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  1. #1
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    Differences between Hotrock 24" straight and curved top tubes?

    I have 2 Specialized Hotrock 24" bikes and was looking to build one for my son. I am trying to figure out which frame to use. Both are mark A1 on them and have front suspension. The 2006 one has the straight top tube with 21 gear. The other is a 2007 7speed with the curved top tube and chain rollers.

    I plan on using a MAG 21 front fork and 1x gearing. I wasn't sure which frame is better to start with to build for my son. Any information would be greatly appreciated.

  2. #2
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    Bent TT provides a bit more standover clearance if that is needed but I would expect that the overall quality, weight of the two frames would be comparable. Go with whichever frame your son likes best....

    Are you planning to make brake post drop brackets like Tig's?

  3. #3
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    the 2006 bike is already disassembled, so it would quicker to sell the other one instead. I will measure the frames side by side and look for differences.

  4. #4
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    Yes I will be making the brackets to drop the brake down. Should be pretty easy I think.

  5. #5
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    Dropping the post down should be significantly easier than the method I tried of shortening the fork lowers. There should be some good weight savings if you were to figure out how to remove the dampener from one leg, one dampener should be plenty for kid use.

    See some of the discussions I have had with Tig regarding mag21 modifications at ;
    Novara Pixie 20" project

    If the frame is already stripped, try weighing it and just verify that it is not grossly overbuilt. You might also check the top tube length of the two frames, if significantly different then that might guide your choice. I have seen some 24" kids bikes with top-tubes that were very long, would make it hard to get a good fit.

  6. #6
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    I weighed the stripped down frame already. I can post the actual weight of it when I get home. The curved top tube frame seems a lot longer than the other bike just by first glance, so I will make some actual measurements.

    We have already ordered a bunch of lighter weight parts that will fit either bike. Should be pretty easy for us to drop 4-5 lbs off pretty quickly.

  7. #7
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    Quote Originally Posted by cboyd1974 View Post
    Yes I will be making the brackets to drop the brake down. Should be pretty easy I think.

    Are you doing something like this?
    Sinz Brake Post Extension Fits Haro Redline SE GT XS PowerLite | eBay

  8. #8
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    Quote Originally Posted by thesmokingman View Post
    Sinz brackets only drop the post by 16mm, not the full 25mm needed to go from 26" to 24" rims. Some brake arms might possibly have sufficient vertical pad adjustment range to compensate for this but many brake arms will not. You also need for the post threads on your fork to be same diameter/pitch as those on the sinz bracket, not all post threads are the same.

    Alternate DIY mag21 bracket relocate tutorial at;
    FAQLoad - Modifying 26" fork for 24" wheels

  9. #9
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    I was planning on making the brackets like second link, or possibly making a new arch out of aluminum. Haven't narrowed that down just yet.

    I am planning on using the curved top tube frame. The extra 1.5" stand over height will help him out. Both frames weighed within 70g of each other with identical frame geometry besides the top tube.

    The straight tube bike weight 30.2 lbs with the 21 speeds. The bent tube bike weighed 27.4 lbs on a digital scale.

    I will be using some parts off of both bikes to get the lightest weight with the least amount of money spent. Carbon handle bars and seat post should be here by Monday. The handle bars alone are 450grams lighter than the ones on the bike.

  10. #10
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    New arch would be a fairly ambitions project unless you have access to a CNC mill.

    Dont skimp on the tires if you want to make it a nice light bike, hard to beat the Schwalbe rocket rons for weight and supple casing if you can find them in stock somewhere.
    Rocket Ron HS 406 | Schwalbe North America

    Rebuilding the wheels re-using the rims with lighter hubs and a light cassette can also help drop a bunch of weight, see Kid specific Wheel Build for 40lb rider NEED HELP

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