Yes. Larger diameter discs, in theory, generate more braking force so they increase the problems already inherent in disc brake systems. Namely, they put more stress on the fork and the wheel components (spokes, hub, etc). To keep weight down, large diameter discs are often the same thickness as their smaller-diameter cousins which may mean that they may be more likely to be damaged.

That said, I've been commuting, mountain biking, and touring with disc brakes for years. The only problem I've ever encountered was a slightly bent 185mm rotor. Figured out where the bend was by watching the disc rotate past the caliper, pushed it back into place with my thumbs and everything was fine. Didn't even have to remove the wheel from the bike...

Larger diameter rotors are frequently made of thicker material and it varies with manufacturer. It is inappropriate to generalize in this way. Furthermore, larger rotors are limited in their "braking force" by traction just as with any brake. They can stress a fork differently due to the different geometry of their mount and this is what concerns MTB fork makers. It doesn't have to do with "more braking force". Arguably, the "more braking force" comes from the extra weight of the rider, not the extra size of the rotor. It would probably be good advice to consult the fork maker of any limit to rotor size but outside of MTB I'd wonder if they even consider that.

The downside of a large rotor, aside from the modest weight increase, is the overly light lever effort that could reduce control. That's rider preference. Large rotors are slightly easier to hit and damage but that seems more a trail riding issue than a touring one. I have also bent a rotor on a ride but it was an aluminum rotor and I took an awkward fall. Bending it back for the ride out was not hard and it's always possible to do the same kind of damage to a rim but with less field fixability.

Make sure your front axle is always on tight when using disc brakes.

A couple of videos I found that demonstrate what can happen.
http://www.youtube.com/watch?v=losWKtO69q4
http://www.youtube.com/watch?v=NIpo2Y-0rGk

Make sure your front axle is always on tight when using rim brakes too.

All they've done there is deliberately remove the QR and show that the wheel will come out easily. No different, or more dangerous, with disc. Don't think that the torque that lifts the wheel in the second video matters once you put a 100 pounds of load on that wheel especially on the front where weight transfer is dramatic.

The real problem for disc brakes is that the forces of braking tend to loosen the QR over time. This means you need to make sure your wheels are tightened regularly (surely you are doing that already, right?). In reality, tabs on the dropouts, the ones specifically added to address this issue, make sure that you have quite a bit of notice that something is loose. Nothing to worry about unless you are negligent. Seriously, people who still make an issue of this must have an agenda.

I have had a loosened wheel on a trail ride. For miles it sounded as though my headset was working it's way loose. Finally I stopped to check it. The wheel wasn't loose enough to be noticed if it weren't for the noise. On the other hand, I once had rim brake pad holders that allowed the pads to drop out when I held the brakes while moving backward at an intersection. That created a far more dangerous situation than discs ever did. Both issues were my fault, not condemnations of any braking technology.

No, it isn't. I own two Magura rotors (185mm and 160mm), two Avid rotors (185mm and 160mm), and a Shimano rotor (160mm). There is no difference in thickness between the different-sized rotors from the same manufacturer. I was also surprised to find that there's very little (max 0.004in) difference in the thickness among all of these rotors.

Honestly, I've been looking for thicker rotors and been unable to find any. Perhaps you have a source? I guess they shouldn't be difficult to find, given the frequent variation in size... but I've been coming up empty-handed.

You've covered three manufacturers and two sizes so you know enough to make a sweeping generalization, right? Doesn't seem like you need any help.

To many, 185mm isn't considered a large diameter rotor nor one that justifies extra thickness. Go up a size and you'll find that rotors do, in fact, get thicker as their intended use changes. Perhaps you should refine your claim to just the size you have personal interest in.

I don't know if I could find a 180mm rotor thicker than a Magura but I can find thinner ones. ;) I own 180mm rotors from five different manufacturers and the thickness varies by 10%. It could be even greater.

Yes.

