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View Poll Results: Does this frame make sense?

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  • Yes, it should be a fun inner-city commuter

    6 75.00%
  • No, you're a moron

    2 25.00%
Results 1 to 14 of 14
  1. #1
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    Does this frame geometry make sense?

    I played around a little in BikeCAD this afternoon, after getting my frame fitting results back. I'm trying to shoehorn my 6'5", 94cm inseam body around a fast commuter frame to fit 700x38c tires+fenders (and an EBB).

    Does this geometry look reasonable? It's 72.5 head angle, 63.5 C-C seat, 63 C-C top. Using a Dimension cross fork (400mm A2C, 45mm rake) the trail ends up being about 62.5mm, the Jones -2.4, and the front projection .067.

    This is my first frame design, so I really don't know what I'm doing. Any advice would be welcome!
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  2. #2
    Old fart JohnDThompson's Avatar
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    Looks ok to me!

    Braze 'er up and tell us how it rides!

  3. #3
    Map maker cbchess's Avatar
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    Front looks to be a bit steep in the head angle and might be on the twitchy side. That is just my personal preference, I like a slacker head angle.

  4. #4
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    Looks good, should work fine. Although I think you'd be better balanced if the chainstays were a bit longer.

  5. #5
    'Cross and Road nut arshak's Avatar
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    I would go with 71.5 or 71.7 degree head tube angle as this is going to be a BIG frame and with correspondingly longer chain stays in the back, my 2 cents worth
    Whole lotta o' bikes

  6. #6
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    Thanks all, I appreciate the advice. I'll add 10mm to the chainstays, since I'll be riding it semi-upright most of the time and will probably have lots of weight on my butt.

    What I really want to get is the 'carvy' feel in making tight turns in small city streets at 20km/h. Sort of like a criterium, but with less pedaling in the turns. That's why I put in the 72.5 head angle. Fingers crossed!

  7. #7
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    Quote Originally Posted by antonyfhilliard View Post
    Thanks all, I appreciate the advice. I'll add 10mm to the chainstays, since I'll be riding it semi-upright most of the time and will probably have lots of weight on my butt.

    What I really want to get is the 'carvy' feel in making tight turns in small city streets at 20km/h. Sort of like a criterium, but with less pedaling in the turns. That's why I put in the 72.5 head angle. Fingers crossed!
    That's what I prefer too- stick w/the steeper HA, you'll be glad you did.

  8. #8
    Industry Maven Thylacine's Avatar
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    My Mods in RED

    I'm assuming this is a steel frame....


    Frame Angles
    *Headangle = 72.5∞
    *Seatangle = 72.5∞ (71.5 if using a straight post)

    Major Lengths
    Wheelbase = 1088.5549 mm
    *Seat tube length (c-t) = 690.0 mm
    Seat tube length (c-c) = 638.6374 mm
    Top tube length (effective) = 632.68585 mm (Might be a tad long for a commuter)
    Top tube length (c-c) = 630.00476 mm
    *Head tube length = 200.0 mm (215)
    *Bottom bracket height = 271.5 mm
    Bottom bracket drop = 77.5 mm (70)
    *Chainstay length = 440.0 mm
    *Front Center = 660.0 mm

    Fork and Headset Specs
    *Fork offset = 45.0 mm (48-50mm would be better with 72/72.5 HTA)
    *Fork length = 400.0 mm (might be a tad short)
    This is a rigid fork
    *Lower stack height = 11.0 mm

    Stability Info
    Trail = 62.855465 mm
    Jones stability criterion = -2.4148805
    Relative front projection = 0.06759858

    Tube Diameters
    *Seat tube diameter = 34.9 mm (31.8)
    *Top tube diameter = 31.8 mm
    *Head tube diameter = 38.1 mm (36)
    *Down tube diameter = 50.8 mm (38.1)

    Seatstay Info
    *Seatstay diameter = 22.2 mm (16mm if using caliper brakes)
    Direct distance from rear axle to center of seatstay at seat tube junction = 566.4608 mm
    Sideways angle of seatstay = 6.1623745∞
    Seatstays are straight
    *Distance from top of seat tube to center of seatstay = 40.0 mm
    *Location of center of seatstay at seat tube junction (0∞ = rear of seat tube, 90∞ = side of seat tube) = 45.0

    Bottom Bracket Info
    *Bottom bracket length = 68.0 mm
    *Bottom bracket diameter = 57.2 mm (38.1)
    Chainstay angle relative to horizontal = 10.356807
    Seatstay angle relative to horizontal = 67.59641

    Welding Clearance Info
    *Head tube extension above top edge of top tube = 8.0 mm (10mm)
    *Head tube extension below bottom edge of down tube = 10.0 mm (15mm)
    Gap between bottom of top tube and top of down tube at head tube junction = 90.58825 mm
    *Seat tube extension above top edge of top tube = 40.0 mm (20)
    Extension of outer face of BB from side edge of chainstay = 3.7928886 mm
    Gap between inside edges of chainstays at BB junction = 15.585777 mm


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  9. #9
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    Thanks Thylacine. I've shortened the seat tube extension above the top tube to 30mm. The 77.5 BB drop and 57mm shell is because I'm using an eccentric - I figure I'll lose about 7-8mm from rotating the eccentric upwards to tighten the chain.

    As for more fork rake... well, it's steel, I'll just have to test-ride it and bend it if necessary.

  10. #10
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    Followup: The frame rides great, it's just as carvy as I hoped for. I did get a bit of pedal strike when riding home drunk, and the top tube is definitely 1cm too long, but them's the breaks. Thank you for your advice.

  11. #11
    Map maker cbchess's Avatar
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    How about some pictures!?!

  12. #12
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    As you wish! (it's a bit ugly, I built it up with cheap used parts from the local bike co-ops)
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  13. #13
    Map maker cbchess's Avatar
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    nice!
    where did you order such a custom frame? how much?

  14. #14
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    Three years later on my XACD chinese Ti frame:

    * I specced the BB too low, top tube too long (as I mentioned before)
    * XACD specced the tire clearance symmetrical on top and sides. This resulted in unneccessarily bent chainstays (didn't need 1cm side clearance)
    * Cable guides not ideally placed - rear brake cable guide too close to caliper, Rohloff chainstay guide doesn't secure cable around bends (could be solved be straightening chainstay)
    * Top tube too high - straight top tubes are too 1970s. Should have sloped the top tube 10-15 degrees, and gotten a taller seatpost.
    * Fork was too short. I replaced it with a 410mm carbon fork which works great.

    Other than that, it's been good!

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