cooleric1234

I have a pretty simple question (for some reason I could find an answer in searching the forums). I just bought a new wheelset and I'm looking at what cassette to get. At first I thought I'd just get the same as my existing wheelset, but I notice that limits my options and I'm wondering if I really need the same. I have a triple crankset (30,42,52?) and current a 12-25 cassette. I was wondering if I'd have any problems going down to a 12-23 cassette? I imagine not, but I thought I'd ask. I will double check the chain length though, because I've noticed some new bikes come with a chain that's too long.

Also, I've heard to replace the chain when getting a new cassette. I'll be switching between this new wheelset and my old one, so what should I do in that case? Would I really have to buy two new cassettes? That doesn't make sense, I'll be using them in different amounts and I'm sure they'll wear differently. Any input?

ehilge

First off, you shouldn't have any problems with that slightly smaller cassette and the chain length. No guarantees, but I'm pretty sure the derailleur should be able to take the extra slack. As far as replacing the chain goes, it depends on how worn everything is. If the chain you have right now is fairly worn and has stretched quite a bit, then it won't work correctly with a new cassette. However, if the chain doesn't have a lot of wear, you would be fine. It just depends on the amount of chain stretch you have. Hope that helps.

Al1943

Any 24 pin interval of new chain will measure exactly 12 inches. By the time any interval has stretched to 12 1/16 inches the chain should be replaced. Chains should be measured with a good steel ruler. Chain checker tools are also good to have but measurements by ruler are better. I use both.
Why do you want a 12-23 cassette instead of a 12-25? Just curious.
Al

cooleric1234

Why do you prefer a ruler? I have a chain checker, I just need to take a look at my chain.

I don't necessarily want a 12-23, it just seems that as I'm looking at cassettes sometimes a 12-25 option doesn't exist and the closest one is 12-23. I should say the closest one with a smaller big cog. I have a triple now but I'm trying to build up enough strength so that I can get by with a compact double for my next bike. This will be for the lighter wheelset I just bought and the one I'll use in the mountains so I might like to train myself with a little tougher gearing.

DaveSSS 

Most chain wear measuring tools add roller wear to the elongation and can report a new chain to be stretched by .25%. This initial false wear must be subtracted from future readings. Even then, the tool can report twice the acutal elongation, since roller wear is much larger than the amount of wear on the pins and innerplate bushings.

Campy chain elongate so little (if properly maintained), that the rollers can be extremely worn, but the chain will measure little elongation with a scale, so the scale method is not reliable for a Campy chain. I use calipers to meaure roller spacing and toss the chain when the roller spacing increase by .035-.040 inch.

Retro Grouch 

Who'd you vote for in the last election?

If you consider yourself a conservative; buy a new chain, keep your old one, and replace the chain every time you change wheelsets.

If you're more liberal, don't worry about it. Chains and cassettes are consumable parts. Use them up and just ride.

Al1943

If you change from a triple to a compact double chances are you'll want a larger big cog instead of a smaller one. Of course this all depends on where you ride and your physical conditioning. But going from a 30t granny on the triple to a compact with a 34 is a big change. If you're doing mountains with a compact double you may want a 12-27.

cooleric1234

True, I wasn't talking about making the change with this cassette. I just mean down the road a few years when I get a new bike I'd like to know if I can handle a compact crankset (with, as you say, a larger rear cog). This will be my way of testing that out.

cooleric1234

What if I'm libertarian? I'm so confused.

Just kidding, I think I'll choose the latter option as I think me being cheap comes into play more than any political leanings.

woodway

No extra slack. Since the current 12-25 cassette has the same size small cog (12 teeth), and goes past a 23 tooth cog on the way to the 25 tooth cog, I'd say your current chain/der. combo will work just fine!

operator

Seriously people.

The only real metric for "replace chain" is if it starts skipping. The rest of this debate is purely academic on measuring chain wear.

woodway

If you wait till the chain starts skipping before you replace it, you'll may have to also replace the cassette and/or front ring(s) depending on how long you rode the chain in it's stretched state. A overly stretched chain will cause the cog teeth to wear unevenly resulting in the new chain skipping or wearing faster or uneven shifting performance.

I just replace the chain on my road bike around 1500 miles (more often on my Mountain Bikes) as preventive maintenance. Waste of money? Maybe, but it makes me feel better.