How can I tell my chain is the right length for an oversized derailleur cage?
First of all: installing an oversized pulley cage requires you to switch to a longer chain. The long cage and large wheels demand extra chain links compared to the stock setup.
An oversized system uses a chain sold at retail at almost full length: 114 links, give or take a few, depending on your frame and chain ring setup.
The easiest way to set this up is to run the chain through the derailleur, over the smallest chain ring and smallest cog on the cassette. Leave the open ends at the bottom, just underneath the chain stay.
Next, measure the chain so it leaves a little tension in the chain. When you’re connecting the two ends of the chain, you can see the cage moving forward when it is starting to build up tension.
Running the chain at this length guarantees the longest chain for your setup, which means the lowest spring tension in your derailleur. Low spring tension equals low drag. (link to installation video when available)