Nature Boy

Nature Boy


Our venerable single speed cross mount is better than ever with an expanded size range and 650B size wheels on the 43,46, and 49 sizes.

Utilizing the 650b wheel size for our smaller bikes allows us to better serve riders by preserving our desired geometry as we scale the bike down the size range. Simply put, there are significantly less handling tradeoffs with a 650b wheel in those sizes, and smaller riders will benefit from smaller top tube lengths and greater acceleration that a lighter, smaller wheel provides.

As always the Nature Boy carries all of the AC hallmarks that you’ve come to expect: beautiful lugged fork crown, custom dropouts, custom BB shell, signature head badge and E.D. coating. It has our proven race-inspired geometry, but since we’re big fans of riding cross bikes every day, we’ve built in plenty of room to fit large tires and even fenders. The 700c bikes fit a 38c tire with plenty of room for mud, while the 650b sizes fit a 650X42c tire.

We are particularly proud of our singlespeed disc dropout. It solves our main frustration with dropouts of this style: where do you position the brake caliper for optimum performance? The answer was to develop a proprietary system where the tension screw is used to pull the caliper mount into the correct position. Just loosen everything up, use the tensioner to achieve desired chain slack and tighten it all back up. No more guesswork, just reliable braking performance.

For racing, cruising trails, gravel, or daily commuting, disc brakes and a singlespeed setup provide unmatched control and reliability.

Nature Boy


    Suggested retailers for "" change

    612 Select Tubing

    Our proprietary blend of 4130 double-butted CroMoly tubes. Every piece of tubing on every frame size has been carefully chosen to provide the best ride possible.

    E.D. Coating

    In Electrophoretic Deposition, or E.D., coating the frame or fork is placed in a paint bath where an electric charge is applied. This fuses a thin layer of black satin coating to the tubes inside and out. This coating acts as both a rust preventative inside and a primer out.

    Custom Details

    We’re way into the handbuilt touches when it comes to our frames. Which is why you’ll find things like internal cable routing, custom dropouts, lugged crown forks, reinforcements on the bottle bosses, hidden fender mounts, etc on our framesets.

    Signature Dropouts

    The disc version of our horizontal dropout not only looks stunning, but improves upon the issue of properly locating your caliper in relation to the wheel.

    Frame + 612 Select CroMoly steel. Double-butted down, top, & seat tubes. Externally tapered, ovalized, & dimpled chain stays, tapered seatstays
    Fork + 4130 CroMoly tapered fork blades, lugged crown & matching dropout. Straight steerer tube
    Rear Spacing + 135mm
    Brake Compatibility + Disc only, 160mm rotor
    Seatpost Diameter + 27.2mm
    Steerer Tube/ Headset + 1-1/8" threadless, EC34 upper & lower, crown race 30.0
    Bottom Bracket + 68mm English
    Chainring + Clearance: 49t max
    Tire Clearance + 43/46/49cm 650b x 40mm, 52–61cm 700c x 38mm
    Extras + Fender mounts, E.D. coated
    Headset + Cane Creek 5 Series
    Stem + 3D forged, 4-bolt stem, 31.8mm
    Handlebar + AL6061, 31.8mm, 80mm reach, 125mm drop
    Tape + Black
    Brake Lever + Tektro RL340
    Brake + Promax mechanical disc, 160mm rotors
    Crankset + FSA Vero, 42t
    Bottom Bracket + 68 x 110mm steel cups, sealed bearings
    Seatpost + AL6061 w/alloy head, 27.2mm, 350mm length
    Saddle + All-City Gonzo
    Freewheel + 17t, 3/32
    Chain + KMC Z610
    Hubs + Joytech QR/disc, 32h, 6-bolt disc mount
    Rims + WTB STP i19 TCS, 650b & 700c
    Tires + Sizes 43/46/49 cm 650b x 41 mm Surly Knard Sizes 52/55/58/61 cm 700c x 33 mm Clement MXP
    Nature Boy Geometry Line Drawing
    Select up to 3 sizes to view:
    43cm (650b)
    46cm (650b)
    49cm (650b)

    Size 43cm (650b) 46cm (650b) 49cm (650b) 52cm 55cm 58cm 61cm
    Head Tube Angle (A) 70.75 71.25 71.25 71.5 72 72.5 72.5
    Seat Tube Angle (B) 75 73.75 73.5 73 73 72.5 72.5
    Top Tube Length (C) 495 520 535 550 565 585 605
    Seat Tube Length (D) 410 450 490 520 550 580 610
    Chainstay Length (E) 392 392 392 435 435 435 435
    Bottom Bracket Drop (F) 52 52 52 70 70 70 70
    Fork Offset (G) 47 47 47 45 45 45 45
    Total Fork Length (H) 376 376 376 395 395 395 395
    Head Tube Length (I) 100 125 150 130 150 175 200
    Standover (J) 703.8 737.7 771 802 827 853 880
    Wheelbase (K) 952.9 964 977.7 1019 1030 1039 1059
    Stack (L) 495.4 520.8 544.5 563 583.9 609.6 633.4
    Reach (M) 359.8 366.7 372.3 377.9 386.5 392.8 405.3
    Handlebar Width 38 38 40 42 42 44 44
    Stem Length 70 80 90 100 110 110 120
    Crank Arm Length 165 165 170 175 175 175 175
    BK8400 43cm Green/White Complete
    BK8401 46cm Green/White Complete
    BK8402 49cm Green/White Complete
    BK8403 52cm Green/White Complete
    BK8404 55cm Green/White Complete
    BK8405 58cm Green/White Complete
    BK8406 61cm Green/White Complete
    FM8400 43cm Green/White Frameset
    FM8401 46cm Green/White Frameset
    FM8402 49cm Green/White Frameset
    FM8403 52cm Green/White Frameset
    FM8404 55cm Green/White Frameset
    FM8405 58cm Green/White Frameset
    FM8406 61cm Green/White Frameset