How many of you have converted to Disc Brake?

[mpulsiv]

Exact, my Endurace is more affected by crosswinds compared to my Scott, altough shallow alloy rims on the Canyon vs 35 deep Bora's on the Scott. Nothing to worry about, but I notived it right away.

You must be really sensitive, I can't tell much difference between my rim or disc bike in cross winds nor the difference in weight of the brake levers as you say and both bikes are Giant TCR's with deep rims (albeit different depths)
Maybe there is, but unless I was to ride the bikes back to back in the same conditions and with the same wheels I could not make a valid assessment.
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Yep, I am! Even very small changes in riding position cause some strange feeling the first hour, sometimes causing back pain etc. And by small, I mean a few mm. As others have said, some of us are very sensitive, others, like my father, don't feel any difference between 2 bikes that in reality behave very differently (weight, geometry etc) Regarding shifter weight, do this simple test : put both bikes upright, wheels in straight line, than lean both bikes slightly to one side. The disc shifter willl cause the steerer to turn the handlebar a lot faster and with less bike angles as the non disc bike! Of course, both bikes with tyres at +/- th same pressure... and assuming both headsets spin smoothly. Ran the disc bike on the rollers today, and what a concentration it takes to stay on them, again (I suppose) the weight of the shifters that tend to amplify every small imput on the handlebar. On the road, the Canyon is a lot more stable than the Scott, on the rollers, it's the other way around

This is exactly what I tried to convey. Understand human sensitivity before you go overboard with comments and recommendations. I wish many of you would mention level of sensitivity in your signature under profile. This is the reason I accept rider recommendations on this forum with a grain of salt. Like I said, some of you are like wood, feel nothing and make utterly terrible test subjects. This a general statement, cycling aside.

[MoPho]

This is exactly what I tried to convey. Understand human sensitivity before you go overboard with comments and recommendations. I wish many of you would mention level of sensitivity in your signature under profile. This is the reason I accept rider recommendations on this forum with a grain of salt. Like I said, some of you are like wood, feel nothing and make utterly terrible test subjects. This a general statement, cycling aside.

Conversely, being oversensitive doesn't necessarily make you a good test subject either



.

[MoPho]

Yep, I am! Even very small changes in riding position cause some strange feeling the first hour, sometimes causing back pain etc. And by small, I mean a few mm. As others have said, some of us are very sensitive, others, like my father, don't feel any difference between 2 bikes that in reality behave very differently (weight, geometry etc) Regarding shifter weight, do this simple test : put both bikes upright, wheels in straight line, than lean both bikes slightly to one side. The disc shifter willl cause the steerer to turn the handlebar a lot faster and with less bike angles as the non disc bike! Of course, both bikes with tyres at +/- th same pressure... and assuming both headsets spin smoothly. Ran the disc bike on the rollers today, and what a concentration it takes to stay on them, again (I suppose) the weight of the shifters that tend to amplify every small imput on the handlebar. On the road, the Canyon is a lot more stable than the Scott, on the rollers, it's the other way around

If you say so...
Your test wouldn't work as my disc bike is Di2 and the rim brake bike mechanical, so the additional housings would change the rate of which the bars turn, not to mention the bars and stem are different, and I am not sure it is even relevant to the bike being on the road. Too many variables in most of this stuff to pinpoint any one cause.

[Miller]

Ran the disc bike on the rollers today, and what a concentration it takes to stay on them, again (I suppose) the weight of the shifters that tend to amplify every small imput on the handlebar.

You may have found the disc bike twitchy on the rollers but I assure you that's not because it has disc brakes. I have tried a variety of bikes on rollers and my disc bike is one of the most stable.

There is an interplay between the geometry of the bike, especially its length, and the distance between the rollers. This is why rollers are generally adjustable for length.

[Delorre]

Ran the disc bike on the rollers today, and what a concentration it takes to stay on them, again (I suppose) the weight of the shifters that tend to amplify every small imput on the handlebar.

You may have found the disc bike twitchy on the rollers but I assure you that's not because it has disc brakes. I have tried a variety of bikes on rollers and my disc bike is one of the most stable.

There is an interplay between the geometry of the bike, especially its length, and the distance between the rollers. This is why rollers are generally adjustable for length.

It was also a surprise to me, as the disc bike, with his more endurance geometry, goes more straigt forward as my Scott on the road. Canyon has 5mm less wheelbase, don't now if I need to adjust the rollers for that. Have to re-read the manual of the rollers. Even when not riding, simply putting the bike upright on the rollers, the handlebar tends to rotate to one or other direction, almost impossible to keep the front wheel straight. Gyroscopic effet tends to solve that, but even, I had to concentrate a lot.

