Sunday, 9 October 2011

Measuring Effective Top Tube & Fork Length

The calculator works well with Focus Bikes data for example, as they measure the effective top tube (ETT) and fork length (FL) as I would. As seen in the Focus Izalco geometry table: ETT is measured from top of head tube C-C and FL from axle to bottom of head tube C-C.

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Other companies measure ETT differently. Cervelo measure slightly below the head tube, along the center axis of the virtual top tube.

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The calculator does not account for the difference in measuring the ETT. It can be calculated, but difference tiny, less than half a millimeter. And there's no difference if the seat tube angle and head tube are parallel.

3 comments:

  1. What does stem length, stem angle and fork length have to do with stack and reach of the frame?

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  2. Hi, fork length is used to calculate stack/reach for frames that don't have that info published.

    Stem angle is used the calculate the stack/reach of the stem. This is added the the frame's stack and reach. Mainly used to compare fit of bikes, as you want to compare them from the centre of BB to centre of stem. E.g you want your new Trek to have the similar stack/reach as your old Specialized. This is assuming you use the same handlebars and shifter position.

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  3. What does the calculation in the second set (headset+spacers+stem stack*0.5) mean? The numbers do not appear to actually be adding headset length to spacer length to half the stem stack, so I dont know what for sure to do with this value. Also the units vary from mm to cm all over the calculator and when downloaded you cant see the formulas (not an excel expert) so its hard to tell if everything is behaving correctly. Dont get me wrong, its the best I've seen by a long shot, I just want to make sure Im approaching it right before dropping cash on a stem for the new frame.

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