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Old 12-03-11, 01:35 PM   #1
Telly
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Chainset & crank swap question from a newbie

Hello everyone,

After a rather informative post in the Commuters section, I've come to the conclusion that I have to swap my crank & chainset which is basically a mountain-bike setup to set which suits my riding style.

My current crank/chainset has three gears, largest being 42t, and is connected to a square-tapered Shimano UN26 B/B with 113m/68m dimensions. After a quick talk with a LBS, he said there was a direct swap by Shimano (Deodore series) that would fit my bottom bracket and was geared 48-38-28 which is ideal for my use. What he didn't mention was the model/type. Please keep in mind that my bike has a 8-speed cassette with 11-30 gearing.
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Old 12-03-11, 01:53 PM   #2
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Depending on your wheel/tire size, 42/11 is a pretty high gear. If you're running 26" rims with even a fairly small tire, you should be topping out at 23 MPH (37 KPH) at a cadence of around 80 RPM. That's moving pretty good. However, if you do need more top end, that swap you are looking at should be fine.
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Old 12-03-11, 02:07 PM   #3
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The bike is a trekking 28 incher, used mostly for commuting to the office and back which is around 15 miles on paved roads with no major hills. I'm not changing the crank/chainset for more top speed, as I am for better management of the gears; with a 38t middle disc, I would have the best arrangement of gears for my daily cycling thus having to change less often to the highest disc (almost never use the lowest one).
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Old 12-03-11, 03:06 PM   #4
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Update:
My current setup is FSA AL-8 Crankset 170mm, triple disc (42,xx,xx), with a Shimano UN26 113mm / 68 mm bottom bracket

Are the following compatble?
Shimano FC-M131 Crankset 170mm, triple disc (48,38,28) and swapping out the UN26 113mm / 68mm with a Shimano UN26-K4 122mm /68mm bottom bracket

...and if they are compatible, will I also need to change the chain to a longer version because of the larger chainset?

Last edited by Telly; 12-03-11 at 03:17 PM.
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Old 12-03-11, 03:57 PM   #5
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If you don't want to swap out the BB, you could probably go with this Sugino Crankset.

http://www.niagaracycle.com/product_...ucts_id=405883 Unfortunately they don't seem to list an exact part # but perhaps Sugino Impel 48/38/28 is enough info with which to search for one on the Euro market.

And unless you're chain is currently a little on the long side then you'll probably need a new chain.

I run 42/32/22 sometimes and it works fine for me. Sure I'm usually in the big ring and just drop to the middle for hills and stoplights, but no big deal.

Last edited by LesterOfPuppets; 12-03-11 at 04:05 PM.
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Old 12-03-11, 04:15 PM   #6
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If your BCD is 104/64mm, like Shimano mtn cranks, then you can just order the 28/38/48 "trekking" chainrings.
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Old 12-03-11, 04:34 PM   #7
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Lester, the Sugino unit looks pretty good, and my BB is brand new (replaced because of a defect in the previous one). I'll have to take a look into finding this part in Europe since the cost of importing and paying customs will probably double or triple the total!

Shimagnolo, my current crank is the FSA AL-8 unit, and unfortunately I can't find any info on it, can you tell me what the 104/64mm measurements are since your solution would probably be the least expensive since I won't have to change crank and B/B.
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Old 12-03-11, 04:35 PM   #8
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If this a MTB with fat chainstays the bigger rings (discs) may not clear (ask me how I know.) Sometimes these swaps are better left to the shop because they have a stock of parts, they have to make it fit. Rather than the trial and error of buying the stuff yourself and finding out it doesn't fit.

Since you never use the smallest ring I would suggest a tight cassette, something like 11-21 or 11-23. This will be much cheaper, 100% compatible with your current setup, and give you a nice tight gearing range.
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Old 12-03-11, 04:50 PM   #9
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Quote:
Originally Posted by Telly View Post
Shimagnolo, my current crank is the FSA AL-8 unit, and unfortunately I can't find any info on it, can you tell me what the 104/64mm measurements are since your solution would probably be the least expensive since I won't have to change crank and B/B.
You can determine the BCD by measuring ctr-to-ctr on two adjacent bolts, and looking up the distance in the table here: http://www.sheldonbrown.com/gloss_bo-z.html
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