[Clingon]

my Endurace is more affected by crosswinds compared to my Scott...

I have no doubt that this is true, but I think that what you are experiencing is more likely to be due to differences in the frames' geometries (trail & head tube angle in particular) than the addition of disk brakes.

I've not seen any data to back this up so it's a pure view point, but I'd be very surprised if a rotor positioned on the hub really made much difference in a cross wind. I'm struggling to see that something on the hub is going to generate much steering torque, in the same way that a deep rim could.

I agree entirely, the surface area of a disk rotor is about the equivalent of adding 2mm to the depth of a rim; this is before you even consider that the force is concentrated so much closer to the hub. The effect on crosswind steering torque is likely to be far beyond the perception of even the most sensitive rider. Indeed, I'm not sure it could even be meaningfully measured in a controlled wind tunnel environment.

[Dez33]

I've not seen any data to back this up so it's a pure view point, but I'd be very surprised if a rotor positioned on the hub really made much difference in a cross wind. I'm struggling to see that something on the hub is going to generate much steering torque, in the same way that a deep rim could.

I agree entirely, the surface area of a disk rotor is about the equivalent of adding 2mm to the depth of a rim; this is before you even consider that the force is concentrated so much closer to the hub. The effect on crosswind steering torque is likely to be far beyond the perception of even the most sensitive rider. Indeed, I'm not sure it could even be meaningfully measured in a controlled wind tunnel environment.

Are you sure? I get 201 sq cm for a 160mm disc, adding that on to the inside of say a 50mm aero wheel would make it a 62mm wheel. But the kicker is the extra 12mm is not aero shaped, its a flat, thin disc effectively tacked at the end of your aero rim. We know that's not ideal from the way wheel and frame shapes have progressed over the last 10 years.

Even Specialized admits with the Venge disc release the big issue is the rotor. It's pretty obvious that a flat, thin disc is not aero.

[Clingon]

I get 201 sq cm for a 160mm disc

It will depend on how you calculate it, yes 8^2*3.14=201, but rotors are far from a solid cross section. Measuring my Sram 160mm rotors I found the brake track section to be about 10mm (it includes various ventilation holes/slots but I am ignoring them here) and to account for the carrier arms I assumed a 15mm depth. Therefore: 8^2*3.14-6.5^2*3.14=68 sq cm. Essentially I am saying that the rotor only has a cross section for about 1/3 of the 160mm disc.
I did make a mistake before when calculating the rim profile (used diameter rather than radius, duh!). So the surface area equivalent is more like a 3.5mm increase in rim depth, admittedly somewhat more meaningful than I had thought.
Assuming a roughly 30mm deep rim (inside diameter roughly 580mm). Therefore adding 3.5mm to the depth: 29.00^2*3.14-28.65^2*3.14=66 sq cm.

So a disc rotor=68sq cm and a 3.5mm increase in rim depth=66sq cm. I am sure some riders would notice the effect of adding 3.5mm of rim depth upon on cross wind handling, but even with the same difference in surface area, a rim applies far more steering torque than a disc rotor located close to the hub. Of course the surface area affect upon drag is unaffected by radial location so it remains the same, hence the relatively poor performance of disc brakes at high yaw angles.

It's pretty obvious that a flat, thin disc is not aero.

I agree, in a front on headwind discs are fine, but I doubt the aerodynamic disadvantage will ever be overcome at high yaw angles. I just don't think the effect upon handling, which is a different albeit related issue to drag, is noticeable in the general scheme of things.

[youngs_modulus]

I'm confused; Clingon...Cannondale's wind tunnel results (the ones you posted, I think) showed that their prototype disc bike was faster than their rim-braked bike. Even if Cannondale's numbers are skewed somehow, it's clear that it's possible to incorporate disc brakes into a design with a minimal or nonexistent drag penalty at yaw angles of up to 15 degrees. In that context, why do you doubt that the drag penalty will ever be overcome? Or are you thinking more of angles as high as 25°?

Food for thought: steering torque arises when the wheel's center of pressure is not on the bike's steering axis. Barring really unusual circumstances, the center of pressure for a brake disc must be within its diameter; the same can be said for a rim. The center of pressure for a brake disc may be only 40 mm in front of the steering axis, while the center of pressure for the wheel could be 300 mm in front of the steering axis. In that case, the extra material at the rim would create nearly eight times the steering torque produced by the same surface area at the disc.

In other words, the max steering torque produced by the brake disc is less than that produced by an extra 3.5mm of rim depth because the brake disc has a much shorter lever arm than does the extra rim depth.

