Seemed like a poorly designed test to me - Only one run per disk vs rim bike in dry and wet conditions each. Plus the guy admits that he had more confidence descending on the disk bike. That by itself could account for the differences. It would be difficult to conceal which bike was being ridden like in some of the aero vs regular frame tests for "feel". Disks sound and feel too different.

I won't say that GCN does science as much as they collect anecdotal evidence. Nothing wrong with that but I would think that really demonstrating difference between the two braking systems would require some pretty careful analysis.

Not hard science, but certainly food for thought.

But some huge problems with this test:

The rim brakes are very significantly handicapped. Rim brakes on carbon rims are generally poor, and they are absolute sh*t on carbon rims in the wet. But rim brakes with optimal brake pads on AL rims are excellent, and they're pretty reasonable on AL rims in the wet (again, this is with the right rim brake pads; with bad pads this is not case).

It would really be interesting to see this test repeated with both systems optimized but with, say, a 215 lb rider in 95 deg temps and direct summer sun. I wonder how things would pan out then. Because disc brakes have some, uh, interesting (i.e., very scary) failure modes in high heat and high brake loads ...

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These plots from SRAM is about all you need to know about the validity of that video. The Red caliper isn't even the strongest rim brake they make, and braking on wet carbon sucks. Throw a HydroR rim brake and a wheel with a PEO coated or machined/textured alu track in the mix, and it's quite possible it could leapfrog the disc performance...seriously.

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Sigh....

I do't even know where to start, there are so many things wrong with this testing/analysis.

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Was thinking this too, that an alum brake track could hAve a real difference in that test.

It's "citizen science" for sure, though they recognize the lack of proper sample size and variables at play. Anecdotal evidence, I like that term. Food for thought. Gotta love GCN!

I feel discs are the future for a reason other than better brake "feel". Its the liberties it gives in terms of frame making. If all anecdotal or real-world evidence points to GENERAL aero and braking performance equality between the two (in dry weather - I think it's already accepted discs are better in wet), discs are going to win because of what you can do with tire clearances and other frame subtleties that come about when you aren't burdened by the need to put a caliper on there. Rims will follow and get better due to no need for brake track, so on, so forth. I don't think this point is news to anyone, and certainly it isn't to GCN, but its worth noting anywhere when having a "are discs the future" discussion. It's not just about the braking.

GCN does science.

HAHAHAHAHAHA!!!!

Carbon rim brakes are shit in the wet? Two weeks ago I did a nice mountain descent -6 to -10% for 13mi. in the rain no less and found my Enve (clincher) wheels performed wonderfully. Granted I wasn't racing but we did reach 42mph on a couple of the straights. Had lot of turns so I got a chance to really test the braking. Other than more lever effort I did't find the braking lacked modulation or strength. My son led the way down on Zipp 404's and never heard a complaint from him either. He left me for dead by the way, so his speed was greater by a bit. I have a gravel/cross bike with discs so they are not alien to me. I just feel they aren't head and shoulders above the rim brakes. Equal IMO. But I believe the terms safety and modulation are grossly overused by the journalists and marketing people. Prudent use of the equipment you have and the mental capacity to use it are far more important issues. Could I have gone quicker on discs? I doubt it. Ultimate grip is decided by my tire choice right?

Tom, when I saw what wheels they were using for the rim brakes I immediately thought of you and these exact reply. Why not use the best rim brake options vs the best disc brake options. I know why they don't because the results would not be close any longer.

It's because no one rides AL rims any more. smh

My $0.02 on road bike disc vs rim brakes: disc brakes are marginally better for stopping power in the wet and noticeably better for modulation\feel
They're roughly equal in the dry

I have a stable of road bikes with mix of carbon and Al wheels; and one commuter bike with a set of really low end Tektro mech discs brakes.

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res, non verba

"GCN Does Science"

LOL

So scientific they didn't bother to use the same depth rims for both bikes (how hard could it have been to find 303 NSWs?)

I'm sorry, but those are both "marketing points" put out that have no basis in fact. Frames and rim brakes have always had the ability to be easily designed accommodate tire sizes up to the point you probably don't want to be on a road bike anyway. It's only in recent decades that frame designers didn't leave space for wider tires in frames and forks, and the current batch of road calipers are all typically what is known as "short reach" models (which can still accommodate tires up to 28mm wide, typically). What used to be known as "Standard", or mid-reach brakes can easily accommodate tires >30mm wide. In fact, I have a 1986 Bianchi road bike that fits 30mm wide tires front and rear with no problems.

