So I'm looking at the Shimano 2x10 front derailleurs, and I noticed they specify a top gear teeth count of 44-38T. Apparently these are intended to be used with their 26/38 cranksets. Let's assume I'm not manly enough (easy assumption) to push a 26T granny, and I swap out the chainrings for 22/34 and lower the derailleur accordingly. Do you foresee any issues with this? Just wondering why they would spec out a top gear teeth count like that.
On a hard tail, I don't see why this wouldn't work. Now on a Full suspension bike, if you lower the front derailluer, the guide cage may come in contact with the chainstay upon suspension cycling. At least that's what I ran into with a 2x9 set up on my ventana. your results may vary. I think if you spec out a double specific front DR, then the guide cage may be shorter to alleviate some of this.
I am no expert but I am sure it has to do w/ the leverage per pull of the FD, it's "optimized" to work in a specific range of gears - they're obviously not saying it wont work . However, don't those 2x specific cranks run different BCD spacing as well? Your challenge will be finding the chainrings to fit the right BCD, I doubt you can go as low as 34, 38 may be the smallest.
The "Trail" versions of the Shimano 2x10 cranks (XT M785, XTR M980) actually are 64/104. It's the "Race" versions that are 88BCD. I'm also wondering if they don't like the angle the chain may be coming through the derailleur at with a 22T chaining. Hmmm...
iunno if I read it wrong, but unless you're planning on racing and motoring the whole time, don't they recommend just getting the triple? I'm pretty sure the XTR has a 22T granny on it already. if you want 2x, you can just put on a bash if its a standard BCD (which is a better way to go for trail riding anyway IMO). update the middle ring to a 34 and bob's your uncle. sell off the middle and big rings and make back a bunch of your money. Plus, a 26/36 granny combo really isnt that high. it's about the equivalent of a 22/30 (a little easier actually). If you have a lightweight/climbing oriented bike, it shouldn't be a problem. I used to run 22/28 on my reignX and that thing would climb anything without too much fuss, and it weighed in at around 38 lbs with a DH build...
I've converted my crank the way bryguy describes. Bike came with 22/32/44. I never use the 44, so I upsized my middle ring to 36 and replaced the 44 with a bashguard. It's been working pretty well so far. I've been lazy and haven't even adjusted my derailleur limits yet.
