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Thread: kids bmx sizing

  1. #1
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    kids bmx sizing

    I have a very recent post about mtn bike sizing but I'm also considering getting my boy a BMX bike and I really need some input as I'm not super familiar with sizing other than that as an adult, I'd probably look at 20".

    My kid is turning 7. He's on the tall side for his age.
    between 51-52" tall. Maybe about a 23" inseam.


    Another user in another post threw out '16"' but I wanted to double-check if this was appropriate. (This is wheel size, correct?) I know bmx should be on the smaller side but that seems pretty small. Wondering if 18" makes sense.
    NOT looking for a bmx race bike. More freestyle if anything....tooling around the parking lot or pump track. Learn wheelies, etc.

  2. #2
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    so for BMX, you are going to look at the length of the top tube first, not the wheel size. In freestyle BMX, the top tube length will be the biggest factor in comfort and use of the bike.

    Head tube angle would be the next factor, but at his age, it won't matter right away since he will just be learning and probably not doing big tricks yet.

    Generally, a 20" TT will fit someone who is 5'-5'8"; 20.5" TT would be comfy for 5'8" to 6', and 21" for 6" or taller. The handle bar angle and placement will make up for some of the fit/comfort.

    I personally would suggest getting him a bike with 20" wheels so he can grow into it. That is what we all did back in the 70's...my first BMX, at age 8, was a 1981 Mongoose Supergoose...20" wheels, 19" TT (was the average size in the 70's/80's). It was "big" for me at first, but I did not know that... I got on it and went.

    If you go to any of the good BMX company web sites, there will be a lot more info and options. I just feel like if you get a smaller wheel size, and he wants to stick with it, you will be buying more bikes as he grows.

    AS his skills get better, then other areas of the fit will come into play, mainly Head Tube Angle....right now, for freestyle bikes, 75.5 degrees is the standard for park and street riding. This makes the bike very "twitchy" and nimble for all of the jump based tricks. Also, shorter chainstays - like 12.5"-13.5" are the norm. These allow for more manual/wheelie type things to be easier. A "trails" bike - which would akin to a dirt jumper MTB, is going to have a more slack HTA...more like 74 degrees, and a longer chainstay - like 14", for more stability...again, this stuff will be more important as he starts to develop his style.

    Check out bikes by Verde (my personal faves);Colony; We The People; Kink; Cult; FitBike;

    ...and prepare for some of the BMX "culture" shock of graffitti, rebellion, vaping etc on the sites...for the most part they try to keep it at least PG-13, but some of the sites you might want to look at first by yourself before he sees it
    " ...the moonlit swamp Krampus is a king among bikes." - geraldooka

    15 Surly Krampus
    LET IT SNOW!

  3. #3
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    My 52" 7yr on a 16" United Recruit. Its a perfect size for him right now. He'll get another season or two out of it for sure to. Going for a bigger BMX bike doesn't make much sense. The 18" is too big still(Cult Juvy). 16" is the ticket.

    https://photos.app.goo.gl/jRPJoLpfH6YSyDJM7


    This is him this summer at 51" on an 18" Cult Juvy: Def too big. He is starting to 180 the half pipe a little bit and ride vertical wall teacup turns at our indoor park and I don't think he'd be able to do much of that with that big of a bike. Too long.
    https://photos.app.goo.gl/ztocW7Cb63TivN4k6

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