SRAM and Quarq power meter spiders are typically paired with DUB crank arms and a SRAM DUB bottom bracket. This is SRAM’s newest interface and is the one we recommend for most frames. However, SRAM doesn’t offer a DUB bottom bracket for Trek BB90 bikes. So if you have a Trek BB90, you have two options:
1) Purchase a DUB bottom bracket from companies like Kogel or Ceramic Speed.
2) Purchase a set of SRAM GXP (24 MM) 8-bolt crank arms to use with your Quarq power meter. The GXP cranks would fit your Trek BB90 bike assuming you have or install a compatible bottom bracket. For GXP crank arms, you have two options:
SRAM Red GXP Crank Arms
SRAM Force GXP Crank Arms