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  1. #1
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    Calculating Di2 wire lengths?

    Anyone know of an easy way to calculate Di2 wire lengths? For me, this is the most frustrating part of a Di2 build, is trying to figure out what wire lengths I need.

    The local shops only care a sample of sizes. They always want you to buy what they have and just use the next size up. This works for some things, but makes a mess under the bars, etc...

    I'm hoping someone has a web tool of some kind that you can plug some numbers into and it will spit out a list...

  2. #2
    'brifter' is a lame word.
    Reputation: cxwrench's Avatar
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    Measuring tape? Measuring tape and a piece of string? You're making this too hard.

    I almost always use 350mm for the shifters, 500-550 for the read der, 250 front der, battery and DT wires vary. AFAIC there is no 'perfect' size. I usually go a little long so it's easier to work on later if (when) needed.
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  3. #3
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    Quote Originally Posted by cxwrench View Post
    Measuring tape? Measuring tape and a piece of string? You're making this too hard.

    I almost always use 350mm for the shifters, 500-550 for the read der, 250 front der, battery and DT wires vary. AFAIC there is no 'perfect' size. I usually go a little long so it's easier to work on later if (when) needed.
    Ditto CX, and note you can always cheat on longer with any excess being hidden in the frame (if doing internal). I used 400 on my 44cm wide h-bar. If you use a WiFi/BT unit, you can use a 15mm length at the battery to the BT unit, then whatever is appropriate for where you stash the B junction. Tom H has a good suggestion to wrap the BT unit in a bit of foam to prevent rattle.

  4. #4
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    I would recommend measuring the amount of space you need to cover with the wire and buy the appropriate size.

    Some manufacturers have internal documents that will specify di2 wire length. Specialized does. I'd be surprised if they're the only one. May be worth a phone call to the manufacturer if you want to save a little time measuring.

  5. #5
    'brifter' is a lame word.
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    Quote Originally Posted by masont View Post
    I would recommend measuring the amount of space you need to cover with the wire and buy the appropriate size.

    Some manufacturers have internal documents that will specify di2 wire length. Specialized does. I'd be surprised if they're the only one. May be worth a phone call to the manufacturer if you want to save a little time measuring.
    Trek does for the Madone 9...but it's so easy to figure it out for yourself it's almost not necessary to spend the time finding the info in the first place.
    I work for some bike racers
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  6. #6
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    Just use a measuring tape, and then go 1 or 2 sizes up. You can always tuck the excess into the frame. The extra weight is negligible.

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