LOL good timing, just dropped down to 140mm in front of my Systemsix!

How much do you weigh? Any long or technical descents in your rides? 140mm on the front with the enormous kinetic energy of road riding?, well, you're a braver soul than me ...

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That's what happens when marketing made you think disc brakes are a bullet proof braking system. Unnecessary risk.

What DSW said!

My priorities vary depending on the activity but typically for racing:

1. Safety
2. Performance
3. Reliability (of non safety critical stuff)
4. Aesthetics

But for many people it seems to be more like:

1. Aesthetics
2. Performance
3. Safety
4. Reliability

Interesting how they completely sidestepped the issue of spoke count.

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"They're made of latex, not nitroglycerin"

140mm seems to be the worst of all worlds.
You get poor braking and you have the extra weight, more difficult set up and maintenance and possibly poorer aerodynamics compared to rim brakes.

I've ridden a ton of miles on Jet Blacks and 140 mm disc rotors. I'd say that the 140 rotor is still better at everything than a black turbine rim brake. 160's are obviously on another level....a huge step up in power for sure.

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24 Hour World TT Champs-American record holder
Fat Bike Worlds - Race Director
Insta: chris.s.apex

How much do you weigh? What kind of terrain? Any technical or extended steep downhills? What brakes specifically (i.e., what calipers, brand, model, etc.)?

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Exactly, 140mm hydro's(Sram Red) on a good bike will out stop any rim brake, I prefer the modulation of the 140mm front anyways. I can see an argument if you were heavy and riding cable operated disc.

Let's look at actual data instead of "impressions"...

This chart seems to imply otherwise (note that the disk is 160mm in the test, a 140mm rotor would produce a curve only ~88% of that...braking force for a given lever/clamping force is proportional to the diameter)...and that's comparing to what I would describe as a "non-optimized" rim braking setup

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http://bikeblather.blogspot.com/

145 pounds in full race trim.

I rode 20,000 miles last year. I did 2 full on full speed descents down Mt. Evans this past summer with the HED Blacks (Trek Madone). Yes I went up 2 times that day as well. Yes they work well. They just as good as 140mm rotors. Not for me anyway on the most technical of descents. All I could think of all the way down Evans was I hope my rims don't get so hot and blow the inner tube. It's happened to me before.

I've also done gravel racing up to 240 miles with some ~50mph gravel descending on my Domane. So plenty of clicks on both rim and disc this year.

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24 Hour World TT Champs-American record holder
Fat Bike Worlds - Race Director
Insta: chris.s.apex

Wait, you rode down mt evans at full speed on HED blacks with rim brakes?

Or rode down at full speed with 140mm rotors with disc brakes?

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Evans on the HED Blacks.

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24 Hour World TT Champs-American record holder
Fat Bike Worlds - Race Director
Insta: chris.s.apex

So is that with rim brakes, or with disc brakes?

(not sure if HED black rims come on disc brake wheels or not ... )

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Jeepers...sorry for the confusion. My fault.

My HED Blacks are the TURBINE RIM track. I descended full out 2 times on Mt. Evans in the cross winds twice the same day with that setup.

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24 Hour World TT Champs-American record holder
Fat Bike Worlds - Race Director
Insta: chris.s.apex

Sure, I have full confidence in the HED blacks with optimized rim brakes.

But have you ever gone down mt evans at full speed in the summer with 140mm rotors on disc brakes ?! That is the more interesting question ...

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Just my thought! Not to mention that positive vs. negative yaw angles will yield different results...

I'd be curious to see whatever the particular changes they claim to have made to the rim for the disc version...and if that shape actually couldn't be used with a rim brake.

A quick perusal of the rim dimensions they give doesn't indicate they're drastically different. I bet whatever the shape is, it would be just fine as a braking surface.

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http://bikeblather.blogspot.com/

I presume you mean that you bet the shape could be used for rim braking rather than that the disk wheel as built could be used for rim braking? I assume disc brake specific wheels will not be designed to cater for compression of the rim by rim brake pads or the removal of material over time due to wear.
I would personally be in favour of a rather perpendicular application of the brakes to avoid unnecessary radial strain on the brakes. That would provide a limitation on the ability to aerodynamically optimise the rim.
Is your view that....

1. The angle of pad application is not important?
2. There is no significant benefit to taking brake tracks out of the mix?
3. Both of the above?

Wait, I though the rotor diameter has nothing to do with the braking force, only the thermal capacity, and that lever/clamping force was more a product of the piston diameter?

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"They're made of latex, not nitroglycerin"

That chart is showing braking force at the tire/road interface. As such, braking force is a function of the braking torque at the braking surface, which is a function of disc diameter.

Think of it this way...if rotor diameter doesn't have to do with braking force, then why are there different sized rotors in the first place, and with more demanding applications using the larger ones? ;-)

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http://bikeblather.blogspot.com/

#3. I'm talking about the shape, not the underlying structure. Rim braking on angled/curved brake tracks has been happening for quite some time now...

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http://bikeblather.blogspot.com/

Think of it in terms of leverage: the smaller the rotor diameter, the longer the lever of the wheel is relative to the brake caliper.

Bigger rotor has more mass and can absorb more of the energy that is converted from kinetic to thermal during braking. Also has more surface area to radiate that thermal energy to the atmosphere. You go "big" to avoid overheating when the mass is higher and/or the likely use case is repeated or long, continuous braking events. In terms of braking force on a single stop where you're not approaching the thermal capacity of the rotor, it's a non-issue.

In a past life, I did a lot of autocross racing. In classes where it's allowed, many racers downsize their brakes from stock. Why would a racer want smaller brakes on their cars? Because the kind of racing we were doing was short (45-75 second) runs through a tight course, followed by a 5-10 minute cooling off period, and we didn't need the thermal capacity of large rotors. We could get all the brake torque we could ever want for the two or three corners on course where a high-g deceleration was called for, but would benefit everywhere else from the lower weight (particularly so, because it was "unsprung" weight). Put us on a traditional racetrack with those brakes, however, and we'd have overheated those brakes in a lap or two.

It's flat as all getout where I live. What few hills we have are typically short and on straight or gently curving roads. I have no doubt I would do just fine around with 140mm front rotors on my bike, even though I'm +/-85 kilos. Out in Summit County, CO, where we vacation? I wouldn't think of it.

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"They're made of latex, not nitroglycerin"