The videos simply shows a disc brake puts a downward force on the axle and what could possibly happen if a QR axle came loose on a downwards facing dropout. I don't think a 100 pounds would make any difference. If the same test was done on a bike with a v-brake there wouldn't be any downward force on the axle wanting to push the wheel out of the fork.

Is it possible that the downward force of the disc brake on the axle might be causing this.
I've never had this happen but heard people say that can happen more with certain types of QR axles.

Not all fork ends are the same, some are much better designed then others and some would be more prone to this failure with a loose axle.
A foward facing dropout is much better then a downwards facing dropout.
The retention tabs on some dropouts are little more then a small burr on the tips. while others which I think are of a better design will have retention tabs that basically enclose the axle ends making it much harder for a axle to come out.

No agenda, I have a couple of bikes with disc brakes and like them.

The title of the thread is Disc vs V brakes, those vids merely show something that could happen with disc brakes that not everyone might know about and should be aware of.

Yep. I've covered the three largest disc brake brands and the two most-used rotor sizes. You haven't provided any data to back-up your claims, so I'm not inclined to believe them. Pull out a dial caliper, take some measurements then post some numbers and we'll talk.

While you're doing that you might also want to look at Magura's DIN 79100 deceleration data for rotors of different sizes. As a layman, it sure looks to me like large rotors cause a bike to stop faster than smaller rotors. That would seem to suggest that there's more force (and thus more stress) involved somewhere between the brake caliper and the ground, wouldn't it?

A video that shows a non-zero force convinces you that a 100 pounds of weight would not make a difference?

Take the entire QR out of a wheel and then ride it. Sooner or later the wheel will come out regardless of what style brake you have. This is not the situation that disc brakes cause nor is it the root of the problem.

Yes, it is related. The problem isn't that the wheel can come out if the skewer is loose, it's that braking will cause the skewer to become loose. Getting a skewer with better clamping force helps and through axle designs solve the problem.

The tabs aren't there to solve the problem, they are there to prevent a catastrophe if the problem occurs. It's one thing to claim that disc brakes can loosen skewers, which they can, and it's another thing to suggest that the skewer suddenly comes clean off as the videos do. The skewer will loosen, the tabs will hold the wheel on, and hopefully the rider will notice and fix it before things get worse. Sure, some tabs are better than others and some designs eliminate the problem entirely.

Actually what they show could happen with any kind of brake. Neither video shows anything related to a disc brake issue.

Hydraulic discs have dual pistons, and by definition the actuating slave cylinders are behind seals.
cable discs are good , and may be a better touring choice,
as no problem with bring a Keeper to replace the disc on Hydraulics..
squeezing the lever is a no-no, when the wheel is removed, hence the 'keeper'.

Just starting to use my Bike Friday with Avid 160 discs, mechanical..

favorably impressed with Magura's Hydraulic Rim Brake.

My previous Load bearing tour bike has Scott Peterson SE cantilevers ,
a very impressive brake .. used with cable out the top Modolo levers..

You've provided data to back up yours? Apparently you missed the fact that I just measured all my 180mm and found a variation of 10%.

Sure, we'll talk as soon as you learn the subject. Go back to your original claim and think about it some more.

You're a layman now? :lol:

A bike is limited in it's maximum braking by either the traction of the tire or by weight transfer that would otherwise cause an endo. If neither of these occur then the rider has inadequate brakes. An upright bicycle is limited in stopping deceleration to around 0.6g and increasing rotor size can't change that. All it does is reduce the effort required to make it happen (which, interestingly, the DIN tests you refer to measure).

The Magura tests assume a standard load and standard lever force and they ignore traction and center of gravity. They do not show what you claim they do but rather demonstrate your lack of understanding. If you had a sufficiently low CoG to support unlimited deceleration rates combined with a tire of unlimited traction and yet had limited grip strength then, yes, a larger rotor would generate more braking force. It's the stuff you've ignored that makes all the difference.

Video 1 had a person on the bike that looked to weigh more then 100 pounds, the QR skewer was attached but loose and the wheel did come out of the fork.

