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  1. #1
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    Project 12" Hotrock

    After spending a lot of time trawling through this forum looking at the great custom kids bikes, I thought I should add my effort. Our eldest daughter (3.5yrs) is currently loving her Islabike Rothan balance bike, but I think it's time to unleash the pedal bike soon. I picked up a 12" Hotrock at a childrens equipment sale a few years ago(!) as it was a bargain at 17.

    So while the Hotrock has a nice frame, most of the stuff hanging off it is pretty disappointing. The caliper brake is marginal at best, cranks don't run particularly true and have a huge amount of friction, and the rear wheel weighs a ton.

    So my idea is to improve the braking, reduce the drivetrain resistance, and hopefully save a little weight in the process.

    So here it is as it stands, and the weights after breaking it down. I'll add more info and pics as things progress.

    Project 12" Hotrock-hotrock-12-weights.jpg

    Project 12" Hotrock-dsc_0686-small.jpg

    Project 12" Hotrock-dsc_0691-small.jpg

  2. #2
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    Finally something to report!

    Ok, simple things first. I machined up an aluminium post to replace the steel original for easy weight saving. Also made a 1" quill to 1.125" Ahead adaptor in order to use the 50mm stem I bought. Note that the ID of the fork is only 21.1mm, so a standard quill adaptor does not fit (found this out the hard way). The stem will be teamed with a 31.8mm aluminium flat bar.

    I was originally going to use a Truvative BMX to BSA threaded bottom bracket convertor, but quite a lot of material would need to be machined off the OD, as the Hotrock BB is only 43mm ID (BMX is 52mm). So instead I'm going to use cartridge bearings with a square taper BB axle (similar to what Demo9 did). This should be lighter and cheaper than my original plan (excuse the old test bearing in the photo).

    The rear hub was a cheap (US$16) ebay item. I had to get creative with the lacing to make the spoke length work. Also, the spoke holes don't seem to be aligned with the holes on the opposite flange, so spoke angles aren't exactly the same. Get what you pay for I suppose! Bearings are smooth Japanese units. I replaced the steel axle and nuts with a machined aluminium one, spacers and steel cap screws.

    Also mocked up the mounts for the rear V-brake. Still need to do a lot of shaping and tap the boss holes, but the concept seems to work ok on the frame.

    Anyway, here are some photos!

    Project 12" Hotrock-dsc_3357.jpgProject 12" Hotrock-dsc_3354.jpgProject 12" Hotrock-dsc_3358.jpgProject 12" Hotrock-dsc_3356.jpgProject 12" Hotrock-dsc_3353.jpgProject 12" Hotrock-dsc_3362.jpg

  3. #3
    Birdman aka JMJ
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    Very nice work. I took the stock seat off my daughter's HotRock 12 and used an Odyssey alloy post mated to a HotRock 16 saddle. Didn't shave a lot of weight, but my daughter appreciated the larger saddle. Also, I can now adjust the angle and setback.

    JMJ

  4. #4
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    Bit more to report. Quill adaptor/stem/bar all mounted and works well. Bar is currently 560mm, so may need to be trimmed a little further.
    Mounted the brake mounts with the mini-v's off the Islabike Rothan. Seems like everything should work. May end up making a more compact/elegant set of mounts now I know what clearances I'm dealing with.
    Mounted the freewheel, which comes extremely close to the drop out. I may have to end up machining a new axle to move the hub over a couple of mm.
    Received a set of Sram S600 cranks, which I'll shorten to 102mm. They will then be moved onto the 16" bike.
    Attached Thumbnails Attached Thumbnails Project 12" Hotrock-dsc_3467-small.jpg  

    Project 12" Hotrock-dsc_3466-small.jpg  

    Project 12" Hotrock-dsc_3465-small.jpg  

    Project 12" Hotrock-dsc_3463-small.jpg  

    Project 12" Hotrock-dsc_3462-small.jpg  

    Project 12" Hotrock-dsc_3461-small.jpg  


  5. #5
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    Nice!

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