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Crumpton BMX, Worlds Lightest PROXL.

Viewing 7 posts - 1 through 7 (of 7 total)
  • #94928
    Keymaster

    I imagine that quite a few people reading this have already seen this project we did for Interbike, but we figured this was a good time to complete the details on it.   Complete finished weight of the bike was just under 5.4kg, (11.89 pounds)

    The frame is a custom handbuilt by Nick Crumpton of Crumpton Cycles.  The frame came in at 957.2 grams.  Being almost the same weight as a superlight 29er frame which is twice the size, this one could certainly have been lighter, however the goal was not to have just the lightest but something that could truly be race worthy.

    The bar/stem combo is a Bombshell handlebar and Enve stem with bonding by Calfee.

    Hubs are custom made by Tune.  The rear started as a Mag150 and had a new axle and end caps machined as well as the alloy freehub body replaced with a titanium single speed version.

    Rims were custom from Velocity based on the tried and true A23 extrusion.

    Spokes were custom Pillar Titanium.  Bladed profile with beefed up 13g ends matched to custom 13g alloy nipples.

    Complete build list below gallery.

    Complete Build List:

    Frame: Crumpton Custom, 957.2gr

    Headset: Kcnc Radiant R1, 46.7gr

    Fork Expander: Tune GumGum  8.7gr

    Top Cap / Bolt: Fair Wheel 5.9gr

    Headset Spacers: Parts of Passion 2.8gr

    Fork: Sinz Carbon (175 lbs weight limit.) 462.2gr

    Crank Arms: Tune Smartfoot 508.2gr

    Bottom Bracket Cups: Extralite PF30 22.3gr

    Bottom Bracket Bearings: HSC Full Ceramic, 33.4gr

    Chainring: Absolute Black, 36t, 51.4gr

    Chainring Bolts: Kcnc SL 4.6gr

    Chain: KMC X9SL 194.8gr

    Cog: Recon Titanium 13t, 21.1gr (includes all spacers)

    Cog Lockring: Far and Near, 5.1gr

    Front Wheel: Tune Mig45 Custom front hub, Velocity Custom A23 rim, Pillar Custom Titanium spokes.  438.5gr

    Rear Wheel: Tune Mag150 Custom Rear hub, Velocity Custon A23 rim, Pillar Custom Titanium spokes. 544.4gr.

    Rim Tape: Rox Superdute 8.1gr.

    Pedals: Bebop Titanium, 146.9gr

    Brake Caliper: Kcnc V-brake, 84.9gr

    Brake Lever: Kcnc Brake Lever, 23.4gr

    HandleBar/Stem: Bombshell Carbon bar / Enve Carbon stem, 407.9gr

    Handlebar Grips: Kcnc w/plugs, 19.6gr

    Saddle: Tune KomVor, 92.1gr

    Seatpost: Tune Carbon, 101.1gr

    Brake Cable: Kcnc Titanium, 7.3gr

    Brake Housing: Aican Bungarus, 12.1 gr

    Tire, Front: Tioga Powerband Kevlar 1.85.  267.6gr

    Tire, Rear: Tioga Powerblock Kevlar 1.75.  301.7gr

    Chain Tensioner: Custom, 14.6gr

    Tubes: Eclipse, front 40.7gr, rear 41.1r.

     

     

     

     

    #94973
    Participant

    What is the mechanism to tension the chain?

    Nothing ventured nothing gained!
    #94974
    Participant

    I’m quite intrigued by this bike. I love the idea of a lightweight race based bmx, takes me back to my teenage years. The frame is stunning as I would expect of Crumpton. The choice of chainring is interesting but there again I’m biased in that department. I would still choose a fibre-lyte single ring, however. Is there something special that I’m not aware of with absolute black chainrings? I’m really not too sure about the handlebars, the narrow section where the stem meets the bars at either side looks to be a weak spot? What I’m very intrigued about is a Mig45 front hub on a race bmx, not too fragile? Despite these small things, still an amazing build.

    #94979
    Moderator

    What is the mechanism to tension the chain?

    I’m not sure what exactly you want to know, but looks like vertical drop outs to me.

    "Nothing compares to the simple pleasures of a bike ride," said John F. Kennedy, a man who had the pleasure of Marilyn Monroe.
    #94980
    Participant

    Ypsylon, thanks for your response. I noticed that there are allen bolts behind the rear axle. Was wondering if when tightened they pulled the rear wheel back to tension the chain. Some motocross bikes used such mechanisms in the past.

    Nothing ventured nothing gained!
    #94983
    Keymaster

    Ypsylon, thanks for your response. I noticed that there are allen bolts behind the rear axle. Was wondering if when tightened they pulled the rear wheel back to tension the chain. Some motocross bikes used such mechanisms in the past.

    It’s a BMX chain tensioner that we modified a bit. You’re right, it’s a washer with a bolt that tightens against a plate that is braced on the back of the horizontal drop out. Very similar to what some motorcycles use. They come in a few different types and shapes but they’re all pretty much the same concept.

    I run the Facebook Page, Twitter Account and write code the rest of the day.
    #94984
    Participant

    Thx for clarification Emiliano!

    Nothing ventured nothing gained!
Viewing 7 posts - 1 through 7 (of 7 total)

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