The whole "rim shapes can change if you don't have to brake on them" speculation is really just wishful thinking...look at the high end aero rims right now. They all basically ignore the fact that the brake track is there, in regards to the shape, and they form nice smooth airfoil shapes already. How would they change that to make them more aero? Make them LESS like an airfoil?? Makes no sense...

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This Slowtwitch article from less than a year ago is a better analysis

http://www.slowtwitch.com/Tech/Disc_and_Rim_Brake_Aero_Drag_6073.html


The GNC guys provide more of a personal or anecdotal look at the difference and how it feels.


For me, much to the contrary of Nick over at Tririg who insists rim brakes are more areo than disc brakes and purposefully overlooks data showing this not be true, I believe based on the slowtwitch study I linked above that rim and disc brakes are nearly identical in terms of aerodynamics. Both can be made to be more aero with fairings such as Tririg does with its rim brakes and Parlee does with disc brakes.


So, if they are aerodynamically similar, then we need to look at other factors. I believe from much experience that disc brakes are better than rim brakes. I am not legally allowed to say more due to the terms of a settlement with a major manufacturer and their rim brakes, but I can assure you that rim brakes are not as safe as disc brakes. I have been in one collision with an oncoming car due to rim brakes and if anyone reading this decides to use disc brakes instead of rim brakes an avoids one accident, their training will be better and their racing better without knowing the alternative of being in the hospital and missing months of training and racing.


Beyond accidents though, rim brakes can be limiting. There was one race I stopped even though I was leading my age group by about 30 minutes because the wet hilly conditions were too unsafe in my opinion for using rim brakes. Also, there are many times in training that conditions are wet when disc brakes are much better and since I use carbon wheels for racing, even when it is dry, disc brakes are better than rim brakes on carbon rims. I also dislike changing over the brake pads when I change over my wheels from training aluminum wheels to carbon race wheels, but this is minor and not as important as the safety factors.


If you only race in dry conditions on aluminum rims, than I could see rim brakes being a better option. If you ever have a wet race or you ever train in the rain or you have carbon wheels, I see disc brakes being better. My concern about disc brakes is not their superiority, but the lack of availability on triathlon bikes right now. I think the three triathlon bikes with disc brakes - the Cervelo, Diamondback and Parlee are all great bikes. But, for me, they are all quite expensive. My current bike is a 2004 Cannondale Ironman that I bought for $650 and updated the components to SRAM Red mechanical 10 meaning I am not a $10K bike kind of guy.

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2018 Races: IM Santa Rosa, Vineman Monte Rio, Lake Tahoe 70.3

Very true!

Anecdotes presented as science can be very misleading.

Another issue with disc brakes:

Have you ever tried to switch out a traditional rear wheel and then have had to curse the fact that different manufacturers can't seem to put their freehub bodies in the same point in space on their hubs? And then you had to completely re-adjust your shifter indexing?

Well, get ready for a lot more hassle. Disc brakes have much much closer tolerances to where the disc rotor cam be in space. If that rotor is off by even a little bit, you gotta completely re-adjust (sometimes move) the disc caliper assembly. Every single time you switch out to a different brand of rear hub.

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I'll go ahead and warn you of the following statements about to come your way:

• You weren't using HED Jets
• You weren't using HED Jet Blacks
• Your brake pads were not Koolstop Salmon
• Your levers weren't good enough
• Carbon in the rain makes you dumb
• You could have avoided your accident with metal brake tracks
• The study you linked to by Damon Rinard is bogus because "it's not best in class" on either bike
• With the right pads and right rim you could have stopped faster (which basically means you should have been on HED Jets because apparently that's the only "best in class" rim ever used in these discussions)
• Disc brakes aren't aero
• You don't know what you are talking about because you are not a mechanical engineer
• Damon Rinard is basically lying to everyone and trying to sell bikes. Funny how the anti-disc brake crowd loved him when he worked for Cervelo developing rim brakes
• The bike manufacturers have this conspiracy to sell more bikes
• The statements from Cam Piper, Damon Rinard, Karl Hall, and others who are experts in their field mean nothing because they are "pro-disc brake"
• Kiley's Wind Tunnel shootout results are pointless because the disc brakes weren't taken off to show how much faster a P5-X might really be
• Only Tom A. can approve of what bikes and wheels anyone can ride
• and the list goes on and on and on and on
  

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lol the anti-disc brake people sound like the anti-full suspension people, the anti-V brake people, the anti-disc brake on mountain bike people, the anti-power meter people. Nice to see some things remain the same even as the bikes get better.

