Originally Posted by
cobba
Why didn't you just buy an adapter for the 180mm rotor?
Because I was at the mercy of what the bike shops had in stock. I went to 4 bike shops and this was the best that the 4th bike shop could come up with. They assured me it was the correct one. It turns out it was the correct one for a 185mm rotor, but I didn't realize that for a few years. A the 2.5 mm larger radius of a 185mm rotor was just the easier fix, since I needed a rotor anyway. So that's what I did. I do see what you are saying. A 17.5 upper/10 lower should be proper for a SRAM/Avid caliper on a 180mm rotor. But this caliper is a TRP caliper and a 185 rotor, hence the 12.5 lower post to compensate for difference in my installation. If the proper 10 mm post was included in the package the bike shop handed me, I surely would have used that & saved all the trouble. Page 8 illustration 25S of the pdf you linked to is the closest illustration the installation I have. I got here by way of experimentation & empirical evidence to derive the best fit. I believe I have succeeded.
If you ever want to replace the rotor, there won't be much of a choice in what you can get.
I'll cross that bridge when I get there. There is hardly anything more common than a post mount adapter & now that I have access to QBP, JBI and the other usual suppliers, none if this is likely to be an issue.
Do the pads overhang the rotor by a couple of mm or do they have full contact?
Nope. the peak of the shark fin edge is about 1/4 to 1/2 mm taller than the top of the pad. Full contact. It's not unusual to have a few mm of unworn area stabilizing rotor edge in the area you seem concerned about. I set up 6 bikes this way today. It is done so that if the rotor wears too thin it doesn't shred to Chantilly lace & self destruct leaving the bike operator with no brakes at all. Something has to connect the rotor spokes to each other to share the braking load.