"vertical compliance" acceleration and comfort

Discussion in 'Cycling Equipment' started by woodgab, Feb 6, 2006.

  1. woodgab

    woodgab New Member

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    I test rode a Seven Axiom over the weekend and had many impressions but what stuck was this aspect, of the four that Seven customizes. The frame was a "signature", or their spec model and had a "3" rating out of 10, 10 being most stiff and 1 being most shock absorbing.

    I'll first size up that I was coming off a reasonably light 853 steel Fuji, which should ride somewhat like ti. What got me was how the Seven was stiffer in the bottom bracket, but was much more plush over bumps. Not entirely a good thing, I latter thought.

    Vertical compliance, if I understand it, refers to a bike's ability to flex when shocked upward, or downward and not laterally (BB). My concern is what to make of the notion that it comes at the expense of sprint/climb efficiency, since the bike stretches out and contracts more under load, instead of better road transfer.

    Am I crazy and should I only worry about a stiff bottom bracket, is Seven's standard bike a Century plus, baby boomer, model, or has Seven thrown a curve ball by being efficient in one respect while not in another?

    BTW, the bike had almost no character to its ride. Very damp. I guess I was expecting ti to perform like a Stradavarious.

    Chris
    PS-I'm dealing with leftover pricing and can't afford custom.
     
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  2. artmichalek

    artmichalek New Member

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    Vertical compliance is marketing nonsense. Diamond frame bikes are essentially rigid in plane. Under any kind of load the vertical deflection of the wheels is orders of magnitude larger than that of the frame. Efficiency loss is the result of of torsional flex. People tend to focus on the bb, but the seat/chain stays have just as much to do with it. Lateral flex only affects handling. The plush feeling of a ti frame going over a bump is the result of high frequency vibration atenuation, and is not inherently related to efficiency.
     
  3. alienator

    alienator Well-Known Member

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    Yup. What he said. Also, without riding bikes with the same wheelset, same tires, and same inflation pressure, it's tough to say where the ride difference is coming from. After that, you have to contend w/ fork differences.
     
  4. woodgab

    woodgab New Member

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    ... and weight differences. My bike was on fully inflated Open Pro's and so was the Seven. Besides that, I'd be curious what others think. While I agree that the diamond shaped frame doesn't give much on the vertical plane, I do think close to 200lbs exerts its toll on said plane when spread over the entire wheelbase.
     
  5. artmichalek

    artmichalek New Member

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    It doesn't. Loading in plane, you're going start fracturing welds before you get more than a few microns of deflection.
     
  6. dhk

    dhk New Member

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    Agree with the observations here. Increased high-frequency damping may be a feature of Ti (and CF) vs. thin-walled steel tubing, but that isn't the same as flex or vertical compliance. On the other hand, the front forks will deflect in response to vertical inputs; believe the fork is where most of the perceived frame "ride quality" comes from. (Tires, pressures, and wheels of course play a big role).

    In "bounce tests" on the garage floor, have observed my CF fork defects less, and has more damping than the steel fork on my older bike. Dropping the front wheel of the steel bike from a height of 3 inches produces noticeable deflection and vibration in the fork which you can see. The buzzing vibration is felt in the handlebars, and takes a second or two to die out. On the other hand, the Ouzo Pro fork deflects less, vibrates less, and damps out almost immediately.
     
  7. Insight Driver

    Insight Driver New Member

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    Listen to the other posters. A triangle (the three main tubes) is very stiff vertically. You do not flex that triangle no matter what your weight is. Granted, there will be small movement, but, as pointed out, tire deflection is so much greater than any movement of the triangle that it totally dominates the perception you have. Fork flex and minor seat-stay flex adds just a tiny bit. Very flexible sidewall tires make the most difference. A frame does not soak up bumps, it transmits them. If you rode on steel wheels you could tell a slight difference between frames, but all would be harsh to ride.
     
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