#confirmation bias

Don't forget the anti-electronic shifting people! Now, everyone wants it and can't imagine life without it. The reality is people hate change.

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To clarify, I was using metal rims on Mavic wheels when I had my accident. I was not using Kool Stop pads, if I had been, I probably would have been ok since it was dry and they are very good pads. I cannot disclose the pads I was using.

In the race I stopped I was using carbon aero wheels, like most triathletes. I was using the brake pads specified by the manufacturer and that combination was not safe enough for me, given the wet and hilly conditions with the problem being rim braking on carbon and not the wheel or pad manufacturer.

In terms of the study, it is not "bogus" specifically because it does not compare best in class. Best in class wasn't available at the time of the study for disc brakes and so it would have been comparing apples to oranges to use best in class rim brakes vs non-aero disc brakes. By using equivalent class rim and disc brakes it created a neutral study. I don't think we have seen best in class disc brakes, but the new SRAM hydraulic brakes and levers and the Parlee disc brake fairing cover are a big step in that direction and could be on the level of aero development by what I believe is best in class aero rim brakes: Tririg's Omega brakes. Redoing that study with top of class rim and disc braked would be a good idea. But, at the time, the best study option was to use rim brakes equitable to the disc brakes available at the time. If they had done anything other than that, it would have created a bogus study whereas the way they did it makes it the exact opposite of bogus.

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2018 Races: IM Santa Rosa, Vineman Monte Rio, Lake Tahoe 70.3

Ummm...no.

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I'd find memes to post but it's not really worth my time

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But it WAS worth your time to type out your Strawmen? Whatever...

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Yup. See: Speed Concept, Look 796 (below), others



Hard to see where a compromise was made on that head tube or fork.

Here's the problem with disc brakes supposedly freeing up the design of rims:
1. Disc brakes need more spokes and more spokes = more drag. This wasn't accounted for in Kiley's otherwise excellent wind tunnel study.
2. The only thing disc brakes would let you do with rim shape is move more lift to toward the leading edge of the wheel which has the unfortunate side effect of making for twitchy wheels in crosswinds.
3. The "wider, wider, wider" argument is not without consequence and the notion that wider tires are always faster is bunk.

IMO the only way you could get additional speed out of some sort of hub braking (disc or drum) is if you went with an asymmetrical design like the Rafael TT bike. Even then the gains are likely very marginal. The best bet to make a bike faster at this point is likely to optimize the tire/rim/frame system. Even then the gains are likely very small. Somebody should probably go out and copy the old Speed Concept 7.0 tube profile, dump some money into dies, stamp L/R sides of frames, weld them together using some of the very slick new welding tech, melonite them, and sell them for $200/per or sell a complete TT bike that's within a few watts of "the best" for ~$1,000.


But, alas, none of these arguments will likely matter as discs = cheap carbon rims and fewer SKUs thus more $$$

I doubt you can get this narrow with rim brakes. The front end of the P5-X would have to be wider to account for rim brakes.


Same with the Andean.

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Tom A, that picture was hilarious. I hope I don't ever find myself the target of one of your meme's - I'll work to ensure any post I make passes muster!

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2018 Races: IM Santa Rosa, Vineman Monte Rio, Lake Tahoe 70.3

Very good pictures Bryan, thanks for sharing

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2018 Races: IM Santa Rosa, Vineman Monte Rio, Lake Tahoe 70.3

Did you even LOOK at the LOOK above? Want to bet that the headtube of the LOOK is narrower than the Andean, and especially the P5X?
No need for doubt. You've been proven wrong already by the picture above :-/

Also, do you want to bet which bike has the smallest total frontal area of headtube, fork, wheels, AND brakes? My money is on the LOOK...and I suspect a Speed Concept is smaller as well when measured that way.

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Oh I LOOKED at it.

Go get some calipers and measure it. If the P5-X was still at my shop, I would measure it myself.

The fork is very close to the tire near the P5-X and the Andean. You can't do that with rim brakes.

If you LOOKED at the photos I posted near the head tube, you would see what I'm talking about. Well...perhaps you did and ignored it.

