gus6464

For those that want even more braking power Shimano just released flat mount versions of their entire MTB lineup and 180mm rotors are now supported. Since they are basically just rebranded Ultegra and DA calipers you will be able to just buy the 180mm flat mount adapter for your current caliper.

https://www.pinkbike.com/news/first-...1-updates.html

But anywho that is a crazy amount of stopping power on a drop bar bike.

msu2001la

Are current disc brakes lacking in power or overheating on long descents? I don't get it.

Unless there's something wrong with your current setup it should be more than sufficient to exceed the available traction and/or throw you over the bars. Larger brakes just seem like they'd add weight.

stevel610 

That was my first thought-more rotational weight. I also have the same question you do as far as current setups be powerful enough.

The bike industry is never at a loss of a new tweak for marketing purposes...

shoota 

The only thing I can think of is that they're thinking about loaded touring? My buddy put some 180mm hydros on his Salsa Vaya when he set it up flat bar and he said it was way beyond overkill. But he's 135lbs so...

gus6464

On an MTB braking is used more often and smaller rotors overheat quicker. While you are not riding your brakes on the road for people who like to ride singletrack with their gravel bikes this will help. This is for the gravel folk who like to take on rougher terrain and not for the road/smooth gravel crowd. Think Grinduro crowd vs Dirty Kanza/BWR.

Also the Shimano Ultegra Freeza rotors are not light because of all those fins to dissipate heat. The 160mm is 134g while an RT66 180mm rotor is 154g. The RT66 with more surface area will cool itself pretty well plus you get the added benefit of more stopping power for 20g penalty which is nothing.

gus6464

Was he using 4 piston ones?

fourfa

Context: I'm 6'2" 200lbs. I live in pretty hilly terrain, every road or gravel ride involves at least a continuous 2000+ft bomber downhill. Sometimes 6-7000 over the day. I routinely spin out my current 46-11 top gear on descents, usually come home with a 45mph high speed, sometimes 50.

The stock 160mm BB7 brakes on my Vaya were a sick joke - as-shipped that bike was never remotely safe to ride at speed for me. 180mm HY/RD front and 180 Spyre rear was better. 203mm HY/RD was pretty good but really caused the steel fork to judder and sing. I mostly rode that bike touring with 30 to 50 lbs of gear.

Current carbon gravel bike with 160mm DA hydros F&R - it's kinda OK but not as good as the 6800 rim brakes on my old road bike. Adjusted a hundred ways, bled a dozen times, faced the fork - just never really enough power to be truly confident. I intend to tour on this one too and I want a sizable safety factor.

I picked up last year's XTR 4-piston caliper to try in front, but haven't installed yet. If this release enables a clean 4-piston 180mm front on a flat-mount fork, I'll be first in line.

fourfa

Ah, sadly looks like no:

https://cyclingtips.com/2020/05/2021...00-m4100-news/
"With all of this, Shimano has released flat mount variants of its two-piston XTR, XT and SLX disc brake callipers. The XTR version (M9110) is designed for a maximum of a 160 mm rotor, while the XT (M8110) and SLX (M7110) variants can handle either 160 or 180 mm rotors. Clearly these products are designed specifically for cross country usage."

So have to choose 180mm 2-piston, or 160mm 4-piston, or try to cobble together some adapters or something if you want both.

dwmckee

I guess I could see it in limited cases. I have been on long and very rough steep gravel decents where you had to brake pretty hard most of the way down to stay in reasonable control, Had to use rear mostly to prevent skidding front on some very loose stuff but this is a pretty limited situation.

msu2001la

Agreed. I've been mountain biking on singletrack trails for 25 years and I've never once overheated a disc brake, but maybe this is more of an issue in some specific cases than I realize.

So, in other words, these will probably become the next "must have" for the gravel bike segment. haha.

Geekage

I like to ride on the hoods, but move to the drops on singletrack or steep stuff, so more power would be useful to allow people like me to stay on the hoods.

Since my bikes are IS mount, I should just get a larger rotor now and see how it works out...