[jdkrause]

It's been a while since I've been on here and trolled through the various posts about gearing, but I seem to remember folks converting their 3x9 cranksets to 2x9. I thought (and could be way off) that they were installing a 38, 40, or 42 to the middle position and a 26 or 28 to the inside, replacing the granny ring. I tried this with a 28 and 42, but ran into issues with the larger 'ring contacting the chain stay. I don't feel comfortable adding another spacer to the drive-side bottom bracket cup as I've got 2 there already. Am I missing something? Is this setup even possible with my current frame/drivetrain?
Thoughts?

'08 Niner Air Nine (scandium)
'09 XT drivetrain (22, 32, 44 crankset (M770?))

My ultimate goal is to find a more-useable gearing for the type of riding I do. I don't necessarily want to drop my larger ring below 40-42.

J

 

[jeffj]

Shimano SLX 28/40 is available, and XTR has both 28/40 and 30/42. However, the chainline on the XTR 2x (46.8mm) is 2mm less than it is on the SLX 2x (48.8mm).

Deore also lists a 28/40 2x crankset, but the chainline numbers are not published anywhere I could find them.

IIRC, your 09' XT crankset would likely have a 50mm chainline, but remember that the chainline for a 3x crankset is measured at the middle ring, and for a 2x crankset, it's measured halfway between the two chainrings.

Race Face makes a 28/40 2x Turbine crankset with 80mm/120mm BCD and has a chainline that is adjustable from 48.5mm to 50.5mm. That is a fair bit wider than your XT crankset's chainline, and with the 40t instead of a 42t, it might be the best chance for you to get what you're looking for.

Of course I am e-speculating based on what I see on their websites, and you'll need to double check this stuff for yourself ;~)

 

[Thor29]

Yeah, chainline is the key here. Most of us that go 2x from a 3x setup just take the big ring off. If you want to run bigger rings then you probably need to get a crankset that's made to run 2x like the ones mentioned.