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  1. #1
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    Questions on upgrading at Trek MT60

    My son is currently riding a 2009 Trek 20" MT60 that my daughter outgrew. He is much harder on the bike than she ever was and it's starting to take it's toll on the bike so I'm planning on doing a complete overhaul on it. The stock SR fork was junk and developed a rather loud "clunking" noise with each pedal stroke. I contacted SR and they were really helpful in sending me a new replacement fork that works much nicer than the one it replaced. (relativity speaking, it's still a very basic fork)

    I'm now looking to upgrade the cranks/BB and wheels. I see a lot of people are using the Sinz cranks and I was wondering if there is a special size BB I have to get to use with a bike this small? Also with regard to wheels, what do I need to know? I haven't yet gotten a chance to measure it but I assume I can use a standard 135mm hub and 20" BMX rims? I've been reading up on this and hearing that folks have had to dish the wheels when using a cassette. Is this something I have to be concerned about if I'm going to have these built for me? I have zero experience building wheels. I have a few buddies who build up mtn and road wheels but I wasn't sure if there was anything special they had to keep in mind if I ask them to built up 20" wheels. Any recommendations would be great!
    Egg

  2. #2
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    Sinz cranks are available for either square taper or an ISIS spline bottom bracket, type needs to be matched to the crank but the frame likely will take any standard british thread (1.37x24) bottom bracket. BBs are available in many different widths, you need the BB width that locates the chainring lined up with middle of the rear casette. Offhand, I would guess that a 110-115mm square taper BB would be about right, not really any different than a standard MTB but you might try to get a reccomendation from sinz, figure out what width BB equates to for the chainline.
    Measure and confirm the frames rear spacing between dropouts. If it was originally 6-speed, it is likely spaced <135mm so might not work with a regular 135mm width MTB hub. Only reason I can see that a wheel might need to be re-dished is if a 135mm hub had spacers removed to reduce it to narrower width, if the spacers were all removed from non-drive side, then it would be necessary to dish the rim back over towared the drive side so it is symetrical in the frame.
    If the bike has a 6-speed freewheel rather than a casette, it might be easier to build the new wheels with an old road bike threaded freewheel hub, re-use the existing 6-speed freewheel so that indexing remains uneffected. (If you switch to a 7-8-9-10 speed casette, shifter will also need to be upgraded to match).

    Just noticed this similar thread,
    Trek MT60 Upgrades

    The rear hub is definitly a 6-speed freewheel, not a casette. I doubt that the frame is spaced at 135mm, probably 126 or 120mm.

  3. #3
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    Thanks! You are correct it uses a freewheel, not a cassette. I was hoping that I could drop some weight from the thing but dropping the freewheel set up. I'm beginning to think it's more work than it's worth now. I'll measure the spacing tonight when I get home. I was hoping it would be a simple wheel swap.
    Egg

  4. #4
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    If you do go to casette, try to find an older 7-speed freehub which has a casette body that is 5mm narrower than 8-9-10 speed casette body, the narrower width casette & body will be easier to fit in the smaller width frame. Hotrocks thread with same freewheel noted that it used a 130mm rear end. Probably most compelling reason to go to a casette is to use a narrowed 8-9-10 speed casette (retain narrow cog spacing but loose 1-2 small cogs), so that you can use shifters other than the original 6-speed shifters.

  5. #5
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    Are you able to build wheels? What i did with my son's hotrock (similar rear wheel to what you are using), is to swap in a generic shimano rear hub. Flange spacing, etc., was a perfect match and it was parts bin free. Not sure where you are at on the bike hoarder spectrum :-)

    I tossed an 8sp freehub on there and don't see any reason not to do that. I just dished the wheel appropriately and re-centered the axle. The drop outs were thick enough to take up the extra axle. He can now run a full range cassette which is helpful with a single front chainring.

    I'm personally not a huge fan of the sinz cranks just because you can only run a 34t chainring minimum. I definitely like that they come in short lengths, though. We do enough climbing that i've switched to a compact crankset (old school bolt pattern) and a 29x32t low gear. That lets my 7yo climb up most of the stuff we do around here. He would complain a bit with a 32 front chainring, but those 3 teeth seems to have taken enough of the edge off. A 34t would be a pretty tall gear unless the hills are pretty mild.

    Just my experience - yours may, of course, be totally different...

  6. #6
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    Thanks for all the advice!
    Last edited by Locotiki; 05-06-2013 at 08:34 AM.
    Egg

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    Getting the dish right is nothing hard for anyone that understands wheel building. Measure your frame, figure out the dropout width. Select whatever hub/freewheel/casette you will be using, set it up (change axel spacers if needed) so that the chain on smallest cog clears the dropout. Get the wheels built up and just tell them to dish the rim symetrical between the axel locknuts (just as most all wheels are done).

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    If he's using the bike mainly for DH, or at least not doing a lot of climbing with it, have you considered making it a single speed? Highland is like a big BMX track for the most part anyway, not like there's much need for a variety of gearing.

  9. #9
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    Quote Originally Posted by slapheadmofo View Post
    If he's using the bike mainly for DH, or at least not doing a lot of climbing with it, have you considered making it a single speed? Highland is like a big BMX track for the most part anyway, not like there's much need for a variety of gearing.
    If it were up to him that's what he would do but he has to be able to pedal uphill when we drag him on XC rides.
    Egg

  10. #10
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    Sounds like he needs more bikes!

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