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Old 08-22-03, 12:16 AM   #1
Psychic Pimp
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Trek 520 owners - crank switch?

Kind of a gear question but since the 520 is a touring bike I thought I might get better response here.

It seems to be a common thing to switch from the 105 cranks to MTB cranks, LX or the like.

From those of you who have done the switch, did you have to switch the BB also or was the spindle the correct length for the LX cranks?

I would like to use a closer geared cluster without losing the granny gear, not too concerned about losing the high range. I think I can achieve this by going to LX crank and choosing a different cluster.
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Old 08-22-03, 04:02 AM   #2
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As I recall it was necessary to use a different BB to mount the LX crank on my 520. My LBS made the switch.

I kept the original 11-32 cluster. A 13-32 cluster would be better, or a crank setup with 42-32-22 instead of 44-, but it doesn't matter that much.
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Old 08-22-03, 04:06 AM   #3
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I think it may be necessary to switch the BB because the OctaLink splines on the LX crank may be incompatible with the ones on the BB that mates with the 105 cranks. Remember that Shimano made at least two versions of OctaLink. Of course there might be spindle length/chainline issues too.
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Old 08-22-03, 04:45 AM   #4
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You do need to replace the bottom bracket to go to an MTB crankset, you also need to replace the front derailure because the large ring on the compact crank is 44 teeth instead of 53 and the radius of the derailure cage will not be compatable.
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Old 08-22-03, 06:45 AM   #5
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arggggg. i love the 52t11, even though i don't use it all the time, its great for when i feel tired and i just want to coast.
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Old 08-22-03, 06:49 AM   #6
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why change it at all?
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Old 08-22-03, 05:11 PM   #7
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My biggest reason to change the gearing on the bike is, in all honesty, the overwhelming urge to tinker. Secondary to that is wanting to have closer gear ratios in the middle range.

Sounds like it would be too expensive for right now. I'll wait until stuff starts wearing out or breaking. 900 miles on it since I got it in June so it shouldn't be too long before I have more excuses to upgrade or replace stuff.
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Old 08-22-03, 09:56 PM   #8
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I had it changed at the bike shop at the time of purchase. I was considering two options:

1. Keeping the "105", albeit with 3 smaller rings: 48-38-26 (which is the smallest compatible granny).

2. My preferred option: a LX or XT drivetrain with 44-34-22. The bike shop made me an offer I couldn't refuse with an XT drivetrain. They changed the BB as well (different design).

They were interested in changing the front derailleur (for a modest fee), sayint it would "shift better". I was not interested. So I still have the "105" front derailleur and it shifts flawlessly. I should add that I use bar-end shifters and therefore shift the front derailleur in friction.

If you also want to use STI, the alternative is either:
- to keep it as is and "enjoy" poor shifts (due to indexing);
- to grind the derailleur cage so it follows more closely the shape of the outer ring.
Front MTB derailleurs (LX, XT) don't work with STI, I was told.

Regards,
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Old 08-23-03, 10:28 AM   #9
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I kept the 105 front derailer on my Trek 520 after the switch from the 105 (52/42/30) to the LX (44/32/22) cranks. And still use the bar-end shifters that came with the bike.

No problems at all.
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Old 08-23-03, 03:59 PM   #10
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i just rode back home on a long straight road with masive tail wind. i couldn't be more happy with that 52t11 combo. i was flying!!!!
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Old 08-24-03, 04:10 AM   #11
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My Campy Mirage front mech and shifters works quite well with an LX chainset.

With the LX you do loose the ability to hammer along with a strong tailwind, but that is more than made up for, when you want to climb a rough mountain trail with luggage.
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Old 08-24-03, 09:22 AM   #12
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I run a 26-38-48 crank with a 13-30 cassette on my 520. I only use it for loaded touring, and that gearing is great for everything.

You will need to replace the bb for a crank switch.
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Old 08-24-03, 09:34 AM   #13
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Hi,
I have Ultegra up front, and a LX/Megarange out back. Swapping the small crank ring for a 28T gives me some shifting headaches; but the result is a 28/34 low gear. And I got to keep the big ring. This may be because I am old, but I found the spacing wonderful. You used to be able to whip up a custom cassette; wonder if you still can.
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