Bicycle Mechanics - Planning on Replacing Cassette and Chain
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I have posted this on another forum (just before I went to work today) came back to realise it wasn't very active so... I'm pasting it here (in this happening place):
I am a bit of a tourer, and I am the proud owner of a classical touring dawes galaxy. I've had this bicycle for a number of years, and have noticed the cassette and chain skipping. I'm in the process of replacing them both, as I had planned since the day I bought the bicycle.
I am surprised with the low range of my cassette (for touring) and I just really need to know whether my 12-24 cassette can be replaced 'simply' with say a 12-28, I have an old basic Shimano RSX 8 speed system; or would this be a problem with the derailleur?
I am on the verge of buying a cassette and chain at the moment, and of-course do not want to buy the wrong one. I understand I would later also need to work out the appropriate length of chain in accordance to the new sized cassette.
Am I going to be fine?
P.S. My chainset range is 30 - 42 - 52. And never do I use the 52 sprocket; It might be worth changing this I assume?
Old Hammer Boy
05-10-11, 08:09 PM
Typical touring gearing is similar to that found on many mountain bikes. On my Surley LHT I have an 11/32 cassette, and (can't say absolutely for sure) something like 46/38/26 on chainrings (Sugino 600). I dragged 75 Lbs of bike, trailer and gear across American without any issues. It worked great. You'll probably need a new, long body RD (mine's an older style XT) and it will probably be easier to just replace the crank, chain and possibly the BB. If you do change the crank assembly, you may also need to change the FD to match the circumferance of the large ring. You should be able to do all of this for between $125-200. This will give you a great touring set-up.
Ben, How hilly is it where you ride? You can start with a new lower geared cassette and chain and if needed move on to the crankset. Since you don't use the 52T that'll probably be sooner than later and if it's not too hilly you can use a 28-38-48, hilly and a 22-32-44(ish), but swapping the crankset may involve only the crankset or also the bottom bracket and front derailleur.
05-11-11, 04:43 AM
...I just really need to know whether my 12-24 cassette can be replaced 'simply' with say a 12-28, I have an old basic Shimano RSX 8 speed system; or would this be a problem with the derailleur?
Probably, but there is a slim chance that the RD will need to be changed as well, though I doubt it.
Thanks for the fast reply's.
It gets pretty hilly around here at times. So I'm thinking changing the crank set is a good idea. And while I'm at that, I will change the Ball Bearings, another 'first' for me.
But first I will sort the cassette, and fingers crossed my rear derailleur will work fine (although I'll do some Internet research first - see what I can find)
OK with a little searching I found this:
I believe that would be the same as mine, and I think it is saying the maximum it can deal with is a 28T and minimum is 11T, but I am not sure what it means with the front chain-ring difference of 20T?
05-11-11, 07:05 AM
I'd reckon (although without 100% certainty) that it's looking at the maximum toothcount difference between the front chain rings. If you've got a 52-42-30 setup then moving from the 52 to the 30 means 22 teeth of difference, which might leave your RD struggling to take up the slack in the chain. For a couple of links it's the kind of thing you might get away with - from my (limited) understanding it seems like the kind of thing which would only cause you problems if you used the small chainring and the smallest sprockets, which you shouldn't do anyway.
If you never use the 52 it might be worth swapping out the chainrings to reduce the gearing so you'd have three chainrings that you actually use.
05-11-11, 09:46 AM
You can change the 30 small ring to a 24. If you have a long cage der. you should be ok with a 12-28, a 13-28 would be better.
You could also switch the front rings to a 48-39-24. The 13 rear and 48 front would give you a 100 inch top gear.
You can use this site to figure out what you need. http://www.jbarrm.com/cycal/cycal.html
05-11-11, 11:16 PM
Taking Contango's & Davidad's suggestion a little further - 22/32/42, with a big ring the same size as your your current middle one, is a common MTB setup. That would extend your gear range down by 36%, compared to 17% for the cassette change you're considering. You'd still have a 91-inch top - the current top gear on your middle ring, which as you've found is plenty for many people. And you'd be free to change the cassette as well later on, if you decided you wanted to go lower still.
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