Video 2 the person is merely showing what happened on the 1st video from a side angle, it doesn't really mater if the axle was there or there's any weight on it.

Rubbish, a rim brake mounted on top of a fork will not put the same directional force on the axle as a disc brake.

The first video has a rider lifting the front wheel off the ground and having the loose wheel come out. No braking is required for that and he clearly lifted up while braking with both wheels at nearly zero speed. The second video has a wheel with only it's own weight as a load and no skewer whatsoever. It shows that a lifting force is present but no indication of it's magnitude or significance to real riding.

Interestingly, a rim brake also does this, it's just that with a rim brake the dropout naturally resists it. Change the disc dropout and it will too. Some do this.

It's clear to anyone who thinks about this for a moment that these videos are reactionary and irrelevant. You claim to not have an agenda and yet you continue to insist that this is important information that disc brakers need to know. Why is that? Everyone should keep their wheels tight. Do so and this is a non-issue, disc brake or otherwise.

It's an experiment you can try with any decent v-brake vs. Avid BB7 setup [using the same standard housing the v-brake is using] vs. a decent hydraulic disc brake. None of these brake systems allows much adjustment of the braking setup [unlike say cantis] so it's an easy comparison.

As your post points out clearly there are folks online who don't know what they are talking about which is why I'd suggest that you give anything you read some critical thought and follow up with tests on the most promising ideas. That way you can satisfy yourself what's accurate and what's nonsense.

I have given this critical thought, that's how I know what is wrong with it. ;) You haven't considered mechanical gain inside the caliper and it has led you to improper conclusions. Perhaps you should ask Jan Heine about it, you do acknowledge after all, in this blog, that your "thoughts" are inspired by his. I would be embarrassed to have written that article, by the way. If you want to know how to set up BB7s, go to MTBR where there are users who take those brakes seriously. The suggestion that BB7s are inherently spongy is hysterical. The chief complaint among mountain bikers is that BB7s are the opposite. Perhaps you have a bad mechanic.

For you to assert that a BB7 has a cable compression problem that rim brakes don't would mean that BB7s require more cable tension. That's easy to prove false. Furthermore, you are wrong to say that BB7s allow little adjustment. BB7s allow for the adjustment of rotor size, a far greater adjustment than anything on a canti. They are adaptable to a range of levers and rotors, allow for adjustment of lever firmness, which you have yet to learn, and they have a range of pad materials available.

Once the pads make contact, further pressure on the lever must result in flex somewhere. That is true for all brakes, it is not inherently a problem for one approach and not another. The big liability of the BB7 as a disc brake is that it is mix-and-match rather than a complete system. It is also a brake that has to meet the contradictory expectations of a wide range of cyclists, including lazy randonneurs.

To provide a shortcut to reasonable solutions for BB7s, if your overall braking effort is too high, get a bigger rotor and consider a larger rotor on the front than on the rear. You may also need to consider your pad material as this can effect braking effort. If your lever feels too spongy, move the non-moving pad closer to the disc. If your brake is too on-and-off, move that pad further away. Keep in mind that some degree of softness in the lever is desirable and designed into various brakes but there is a degree of preference involved. If a lot of flex is required of the brake, it will occur at the lever or in the cable, it won't occur inside the caliper. The BB7 makes contact with one pad before the other and relies on rotor flex. You take advantage of this to provide the feel you desire. Yes, I own BB7s as well as rim braked bikes. I know the differences.

You measured five rotors, all of the same diameter. How does that support your argument that larger-diameter rotors are frequently thicker than smaller-diameter rotors? All you've shown is that different manufacturers sell rotors of (slightly) different thickness...

So, it sounds like there's absolutely no reason to install larger rotors, correct? I feel like a fool! Can't believe I was scammed, multiple times, by Specialized, Avid, and Magura :( Anyway, thanks for pointing this out! I'll be able to save money by switching back to 160mm rotors the next time I need replacements...

