Velo tests aero drag of disc vs. non-disc Tarmac
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  1. #1
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    Velo tests aero drag of disc vs. non-disc Tarmac

    Well, you know, that's just, like, your opinion man. - The Dude

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    On on mountain bike? Yes. On CX bike? Yes. On a road bike? Absolutely silly.

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    Until they design a brake that is easily adjustable somehow for disc flanges differences I say no for racing.

    You can space your discs all the same on your own bike so it isn't a pain in the butt to change wheels but if you race you can't take a neutral wheel.

    Maybe good for endurance type bikes where you might ride some steep descents or gravel roads with fat tires more often but with aluminum rims and good rim brakes I have never needed more braking. Not to mention most of us don't ride that much in the wet with carbon rims.
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    if my memory is right, those drag differences translate into something like 2.5 watts at 30 mph - not exactly huge and could likely be compensated by improved rim shaping (without a brake track free to make the rim curve smoothly to tire like the old toroidal ones tried.

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    They noted that the numbers were smaller with a rider. And there will definitely be advancements in the technology reducing the drag even further.

    Even if it is 1 watt @ 30 mph, in a competitive situation over an all day ride, that extra work means something. So that is definitely a strike against disk for racing. But, I can see disks being a useful option to have. On a rain soaked day where there is a lot of descending, maybe the better breaking is worth the extra 1-2 watts of energy.

    Disclaimers: I don't know my ass from my elbow in regards to this topic. My first bike has disks, my 2nd does not.

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  6. #6
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    Personally, I have no problems stopping with rim brakes, even on carbon wheels. I'm not in the mountains so I don't have to worry about long descents either. However, I don't know that discs would be a better option as they are prone to over-heating as well. Plenty of reports for DH racers boiling the fluid on long descents. I'm not sure how cabled brakes would handle heat.

    I do think the possibility for rim shaping would be interesting as well as the ability to negate the reinforcement in the rim needed for the braking surface. I don't know how well the low spoke count wheels on many road wheels would handle disc brakes since radial lacing isn't possible with them and they torque the wheel differently from the braking forces.

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    Velo tests aero drag of disc vs. non-disc Tarmac

    8w was mentioned.. That's alot
    PO is a liberal echo chamber.

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    Quote Originally Posted by spdntrxi View Post
    8w was mentioned.. That's alot
    The disparity is 1-3 W at typical yaw angles, but the more extreme differences appear mostly on the left side where the discs are. That isn't surprising.

    Personally, I'm okay with rim brakes for the time being, and I don't plan on going out of my way to get discs.
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    Velo tests aero drag of disc vs. non-disc Tarmac

    Same here... No rush
    PO is a liberal echo chamber.

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    There's an interesting discussion with many of the people who did this test and other wind tunnel disc tests on slowtwitch.

    I do ride in the mountains, often use carbon clinchers and don't feel the need for discs. Although if I were to build a dedicated rain bike I'd put discs on it.

  11. #11
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    Velo tests aero drag of disc vs. non-disc Tarmac

    Quote Originally Posted by bikerector View Post
    I do think the possibility for rim shaping would be interesting as well as the ability to negate the reinforcement in the rim needed for the braking surface. I don't know how well the low spoke count wheels on many road wheels would handle disc brakes since radial lacing isn't possible with them and they torque the wheel differently from the braking forces.
    I don't know how much the material or shape needs to be modified just for rim braking vs. mechanical strength and aero considerations. My guess is not that much so removing the braking requirement from the design constraints isn't going to make much difference. You make a good point regarding lacing, # of spokes, etc. which may further impede the performance of disc-based road bikes.

    I'm a bit surprised that the disc fans haven't chimed in with how the improved modulation with discs is worth up to 8 watts! :^D
    Well, you know, that's just, like, your opinion man. - The Dude

  12. #12
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    Quote Originally Posted by Notvintage View Post
    On on mountain bike? Yes. On CX bike? Yes. On a road bike? Absolutely silly.
    +1...

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    I don't think that those that see the disparity as minor really understand that a 1-2 watts to a racer could be the difference between a win or a loss. Racing is what determines the success of technology. Same goes for cars. Racing is the testing ground for features the masses will get.

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    That's a relief. Since I don't race I don't have to worry that my Colnago or my Moots with disc brakes are silly!
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    Here's the way I see it, discs are not needed for road riding/racing since you hardly ever use the brakes and when you do use them, it's rarely at 100%. If you're a commuter who sticks it out in the rain, then discs are a good idea. Certainly in the CX and MTB scene I can see the value. Quite frankly, I couldn't imagine going back to rim brakes for MTB. Also, these aero debates crack me up since the rider is the big drag and only elite riders are of a size and shape where the rest of the equipment comes into play.

