Just realized the irony of disc brakes on an aero bike.

[Ed-B]

Originally Posted by zmalwo

....The whole purpose of an aero bike is to use them....where constant speed is high enough that the aero advantage of aero tubes offsets the weight penalty....caliper brakes would offer better aero gain than disc brake, as well as reducing overall weight.... But since everything in the bike industry is about marketing and forced gear retirement, the manufactures probably don't want you to know this.....

See, with a little editing, the theory in the original post is true, and the poster vindicated! (I just needed to clip out the parts about flat roads and relative braking performance.)

Originally Posted by Mark McM

This seems to be borne out by a recent Tour Magazine test of the latest aero bikes. A link to the test and a discussion of it can be found here:

https://weightweenies.starbike.com/f...p?f=3&t=154692

Here's a summary of the results:



The aero road bikes from every manufacturer in the test got slower when they redesigned it for disc brakes, except for Cannondale. But even for the Cannondale, they redesigned and re-optimized the entire bike, so who knows whether redesigning and re-optimizing around rim brakes wouldn't be faster still?

I've read the Cervelo white paper on the S5 Disc, which claims that the S5 Disc is faster than the previous S5 (no surprise there - every manufacturer claims their new bike is better than their old bike). But if you look closer, you'll see that they changed many aspects of the design (such as routing all the cables internally through the special stem, headset and fork). They mention how much power each change saved, and it adds up to more than the power saved by the whole bike - which implies that switching from rim to disc resulted in a power loss, for which they had to redesign other parts to make up for.

[ergott]

All tested at 45kph:

2019 Cannondale SystemSix Disc - 203w
2016 Trek Madone - 204w
2016 Specialized Venge ViAS - 204w
2016 Cervelo S5 - 205w
2016 Felt AR FRD - 205w
2019 Cervelo S5 Disc - 206w
2016 Canyon Aeroad - 208w
2019 Specialized Venge Disc - 208w
2016 Giant Propel Advanced SL - 210w
2016 Scott Foil Premium - 211w
2016 BMC Time Machine - 211w
2016 Look 795 - 212w
2019 Trek Madone Disc - 212w
2019 Ridley Noah Fast Disc - 213w

Unless these were all tested in the same session there's too much margin of error to be valid.

[echappist]

Originally Posted by ergott

Unless these were all tested in the same session there's too much margin of error to be valid.

someone on slowtwitch independently stated (with evidence, though can't seem to find it right now), that the older Trek Madone was more aero. He expressly advised that I buy a new old stock Madone rim-brake when I was contemplating buying a new bike, stating that neither the newer rim-brake nor the disc-brake matched the older rim-brake. That was why this report resonated

[ergott]

Originally Posted by echappist

someone on slowtwitch independently stated (with evidence, though can't seem to find it right now), that the older Trek Madone was more aero. He expressly advised that I buy a new old stock Madone rim-brake when I was contemplating buying a new bike, stating that neither the newer rim-brake nor the disc-brake matched the older rim-brake. That was why this report resonated

Okay that was said, but based on what evidence? Unless they were tested side by side in the same wind tunnel session it's inconclusive. Trek isn't going to spend time testing that (or publishing if that's the case). I doubt any privateer would spend the time/money.

[ergott]

Even if it was tested properly and the results were 8w I personally would prefer the disc bike. I tried the rim brakes on the Madone once and wasn't impressed. I sure as heck wouldn't want to service cable brakes on that bike either. Once installed, there's really no reason to ever go in and replace any of the disc brake system year to year.

[echappist]

Originally Posted by ergott

Okay that was said, but based on what evidence? Unless they were tested side by side in the same wind tunnel session it's inconclusive. Trek isn't going to spend time testing that (or publishing if that's the case). I doubt any privateer would spend the time/money.

apparently Trek's own white paper

http://trek.scene7.com/is/content/Tr...aper_EN-GB.pdf

note that the difference is well on marginal (1% faster for the older one), but this doesn't add all lend credence to the assertion that disc-brake frameset is faster

[Bonesbrigade]

Originally Posted by ergott

Unless these were all tested in the same session there's too much margin of error to be valid.

