1. ## XTR Dynasis compatability?

im looking to get my hands on a xtr double drivetrain. My plan is to run a 42/30 up front and run the 11-36 casseste in the rear. i'm setting it up on a hardtail 29er with a chainstay length of 17.72. my question is about the rear derailler. should it be the mid cage or the long cage? im assuming the mid is for double drivetrains and the long is for triple but i'm looking to run the 42 up front so im on edge before i order.

Any input would be greatly appreciated!

2. with a 11-36 cass i would deffently go long, with a double. for me the only time your going to get away with a med cage would be eather a smaller cass. or single up front !

3. A mid cage will work fine. I've seen people use dura-ace derailleurs with 2x setups.

4. Cage length determines the total capacity of the derailleur, that is the size difference between the largest and smallest chainrings, and the size difference between the largest and smallest sprockets on the cogset, added together. A larger sum requires a longer cage length.

For a 42/30 crankset and a 11-36 cassette, that would be (42-30)+(36-11)= 37T capacity

Manufacturer stated derailleur capacities are as follows: Shimano long = 45T; medium = 33T SRAM long = 43T; medium = 37T; short = 30T

5. Long cage it is. Thanks that equation is very very helpful!

6. Most derailleurs are under rated by two teeth from the real maximum of what they can truly accept.
http://www.bikepro.com/products/rear...lleurover.html

7. Keep in mind that the Bike Pro derailleur article dates back to the early days when 30T cogs were just being introduced in 7 and 8 speed cassettes that had been 12-28T, so that 2T extra capacity relates to 739 and 950 series XTR derailleurs. Now that we're up to disc rotor size big cogs the amount of excess capacity tolerance may not be as large or consistent in all drivetrain scenarios.

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