Joe Perez

iTrader: (8)

Also, I've heard you talk about cost, "engineered forks" and so on. I won't claim to fully follow everything you've said here, but a very quick perusal reveals a number of very reasonably-priced road forks which have the attachment points for a disc caliper already incorporated into the design. For instance:

Nashbar Carbon Cyclocross Fork - Road Bike Forks

Nashbar Disc/V-Brake Compatible Cyclocross/Touring/Hybrid Bike Fork - Road Bike Forks

It seems that if you can buy an "engineered" aluminum fork for $50 which is already set up to accept a disc caliper (or a 690 gram CF fork for $130), and if the whole disc / caliper setup costs about $85 total for both front and rear, and the cost of a disc-compatible wheel is identical to that of a rim-brake wheel, I just can't see the problem here other than an institutional unwillingness to accept new technology.

Joe Perez

iTrader: (8)

I mean, it's entirely possible that there may be some extremely minor difference between a lever intended for mechanical discs vs. one intended for rim brakes. I can't imagine why there would be, but it's possible.

I'm just saying that if there is a difference, it's so small that I am unable to perceive it. And I have done a number of conversions using these same levers.

hustler

iTrader: (6)

Those forks have big v-brake mounts and it will flex and turn the bike when you apply the brake. That also doesn't get a disc brake on the back of the bike. I would have to buy hubs and lace my own wheels because there aren't many affordable options out there yet.

I realize that it's coming, like it or not, necessary or not, but I'm not getting off the bike every night and saying, "man I really wish I had disc brakes". No one is ever going to win a grand tour because they had disc brakes and 2nd place didn't.

hustler

iTrader: (6)

I believe you're right, marketing drives this sport. However, after comparing my MTB with hydro-disc to a friend's bike with cable disc...I'd want the hydro, without a doubt. So I guess that maybe, sometime around 2020, you may see me on a hydro-disc road bike (with internal hose routing). As of right now, I'm not clamouring for it.

Joe Perez

iTrader: (8)

Hmm.

I've never ridden a bike with hydro brakes, so I can't really comment there. I'm curious- to me, going from cheap rim brakes to equally cheap cable-operated discs is about a 100% improvement in everything- totally night and day. In your opinion, is the jump from cheap mechanical discs to any reasonably-priced hydro disc equally significant?

I ask because there are, in fact, some extremely inexpensive hydro kits out there. The road parts seem to cost a tad more than the MTB parts, but neither are really outrageous. For instance:
TRP Hylex Hydraulic Disc Brake System > Components > Brakes > Road Disc Brakes | Jenson USA Online Bike Shop
TRP Hyrd Disc Brake > Components > Brakes > Road Disc Brakes | Jenson USA Online Bike Shop

The latter one, in particular, notes "The HY/ RD is an open hydraulic system that is fully compatible with all existing cable actuated levers. -True 'plug-and-play' compatibility with ALL existing cable actuated systems"

Leafy

iTrader: (1)

Not sure Joe. My MTB friend's always complain about their "cheap" hydro brakes being noisy and annoying. I think the ones they complain about are avid's though.

Joe Perez

iTrader: (8)

Well, depending on your definition of "loud," I think pretty much all disc brakes fit into that definition to some degree. The mechanical disc brakes on my e-bike are also pretty noisy, but then, so are the brakes on most of our cars. I just don't consider it to be a big deal.

shlammed

iTrader: (8)

Noise is mostly adjustment. If your pulling the rotor all over the place warping it because you havent properly adjusted it, the noise turns from a grind to a screech.


Joe, I dont think the engineering is in the fork.
The engineering is in the frame to withstand the extra forces of the fork pulling on the frame with the disc brakes. Caliper and V brakes put the forces more into the vertical plane of the fork with less torque on the frame components. Disc brakes puts more torque force into the low part of the fork torqiing on the frame.

I may be wrong, but I believe this is the reasoning behind the engineering part of it.

Leafy

iTrader: (1)

The vibe I get is that they sound like car brakes that have the squealer finger engaged.

