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  1. #1
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    Reputation: ghglenn's Avatar
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    I need some help with my Daughter's 20" Hot Rock

    Hey Guys, took my 6 y.o. out on some singletrack and realized, I have to do something to
    give her more "Mechanical Advantage" for climbing. So, I was thinking of changing out the
    cranks to Sinz, to run a smaller chainring with bashguard to start. Is this the way to go?
    Or would you go to the Mega-Range 7 Speed set up and just run the front as is. I am under
    a tight budget, any help would be appreciated. Thanks.

    BTW, if I did the Sinz, what is the smallest chain ring I can fit on them? And, did you stay with 135mm?

    Thanks.

  2. #2
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    Sounds like you're on the right track. Does she shift the gears easily? Sinz are 110BCD so you could go down to 32 I believe. Have her practice down shifting into low gear for the hills then back up. I would try that before the mega-range.

  3. #3
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    You've said budget is tight so I'd go Mega7 to give her the climbing gear and see how she gets on.
    However changing the crank will give you more flexibility in gears in the long term.
    Buying a new crank, Chainring, BB adaptor (if needed), and Bottom Bracket is going to cost considerably more that the cassette/freewheel.
    Price comparison (UK) 23 for cassette vs 110 for crank set up. Not sure what prices and availability is like in Canada.
    MTB:
    09 Stumpy Elite
    10 Enduro Pro Custom
    16" HotRock Custom

    Road:
    08 Jamis Xenith Comp
    13 Pinarello Dogma 65.1

  4. #4
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    34t is smallest commonly available 110mm BCD chainring. There are rare 33t rings available too but these may require grinding the chainring bolts for chain clearance.
    http://sheldonbrown.com/harris/chainrings/110.html#33
    1 chainring tooth is only 3% lower, not worth the hassle over a 34t . The jump from a 40t to a 34t will be a good start but still only equivalent to going to a larger rear cog that is less than +2 teeth in size.

    Instead of buying a 135mm long 110bcd crank, you might also consider shortening a MTB crank that can get you even lower gearing.

    One caution- also check that rear deraillerr has capacity for a larger rear cog before buying.

  5. #5
    I like bikes
    Reputation: ghglenn's Avatar
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    Thanks for the quick replies. She shifts the bike well, so it is just a matter of gearing, to help her gain more torque. GrayJay, you nailed it. I have a good friend that is a machinist. I can have him shorten the cranks, and make them look "factory" for a bottle of Rum. Now I need to raid the parts bin. I will post up the final result.

  6. #6
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    Shortening the cranks only will reduce the leverage but enable effective spinning assuming the gears can be turned over in the first instance.
    If this is all you do you will be making it harder for her to climb not easier.
    MTB:
    09 Stumpy Elite
    10 Enduro Pro Custom
    16" HotRock Custom

    Road:
    08 Jamis Xenith Comp
    13 Pinarello Dogma 65.1

  7. #7
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    Quote Originally Posted by griffter18 View Post
    Shortening the cranks only will reduce the leverage but enable effective spinning assuming the gears can be turned over in the first instance.
    If this is all you do you will be making it harder for her to climb not easier.
    Suggestion was to shorten regular long adult MTB crank down to kid length. Benefit is that this could be done to get chainrings smaller than 110mm BCD allows. Just note that you will need left-hand thread tap for the left side pedal hole.

  8. #8
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    Last edited by Rondo; 05-07-2013 at 06:00 PM.

  9. #9
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    Quote Originally Posted by GrayJay View Post
    Suggestion was to shorten regular long adult MTB crank down to kid length. Benefit= chainrings smaller than 110mm BCD.
    Totally appreciated what you where suggesting, but wouldnt this require a triple crank to be used in order to get the smaller bcd. And wouldn't it then leave 2 spare slots which would need to be filled with a bash ring to remove the sharp edge where the outer ring sat.
    It may also put the chain out of alignment and need the frame BB threading and other bearings to make it all fit.
    Not saying it's not do-able, just seems a lot of effort and possible cost.

    As with anything theres always compromises to make and it may be that the best option is a combination of all of the above.
    MTB:
    09 Stumpy Elite
    10 Enduro Pro Custom
    16" HotRock Custom

    Road:
    08 Jamis Xenith Comp
    13 Pinarello Dogma 65.1

  10. #10
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    Quote Originally Posted by griffter18 View Post
    Totally appreciated what you where suggesting, but wouldnt this require a triple crank to be used in order to get the smaller bcd. And wouldn't it then leave 2 spare slots which would need to be filled with a bash ring to remove the sharp edge where the outer ring sat.
    It may also put the chain out of alignment and need the frame BB threading and other bearings to make it all fit.
    Not saying it's not do-able, just seems a lot of effort and possible cost.

    As with anything theres always compromises to make and it may be that the best option is a combination of all of the above.
    104mm BCD (4-bolt pattern) take 32t chainrings, older 94mm 5-bolt pattern can get as low as 29t. Could also try to make use of the even smaller inner granny ring position. If not using a inner granny ring, you could use a narrower road width bottom braket to keep the q-factor (pedal width) narrow. Outer bash-guard is a good idea to keep the chain in place without a front derailler, even if they never bash anything with the ring. So long as the exising bottom bracket is threaded, most any modern ISO (british) threaded bottom bracket shoud thread right on, new bikes have not used threaded BBs other than british for 20 years or so. Doubt that a kids bike is setup for newer press-fit standards.

  11. #11
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    BB on most Specialzed Kids bike is very basic.
    1 piece crank with press fit cups and loose ball bearings.

    If this is the case then you will need to use something like a DMR Wondercup to adapt.
    MTB:
    09 Stumpy Elite
    10 Enduro Pro Custom
    16" HotRock Custom

    Road:
    08 Jamis Xenith Comp
    13 Pinarello Dogma 65.1

  12. #12
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    If this is the multi-geared 20" hot rock, I would go Mega-Range 7 Speed, 34 tooth rear.

    The stock 28 tooth vs. the 34 tooth is huge. Much more than a front ring can achieve.

    If it is the single gear then a front and rear gear change would be in order. On the cheap, a rear cog with new chain. The cog is just slid on, with a snap ring to keep it there. I'm guessing $5 for the cog?

    P

  13. #13
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    I agree. You can upgrade the whole bike to 7 speed with the 14-34 freewheel for the same price as a new crank, chain ring, bottom bracket and bolts.

    I just did my son's with:

    Altus RD-M310 rear derailleur - $16.61
    Altus Sl-ML310 trigger shifter - $12.95
    Tourney 14-34 freewheel - $9.87
    KMC X8.93 chain - $9.80

    The advantage is you get a lower gear and the bike shifts infinitely better. My son struggled with the gripshift and has no trouble with the trigger shifter. I did put a thick washer under the right side axle lock nut for spacing. I also added a set of Avid FR-5 levers while I was there.

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