[Calnago]

Here's where that extra surface area really gets noticeable.... You're bombing down a canyon/mountain descent flanked by forests or cliffs on either side. It's very windy but not really affecting you because you're protected on both sides. Then you suddenly come out of that protection and get hit by a gusty crosswind, hard. It's scary and if you've got a lot of surface area catching that gust, it's like a kite. Forget the 0-15 degree yaw, you get nailed with a 90 degree gust that makes you think twice or thrice about everything on your bike that catches that wind. High profile wheels, aero tubes on the bike, and yes, a big pie plate of a rotor on the wheels. It all adds up into a scary mess at the moment of impact with that gust.

[Clingon]

I'm confused; Clingon...Cannondale's wind tunnel results (the ones you posted, I think) showed that their prototype disc bike was faster than their rim-braked bike. Even if Cannondale's numbers are skewed somehow, it's clear that it's possible to incorporate disc brakes into a design with a minimal or nonexistent drag penalty at yaw angles of up to 15 degrees. In that context, why do you doubt that the drag penalty will ever be overcome? Or are you thinking more of angles as high as 25°?

Correct, I should have been more clear, I was referring to extremely high yaw angles. Honestly, I don't think beyond 15° degrees is relevant to most riders, in which case discs have no meaningful aerodynamic penalty.

Food for thought: steering torque arises when the wheel's center of pressure is not on the bike's steering axis. Barring really unusual circumstances, the center of pressure for a brake disc must be within its diameter; the same can be said for a rim. The center of pressure for a brake disc may be only 40 mm in front of the steering axis, while the center of pressure for the wheel could be 300 mm in front of the steering axis. In that case, the extra material at the rim would create nearly eight times the steering torque produced by the same surface area at the disc.

In other words, the max steering torque produced by the brake disc is less than that produced by an extra 3.5mm of rim depth because the brake disc has a much shorter lever arm than does the extra rim depth.

Yes, this is what I was trying to say in my last post. The effect of a disc brake upon handling is entirely negligible.

[youngs_modulus]

Here's where that extra surface area really gets noticeable...High profile wheels, aero tubes on the bike, and yes, a big pie plate of a rotor on the wheels. It all adds up into a scary mess at the moment of impact with that gust.

Eh. I've ridden TTs with a shallow front wheel (Araya ADX-1 FTW!) and disc wheel on the back with buffeting crosswinds; you can feel something, but it's not much. Aero frame tubes don't have much of an effect; it's really the surfaces that rotate wth the fork that have an effect.

[youngs_modulus]

Correct, I should have been more clear, I was referring to extremely high yaw angles. Honestly, I don't think beyond 15° degrees is relevant to most riders, in which case discs have no meaningful aerodynamic penalty.

Yeah, we agree. The only exception, I think, is maybe age-group triathletes. A slow-but-not-unusual bike split at Kona is 7:30, which works out to about 15.5 MPH. At that speed and at Kona (I've ridden there several times) I could see 30-40-degree yaw being fairly common. But for "pure" bike racers? Nope.

Yes, this is what I was trying to say in my last post. The effect of a disc brake upon handling is entirely negligible.

I agree in terms of both theory and practice. I rode my disc-braked fixed-gear belt-driven cyclocross bike to work today, and got some gusting crosswinds. This bike has 35-mm U-shaped Light Bicycles rims on it, and the steering torque was considerably less than I would have expected on my road bike, which has 30mm Kinlin v-shaped rims. Blunt rims handle crosswinds better, and the addition of a brake disc didn't make the steering torque subjectively worse.

[Calnago]

Doesn't sound anything like the scenario I described. I'm describing a scenario where you're completely protected then get hit hard all of s sudden from the side at speeds probably much higher than on a tt course. It's scary.

[youngs_modulus]

Doesn't sound anything like the scenario I described. I'm describing a scenario where you're completely protected then get hit hard all of s sudden from the side at speeds probably much higher than on a tt course. It's scary.

Increased speed makes the penalty for falling worse, yes. But more speed actually helps crosswind resistance, as the centering torque from the bike's trail increases with speed, attenuating steering inputs from the wind.

And I didn't say "a crosswind," I said "buffeting crosswinds." That means crosswinds that gust violently and unpredictably. It's not the same situation, but it's a reasonable analogue.

I don't doubt that you were in a scary situation; I was only pointing out that the aero frame tubes and the high-profile rear wheel didn't contribute much to the scary situation you were in, at least compared to the high-profile front wheel (and possibly aero fork).

When a rider in the field overlaps his front wheel with another rider's rear wheel, and they touch, the rider behind often goes down. In those cases, no matter how hard he fights the steering input from the other rider's back wheel, he falls anyway. What's remarkable is that often the rider in front won't feel a thing, even though the rider behind is (momentarily) turning his wheel against the front rider's wheel with all his might.