Bicycle Mechanics - Swapping chainrings

I'm looking to get a specific set of chainring sizes: 24-36-48. I can only find one crankset that comes that way for something like $160.

Looking around the internet it seems you can buy individual sprockets that have a standard BCD, more or less. So how do I assemble a crankset with the chainring sizes I want? Can I start with a triple that has a 48T and replace the other two to be 24 and 36? Is there a standard BCD for the middle and inner sprockets, on those cranks you can replace them on? I'm rather mechanically inclined, and it seems like it should be an easy job. I just don't know what the standards are.

I'm not even sure if it's more expensive this way - I just need 24-36-48 at 170mm on square taper as cheap as I can.

This is close: http://www.universalcycles.com/shopping/product_details.php?id=9824

I put one of these on the ex-GF's bike (before the "ex" part).
I was very impressed with it.

BTW I don't know why they list these as compatible with 6/7/8 speed chains.
I put it on a 9s system where it worked like a charm.

Typical triples in that range will have 110MM BCD for the 2 larger rings and a 74MM BCD for the granny.

You might try looking for a crank that only requires the large ring to be changed. It "MIGHT" save a few $??

Shim that's funny you post that, because the expensive one I want is the Sugino XD500.

In any case, I found this Alivio M430:
http://www.universalcycles.com/shopping/product_details.php?id=46862&category=62

Which should accept this 24T granny:
http://www.universalcycles.com/shopping/product_details.php?id=306&category=50

Right? If so, after shopping around that could be less than half the price of the Sugino.

I'm not even sure if it's more expensive this way - I just need 24-36-48 at 170mm on square taper as cheap as I can.

As cheap as you can = used. I often pick up cranksets like you describe in the form of a used MTB. Last one cost me $20 at a garage sale (for the entire bike of course). Nice Shimano STX components, all of the parts will go onto another MTB frame I am building up for my wife. A lot of used bikes get rarely ridden, so a used crank may be in quite good condition.

Older MTBs can make good donors, the better ones had some pretty decent components. Now the cheap ones with riveted and stamped cranks are junk.

One other thing you need to consider is your front derailleur. Many have limitations with respect to the gap between the gears. For example, the derailleur on my MTB could not handle the gearing you want to use, as it is 2 teeth beyond what it was designed for (it could handle 26/38/48 but not 24/38/48).

One other thing you need to consider is your front derailleur. Many have limitations with respect to the gap between the gears. For example, the derailleur on my MTB could not handle the gearing you want to use, as it is 2 teeth beyond what it was designed for (it could handle 26/38/48 but not 24/38/48).

I doubt the FD would notice 2T less on the granny ring.

On my 2 bikes I replaced the large ring on 22-32-44 cranks with a 36 & 38.
Shifting isn't "immaculate", but totally serviceable.
The gap between the large ring & FDER does look awful though.

One other thing you need to consider is your front derailleur. Many have limitations with respect to the gap between the gears. For example, the derailleur on my MTB could not handle the gearing you want to use, as it is 2 teeth beyond what it was designed for (it could handle 26/38/48 but not 24/38/48).

Yes, this is something I had to replace anyhow. The one I've got for my 22-32-42 looks like it would fit a 50 - somehow my LBS managed to adjust it to work. In any case I plan on replacing that as well - although I was under the impression that the capacity on the front mech wasn't absolute (I think I read this at Sheldon Brown or maybe Crazy Guy). As long as the chain doesn't rub on the mech, one designed for 22T capacity should work as a 24. Here's a mech I was looking at:
http://www.masherz.com/products/shimano/fdm773.htm

So do these things sound compatible? The Alivio M430 and a replacement 24T granny as noted above, plus some 48T derailleur that has a 22 or 24 tooth capacity?

I will be switching to friction by the way, if that makes any difference. I don't have to worry about indexing and shifter issues between companies. It also means I can put most any components on the bike.

I would vouch for those Sugino cranks. I had a Sugino XD-350 (cheaper version), and it was great. If you are on a budget, I would suggest getting that over the XD-600. It is actually more durable with 2 steel chainrings instead of 1 or none. I got it for a pretty good price here: http://www.benscycle.net/index.php?main_page=product_info&cPath=75_128_135_772&products_id=8654

There is also a 170mm version for the same price. I loved the crankset before my bike got stolen a few weeks later :(

So do these things sound compatible? The Alivio M430 and a replacement 24T granny as noted above, plus some 48T derailleur that has a 22 or 24 tooth capacity?I would like to think that if a manufacturer rates a front derailleur as having a 22-tooth capacity, that you should probably stick within those limits. After all, why wouldn't the manufacturer list the derailleur as having a 24-tooth capacity if it could handle it? I'm not saying that what you want to do is not possible, because if very well may be. But there is a reason why the manufacturer has listed the 22-tooth capacity.

I would personally stay within the manufacturer's spec, but that's just me.