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Making some custom rear dropouts (vertical) for a project (nonstandard bike, they must be custom) and as I look to dropout examples, I notice that "vertical" dropouts never seem to have the slots completely vertical, as in 90 degrees from horizontal. Is there a reason for this? My design keeps the slots perfectly vertical for ease of drafting, cutting, etc.

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Likely to clear the derailleur. Angling the dropouts somewhat gives more clearance between the derailleur and the cassette as the wheel is being removed or installed.

While the derailleur could also be moved more rearward and upward to provide the same clearance, that would reduce the length of chain that engages the sprockets.

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  • Hadn't though of that. It's only a few mm in most cases that I've seen, but maybe that's enough to matter. I'll throw a derailleur and wheel onto a straight slot and see if it matters for my use.
    – user36575
    Dec 19, 2018 at 15:28
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    Furthermore maybe also to differentiate from 'horizontal' drop-outs (that are not always horizontal) where the wheel can be moved back and forth, whereas in 'vertical' ones it sits in one position.
    – Carel
    Dec 19, 2018 at 17:25
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The angle is to do with the rear derailleur shifting requirements. The vertical is actually measured from the center of the axle to the outside of the hanger, hence the slight angle. You'll find the Shimano framebuilders specs here very useful, you may be able to get the angle closer to vertical depending on the thickness of your derailleur hanger: http://www.peterverdone.com/wiki/images/7/7f/Dropout-Configuration--web.jpg

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  • I've got those specs (and used them in my design) and I thought maybe it mattered too, but then I looked at all the movable axle bikes out there (where the derailleur mount stays put but the axles move quite a bit) and I figured it can't matter that much. Then, I looked at some of the custom dropouts on some of my custom bikes, and they're all over the place, way out of that Shimano spec. All shift well. I'll find out soon enough if my more vertical dropouts matter. I'm bonding the chainstays on with carbon fiber today, and I'll fit a wheel and derailleur after that to see how things go.
    – user36575
    Jan 19, 2019 at 17:55
  • I designed the bike to have bolt-on dropouts, so worst case scenario, I'm just dancing with the hacksaw and file another afternoon to remake the dropouts with more of a forward lean.
    – user36575
    Jan 19, 2019 at 17:57

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