History of ISCG

Discussion in 'Downhill & Freeride' started by PhilipW, Dec 10, 2009.

  1. PhilipW

    PhilipW Monkey

    0 / 0
    Mar 13, 2007
    Leominster, MA
    The official International Standard Chain Guide mounting interface has had several major revisions since its inception in 2000. As ISCG has been a source of confusion for consumers as the years progress, we at e*thirteen components felt it is time for a refresher on the current standards being used, as well as a little bit of background information. :thumb:

    The original ISCG pattern was created in 2000 in a collaborative effort between Bob Barnett of Mr. Dirt and the engineers at MountainSpeed/MRP. While extremely well received by the industry, the design had several features that allowed for interpretation of the standard. Downhill racing technology had also evolved to the point where technical steep race courses became common, putting a demand on the ISCG interface. The following picture is of the standard currently used by many companies, called ISCG/ISCG-03/ISCG-OLD.

    We (as an industry) saw the need for a new mounting interface, and so we decided to start with a clean sheet of paper and incorporate everything that we had learned about chainguides and mounting since 2000. In April of 2003, the basis of a new standard was proposed. Industry wide, there was much great feedback given. At Interbike 2003, members of the ISCG 05 consortium met in person and discussed the details of this proposed new standard. Revisions were made, and ISCG 05 was officially created.

    The goals for this new ISCG 05 standard were multifold. This new standard improves on the original ISCG in several important ways:

    1. The ISCG 05 is compatible with all currently available bottom bracket types that we are aware of. Drawings are provided for standard european, BMX, and ISIS Overdrive designs, in both aluminum and steel materials to take advantage of each materials properties. The new ISCG 05 is broad enough in its scope that other types may be easily integrated in the future (BB-30, press fit). This addition offers simplified chainguide installation for shops and consumers and aims to cut down on chainguide model variations industry wide.

    2. The ISCG-05 standard tab clocking is now defined in relation to an imaginary line running from the center of the bottom bracket shell to the center of the rear wheel. This clocking method is identical to that used with conventional derailleurs, and aims to eliminate the guesswork that plagued the past standard. Big thanks to James Gardner and Dan Connors at Cannondale for this well thought out addition to the standard.

    3. Tab thicknesses, tab offset, and tab parallelism to the bottom bracket face are now all defined simply and completely. This aims to eliminate the guesswork that previous ISCG users faced. Tab thickness was increased from 3.5mm to 8mm thick for aluminum frames for extra durability. The additional tab thickness resists twisting on angled chainguide hits. Tab offset is only in 2.5mm increments.

    4. A new larger 73mm bolt circle diameter makes for more robust mounting. ISCG 05 frame tabs can be lighter for the same strength, or stronger for the same weight versus previous incarnations. Chainguide rotation is far less possible as well.

    5. Outside vendor supplied ISCG-05 adapter plates are now governed by a 2.5mm thick mounting width. This allows simplified setup for consumers using external cup bottom brackets like the Raceface X-Type and Shimano Saint. Big thanks to Bryn Johnson from Raceface for this forward thinking addition.
    #1 -   Dec 10, 2009
    Last edited: Jan 29, 2010

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