Total Drivetrain Capacity

SRAM has specific Total Drivetrain Capacity (TDC) ranges they use to figure out when to use which size derailleur. TDC is a number that is the sum of the tooth differentials on both the cassette and chainrings. Let's say you have an 11-34 cassette. take 34 subtract 11 and you're left with 23. Then you have a 44/32/22 combo up front. Take 44 subtract 22 and you're left with 22. Add the differential in the rear to the differential in the front, 23 + 22 and you get 45, which is TDC.

TDC Expressed as an Equation


TDC= (biggest cog minus smallest cog) + (biggest chainring minus smallest chainring)
You might be wondering what will happen if you go with the wrong size. If you have less capacity in your derailleur than you need, you'll end up having to choose between having the chain loose on the small ring and smallest cogs or having the derailleur break on the big ring and biggest cogs. If you have more capacity than you need, you'll just be running more chain than necessary.


Short TDC = 30t capacity

Medium TDC = 37t capacity

Long TDC = 45t capacity

OK J'ai trouvé la réponse à ma question.
La formule est (grand plateau - petit plateau) + (grand pignon - petit pignon)
Puisque j'ai remplacé mon grand plateau par un bashguard, ça me donne:
(32-22)+(34-11)=33.
Un medium est donc suffisant.

Lol, beat me to it.