassette. 30/25 will get me up the 15% climbs for a mile round here with a gear or so to spare.

If you rarely use the small ring on the crank- you will find that 30/25 will not be high and the closeness of the ratios will give you better gearing aswell. No more mashing in one gear and when you change down you are spinning too high.

I see you're from Central PA. I'm from Shamokin. I ride a mountain crank with a 26 low ring. Cassette is an Ultegra 11-28. There are hills around here I cannot ride even with that low gearing. I know you will see a big change. Not sure you're gonna like it. Try it if you want, the close ratios are nice. But I don't think you will like pulling hills with that combination. Good luck. BTW where are you from?

Mark Shuman

With an 11-3X, your 3rd gear is likely about 26T.
IF that gets you up the hill without busting a gut, the 25T should.
The upside is that you'll have more usable, closer spaced gears in between.

I'm curious how this works out, so update us when you decide, jlsrat.

Personally I'm rooting for you to go for it. Having a spread out cassette with a triple just doesn't make as much sense, and the 12-25 is more logical. I'm betting you can handle the hills fine (my clue on that is when you said nothing you climbed was extreme).

I'm from Harrisburg...

yea, guess the 34,28,24 is, perhaps, the sequence from low on the 3rd ring.

ride around without using the lowest 2 and see..

I'm thinking that any brutal climbs I do will take me to the small chain ring. When I first started cycling five years ago I used the small ring all the time. Barely use it now and I think in time, the 25/middle chain ring will be fine for climbing.

Agree on the comment, that your question is one only you can answer. Depending on your riding style or preference, terrain, and conditioning, you have multiple options to consider.

Here's my current gearing and some thoughts behind it. Using a compact 50/34 chain ring with an 11-34 MTB cassette. I originally started with a 12-25 cassette, then switched to the 11-34 after running out of gears climbing hills. A pretty common problem..... new out of shape rider without enough leg strength or endurance (stamina) to tackle any significant incline. Changing the cassette to the lower gearing was and is a life saver.

Fast forward a couple years, I don't really need the 30 or 34 gears, but I still feel comfortable having them in reserve. On longer rides (50+ miles) the legs may start cramping or I start losing stamina, the low gears are just extra insurance.

The biggest benefit with a 12-25 cassette, is tight spacing between gears. As a new rider, I found the tight spacing annoying, always up or down shifting 2 gears at a time. Changing by one gear often left me still one gear off to match my effort and preferred cadence. This has much to do with how I ride. I'm really annoyed by constant shifting and would rather vary my cadence, often between 80 - 100. I actually like this style of riding without trying to maintain a narrow rpm range.

An 11-34 cassette, with wider spacing allows me to shift once to find the right gear. Looking at the wear on the cassette, I'd say my primary gears are the 15, 17, and 19, all in combination with the 50 tooth chain ring. I never use the 34 chain ring except for climbing hills.

When the current cassette wears out, I may opt for an 11-30 cassette, maybe an 11-32, but seriously doubt I'd ever want a 12-25 cassette. I'd always want some insurance along for those longer hills where the burn gets to much for the legs or lungs.

Your new lowest gear in the granny ring will be about the same as your current lowest gear in the middle ring (assuming 30 and 39 tooth rings). If you can completely do without your granny ring now, you'll be fine with the change.

I should add, that riding a SS for 6 months with a 42 x 16 combination may have changed my preference regarding cadence and shifting. With the SS, you just learn to HTFU when encountering tougher conditions.

This is my approach as well. If I'm going to reach down to shift ;), I want it to make a substantial difference. I can happily pedal in a wide range of cadences.

One small glitch: I have a long cage derailleur. Is that still compatible with the 12 - 25 cassette? I installed the cassette and a new chain, and the lower pulley catches the chain every couple of spins or so in the small/small combination. Granted, I'll never use that combination, but I'm wondering if I need a shorter caged derailleur.

What you are describing is a chain cut too long.

If it was cut too long, why didn't he have problems with the 11T cog?
OR
Did the OP not size the chain?

Going from 34 to 25 is a huge jump. And you're going to feel it the next time you need your lowest gear on one of your long, steep climbs, especially if you rarely make that kind of climb.

On the other hand, if you do a lot of tough climbs, you'll get stronger over time. No matter how strong you get, though, a 30/25 will likely mean a relatively slow cadence up a relatively steep hill.

Dude's right. I used the various methods on the Park Tool site. I went back today and used the Large Cog/Large Chain Ring method; the chain was way long. Running fine now. Thanks much.

Did some climbing today and it was windy. Even so, it was easier in the low gear at 25 than I expected, although I could feel it. Let's see what happens when I try some climbs over Blue Mountain...

...and you are also describing cross-chaining. Small/small or big/big is bad mojo.

As others have posted only you know. What I can say is if you are using that 34 because you need to going to a 25 may not be advisable for you at this time. If you want to test that range before you swap ride with out using anything bigger that a 25 on the rear and see if you are ok if so swap it if not leave what you have.

jlstrat-The obvious answer is not to be found above. Why would you mess with a bike you like the way it is? What you need to do is build a new bike around your new cassette!:D I say this only somewhat facetiously. I have 2 road bikes which are each geared somewhat differently. One I ride more in the spring when my legs are young or when I'm going to be hitting a lot of hills which around here have a tendency to be short but steep. My other roadbike gets used more later in the season as my legs have matured or when I'm doing somewhat flatter rides. I hasten to add that I have a hybid as well which is used exclusively on the local rail trails. Viva N+!

It won't surprise me if I go back to the old setup in a month or two. Probably sell the used stuff of E Bay. But maybe I'll build some strength and be OK with this setup.