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I am considering upgrading my crankset, or rather I am considering considering to upgrade it. I would like to gain a few teeth since I am permanently riding on the 48/13-15 making the 38 pretty useless.

I currently have this: Suntour NEX, 48/38/28. If I were to upgrade to something like : http://www.rose-vpc.fr/article/shimano-pedalier-fc-2303/aid:417044 what should I consider? Do I need to buy a new bottom bracket as well? Will my derailleur require any update apart from raising an inch higher to accomodate the 4 extra teeth?

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1  
Have you considered a cassette swap to something like a 11-28 tooth? Not as effective as a crank swap but cheaper and easier. –  mikes Dec 28 '12 at 20:47
    
Pretty much what I have already... –  tisek Dec 28 '12 at 21:58
    
Depending on how much use you've had it might be an idea to swap out the BB in any case, just because if you've gone to the trouble of getting the cranks off anyway, its an ideal time to do it. –  PeteH Dec 29 '12 at 19:49
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48/11 is standard road compact sizes. Are you really needing a bigger large chain ring? What is your cadence? –  mattnz Dec 29 '12 at 23:21

2 Answers 2

up vote 5 down vote accepted

The crank you point to would probably fit on your bottom bracket, but might result in a bad chainline.

There are two things to consider when replacing your cranks: the interface between the cranks and the bottom bracket, and the distance from the centerline.

Your old Suntour cranks and the Shimano you link to both use a JIS square taper. So the interface is fine.

However, your old cranks are designed to be installed on a 122-mm bottom-bracket spindle (and I'll assume that's what you've got), while the Shimano you link to is designed for a 113-mm spindle. You would be going from a triple to a double, which would make up for some of the difference, but I think the Shimano would wind up riding a few mm farther outboard than it's intended.

If you could find replacement chainrings that fit your cranks, that would be an easier and cheaper option, but large chainrings for mountain-bike cranks are apparently impossible to find. And I'm not sure what the BCD measurement is on your Suntour cranks.

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Both of the cranksets you mention are square taper. That's pretty standard and you shouldn't need to change the bottom backet.

To actually do the change you'll need a crank puller and a large hex/allen key (often around 8mm). It can be quite tough to pull the old ones off, even with the right tools. Don't even try and hammer them off, you'll just mash everything up.

If the square tapers are corroded underneath the cranks then to get a decent fit you might have to change the bottom bracket too. The problem here is that you wont know until you've pulled the old ones off.

When you're putting the new ones on, you'll find they go on easily, but getting them on straight can take some time.

There's some debate, I believe, about whether or not to grease the tapers when you're installing the new cranks, I didn't last time I did this. You'll want to get the bolt threads good and slimy though.

http://sheldonbrown.com/brandt/installing-cranks.html

The derailer should be fine, 4 teeth wont change the size dramatically. If you can find the model number you should be able to find something that tells you the maximum size it'll comfortably take.

One last idea, if you're comfortable with just the 48 and there's no hills in sight, you could ditch the other 2 rings, front derailer, shiter etc. and save some weight.

From the rather blurry photo on the suntour site your current crank doesn't look like it'll rebuild easily, but there are plenty of suitable single cranksets available.

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