Some manufacturers forcing pros onto disk brakes for the 2019 season

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Calnago
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by Calnago

The pros have all had ample time to experiment with discs. Discs are not new to any of them. Yet the vast majority of pros riding discs are on teams where they have no choice. And Road is not Mountain.
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by Weenie


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C36
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by C36

TheRich wrote: Pros do not make the best choices by default, many are very resistant to change..like when the World Cup mountain bikers held onto 26" wheels when everyone should have known that 29ers were faster.
Well that’s a 20th century way of looking at things long gone for top teams.
I keep reminding the same 2 clear examples...
Both Sky and Movistar looked in real details the real performance and the riders feelings (that has a part in the performance) and both rejected the discs strongly with comment such as “we are here to win the tdf, let the others do marketing” or “good, let the others (teams) ran them”.

This pushback is likely the cause why katusha had to run disc brakes, canyon couldn’t have its two teams exclusively running on rim brakes (this is an indirect intel while the first 2 examples are direct ones).





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Last edited by C36 on Wed Jun 05, 2019 4:33 pm, edited 1 time in total.

zefs
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by zefs

Do these comments aim at the slower wheel changes? I'd imagine.

TheRich
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by TheRich

Calnago wrote:
Wed Jun 05, 2019 4:20 pm
The pros have all had ample time to experiment with discs. Discs are not new to any of them. Yet the vast majority of pros riding discs are on teams where they have no choice. And Road is not Mountain.
It's an example of the mindset of resistance to change. Wheel size, brake type, electronic shifting, etc.

But then they'll have their jerseys flapping in the breeze while people complain about the minimal areo penalty from disks.

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C36
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by C36

zefs wrote:Do these comments aim at the slower wheel changes? I'd imagine.
Not sure if refers to my message but if that’s the case, no, wheels changes had little to do (actually in Movistar case it wasn’t even mentioned to me) but overall bike behaviour was evaluated poorer than the rim brake equivalent, less reactive, heavier, not providing any performance benefit and “evaluated slower” on the Pinarello case.


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Calnago
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by Calnago

Without trying to start another full fledged war on the subject, it is true that a rim brake bike feels more “reactive” for lack of a better word. And it’s not very hard to understand why that might be.
First, generally speaking the forks and stays have to be beefed up a bit to withstand both the assymetric forces that disc brakes create. In addition to that, the braking force has to be transmitted, through the spokes and rim, all the way from the hub to the road surface. As a result, you generally can’t get away with as few spokes as you could on a rim brake bike, and those spokes certainly can’t be laced radially.
And secondly, overall you’re going to be carrying around 500g of extra weight (all else being equal) due to carrying disc brakes around.
But more importantly, you’re placing the caliper and the rotor much further down the steering axis, at the axle, versus where it exits the head tube in the case of a rim brake. Let’s forget about the forces of wind against the cross section of the rotor for a moment, which does indeed have a noticeable impact in certain conditions compared to rim brakes, but instead just focus on this analogy...
Take a longish hammer for example. Hold it like this, emulating where the weight would be with a rim brake...
Image
Go ahead, pretend it’s the fork on a bicycle, move it around, turn it, lean it, twist it... it’s pretty easy, right.

Now, turn the hammer around, like below, and do the same stuff. Then tell me which is easier to maneuver...
Image
I like putting things in a real world perspective that is easy to understand. No controlled “lab experiments” designed to show, well, whatever it is they want to show. No logarithmic charts blowing the tiniest of differences out of proportion. They all have their place for sure, mostly for marketing fodder, but sometimes all it takes is a little good old fashioned common sense to be able to see things pretty clearly.
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TobinHatesYou
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by TobinHatesYou

Except you’ve got it backward. The weight on a disc brake bike is closer to the fulcrum / pivot point (the ground)... lolololll

Aka why it sucks to corner with a high center of gravity.

Now if you want to use pseudo-science to imply handling changes, you should have just mentioned that a heavier wheel (not fork) will have a stronger gyroscopic effect.

