HotRock 20 Weight Weenie Build on a parts bin budget- Mtbr.com
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  1. #1
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    HotRock 20 Weight Weenie Build on a parts bin budget

    And so it begins.

    HotRock 20 Weight Weenie Build on a parts bin budget-i-4bd7twp-m.jpg

    Totally stock HotRock procured from a MTB skills camp end of season sale.

    Firm Plans at this point:
    Titec Ti Bar (free from the parts bin of Matt K)
    Doric LTD Pro carbon seatpost (my parts bin)
    TRP Spyre Carbon Road/CX mech brakes (parts bin)
    Suntour XCM HLO Air SL 20 - $143 shipped on the current end of summer sale
    SDG Fly Jr. Saddle - $35
    Sram X7 10 Speed Rear Deraileur - Free my parts bin
    Sram 1090 chain - free my parts bin
    Sram X9 shifter - $25 ebay used
    10s cassette - have about 4 in the bin ... need to figure out what's lightest

    Fuzzy plans
    Cranks - open to suggestions - thinking Sinz and a bb51 bottom bracket. Other thoughts?
    Wheels - looking at some of the Ali Express wheelsets at about $100-$150 delivered. I don't have any disc hubs lying around or I would build from scratch - again open to ideas & suggestions here.
    Tires - thoughts? What's light and relatively puncture resistant? We live in the foothills near Denver so lots and lots of sticky stuff on the trails in the fall and spring.

    Any thoughts / suggestions are welcome. It's been more than a few years since I've done a kiddo build. Little one is currently ripping on a Prevelo Alpha 2, only upgrades are stans in the the tubes and an EC70 seatpost...

  2. #2
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    First 67 gram reduction.

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  3. #3
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    Knocked another 220g off. Saddle and post.

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    As she sits...

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  4. #4
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    Another 96 Grams for the pedals.
    Old:

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    As she sits:
    HotRock 20 Weight Weenie Build on a parts bin budget-i-fzghk49-m.jpg

  5. #5
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    very cool.
    Ride Bikes, Drink Craft Beer, Repeat.

    Know these before you post:
    MTBR Posting Guidelines

  6. #6
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    Thank you!

  7. #7
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    As an FYI, the set of reflectors and the dorc disc should be about 30g each, which makes 60g of rotating mass you can drop at no cost.

  8. #8
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    Quote Originally Posted by TimTucker View Post
    As an FYI, the set of reflectors and the dorc disc should be about 30g each, which makes 60g of rotating mass you can drop at no cost.
    Thanks Tim, new wheels sans reflectors and dork dial have been ordered. Game plan is to Stanís those, get the cassette mounted and do a stock as shipped vs new weight comparison. I figured I would leave the fork disk and reflectors in place.

    Any tips on cranks? Right now Iím debating spawn vs trailcraft. Need to be 127 or 130 length. Certainly open to other ideas that are a - lighter at the same price point, or b a cost a little less and are a little heavier

  9. #9
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    Most of the options < 140mm seem to all be square taper, so you'll likely save some weight by moving to a lighter bottom bracket.

    I just ordered a titanium square taper bottom bracket from aliexpress for $28 -- it's listed as 144g, although some of the reviewers noted weights around 155g:
    https://www.aliexpress.com/item/32952847076.html

    What are you planning on doing for gearing?

    We're staying a little behind the curve for cranks -- recently moved to 102mm Spawn cranks with 20", which still use 64 BCD.

    On 64 BCD, we can go all the way down to 22T up front, which gives us more low range than we'd have with the 104 BCD rings on the 127mm cranks:
    https://usamadeco.com/collections/sh...-pro-64mm-74mm

    That way we can still stick with a 11-34T cassette and not have to worry about having less ground clearance for the derailleur from larger cogs in back.

  10. #10
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    Wonder just how much these weigh?
    https://www.ebay.com/itm/Kids-Tandem...t/283540398134

  11. #11
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    These BMX cranks plus a narrow-wide ring from USA Made would be lighter, but would force you to a larger 110 BCD chainring (I think the min on those is 36T):
    https://www.ebay.com/itm/Redline-Mic...k/223584846518

  12. #12
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    Quote Originally Posted by KarmaBiker View Post

    Any tips on cranks? Right now Iím debating spawn vs trailcraft. Need to be 127 or 130 length. Certainly open to other ideas that are a - lighter at the same price point, or b a cost a little less and are a little heavier
    I bought the spawn cranks, they were heavier than expected. I emailed trailcraft and theirs are lighter, I would go with those next time.

  13. #13
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    Quote Originally Posted by End_User View Post
    I bought the spawn cranks, they were heavier than expected. I emailed trailcraft and theirs are lighter, I would go with those next time.
    What's the length and weight of your Spawn crank?

  14. #14
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    Quote Originally Posted by End_User View Post
    I bought the spawn cranks, they were heavier than expected. I emailed trailcraft and theirs are lighter, I would go with those next time.
    Not sure on the larger cranks, but the 89mm cranks I got when I ordered for Spawn last year were old stock (plain white box vs. Spawn branded brown box / steel vs. aluminum bash guard / chain ring bolts go through rather than screwing directly into the cranks). They were quite a bit heavier than the newer style.

    Might be worth checking to make sure that you got the most recent version.

  15. #15
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    Quote Originally Posted by ghabe View Post
    What's the length and weight of your Spawn crank?
    Brood Styx 130mm (new this year),

    Here are my weights (sans chainring):

    Drive Side: 364g
    Non-drive arm: 204g
    BB, spacers, HW: 158g

    Thats 726g plus maybe 40-150g for a ring depending on material.

  16. #16
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    HotRock 20 Weight Weenie Build on a parts bin budget-superfly-20.jpg

    Just chiming in because I just started doing kind of the same thing with my son's bike. It's a Trek Superfly 20 that was a hand-me-down. Came to us as stock and we've since made a few changes and have more planned. Would love to be in on the conversation to compare notes and nerd out!

    Mods so far (photo above):
    Bontrager RXL Bars
    Sram X4 rear deraileur
    Sram X4 7 speed rear shifter
    Goodyear 20x2.20 (I didn't weight them but they're pretty light. And there is one on the rear now)
    35mm stem from Amazon - He's just able to fit on this bike and he needed the shortest stem available.

    Mods in the works:
    Stans 3.30 rear hub (ebay) - build on current rim
    Sram 1070 11-28 cassette (new but in my parts bin)
    Sram 1030 chain
    Sram GX 10 speed shifter (used)
    Sram Force road derailleur - short cage (used)
    Sram 6000 cranks DIY shortened to 120mm (used)
    28t North Shore Billet chainring from eBay
    Ti square taper BB - Will take your suggestion from above

    I didn't even think about the saddle and pedals. Do you have a link for those pedals?

    This has been super fun so far!

  17. #17
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    Quote Originally Posted by kylerodland View Post
    Click image for larger version. 

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    I didn't even think about the saddle and pedals. Do you have a link for those pedals?
    Nice looking build. I'm still debating the cranks. Fortunately those are easy to source

    Fly Jr Saddle:
    https://www.amazon.com/SDG-Component...a-466178351193

    Pedals:
    https://www.aliexpress.com/snapshot/...Id=32467519374

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