Rim brake vs Disc Brake Aero test.
#76
Uber Goober
My thinking on the rider-vs-not issue is that the rider's legs are directly upwind from the rear brake, so how they interacted could have a major effect on results. And more specifically, does a rider shield rim brakes more or less than disk brakes, considering they're at two different locations on the bicycle?
You would logically think that the front brake is all that mattered, seeing as how it hits the air first, but one of the points of testing is to see if those kinds of intuitively-obvious conclusions really hold. That same logic would say a tail-box on a bike has no benefit. I seem to recall that back in the 1930's, they had some cars with big roundy fenders and all, that were intended to be aerodynamic by inspection, but didn't look anything like what they came up with when they actually started testing cars in a wind tunnel.
You would logically think that the front brake is all that mattered, seeing as how it hits the air first, but one of the points of testing is to see if those kinds of intuitively-obvious conclusions really hold. That same logic would say a tail-box on a bike has no benefit. I seem to recall that back in the 1930's, they had some cars with big roundy fenders and all, that were intended to be aerodynamic by inspection, but didn't look anything like what they came up with when they actually started testing cars in a wind tunnel.
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#77
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I'm trying to explain that, despite common belief around here, aerodynamics testing without a rider present does actually serve a useful purpose, and the importance of having the rider present depends greatly on what is being tested. I'm not an aerodynamicist, but it's likely, in the case of a braking system, that the rider is going to have limited influence on the aerodynamic properties of the components involved at the front end of the bike. The rear brake is a different story, but also less influential on overall aerodynamics because of how dirty the air is once it hits that part of the bike. The massive amount of superfluous noise introduced by putting a rider on the bike could very plausibly make it harder to accurately measure the differences between braking systems, especially if those differences are small.
It's perfectly reasonable to want to make measurements with a rider, but this idea that you MUST be as close as possible to the real world or the data isn't useful is just wrong. And is the result of a failure to understand how productive scientific testing actually works. I know it's counter-intuitive, but more realistic experimental conditions do not necessarily get you more accurate results.
Last edited by grolby; 12-11-14 at 04:22 PM.
#79
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so, is 1-3watts of power loss worth it for better braking?? is it better braking? who really cares who has disc and who doesn't? FTR - I think disc is nice tech, but my next bike will be rim brakes, I simply don't have a need for the added cost. I live in IL (no hills to speak of), I don't ride in the rain or even in the threat of rain. so the tangible benefits simply aren't there for me so I cna't justify the cost.
Where I live the disc brakre OPTION makes a lot of sense as it us mountainous and often rains.
For me, it comes down to consumers having choices.
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Some of us are extremely skeptical about Specialized's forays into the wind tunnel. I'll leave it at that. If you want road disc, and you're excited, great, it's available. Don't act like we all should be, especially us tri-focused sorts. I hope lots of guys in M30-34 try it out.
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BDop, what sort of changes in rim technology are possible with disc brakes? Since there's no need for a braking surface, will the rims become more aerodynamic or lighter or both?
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What can happen is a weight savings as the material needed to support a braking surface is no longer there. Depending on the width and depth of the rim you could expect to see a 30~60g savings per rim. Those saving directly offset the current weight penalty with discs.
That weight penaly will dissappear as componant makers design caliper specific to road instead of simply carrying over much beefier MTB parts as they are now. Shimano already has new calipers designed and in testing.
#85
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Some of us are extremely skeptical about Specialized's forays into the wind tunnel. I'll leave it at that. If you want road disc, and you're excited, great, it's available. Don't act like we all should be, especially us tri-focused sorts. I hope lots of guys in M30-34 try it out.
My SECOND post points out the shortcomings of this initial data. Further posts state clearly that discs in a TT situation are just dumb.
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#87
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I just want the converstaion to move along and not in circles. This was an ok first step.
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First, "accurate" is undefined......(removed babbling)
The massive amount of superfluous noise introduced by putting a rider on the bike could very plausibly make it harder to accurately measure the differences between braking systems, especially if those differences are small.
The massive amount of superfluous noise introduced by putting a rider on the bike could very plausibly make it harder to accurately measure the differences between braking systems, especially if those differences are small.
There are benefits to measuring parts and measuring the whole, but in measuring the whole the variations within the parts may be negligible/indeterminable based upon the the testing tool and conditions.
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Oh, and I wish we had access to Cervelo's disc brake wind tunnel data. That'd be more trustworthy.
