I am looking to buy some used Giant Anyroad 2 2015. The groupset is already upgraded to Shimano 105 2x11, with cassette 11-34t. Crankset are Tiagra. Everything look fine, except the brake, which still using SRAM Avid BB5. Based on some review, SRAM Avid BB5 is having bad review. So I think, i need to upgrade the brake at least to SRAM Avid BB7. But I'm not sure because the Avid BB5 are using 140mm rotor, can I use SRAM Avid BB7 using these rotor, or I should upgrade to 160mm rotor and do I need adapter to upgrade the brake. Need some input.
You can directly change for BB7 without needing new rotors.
If you want 160mm rotors with BB7, you would need new caliper mount adapters. Changing to 160mm rotors will give you slightly more stoping power, but whether it's worth it, is completely subjective.
It's pretty straight forward to do. Once you get the bike, you can ask a specific question about it.
I actually own a 2015 Anyroad Comax frame that I built up so I have some feel for what works on the bike.
On the front I have 160 mm rotors with BB7 road calipers (don’t get the mountain as they will have the wrong pull ratio for road levers). You will need an 20 mm adapter from SRAM, Shimano adapters will not work. 140 mm rotors on the front, with mechanical disc brakes leads to very soft braking, even with compressionless brake cable housing (another recommended add on).
For the rear leave the 140 rotor and just upgraded the caliper. BB5s burn through pads, are hard to adjust (they have no inner pad adjuster) and are substandard for anything but the occasional slow speed ride.
Having a smaller rotor on the back actually balances out the braking forces better so that you are not locking up the rear as easily (the front wheel has most of the traction under braking). Mountain bikes are spec’d with different rotor sizes, not sure why this is avoided by manufacturers for road/gravel bikes.
As for the shifters, 105 is a solid groupo, no change needed. Tiagra cranks are keepers as they shift well, their only short coming is the lack of bling and some extra weight.