A Bit More Geometry...

Discussion in 'Track Racing' started by Snicks, May 9, 2011.

  1. Snicks

    Snicks New Member

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    So, I've had a look around the net but I can't seem to find anything definitive - could someone explain to me bottom bracket/crank clearance for a track bike, and how this differs from road. I was considering possible converting a TT frame that I have (so it already has horizontal dropouts) to use in IP's, but am unsure as to how the clearance for the bottom bracket, and thus whether or not the crank/pedal would work for this. If anyone could explain a little further - i.e. minimum clearance required etc etc that would be awesome...
    P.S. Should it matter, almost 100% of my time I will be riding a 250m track :)
     
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  2. alfeng

    alfeng Well-Known Member

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    FWIW. This is NOT definitive ...

    If you are planning to use your TT bike on a track -- presuming the track operator allows it -- then you may find yourself quickly moving as many of the components (crank + possibly the wheels) to a "true" Track frame sooner rather than later ...

    Most Track frames exhibit the design legacy established decades ago ...

    • The REAR dropout spacing is generally 120mm. Your TT bike undoubtedly has 130mm rear spacing ... although spaced for a 120mm rear hub, it appears that the single-sided MICHE Track hub (at least, the one that I have which is gathering dust) can be laced symmetrically for a 130mm spaced frame because the flanges are set slightly wider apart ...
    • Surly makes Flip-Flop hubs for various width dropouts (and therefore, wider chainlines) ...
    • The "standard" Flip-Flop hub seems to be designed for a frame with 120mm rear spacing
    • Most older Freewheel hubs can be used for SS applications -- either Freewheel or Fixed Cog

    I believe that the Bottom Bracket is almost always higher on a Track frame -- that is, expect a BB "drop" of about 55mm (+/-) ... you quickly can identify this comparatively minimal drop by the almost horizontal rear chain stay (a vintage 26" 3-speed and/or 26" Hardtail will have a similar chain stay angle).

    Unless you get some really short, Circus-Clown cranks, then your pedals will probably interfere with riding anywhere on a track except closer-than-not to the line painted on the inner edge of the track.

    The head tube angle on a Track bike is usually about 74º ... much steeper than I believe the angle of your TT frame's head tube. For simply riding around the track, the angle probably isn't a factor, but once you get into strategic riding, it probably makes a huge difference.

    Your track's operator can elaborate.
     
  3. Snicks

    Snicks New Member

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    Okay, no problems thanks for the help guys. I think my biggest issue, as you have said alfeng will be finding a rear wheel where spacing will be appropriate... Hmmm will look into it...
    Though geometry otherwise shouldnt be an issue - as it is I'm only planning on using it for IP, and my TT position is already very very aggressive (one of the perks of being young i suppose) Thanks for the help but guys, will look into it...
     
  4. alfeng

    alfeng Well-Known Member

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    BTW. Because a rear "track" hub will have a solid axle, if you can achieve a satisfactory chainline with your cosmetic choice of which shoulder you mount the chainring on (you can, BTW) with a standard track hub, then you can simply put a 5mm spacer between the cones & nuts on each side of the hub to accommodate the 130mm rear dropout spacing ...

    • It appears that many people put their chainring on the inner shoulder to achieve a straight chainline
    • you do not have to dish the wheel symmetrically, so that is an option, too
    • except for the hollow axle & quick release, you could use most vintage Freewheel-type rear hubs (e.g., a Campagnolo Nuovo Record rear hub)

    FYI. The SURLY hubs which have wider flanges result in the Cog-or-Freewheel being mounted more outboard than on a traditional "track" hub ... mostly, I think they were originally (?) designed for SS MTBs which have aluminum frames but there may have been another reason ...

    You will have to ask your track's operator if a front wheel with a quick release is acceptable, or not.

    There are 3/32" track cogs available ... but, you'll probably want to use something more robust (and cheaper) than a 10-speed chain.
     
  5. keyon

    keyon New Member

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    he purpose built track has been engineered in Germany by Velotrack, the team that built the velodromes for the Atlanta Olympics and the Delhi Commonwealth Games. The Red Bull Mini Drome track will maintain race-worthy
     
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