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I'm looking to adapt my 160mm post mount front fork to accept a 180mm rotor.

As I'm looking between adapters, I find them falling into two very distinct categories, and I'm wondering if there are any trade offs or reasons for preferring one style over the other.

The first style bolts to the 160mm post mounts with separate standard length bolts, then juts out farther and drops down to accept the brake with standard length bolts.

Dual Mount Adapter

The second looks smaller and lighter, and comes with longer bolts and rounded washers that go through both the brakes and the adapter and into the 160mm post mount.

Through Mount Adapter

Here is the difference when mounted:

Dual Mount Adapter - On Bike Through Mount Adapter - On Bike

Would there be any particular advantages of one way or another?

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    Well, the first guess has to be "Two incompatible engineering solutions to the same problem; this is normal."
    – David Richerby
    Commented Feb 23, 2018 at 10:56
  • Those were my initial thoughts as well, in which case I think the through bolt version is probably lighter due to less material in the adapter and only one pair of bolts, as long as everything else is equal. They do put the caliper in a different positions, and the bolts aren't meeting the caliper in a perpendicular fashion on the through bolt version.
    – Ehryk
    Commented Feb 23, 2018 at 21:53
  • I prefer the second solution as the caliper is tucked closer to the fork (lever actions, stiffer, vibrations etc - overall looks better engineering), the first solution has the caliper adapter dropping below the fork and more exposed to rock strike. (Enough that it matters, probably not, who knows?)
    – mattnz
    Commented Feb 24, 2018 at 8:35
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    There is a difference in how the caliper gets angled wrt to the disc, depending on the shape of the pads one system might have a bigger pad contact area than the other one. Just guessing here..
    – stijn
    Commented Feb 24, 2018 at 8:45
  • Is the first (red) one for a rear brake and designed to make the caliper fit around the seat stay?
    – brendan
    Commented Feb 27, 2018 at 15:44

1 Answer 1

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While I can't find anything from Shimano themselves, this description is used in regards to the second one on a number of websites selling them (so perhaps it is in Shimano's sales literature?):

2nd version of adaptor, lighter and better hose routing

Since this is the best I can find, I'm posting it here as an answer, but by all means if someone else finds more details post that up.

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