I dont think you have the twisting part right. Theoretically the disk on one side wants to make the wheel rotate in the forks towards the rotor side. I dont see the fork being weak in that direction assuming your axle is properly tightened and your fork isnt made from cheese.

Joe Perez

iTrader: (8)

On mine, the brakes are silent when coasting, and merely make a sort of scraping sound when engaged. They're perfectly adjusted, it's just the noise of the pad itself rubbing against the ventilated friction surface of the disc.



As for all the rest of this business about twisting, loads, etc., (and I am NOT specifically addressing shlammed here), I can't help but think that this all sounds like a lot of armchair-quarterbacking to me. Has anyone here actually ridden a bike with disc brakes and thought "Gee, that's odd, it seems like the bike is twisting and torque-steering when I apply the brakes"?

Admittedly, I am speaking from a small sample size. But in my experience, disc brakes simply work. And I am not talking about expensive bikes here- this is all Chinese-made, aluminum-forked, $500 and under stuff.

shlammed

iTrader: (8)

the fork doesnt matter. its the forces the fork puts on the headset which go into the frame.

The frame may not bend specifically but after repeated loading, it could break the tube off the frame. Not so much of a problem on a heavy mtb frame-but on a super light butted hydroform aluminum frame it might be a concern at the welds.

Leafy

iTrader: (1)

Um, there is no force transmitted to the headset from the disk brakes that would not be transmitted by a rim brake. The only force transmitted to the headset from either brake style is the reaction force at the tire causing the bike to slow down. The only way the disk brake is going to make the bike pull side to side is if the forks are so flexible at the between the caliper connection and the axle that they twist and cause the axle to not be parallel with the handle bars anymore.

Joe Perez

iTrader: (8)

^^ This.

I realize that physics of this sort isn't easy to conceptualize, and often seems nonintuitive. But there are a few broad generalizations which can be safely made. One is that if the wheel and braking mechanism, as a whole, are attached entirely to the fork, then the specific location and design of the braking mechanism relative to the wheel is irrelevant. For any given deceleration (due to braking force), the exact same stresses will be applied to the exact same points on the frame.

The stresses on the fork itself do change a bit when you move the brake mechanism from one place to another, and that's where we assume (usually correctly) that a fork which is commercially manufactured with mounting points for both a rim brake and a disc brake is capable of using either one without unduly deforming under load or otherwise being compromised.


TL;DR: Too much speculation, not enough people actually giving it a try.

shlammed

iTrader: (8)

not true.

The point at which the axis of rotation for torque with a disc brake is further from the headset and closer to the axle. it puts more force on the axle that is further from the headset.

you just effectively increased the lenght of the torque arm and at the same time increased the load at the hub (torque arm).


This is (one of) the reasons you shouldnt upgrade a caliper brake mtb to disc...

You are right thinking that it takes the same energy to reduce the speed of the bike, but not how it is applied to the frame components and the geometry within it

Joe Perez

iTrader: (8)

Yes, and therefore the stresses on the fork itself did change.

But this is not relevant to the frame. It "sees" only the fact that the fork, as a whole, is transmitting "X" amount of force to it through the coupling at the neck, and that force is a constant for any given rate of deceleration.

Leafy

iTrader: (1)

That still has no effect on the head tube. This torque that you think exists is along the axis of rotation of the steerrer tube anways, so even if by some magic it was torquing the whole fork it wouldnt ******* do anything but make the whole fork assembly turn. Which of course it cant do because the caliper is mounted to the fork.

Joe Perez

iTrader: (8)

Perhaps putting this another way will make it clearer:

The only thing that the neck / frame care about (relative to stresses from braking) is the location of the contact patch between the tire and the road. THAT is what defines the geometry of the system insofar as the distribution of force under braking from the frame's point of view.

The contact patch is the fulcrum in this system, and that does not move when you change from one type of brake to another.

hustler

iTrader: (6)

mgeoffriau

iTrader: (7)

hustler

iTrader: (6)

Don't forget that the fork can flex relative to the other tein and easily flex the skewer. Not only does the tein bend, but so does the wheel. On super hard braking on my MTB with the Rockshox fork a wide front tire will rub the fork. I need a "through-axle".