StephenH

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.

grolby

First, "accurate" is undefined, here. "Accurate" with respect to WHAT? If you want to talk science, define your terms. If accurate means that your experimental design more closely resembles real life, that's self-evidently true. If accurate means that your result from this experiment gives a better picture of real-world performance, that is not necessarily true. Noise and increased confounding factors don't equal a more realistic result, they mean just what they say - more opportunities for random or uncontrolled factors to give you a false positive or false negative result. We don't simplify the system because we're lazy. Making an experiment too realistic can make your result LESS informative about reality.

Saying that a wind tunnel experiment with a rider or mannequin is closer to "reality" is like saying the Lord of the Rings is more historical than Star Wars. It bears a closer resemblance to the real thing, but it's still fictional.

No, that's not the conclusion. If there is a difference, there is an experimental design that can find it for you. That's why these more synthetic tests are useful - they contain some information about the question you want to answer.

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.

Bob Dopolina 

Incorrect.

It's just math.

Bob Dopolina 

You would be a perfect example of someone who has no need for discs. For you, the rim brake OPTION is the best choice.

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.

Bah Humbug

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.

bbattle

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?

bt

fixed for ya

Bob Dopolina 

Go away.

Bob Dopolina 

At the moment it seems overall rim shapes won't change that much as the aero properties remain the same. That doesn't mean that someone smarter than me might literally re-invent the wheel but, for now, I don't see huge changes in shape afoot.

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.

Bob Dopolina 

Please read the entire thread.

My SECOND post points out the shortcomings of this initial data. Further posts state clearly that discs in a TT situation are just dumb.

Bah Humbug

I saw that. Wondered why you were crowing so hard about this flawed data.

Bob Dopolina 

I was excited as data is finally starting to flow and intial results were better than I had expected. What I am actually excited about is the viabilty in this area and the fact that it is the first area open to innovation in quite some time vs the incremental improvements of the last decade.

I just want the converstaion to move along and not in circles. This was an ok first step.

BigJeff

Awesome, so we are in agreement.

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.

Bah Humbug

Nothing to do with the margaritas, then? I'm honestly surprised they're over there. Maybe I shouldn't be.

Oh, and I wish we had access to Cervelo's disc brake wind tunnel data. That'd be more trustworthy.

Jiggle

Physics, where math and reality converge. There was a huge thread in Bicycle Mechanics last month where road disc brake worshipers were roundly curb stomped.

Bob Dopolina 

Link please?

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.

bt

come on bro this is going overboard.

grolby

Yes. Although I would strike the "negligible" part. But that detail is negligible.

Bob Dopolina 

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?

Brian Ratliff

People use their brakes when on their road bike? Huh. Always thought road cycling was an exercise in going fast...

bt

how much lighter (grams) will your fantasy road brake calipers and discs be than the current XTR?

forget about the lever for this question.



when you use the term "much heavier MTB stuff "
it starts getting hard to follow.

Brian Ratliff

Not that I agree with the opinion, but in an expensive sport where people have seen many trends come and go and leave people stranded with nonstandard equipment, either from a previous trend obsolesced or a stale trend turned sour, I can see why the nervousness about moving to yet another new standard. It's the same sentiment driving opposition to the N+1 gear cluster trend of the last 30 years on the other thread.

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.

Brian Ratliff

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).

Jiggle

They will never vanish. Discs require heavier hubs, more spokes, rims of the same weight, heavier levers, and a heavier front fork. Physics. Why do you think mountain bikers are going to through axles?

But, you've heard all this. You're just ignoring it.

Beat that straw man. No one is saying that.

bt

unless you wanna go down a big hill without boiling or are heavier than a tdf guy.

I know weight can be saved, however minuscule, but at what cost for safety??