Cable Routing – Experimental Results



















  • Route cables to minimize total change in direction.



A few closing disclaimers and comments:




6 thoughts on “Cable Routing – Experimental Results”

  1. Killa, that was an interesting experiment re: cable routing.
    I have one for you, which I haven’t found a satisfactorily scientifically derived answer to.
    Are disc brakes really any better than linear-pull rim brakes?
    Disc brakes can be significantly more powerful than rim brakes, given that you don’t have to worry about either crushing the rim or stressing whatever the brakes are attached to (the fork or the frame’s rear triangle).
    But… it seems to me that the very small circumference of a disc-brake disc, versus the widest-possible circumference of the rim would negate much, or even all the advantage of the increased power that discs give.
    After all, it’s not raw power that we want in brakes – it’s the modulation that all that power affords. And it’s much easier to slow or stop a spinning wheel at its widest diameter/circumference than near its center.

    Looking forward to your next experiment!

    1. Hi Fred! Thanks for the comment. You’ve got me interested. Your first question “Are disc brakes really any better than linear-pull rim brakes?” Is impossible to answer without a technical definition of “better”. I googled “disc vs rim” and got like a gazillion hits. One more forum on all the pro’s and con’s won’t add anything new, so I won’t go there.

      What intrigued me is the question you raise about the radius difference. There is no doubt that disc brakes can generate more stopping force at the tire/road (or trail) interface, for better or worse. The question is, how can a disc with a ~180mm diameter generate more stopping force than a rim brake with a diameter of 622mm – using the same hand force and range of motion – without breaking the laws of physics? I’ve got some ideas, but I want to take some measurements and do some calculations before I answer. I’ll post something in the next day or two.

      1. Glad to see I’ve piqued your interest! I think what defines “better” in braking boils down to increased modulation. You’ll notice that sports cars not only have bigger, stronger calipers and pistons, but they also have larger diameter discs. Why? Even smaller disc brakes will lock (let’s leave ABS out of the picture for now). Similarly, any linear-pull brake on the front wheel has of any bike I’ve ever ridden has enough stopping force to lock the wheel at speed, and make the bike skid in a turn (on a loose or slippery surface) or make the bike flip over. And any caliper-type of brake (not just linear pull) that I’ve ever ridden can lock and make the rear wheel skid. So the raw stopping force is not what’s at issue. It’s how well you can modulate that stopping force — as in increments. Let’s say 0 is not braking, and 10 is a locked brake. A poorly modulated brake might go directly from 9 (braking very hard but still safely braking) to 10 (locked). But a better modulated brake might let you get to 9.5, or even 9.9, before going to 10. And something that makes modulation even more important is that what constitutes a “10” changes with the weather, the road surface and the condition of the tire. So you have to have better modulation throughout the entire range. To go back to the ABS issue in cars, nothing really changes here — the point is to modulate more precisely up to the point where the ABS has to kick in.

      2. I think it’s about leverage, or mechanical advantage.

        Brake lever has a fixed travel length, for obvious reasons:
        – one limiting factor is an average hand length, so the lever can’t be very far from the bars.
        – the other is the very existence of bars, a lever can only travel until it hits the bars (preferably, operating range should be even smaller, so that the lever can be operated with one or two fingers, not squeezing the other fingers still left on the bars).

        So this leaves playing with the pad travel length. Disk brakes enable placing the pads much closer, so instead of traveling a few mm, they travel up to one mm, usually sitting even closer than that to the disk. Hydraulic system has other advantages on top of that, like elimination of cable friction, but the main benefit of disk vs rim brakes is the higher mechanical advantage due to significantly shorter pad travel distance.

        Rim brakes need to be placed a bit further away from the rim, since the wheel will move more on the outer part – wheel flexing a bit under loads, not being 100% true etc.

  2. There are a number of variables to consider, mechanical advantage at the lever, mechanical advantage at the caliper, brake surface area, coefficient of friction of the pad, material of the braking surface or coefficient of friction of the braking surface and travel. That is just the braking system. I would not be surprised to find that the diameter of the disk is related to temperature while braking.

    Then there is the issue of forces generated and applied to the fork and frame all the way down to the hub. Your definitely don’t want radial spoke pattern for a disk brake!

    1. Patrick,
      Thanks for the comment. The torque load that a disc (or any other hub-mounted) brake system applies to the spokes is especially interesting to me.
      It would be fun to lace up a disc wheel radially and see how much windup occurs.. and how long it takes the spokes to rip thru the eyelets.

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