  16. #16
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    Finally...I now can justify buying a disc-equiped bike and then blame it for always being dropped

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    Quote Originally Posted by CBus660R View Post
    Here's the way I see it, discs are not needed for road riding/racing since you hardly ever use the brakes and when you do use them, it's rarely at 100%. If you're a commuter who sticks it out in the rain, then discs are a good idea.
    Apparently you do not live in an area where some rides are up a twisty switchbacked mountain road of 3-4K elevation gain in less than 8 miles. Descending those roads is really nicer and safer with disc brakes.
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  18. #18
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    Quote Originally Posted by Special Eyes View Post
    Apparently you do not live in an area where some rides are up a twisty switchbacked mountain road of 3-4K elevation gain in less than 8 miles. Descending those roads is really nicer and safer with disc brakes.
    Actually, you are quite correct and I didn't think about descending like that. Add another check mark in the pro disc column for road bikes ;)

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    Quote Originally Posted by bikeguy0 View Post
    Until they design a brake that is easily adjustable somehow for disc flanges differences I say no for racing.

    You can space your discs all the same on your own bike so it isn't a pain in the butt to change wheels but if you race you can't take a neutral wheel.
    Its not an issue with shimano brakes, they have a wider pad gap. And they will self adjust unlike sram hydros. Using through axles also eliminates the issue.

    It's quick releases and the impressions the knurling leaves on the dropouts that causes misalignment when you pull the wheels off and reinstall. No decent hubs have enough variance in tolerances that would cause the disc to not align with the caliper. With through axles everything will line up right every time, assuming your back up wheel has the same brand hub and rotor.
    Last edited by 92gli; 01-23-2015 at 09:26 AM.

  20. #20
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    Quote Originally Posted by CBus660R View Post
    Here's the way I see it, discs are not needed for road riding/racing since you hardly ever use the brakes and when you do use them, it's rarely at 100%. If you're a commuter who sticks it out in the rain, then discs are a good idea. Certainly in the CX and MTB scene I can see the value. Quite frankly, I couldn't imagine going back to rim brakes for MTB. Also, these aero debates crack me up since the rider is the big drag and only elite riders are of a size and shape where the rest of the equipment comes into play.
    It's not about the power, it's about the modulation and force needed to engage the brakes.

    Ever wonder why a lot of mtb disc brake levers are so damn short?????????

    It's because it only takes one finger to engage them to full power and everywhere inbetween
    It's a fire road.............
    I'm on a road bike..........

    They have enough in common to blast down it.

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    Quote Originally Posted by ziscwg View Post
    It's not about the power, it's about the modulation and force needed to engage the brakes.

    Ever wonder why a lot of mtb disc brake levers are so damn short?????????

    It's because it only takes one finger to engage them to full power and everywhere inbetween
    Are you saying that like its a bad thing or a good thing? Your intent is unclear to me. If you want my opinion, that is a good argument for using discs everywhere Easy to use and modulate seems like good trait to have.

  22. #22
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    Quote Originally Posted by Special Eyes View Post
    Apparently you do not live in an area where some rides are up a twisty switchbacked mountain road of 3-4K elevation gain in less than 8 miles. Descending those roads is really nicer and safer with disc brakes.
    In fact, not only do I live in such an area and have never felt the need for "better" (heavier, less aero) brakes, but this autumn I descended 3800' in 7.7 switchbacked miles with rim brakes and carbon rims, in the rain, and was just fine. I continue to maintain this is a total strawman argument put forth by those who could benefit from more experience and better descending technique. As I've always said, equipment is no substitute for experience and technique, whether you're climbing or cycling.
    Well, you know, that's just, like, your opinion man. - The Dude

  23. #23
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    Quote Originally Posted by OldChipper View Post
    As I've always said, equipment is no substitute for experience and technique, whether you're climbing or cycling.
    Not a substitute at all, but rather an enhancement. More effective components do add to the safety and pleasure.

    Chip, I'm sure you are an awesome rider.
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  24. #24
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    When disc for road was first being considered, overheating while descending seemed to be the primary concern, not aerodynamics. Has that been solved or was it something that wasn't really an issue in the real world anyway? The solution at that point seemed to be that you would need big honking disc rotors to dissipate the heat.

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    Quote Originally Posted by bikerector View Post
    When disc for road was first being considered, overheating while descending seemed to be the primary concern, not aerodynamics. Has that been solved or was it something that wasn't really an issue in the real world anyway? The solution at that point seemed to be that you would need big honking disc rotors to dissipate the heat.
    There was some issues with overheating as I remember. This was the classic case of miss matched components from the accounts I read. If you take a super light, low surface area rotor at 140 or 160 mm, it's not going to do well unless it's designed into the whole brake equation. This also hold true for mtb as well. So, it's not new.

    I think road disc set should be the "whole package" for now. For example, Shimano brakes, calipers/pads and rotors. That way everything is designed and tested to work together.

    At some point, I think you will be able to mix 3rd party rotors in there like you can now with mtb. Even mtb mix and match is trial and error.

    From what I have been on, 160 mm seems to be fine. I don't think we'll see anything bigger on the road.
    It's a fire road.............
    I'm on a road bike..........

    They have enough in common to blast down it.

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