[Dan89]

hey
so i need a chainguide for my sx trail and i want to get the blackspire NS-1, but i dont know what size to get and what mount(bb mount or iscg mount)....
94mm, 104mm, and 110 mm are the sizes but i dont know how it is measured...


thanks,
Dan

 

[binary visions]

There's only one 4-bolt standard: 104mm. If you have 4-bolt cranks, it's 104mm.

If you have 5-bolt cranks, it'll be one of the others and the measurement is taken by the diameter of the mounting spider. So, measure from the center of one bolt hole (on the spider) to the center of the BB mounting bolt, and double it.

Your SX trail has an ISCG mount, so you can use either kind of mount. I prefer BB mount since, if you hit the chainguide really hard, it won't damage the frame.

Hope that helps!

 

[Dan89]

Hey thanks the answer!

 

[gastro]

I prefer BB mount since, if you hit the chainguide really hard, it won't damage the frame.

That makes perfect sense. FWIW, I ended up going with an MRP System 3 using the ISCG - foolhardy, perhaps, but I really can't see tweaking this forged assembly:

 

[binary visions]

That makes perfect sense. FWIW, I ended up going with an MRP System 3 using the ISCG - foolhardy, perhaps, but I really can't see tweaking this forged assembly:

Well, here's the way I see it - and I mentioned this in a recent thread - no matter what, you're eventually going to whack your chainguide, hard. That force has to go somewhere, so there's going to be a "weak link" in the equation.

You're right, that looks like a burly setup and it sure doesn't look like it'll break. So, if you're lucky, all of the bolts will shear off and you'll just have to figure out how to extract the headless bolts from the ISCG holes. If you're unlucky, the bolts won't shear off, all the force will be transmitted into the boomerang, and you'll be replacing an $80 MRP backplate.

I'll tell you, it sure makes for an easier installation though! I don't think going with the ISCG mount is foolhardy, you're simply doing a tradeoff - easier installation and resistance to moving on the small hits, at the risk of breaking something on the big hits. But hey, it's mountain biking - something is always breaking anyway