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Wrong. Isn't that the problem most people have with fitting wider tires in current forks...as in the crown is TOO close?

Anyway...who says having the fork close to the tire is a good thing? Some aerodynamicists say the opposite...



...and YOU keep ignoring all the stuff (extra surface area) happening down at the hub area <smh>

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No...not really. I haven't ignored anything. If you really want to measure stuff, let me know. I'll get the measurements off the P5-X.

The P5-X, tested with disc brake wheels, against the P5 with the same wheels for rim braking, beat it. Even with more spokes and a bigger hub. Care to explain how that happened?

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WTF? You are really going to try to argue a P5X is faster than a P5 simply because disc brakes are more aerodynamic? News flash: The P5 was designed within UCI tube shape limitations and rules. I could easily make the P5 much faster than the P5X just by deepening the tubes and adding any number of artificial fairings onto it.

Your disc brake bias is showing. Let me guess, you think you will sell more bikes by forcing incompatible wheels and fooling them that they are faster with marketing speak.

LOL.

Don't you have a physics model to go tweak so you can prove everyone wrong about shallow wheels?

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Sure. The P5 isn't the best rim brake design they could develop TODAY.

It was the best they could do 4-5 years ago (with the constraints they gave themselves at the time)...but I'm sure they could beat it today, and most likely by more than what the P5X did. Especially if they went with a "non-UCI-legal" approach like the P5X.

It's really not that hard to understand for someone taking an objective look...and it would be pretty easy to test how a nearly equivalently designed P5X rim brake version would perform by simply removing the discs and calipers (as has been pointed out to you ad nauseum). Sure, some folks associated with Cervelo say the head tube area couldn't be the same for a rim brake version P5X, but the pics above of the LOOK (and the front end of the Speed Concept) imply they're "blowing smoke" on that subject.

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Have you seen the P5-X in person?

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Bryan,

The difference between the P5 and P5X is a great question though the designs are so different it is hard to isolate one factor. I mean it is missing a dern seatpost for example. I think the P5 sets a high bar for aerodynamics and I am glad to see the Parlee TTIR, DB Andean and P5X testing faster than the P5 in the wind tunnel from what I have seen not to prove that disc brakes are faster, but to rob the disc brake deniers of an arguement.

I think the whole rim vs disc brakes and aero is extremely small and far less than the rider effect. Both rim and disc brakes can be optimized to reduce aero drag. Even as focused on speed as I and other triathletes are, we should pay more attention to safety than speed. Especially given that there is negligible if any difference in speed between rim and disc brakes, we should seriously consider disc brakes for their increased safety even if that increased safety is only in wet conditions.

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2018 Races: IM Santa Rosa, Vineman Monte Rio, Lake Tahoe 70.3

I don't disagree with anything you have said. I agree that better brakes are needed. I rode in the rain yesterday on my METAL BRAKE TRACK rims and it sucked.

All I have been saying from the start is that disc brakes can allow for bikes to be faster than rim brake bikes with good design. Cervelo proved this.

What everyone is struggling to understand is WHY disc brakes here.

It's pretty easy to understand that we have hit the point of marginal gains. Better braking is the new aero. If we can make a disc brake bike as fast as the current leaders in rim brake bikes, GOOD. That is the start of what is to come.

But to stay on the path that we are on with rim brakes? Nah. Just like removing the headphone jack on the iPhone 7, change is coming. YOU WILL BE OKAY.

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Haven't had the chance yet.

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I think I won that thread. People admitted they don't account for any physiological stresses in their physics models.

And if you are so set on "safety" as your argument for disc brakes, you should be wholly supportive of shallow rims. Not only do shallow rims allow you to climb faster, they are also safer. Wind gusts to the side won't torque your handle bars with shallow rimmed wheels versus deep rimmed ones. After all, "safety" just like with disc brakes, right?

The ideal solution would be low profile 3-cross aluminum wheels with rim brakes for ease of maintenance, wheel changes, durability, braking, faster hill climbing and stability in windy conditions.

There is no reason we should be spending all this needless money on more aero this and more fancy that when way better safety is just a low profile aluminum wheel away.

In fact, why do we even have aero bars? Those things are death traps and should be made illegal in the name of safety.

Well, duh...riding in the rain always sucks. But, if what sucked was your braking...well, then you're doing it wrong :-/

BTW, how did that experience compare to your experiences riding road bikes with discs in the rain?