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And remember, other than levers there is no specific road disc equipment on the market yet. It is all much heavier MTB stuff being carried over.
As road specific products are introduced the weight penalty arguement will become moot.
#93
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Yes. Although I would strike the "negligible" part. But that detail is negligible.
#94
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How?
Current hydro calipers are all designed for MTB. Until we see what is possible for road, based on needs for road, we only have products designed for MTB to consider. Those parts are designed to be much beefier and impact resistant than is needed for a road specific application. That means weight.
The aero argument against road discs is losing validity so now objections are moving to weight. Soon those will vanish. So what will be left? Aesthetics?
What I don't understand is why those who don't want or need road discs (and there are plenty in this category) insist on denying the OPTION to those for whom it may be a sensible choice. If you don't want them, fine, but why tell other they don't need them or can't have them?
Current hydro calipers are all designed for MTB. Until we see what is possible for road, based on needs for road, we only have products designed for MTB to consider. Those parts are designed to be much beefier and impact resistant than is needed for a road specific application. That means weight.
The aero argument against road discs is losing validity so now objections are moving to weight. Soon those will vanish. So what will be left? Aesthetics?
What I don't understand is why those who don't want or need road discs (and there are plenty in this category) insist on denying the OPTION to those for whom it may be a sensible choice. If you don't want them, fine, but why tell other they don't need them or can't have them?
#95
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People use their brakes when on their road bike? Huh. Always thought road cycling was an exercise in going fast...
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How?
Current hydro calipers are all designed for MTB. Until we see what is possible for road, based on needs for road, we only have products designed for MTB to consider. Those parts are designed to be much beefier and impact resistant than is needed for a road specific application. That means weight.
The aero argument against road discs is losing validity so now objections are moving to weight. Soon those will vanish. So what will be left? Aesthetics?
What I don't understand is why those who don't want or need road discs (and there are plenty in this category) insist on denying the OPTION to those for whom it may be a sensible choice. If you don't want them, fine, but why tell other they don't need them or can't have them?
Current hydro calipers are all designed for MTB. Until we see what is possible for road, based on needs for road, we only have products designed for MTB to consider. Those parts are designed to be much beefier and impact resistant than is needed for a road specific application. That means weight.
The aero argument against road discs is losing validity so now objections are moving to weight. Soon those will vanish. So what will be left? Aesthetics?
What I don't understand is why those who don't want or need road discs (and there are plenty in this category) insist on denying the OPTION to those for whom it may be a sensible choice. If you don't want them, fine, but why tell other they don't need them or can't have them?
forget about the lever for this question.
when you use the term "much heavier MTB stuff "
it starts getting hard to follow.
#97
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...
What I don't understand is why those who don't want or need road discs (and there are plenty in this category) insist on denying the OPTION to those for whom it may be a sensible choice. If you don't want them, fine, but why tell other they don't need them or can't have them?
What I don't understand is why those who don't want or need road discs (and there are plenty in this category) insist on denying the OPTION to those for whom it may be a sensible choice. If you don't want them, fine, but why tell other they don't need them or can't have them?
I wouldn't mind moving to at least a front wheel disc standard for road bikes. I do think that having two disc brakes on a road bike is overkill. The rear wheel has enough crap hanging off it as it is.
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Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
#98
Senior Member
You don't need as large a radius for the disc on a road bike, nor as much leverage on the brake shoe. Both of these will have the effect of shaving weight from the system (and improving aerodynamics).
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Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
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How?
Current hydro calipers are all designed for MTB. Until we see what is possible for road, based on needs for road, we only have products designed for MTB to consider. Those parts are designed to be much beefier and impact resistant than is needed for a road specific application. That means weight.
The aero argument against road discs is losing validity so now objections are moving to weight. Soon those will vanish. So what will be left? Aesthetics?
Current hydro calipers are all designed for MTB. Until we see what is possible for road, based on needs for road, we only have products designed for MTB to consider. Those parts are designed to be much beefier and impact resistant than is needed for a road specific application. That means weight.
The aero argument against road discs is losing validity so now objections are moving to weight. Soon those will vanish. So what will be left? Aesthetics?
But, you've heard all this. You're just ignoring it.
What I don't understand is why those who don't want or need road discs (and there are plenty in this category) insist on denying the OPTION to those for whom it may be a sensible choice. If you don't want them, fine, but why tell other they don't need them or can't have them?