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  1. #1
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    Hotrock bottom bracket?

    Finally got to tear my Craigslist find down. To my surprise, it is a older cromolly frame (not alum). It had a generic bottom bracket, sorta a one size fits all. Anyone know what size to replace with? I'm trying to save weight

  2. #2
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    I replaced a Hotrock 20" BB with a Shimano UN54 but this was on an aluminium frame, it was a 2009 model. The Shimano BB wasn't a weight saver but at least it wasn't an open style like the original. There are (were?) some Ti BB's in the same size but they were very expensive. You might get lucky and find one on E-bay?

    Kind regards,

    Clemens

    PS: I checked my old mail and found the one for the HotRock was a 68-113 mm version, maybe this helps. White Industries has a Ti version for just below $ 200...

  3. #3
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    You probably have a "one-piece" crankset. These have a single piece of steel, from the right pedal to the left, requiring the frame to have a large-enough opening so they can twist their way in. This opening is called "American" bottom bracket. It's fairly large, and has no threadings.
    If you wan to convert an "American" bottom bracket to "normal" BB (threaded, English), You need:

    1. Conversion kit (like this: http://www.amazon.com/Truvativ-00-64...bottom+bracket)

    2. Bottom bracket matching the crankset you wish to install (most kids cranks require sqaure BB)

    3. The crankset itself (Kids cranksets are available from Spawn Cycles, Sinz, Turn3 and maybe some other brands)

    4. New Junior-size pedals, with 5/16" thread (One-piece cranks have another threading standard, so they won't fit!)

    This conversion is not exactly cheap. I did it for my son's Hotrock 12", and the total weight saving was ~150gr (Steel BB, Spawn 89mm crankset with chain-guard)

    So, $-to-gram, it doesn't make much sense. You'll have a much better deal buying him/ her a light, good quality kids bike.

    Still, for my son it was an upgrade, because the Hotrock 12" original crank arms where too short (around 75mm). The 89mm enabled him to climb grades which stopped him before, and to feel safer on the descents (because his coaster brake became more powerful)

  4. #4
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    Specialized emailed me back, said 68x110 or 68$113. The 2nd number is the spindle length, correct? 3mm shouldn't make that much difference should it? Gonna try to get to a bigger bike shop this week and see what they say. Looking at token tk838hal. Anyone heard of em? EBay special and 60g lighter than shamano

  5. #5
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    2nd number is the spindle length. Try the Token; worst case your out $20. I put a UN-55 on my boys' bike. A little heavier, but I know I won't have to mess with it again.

  6. #6
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    Quote Originally Posted by Sorefoot View Post
    3mm shouldn't make that much difference should it?
    That's no always the case. In my conversion process, the Truvative adapters didn't slide all the way in, because of an internal "step" in the Hotrock Aluminum frame.
    A 68x107 BB worked OK, but resulted a somewhat too-far-right position of the crankset (I'm talking about 2-3mm, not more)
    Trying to install a 68x103 BB caused the chainring to hit the adapter, so I re-installed the 68x107 BB.

    You can easily go wrong in this area. I would buy the cheapest Shimano or Truvative BB, so the financial damage in kept small if you made a mistake.

    If you buy Spawn Cycle's crankset, you can get rid of the aluminum chainguard. Expect your kid to suffer some mild injuries, occasionally, without it.

    If you want to reduce weight, try replacing the steel handlebar to an Aluminum one (like Fly Racing mini 22.2 mm bar), and the steel seatpost/ seat combo to an aluminum one (like T.H.E Mini Dice or Sinz Mini/Junior combos - if they're alloy and not steel)

    You didn't mention the age of your kid. If he/she are 4-6, get rid of the stupid caliper front brake. It's completely useless for small kids (requires a lot of force, and comes with an ergonomically incorrect lever)

    After doing all the above, you still won't be able to reduce the weight to something which is even close to this: Belter 16" 2015 ? Early Rider
    Or this: http://spawncycles.com/bikes/spawn-cycles-banshee

  7. #7
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    Thanks for all the good information. He is 6 and just finished kindergarten, but was the tallest in his class, taller then most of the 1st graders. I have his Hotrock 20 seatpost up as high as it goes. This new older bike has different geometry than new models. Hope the learning curve isn't too steep. If he keeps growing at this rate he will be in my old Gary Fisher by next year....

  8. #8
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    Quote Originally Posted by Sorefoot View Post
    . . . but was the tallest in his class, taller then most of the 1st graders....
    The Hotrocks - at least the modern Hotrocks - are relatively long bikes. But, if you feel that the one you bought will soon become too small, it's just another reason not to "invest" money in a weight-whining project.

    The cleary's, I think, are the longest kids bikes, so the 20" Cleary Owl might be perfect for him for a couple of years, maybe even more:

    Owl - Cleary Blue | Cleary Bikes

    Since you're weight-aware, it'll be easier for you to resist the heavy, mostly useless, suspension forks and multiple gears which so many 20" kids bike have. IMHO, for a 6 year-old, light weight, good ergonomics and low rolling resistance is the best way to go.

    Check out the Specs page, and look for "Top Tube Length (Horizontal)" measurement.

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