"Effective" Top Tube Length- Mtbr.com
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  1. #1
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    "Effective" Top Tube Length

    An intersting topic IMO.

    More and more frame builders/bike companys list their bikes 'effective TT', often totuing that the same frame can accomodate a wide variety of rider heights/sizes. Some even are so bold as to describe it as adjustable sizing when there is a seat mast with multiple positions. YES its a customizable feature, an adjustability - NO it is not a means of sizing the bike up (or down).

    My respsons? INANE. The relationship of the BB position and distance from there to the handlebars is the critical sizing factor that defines whether or not a bike fits, and in turn where your weight/COG will be.

    Moving the seat up/back due to a 66deg seat tube moves the riders weight back, and pedaling posotion back - but only in a seated position.

    1 - this does not equal a fit, but simply gives room so you dont bang knees, etc but is far from ideal for the described purpose.

    2 - when the hell am I seated on DH or FR bike for any significant portion of technical riding?

    --

    Obviously I have a strong, passionate opinion -- how do you feel? what do you think.

  2. #2
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    I agree with you 100%.

    Effective top tube means nothing on a bike that sees little seat time. The relationship between the two touch points (cranks and bars) is most important. Some BMX companies used this measurement. It is often referred to as "rider area". Another somewhat useful measurement is "front center". The length between the BB and fron axle. Of course this will vary with fork length and head tube angle.

    My large Yeti AS-X with a 24" ETT and 67 seat angle feels very different from my 4X bike with a 23.5 ETT and 72 seat angle.

  3. #3
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    Quote Originally Posted by Huck Banzai
    often totuing that the same frame can accomodate a wide variety of rider heights/sizes. Some even are so bold as to describe it as adjustable sizing when there is a seat mast with multiple positions.
    Nobody's done that for years.

    I measure downtubes. ETTs are useless.
    STRAVA: Enabling dorks everywhere to get trails shut down........ all for the sake of a race on the internet.

  4. #4
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    Quote Originally Posted by kidwoo
    Nobody's done that for years.

    I measure downtubes. ETTs are useless.
    How do we get the industry to do this? TT lenghth as a sizing measure is massively outdated since bikes are so non-standardized.

    I still see companies claiming that a slack ST angle allows for an adjustable ETT and thusly vary in sizing. I dont see the seat mast solution any more, happily!

    Waah.. ok.. focussing...

  5. #5
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    Quote Originally Posted by Huck Banzai
    How do we get the industry to do this? TT lenghth as a sizing measure is massively outdated since bikes are so non-standardized.

    I still see companies claiming that a slack ST angle allows for an adjustable ETT and thusly vary in sizing. I dont see the seat mast solution any more, happily!

    Waah.. ok.. focussing...

    This topic has been beaten down pretty thoroghly both on here and on ridemonkey. Do a search for my username, 'effective', downtube etc and you'll probably find a good bit.


    The answer is who cares what the industry does. Find the bike you're interested in and take a downtube measurement and compare it to what you're currently on. Bikes with similar angles like dh bikes will offer similar comparisons.

    Comparing your xc bike to your dh bike won't do you much good because the angle of the headtubes affect the handlebar placement too differently.

    I've been measuring bikes like this for years. It all started when I bought a karpiel that was too small for me. It had an adjustable seat mast and half the morons I talked to just said 'move the seat tower back'

    So yeah, I needed a seat independent measurement. Bottom bracket center to the intersection of the centered lines of the downtube and headtube. Like I said, on bikes with similar angles this gives you a comparison of where your hands will be relative to your feet.
    STRAVA: Enabling dorks everywhere to get trails shut down........ all for the sake of a race on the internet.

  6. #6
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    Yeah, to make things more confusing, some bikes have non-straight seat tubes (and setback seatpost), so the effective TT is based on "effective" SA!

  7. #7
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    As for EFTT, some manufactures include seatpost setback in the effective TT length and others do not. Including setback in the EFTT is bogus IMO since seatpost, stem, handlebars are user tweaks to a given frame geometry.

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    This is all a huge pain. The only way to tell if a bike fits is to ride it and that never happens with expensive bikes because local shops don't stock them.

    So all we have to go buy are these inadequate geometry specs. And since almost no one has given bottom bracket to headtube measurements, we have nothing to compare. I got in an argument with DT about this when he wouldn't give me an effective top tube measurement for the new DHR. He said it was a useless measurement but it is the only thing I can compare to other bikes. I crossed my fingers, whipped out the plastic and got a new DHR and it fits. It is kind of stupid to have to buy high end bikes this way.

