So, building my mini DH bike and I thought I had a set of 4 piston 8120’s, alas they’re 8100 2 piston brakes.
I found a single 8120 caliper so I can swap that in the front but I’m wondering if, rather than sourcing and swapping the rear also, I just run a 220mm rotor out back?

Or, with 220mm is 2 pistons enough both ends?

Having read something on Enduro mag I think it was, the suggestion was to run 203 front 220 rear with 4 pots all round. Better modulation front, more heat dissipation rear

The big rotor on the rear idea is only relevant if you are overheating the rear brake. If it were me, I’d try it with the 4-pot on the front and the 2-pot on the back and see how it went. If you already have 200 mm rotors, try them and see how it goes. If you already have 220 mm rotors, you might as well use them, but I would try the bits you have before buying new stuff because of something you read in an internet article. If I had one 220 mm rotor and one 200 mm rotor, I’d put the bigger one up front because that’s the brake you rely on most when you really need to stop in a hurry. Having the same sized rotors front and rear means that you only need one spare rotor in your tool box instead of two different ones.

Are the 8100s really that bad?

Your usage’ll be different to mine no doubt but, there seems to be a lot of weirdness about brakes these days… E-bike weight aside, anyway. I mean, my dh bike and my enduro bike both have the same decade old 2-pots on them, 203/180 (160 on the little bike) and they never miss a beat. Good power, fantastic modulation, no heat issues with dirt-cheap pads and standard metal discs. Light, too. I’ve tried a bunch of the new breed and none of them’s been obviously better… It seems like it’s all just a long-solved problem that suddenly’s been unsolved and apparently needs new tech or more pots or bigger rotors to do the same job?

Especially with Shimano and SRAM, is “2 more pots” really what we were all crying out for? Or was it “Just make them bloody reliable”.

Nothing wrong with 2 piston brakes for trail use that’s for sure. I’ve 8000 xts on my Solaris 203/180 and they’re better power wise than my 203/180 xtr 4’s. Previous DH builds have always been saint/zee builds and bonkers powered Gustav before that

Ive had 4/203fr, 2/180rr m8000 brakes on a ransom built for trail use and on the bike park i was definately wanting more….likely due to having to spend check against gravity when behind the kids..although that’s changing pretty quickly now.
Will give what I have a go.
Cheers

I ran 200mm rotors on 2 pot SLX on my DH bike and it was absolutely fine at Revo and in Morzine, even on Porridge