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Calnago
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by Calnago

I know what you’re trying to say, and you’re wrong, again.
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TobinHatesYou
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by TobinHatesYou

:roll:

You are holding a lever at the fulcrum. When all the weight is on the fulcrum, it's easy to move the lever. When all the weight is on the end of the lever arm, it is difficult to manipulate the lever with force applied near the fulcrum. Conversely, if you hold the lever at the handle, anchor the hammerhead to a fixed pivot, it's quite easy to move the handle around an arc...because you have...leverage. Now a disc caliper isn't at the fulcrum, but rim brake calipers are even farther away. The majority of the weight being thrown around the fulcrum (ground) is you. You significantly outweigh a brake caliper and even a whole bicycle, and much of your weight is farther away from the ground than the highest point on a bicycle. I call it a wash without having specific numbers to work with and considering the forces overcoming such minute differences.

There may be OTHER reasons why a disc brake bike doesn't subjectively handle as well, but it's probably not for the reason you mentioned. Maybe youngs_modulus can chime in.

mattr
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by mattr

Actually you're both wrong. Or at least, arguing at cross purposes.
Steering will be all but unaffected by the caliper change as you are moving weight (caliper) from the front of the crown to the back of the hub, so the net change around the steering axis is probably pretty much zero, same with the increase in weight, it's all centred. Heavier shifters will have a bigger effect, probably an order of magnitude more than the caliper change (100+ grams 150+mm from the steering centre). If you were whipping the bars from side to side, you might be able to feel it...... but other than that, unlikely.

Pendulum effect will also be fairly much zero as well. Some weight moves down (calipers, slightly heavier hubs, discs, more spokes), some moves up (reinforced crown, heavier hydro shifters.) Full Vs empty bottle will have a bigger effect.

Some one who cares can do the detailed maths.

TobinHatesYou
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by TobinHatesYou

Rotating the steerer hardly matters except in low speed situations, why even bother mentioning it? You initiate a lean with a slight bit of countersteer and that’s about it.

Also please reread my post because I specifically mention that body weight and position really make this argument moot. We’re talking about a total difference of about 500-600g at various heights...insignificant when a human torso weighs so, so much more and is positioned even higher.

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pdlpsher1
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by pdlpsher1

I was watching a video on aero bikes by Hambini. He's an aerodynamicist and is someone I would trust because he has nothing to gain or lose by expressing his honest opinions. He said the aero loss on disks is significant because a disk is a spinning object vs. a stationary object. He said the disks are akin to a spinning wheel and that the wheel generates loads of drag. He reckons the aero penalty is around 8-9 watts at 40kph versus a claimed loss of only 2 watts by the bicycle manufacturers. If you are interested in the video here's the link. You can fast forward it to the 3:30 mark. https://www.youtube.com/watch?v=IgxFRNJ_HGs
Last edited by pdlpsher1 on Wed Jun 05, 2019 9:04 pm, edited 1 time in total.

mattr
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by mattr

Calnago is talking about steering axis, you are talking about pendulum effects.

And yes, it's a pointless exercise. Body weight, bottle fill, prescence of a saddlebag all make far more difference.

Frame stiffness will make much more difference to handling than moving tiny bits of weight about.

TobinHatesYou
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by TobinHatesYou

I don’t even know why Calnago mentioned steering axis other than the fact that he doesn’t know what he’s talking about. As you said, twisting a hammer around it’s axis is just as easy no matter which side you hold.

I just found his post amusing because his example shows exactly the opposite of what he is trying to prove when it comes to using a bike as a lever.

by Weenie


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Calnago
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by Calnago

mattr wrote: Steering will be all but unaffected by the caliper change as you are moving weight (caliper) from the front of the crown to the back of the hub, so the net change around the steering axis is probably pretty much zero, same with the increase in weight, it's all centred.

Some one who cares can do the detailed maths.
Except that road forks have an offset at the axle usually in range of 4-5cm. The offset at the crown is pretty close to zero.
And yes, I agree... someone who cares can do the math.
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