I've got some observations on that matter related to some rides I took last spring in downpours on a disc-equipped road bike, but I want to hear your observations first before sharing...

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Since I know what you are trying to prove, no I have not ridden disc brakes in the rain.

Get back to me when you go see the P5-X

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So then...if you haven't actually ridden a disc-braked road bike in the rain, how do you KNOW they are necessarily "better"? Are you taking what you are being told on faith?

I'll tell you what...when things are REALLY wet, there's STILL a second of "oh shit, nothing is happening!" when you first pull the lever with disc brakes. But then, just like a good brake track and pad combination, you then get consistent, if somewhat degraded braking.

Same-same.



...and that is relevant to the discussion at hand how??

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I think cyclenuts or someone else on the forums here maintains a pretty detailed spreadsheet of frame measurements. I know he has the P5. He might have the Speed Concept. He might even have the Look (796?). If we ask nicely I'm sure he'd be willing to measure the P5X

Also, a lot of aerodynamicists have said that tight fork spacing is bad. If you look at pressure studies, you'll see an area of high pressure is common in the area where the tire is close to the fork crown.

You know, one could easily determine braking points and rates from the speed trace and power file...using VE ;-)

<Paging RChung, paging RChung...please pick up the house courtesy phone>

I wonder if Si would be willing to publicly post the speed/power files?

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Hybrid,

I don't get your arguments, they seem to be for the purpose of arguing rather than making a point. It was I not the others who was talking about disc brake safety. But, what you missed in your rush to glamorize shallow aluminum wheels is that I said that the aero difference between rim brakes and disc brakes is negligible to the point that I am not going to argue with anyone about the difference, I think they can both be made to be aero. Given that there is negligible difference in aero effect, then there is no reason a triathlete shouldn't consider a disc brake for the increased safety gains with little/no downside on aero drag.

The shallow aluminum wheel has a clear and measurable negative aero effect compared to a deep wheel rim. In races, people, especially those of us who do triathlons to compete (hopefully against ourselves and our goals instead of others) want to go faster. When you are giving up minutes, it is hard to make the safety argument as effectively as when you don't have to give up any time to be safer as with disc brakes.

But to your point, the reason I train in shallow aluminum wheels is for the increased safety. But even the aluminum wheels are not as safe in wet weather, something I imagine we all experience while training, than disc brakes and so you have inadvertently made the argument for disc brakes as they are safer than aluminum rims without any loss in speed - thanks!

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2018 Races: IM Santa Rosa, Vineman Monte Rio, Lake Tahoe 70.3

You are seriously arguing for deep rimmed wheels while talking about safety? For Pete's sake, you just have to watch any Tri and see that half the people can't even ride a straight line. Why endanger so many people for "speed" with expensive deep rimmed wheels when we could just make a rule that everyone has to ride low profile aluminum rims? They are cheap, simple, have excellent braking, stable, and compatible with all bikes. Have you ever even seen a typical age grouper ride a tri bike in a cross wind???

Sigh, I'm not sure this is worth it, but here:

1. my deep wheels are actually more stable in crosswinds than my shallow aluminum rims. I am not quite sure why.
2. I do in fact see many age groupers ride as I am sadly, quite bad at the swim and quite good at the bike and run meaning I pass many in races on the bike and I see them biking for awhile as I catch up to them. I think you are being condescending towards most triathletes in deriding their riding ability. While they may not be as fast or as good as the folks at the very front, they train, they sweat, they strive just like everyone else. In fact some of the slowest triathletes I know work very hard and are dedicated to triathlons, just not blessed with the same ability as those at the very front.

But in the end, you clearly enjoy your shallow aluminum rims. Great. I hope you have fun on them. Do I think a slow triathlete needs expensive deep wheels? No. But, am I going to mock them for not using aluminum rims? No - I'll leave that to you.

My point is that regardless of the wheel choice, disc brakes are equal or safer to rim brakes and with no areo difference, why not transition to a safer standard for our sport?. Yes, the difference is less between disc brakes and aluminum rims than disc brakes and carbon rims, but if you could detach yourself from your rooted position, wouldn't it make sense if all wheels were equally safe regardless of the type of wheel? Wouldn't that make life better?

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2018 Races: IM Santa Rosa, Vineman Monte Rio, Lake Tahoe 70.3