All this tells me is that for each manufacturer the rim and disc versions are pretty damn close and not worth getting excited about. You are free to choose which version you want with basically no aero penalty.

As much as I love my rim brakes and don’t really see the point of discs on a pure road bike, I don’t think the big manufacturers will be putting much R&D into rim brake optimization. Almost all the world tour teams are on disc this season.

[ergott]

Final new Madone
numbers show an average of 3,216 g across a -12.5° to
12.5° yaw sweep vs the current Madone at 3,202 g. A 14 g
difference that is within Trek’s project goal and within a wind
tunnel’s experimental error band.

Within margin of error. That's not a clear difference.

Hey I'm skeptical that any of those bikes are significantly faster than my old Cervelo S2. I've got much smaller frontal surface area on this bike than the current fat tubes used.

[bikinchris]

Wait...how are these people up in arms over disc brakes, but they are okay with direct mount brakes?

[Bonesbrigade]

I would tend to agree with the S2 being hard to beat aero wise. I’m still using my 2008 cervelo SLC-SL and my my soloist team. They are both getting long in the tooth though.

[echappist]

Originally Posted by ergott

Within margin of error. That's not a clear difference.

which is to say, we shouldn't trust the ad copy saying that disc-brake is faster

i don't know about your riding style and attributes, but i was the type to go for any little aero advantage possible back when I raced. I couldn't accumulate points from sprinting, so I had to get away solo or in a small group, and aero helps there.

The S2 was ahead of its times, and i'd venture that few framesets represent a significant upgrade over yours (earlier S5 being one of those)

only minor quibble is that you can save a bit more by using an aero road brake such as the Tririg Omega

[Mark McM]

Originally Posted by Bonesbrigade

Almost all the world tour teams are on disc this season.

I guess that's what the bike company marketers want you to believe (and it looks like you've been drinking the Kool Aid). But when this was discussed a few weeks ago, it was found that the majority of world tour teams are not using disc brake bikes (10 out of 18). Of the other 8 teams, 4 are using a mix of rim and disc brakes, and only 4 are using disc brakes exclusively.

https://forums.thepaceline.net/showthread.php?t=233038


I suspect that it has nothing to do with extra aero drag, and the reason racers use rim brakes instead of discs is similar to why they use tubular tires instead of clinchers:



By many measures clincher tires give a performance advantage over tubulars because clinchers have lower rolling resistance (and also often lower aero drag as well),

BUT:

The performance advantage of clinchers over tubulars is very small, and because clinchers are more prone to pinch flats and can't be ridden as fast when flat, the risk of losing a lot of time due to flat clinchers is of greater concern than gaining a little bit of time due to their lower rolling resistance.




By many measures disc brakes can give better braking performance than rim brakes, by giving more consistent brake performance over a wider range of conditions.

BUT:

The time gained due to the braking performance of disc brakes over rim brakes is very small, and because disc wheels are slower to change and disc brake wheels have more interchangeability issues, the risk of losing a lot of time with disc brake wheels in case of flat tire or other wheel problem is of greater concern than gaining a little bit of time due to their more consistent performance.

[Burnette]

Originally Posted by vqdriver

relax guys. everyone's had shower thoughts that withered in the light of day.

besides, we all know coaster brakes are the most aero.

Coaster brakes were so rad!

[ergott]

Originally Posted by echappist

which is to say, we shouldn't trust the ad copy saying that disc-brake is faster



only minor quibble is that you can save a bit more by using an aero road brake such as the Tririg Omega

Agree on both accounts. I'd say all these aero bikes are pretty damn slick compared to the old, round tubed bikes.

You can get very close to these car-priced bikes for a lot less.

I've been thinking about a more aero front brake for a while.

Sent from my SM-G950U using Tapatalk

[Bonesbrigade]

Ha, ha no kool aid here! I’m still happily using my 2005 and 2008 cervelos for road cycling. I could care less to be honest, but it doesn’t take a genius to see where this trend is going regardless of the actual number of teams using disc bikes right now.

I’ve seen this story play out in the bike biz with many changing standards over the years.

It’s clear to me that the majority of R&D is going into disc brake bikes and not rim brake bikes regardless how anyone feels about it.