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  1. #1
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    experienced framebuilders: need some help on road fixed gear bicycle geometry

    Hey everyone,


    I posted this question in the fixed gear / single speed forums a couple days ago, but people told me I would be better off / get better answers asking in the framebuilder section, so here we go:


    Im about to start working on a new frame which is going to be my fixed gear bicycle; but I need some advice on the frame geometry.

    This fixed gear bike is mostly going to be ridden around town, used on roads, I might take it to our local velodrome, too, but yeah its mostly going to be for road use.

    Still, from the feel and how it rides, reacts; I want this fixed gear bicycle to ride like a track bike, or very similar to it: a fast racing geometry, agile, twitchy, responsive.


    So what Ive been wondering: Can I therefore just copy the main characteristics of track geometry onto this frame which im about to build?
    Or are there a couple things which feel that way on the track, will feel different on the road and therefore need to be adjusted or changed a little bit for road use?


    Heres what Ive been thinking: Keep the short wheelbase and the steep angles, to make the bike twitchy and responsive. Keep the high bottom bracket, too, to avoid pedal strikes in turns. However, although keeping the angles steep, still make them a little less extreme, to generate a more relaxed riding position for more comfort. Also make the headtube a touch longer, to make the sattle / bar drop a little less sharp, which should also create a little more comfortable ride.


    Would you agree with that? If not, what would you change?


    .. I know its a bit of a wall of text, but thanks a lot for reading, posting info and helping out!

    cheers

    Fabian

  2. #2
    Framebuilder
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    I think you're on the right track. How relaxed or "road like" you want your new bike to be is up to you. Where will you ride it the most?
    Also, keep in mind that track bikes are made to be ridden in a racing position, you don't have to turn the bars much, and there are no hills in the velodrome.

  3. #3
    Randomhead
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    In my experience, track bikes are not actually twitchy. Low rake makes for high trail, which is actually more stable. You hear the opposite a lot, it isn't generally true. Of course, the short rake is counteracted by steeper angles. But on a track, you really want to be going forward, not sideways.

  4. #4
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    I did most of my track racing on relatively relaxed frames. Especially for someone specializing in longer races, "road" geometry works fine.

    So the short answer is that the bike the OP envisions will be just fine for his purposes - but so will an aggressive "sprint" geometry and a relaxed "road" geometry.

  5. #5
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    I
    think you're on the right track. How relaxed or "road like" you want your new bike to be is up to you. Where will you ride it the most?
    It will mostly be ridden around town. Its not for big distances, but more to quickly get from point A to B. Bobbing and weaving through traffic, sprint over a cross section, pass that slow van, dodge that motorbike .. I love to race through town and be quicker than the cars in traffic =) .. it really should be a fast, aggressive racing geometry, agile and responsive, sprints.

    Thats why I figured I would copy most of the geometry from a track bike, cause thats what I imagine a track (sprint) bike should feel like.

    Still, of course if I ride my bike its not about making money and I dont have to fight for fractions of seconds; so I dont need a super extreme track geometry which will be very fast, but also very uncomfortable outside the velodrome. So yeah what Im trying to achieve is a geometry which keeps the fast racing aspect of track geometry, but softens it a bit for road / town use.


    A typical track headtube angle is around 75 degrees (?), so I was thinking maybe 74, 74.5 in my case; for a bit more relaxed position.. ? (when road is around 73, 73.5 ..)

    Also, by how much would you lengthen the headtube to make the saddle / bar drop less extreme / more confortable?


    In my experience, track bikes are not actually twitchy. Low rake makes for high trail, which is actually more stable. You hear the opposite a lot, it isn't generally true. Of course, the short rake is counteracted by steeper angles. But on a track, you really want to be going forward, not sideways.
    Of course, but you still want your bike to be responsive enough to be able to quickly dodge and get around a falling racer in front of you... so a track bike would be stable but still be pretty agile .. ?

  6. #6
    Framebuilder
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    Well, a lot of what you're asking falls into the design part of custom framebuilding and I get a lot more info and measurements from a customer before I can determine things like seat tube angle/bar drop/wheelbase, etc.
    I can tell you about my own preferences for road-going fixed gears:
    -Higher bars are always good for general riding.
    -Low trail/high rake forks and steeper (74) hta's rule for quick steering because fixed gears will never see road bike speeds.
    -A high bottom bracket feels good when you stand to sprint and let's you turn sharper- the raising of your cg and how it affects handling is a moot point because, once again, you can't take a corner as fast as a road bike so you might as well maximize your clearance.
    -Forward facing semi-horizontal drops are much more practical...must be why nobody wants them

    Is this the last frame you'll ever build? Why not experiment some? Build two frames with different angles/fork rakes and compare them back to back. Swap forks and try it again....that's what I did. Only it was more like 10 frames.

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