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  1. #1
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    Best 20" rim option for Hotrock upgrade?

    So anybody have anything to say about the 20" (ISO 406) rims available? Any advice for a 1st time wheelbuilder? This will be for a little 20" Hotrock for my son. Trying to shed some weight and spruce it up. I have some parts lying around and an old S-Works to cannibalize. I am going to use some old 28 spoke Sun hubs for these wheels. My thoughts are this will save some weight, be relatively inexpensive, plenty strong for a 50lb rider, and allow me to use 9 speed drivetrain parts I have available. What I have found so far:

    Sun CR-18 350g - $24
    Velocity Razor 315g - $35
    Crupi Expert 335g - $47
    Velocity Aeroheat 340g - $60

    I am thinking of going with the Sun rims as the are the most readily available, cheapest, and the black Sun rims will match the black sun hubs... these things are important you know!

    Also, How do I determine the spoke length I will need other than to measure when the rims arrive? I figure I will lace these just like the wheelset they are on now. So I have a model to refer to since this is my first wheelbuild. The front is radial and the rear is 3 cross.

    Your thoughts? Should I post this in the wheelbuilding forum instead?

  2. #2
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    Hey there!

    I'm thinking at building some 20's as well. I want to go with a 1 1/8" rim though and mount up some 1.75's

    Goto "Tools" on this link and you can check out the spoke length calculator!

    United Bicycle Institute


    Keep me posted on your build!


  3. #3
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    Not sure if you can get a MTB tire on the CR 18... If check out Alienation BMX rims.

  4. #4
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    Hummmm.... I didn't think about that. Why wouldn't a 20" tire fit on a 20" rim?

  5. #5
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    Quote Originally Posted by Rondo View Post
    Hummmm.... I didn't think about that. Why wouldn't a 20" tire fit on a 20" rim?
    There are two different sizes of 20" BMX rims: 1) trial BMX and adult racing BMX = 406mm bead seat diameter and 2) "mini" and "expert" sized racing BMX = 451mm in diameter. Normal tires for 406mm rims would not fit 451 mm rims. For those you would need 20"-1 3/8" or 20"-1 1/8" tires. I searched everywhere to find some 451mm tires suitable for XC-type riding for my son. Found only two which are wide enough: Maxxis DTH:20 x 1-3/8"
    https://www.danscomp.com/products-RA..._DTH_Tire.html
    and Tioga Comp X 20 x 1-3/8":
    Tioga Comp X BMX Tyre | Buy Online | ChainReactionCycles.com
    I've got both and so far we're happy with them Although tioga wear really fast (not a problem at its cost) and maxxis DTH are semi-slicks and only good for the rear.
    P.S. There is also Schwalbe Moe Joe in this size, but I haven't succeeded to find any.

  6. #6
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    Wow! I didn't know they had two different sizes.

    I have two rims I'll check. Sun M14A and Odessey T-1000. I'll measure when I get home.

    Thanks for the great info!

  7. #7
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    OP: Did you end up building a set of rims? If so, what did you end up with?

  8. #8
    turtles make me hot
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    I built a set of Velocity Aeroheats for a 20" bike for my son and they were great.
    Right now, he's riding a 24" wheeled bike with Sunringle' Rhynolites. Since I put disc brakes on this bike, I got the rims with black sides. They look pretty damn cool.
    I like turtles

  9. #9
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    2009 Hotrock 20 front wheel weight.

    Hi, I am currently doing some mods to my daughters 2009 Hotrock 20. I just purchased a XT front hub on ebay that only weighs 125 grams. I was pretty excited getting ready to order the 350g CR-18 32hole in the 406 size. (there are only a few people selling the 32h now, and I think they are discontinued.)

    I finally got around to weight the stock complete front wheel: 758 grams with reflector!
    So by the time I got the lightweight XT hub, CR-18 rim, 128 grams for good spokes, a rim strip, qr, and nipples I was only going to save about 80 grams! I decided my money might be better spent. Guess I'll sell my XT hub.

    I have 2 Kenda Small Block 8's coming in the mail which is a much more cost effective weight savings, not to mention the traction will be nice.

    So before you decide to build up new wheels make sure you are actually going to have a weight savings if that is your primary reason.

  10. #10
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    I'd like to upgrade the stock rear wheel on a HotRock.

    If anyone's kid has outgrown that nice 20" wheel you built them,
    I might like to buy it !

    thanks.
    Last edited by client_9; 01-31-2013 at 09:07 AM.

  11. #11
    GMF
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    I mentioned this in a different hotrock thread, but it is pretty straight forward to swap out the hubs in those wheels if you have any wheel building experience. The rims are light enough, and any typical shimano hub should work just fine (similar flange spacing and diameter). You can upgrade to a cassette hub in back and QR in front (although really, that is just an axle swap).

  12. #12
    Fight the Kakistocracy!
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    Re: Best 20" rim option for Hotrock upgrade?

    Others are right, the rim weight won't save much. I swapped a 36 hole xt hub straight into the same spokes and rim on my son's 20, saved a little weight, but the rotating mass stayed the same. Biggest differences were the bearings, way better, and the qr. We really did it for the qr to put his bike on the racks with mike and make him a "real" mountain biker. I am still looking for a 36 hole qr road hub to swap the rear.
    veelz

    Gravity, not just a good idea, it's a law.
    The only one consistently and constantly applied, no exceptions.

  13. #13
    GMF
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    Quote Originally Posted by veelz View Post
    I am still looking for a 36 hole qr road hub to swap the rear.
    You will likely have luck on eBay. There should be tons of old rsx or 105 hubs for super cheap.
    Alternatively, just go with a MTN hub. Older ones had a 130 axle, or simply swap the axle
    Another option, get an 18h hub and run half the spokes for a weight weenie build. I had a friend who ran a full radial 16 spoke rear wheel with no problems (these kids are not putting out a ton of power :-)

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