[andrewface]

Can someone help me out with this? What length of mounting bolts do I need to directly post mount (180mm rotor) a shimano brake caliper to a rockshox pike? Can't figure this out with a google search and it's driving me crazy! thanks in advance.

 

[kevin_sbay]

20mm should work with you. I was just in same situation as you, to install my new Pike (180mm brake mount; no adapter).

Most any bike shop should have such bolts, maybe even just laying around as spares.

For my situation, I bought some:
https://www.amazon.com/gp/product/B06Y3XZ4C6/

 

[Cleaner]

A general rule for threaded fasteners to be safe (steel bolt into aluminum thread) is 2x the nominal diameter of the fastener. i.e. if you have a M3 bolt then you want at least 7.5 mm of thread engagement length. This 2x ratio should give a factor of safety.

The design principle is that the bolt should fail before the female thread shears. Since you likely have a steel bolt going into a softer and lower strength hole you should add a bit of engagement if possible.

Your fork lower is likely magnesium so I would run a minimum of 2.5x engagement unless the spec indicates otherwise. Ideally you should check with the fork manufacturer for specification.

 

[cobba]

EV documents for brake calipers list M6 x 18.7mm for Caliper Fixing Screws.

https://si.shimano.com/