Just building my new bike & iam after rotor sizing for rear brake.

Depends on you and the build.

I like ‘assertive’ brakes, so my XS BFe runs a 180mm rear and 203mm front (2012 XTs).

This might well be overkill for most people. Unless you weigh WAY more than me (13 stone or so I guess), 160mm rear and 180mm front ought to me more than enough.

slainte 💡 rob

The BFe doesn’t have a post mount rear brake so you will need to use a mount whatever rotor you use.

As above, use what suits your riding style. I’m a skinny XC mincer so I’m using a 160mm rotor as it also means my wheels are interchangeable with other bikes.

180 front, 160 rear is most common these days. Why not go 180 all round to be different?

183/203 here

Dinner plate 200 on front, 180 rear for me.

203’s all round 🙂

Don’t know about the latest iteration of the Bfe but the last one had a limit of 180mm for a rear rotor. I’ve got a hope 183mm in mine and there’s definitely no room for anything bigger!

203mm/180mm here.
More than enough for my riding!

depends on many things, your weight, riding style and most of all the brakes…

I tend to run 160/140 with modern brakes cos they’re so powerful anyway and absolutely HATE brakes with too much bite, I find using smaller rotors helps calm them down and I don’t have issues with overheating, bizarrely pads seem to last longer too :-s

I’ll run 180/160 if they are a bit older and not quite as powerful, eg older hope minis etc.

I tried 200mm rotors for a while but they just upset me by being too powerful and too grabby, but with most bike things it’s personal preference, easy enough to go up or down anyway.