    Forget the measurements, we need test ride centers.

    OT - The DHR rocks! more bike than I deserve.

  9. #9
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    I posted this same thing in the spring. I think that measuring the DT is useless as well cause the length can stay the same, but if the angle changes, it will make a world of a difference. the measurements needed are from the steerer tube back to the BB (measured horizontally) and the height difference from the BB to the ETT height.

    Canfield is the only company I've seen step up to this important measurement so far. Fahn
    Hubbard Bike Club

  10. #10
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    Quote Originally Posted by LarryFahn
    I posted this same thing in the spring. I think that measuring the DT is useless as well cause the length and angle can change and make a world of a difference.

    Canfield is the only company I've seen step up to this important measurement so far. Fahn
    Kidwoos response regarding taking that measurement from bikes with comparable geometry makes sense for me.

    The tricky thing is, as with so many other things, the MFR will inevitably add their subjective considerations and start reporting Effective measurements rather than actual if they ever started providing this.

    I think im going to continue to inspect, compare and jusge rather than just look at the #'s; I recently got all huffy because SC changed (or appeared to change) geo on the new chameleon. I hadnt taken into consideration that the #'s reflected a fork with a 2.5" greater a2c than the #'s for the previous model (old was based on 100mm fork, new on 160mm fork) although they DID make it .5 degs slacker and the XL is .5" longer (Gravy, now I can runa 50mm instead of a 70!)

  11. #11
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    turner now lists front center measurements on their web page for the dhr, with no eftt!
    it is a start....

  12. #12
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    I've seen Turner's DHR has a measurment from BB to bottom center of the head tube. It's close but I feel the top center to BB is the best measurment. From top center, the fork angle doesn't affect the fit. It's your bars to your bb center thats the fit your looking for, completely seperate from geometry.

  13. #13
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    Quote Originally Posted by LarryFahn
    I posted this same thing in the spring. I think that measuring the DT is useless as well cause the length can stay the same, but if the angle changes, it will make a world of a difference.

    What part of this

    Bikes with similar angles like dh bikes will offer similar comparisons.

    Comparing your xc bike to your dh bike won't do you much good because the angle of the headtubes affect the handlebar placement too differently.
    did you not see?

    Quote Originally Posted by LarryFahn
    the measurements needed are from the steerer tube back to the BB (measured horizontally) and the height difference from the BB to the ETT height.

    Canfield is the only company I've seen step up to this important measurement so far. Fahn
    This would work, but would be even farther from a likely new standard because it entails three measurements. The two you listed plus making sure your ETT is truly horizontal......one of the initial downfalls of the current system.

    And where on the 'steerer tube' would you measure? I'm assuming you meant headtube? If it's anywhere other than an intersection, you're going to fall prey to variances in headtube lengths between manufacturers.
    STRAVA: Enabling dorks everywhere to get trails shut down........ all for the sake of a race on the internet.

  14. #14
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    Your prolly right but, at least it is a step in the right direction...or maybe not at all?
    Whatchou think?

  15. #15
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    Quote Originally Posted by flymybike
    I've seen Turner's DHR has a measurment from BB to bottom center of the head tube. It's close but I feel the top center to BB is the best measurment. From top center, the fork angle doesn't affect the fit. It's your bars to your bb center thats the fit your looking for, completely seperate from geometry.

    But again, this is subject to headtube length.

    That's why I do the intersection of the lines. Length of headtube above or below is irrelevant.

    Anyway......these are all similar measurements that are by far better sizing methods than an ETT measurement. Especially for bikes you ride standing up most of the time.
    STRAVA: Enabling dorks everywhere to get trails shut down........ all for the sake of a race on the internet.

  16. #16
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    Front center measurements are a step in the right direction, but for me I prefer to know where my pedals and hands are going to be.

    There should be a way to number this. Maybe measure center of the BB up to a "head tube height" line or something. (Dependant on a axel to crown height, and head tube length of course.)

    A up and down measurement, and a horizontal measurement at the same time... How's everyone's brain doing so far?
    Quote Originally Posted by kidwoo
    The internet sounds like a tough place to ride.

  17. #17
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    I think this should be just like buying a nice suit....if you are going to drop that kind of money on a bike then you should go into a shop have them measure you leg length torso length and arm length or something like that. Another alternative is companies could put out a jig(not the right term but I couldnt think of anything better) where they have sort of an adjustable frame to see what size you need. I dont know if those would ork though, im just throwing some ideas out there...

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