I don't see the rider lifting the front wheel of the ground and I don't see the front wheel even leave the ground. The rider seems to be seated, isn't pedalling and I can't see him lifting upwards in anyway.
As for nearly zero speed, do you think that this couldn't happen at a higher speed, I'm not going to prove it will, can you prove it won't ?

Does what ?

So you can see the directional force on the axle from a rim brake is different to that of a disc brake and it doesn't want to expel the axle from a downwards facing dropout as a disc brake would.

Some fork manufacturers have done this and probably for a good reason, but a lot of manufacturers haven't.

Reactionary, it certainly got a reaction from somebody.
Irrelevant, possibly but it doesn't hurt to see some things.
Agenda, if you think that I'm trying to stop people from using disc brakes, I'm not, I don't care what sort of brakes they use, if they're happy with them then that's good enough for me.
Important information, I never mentioned 'important' but I do think that it's important to make sure the axle is on tight as you've stated yourself and if this does make someone pay a little bit more attention to their axle and check it a bit more regularly, this can't be a bad thing can it ?
After all you have said yourself that disc brakes can make QR axles work loose and you seem to be able to see that there is a downward directional force on the axle from a disc brake .


I have no more to say, happy riding.

Yes, that's all I showed because I was contradicting a specific claim if yours. I was not offering evidence of anything else. I have shown, though, that there is variation in rotor thicknesses. It will be hard for you to argue there is none in the broader context. Again, you need to consider what a "larger rotor" really is and why it would be used. A simple, "+1" size intended for the same caliper will likely be the same thickness and it will be thick enough as it was considered by engineers in the first place.

Wheel size, load, grip strength, heat dissipation...but yeah, other than those, absolutely no reason! Here you demonstrate the problem once again, you aren't really thinking about this.

You may have been scammed. Perhaps you should switch to rim brakes instead. ;)

You won't see what you don't want to see.

The nearly zero speed enables the rider to control the weight transfer and keep the force off the front wheel. It would be harder at higher speed.

I prove that it is no problem each time I ride my disc brake bikes. ;)

The "directional force", as you call it, is the "does what" and it is only different in its direction with a rim brake. That is because of the location of the rim brake compared to a disc brake. Orient the dropout wrong and a rim brake would do the same thing. Not all disc brakes exhibit this issue because of the way they mount on the bike and the way the dropouts open.

The downward force on the axle is what is demonstrated in the videos and it isn't what the problem is. I have said this over and over. The problem is the loosening of the QR over time. That is not what the videos show. This issue was the focus of a lawsuit and it is natural that there is some plaintiff-generated hysteria over it. Those efforts clearly worked and have been repeated here.

Frankly, I don't understand why people even use QR skewers anyway. They don't serve much function outside of racing anyway. Certainly the external cam models with their weak clamping forces are poor choices and those are the ones most problematic with discs. Get a real QR, or better yet a bolt-on variant, and stop worrying about this.

the place where the disc caliper is becomes a torque center..

2 Custom Builder's solutions, fork dropout faces forward not down,

and the caliper gets mounted ahead of the Right fork blade ..

Of course the Mountain Bikes with a Non QR Through-axle, do a pretty solid mount.

the place where the disc caliper is becomes a torque center..

2 Custom Builder's solutions, fork dropout faces forward not down, EX: Tout Terrain
also builds a stronger blade on the left of the fork.

OR the caliper gets mounted ahead of the Right fork blade .. torque center forces the axle In ,then.

Of course the Mountain Bikes with a Non QR Through-axle, do a pretty solid mount.

Can't you just carry a replacement rotor?

You do realize that a v-brake is a essentially a disc brake on 20"+ disc...:rolleyes: :twitchy: LMAO.

that goes down close towards the mud and water with every rotation.

The braking force required at the pad to achieve a specific amount of speed reduction depends of the type of brake being used. As you so rightly pointed out if you need to brake with less force use a bigger disc - such as a rim brake on a 26"/700c rim. Using less braking force means that the amount of compression in the housing for a cable brake is less. As soon as you switch to a hydraulic disc you'll see that the higher braking force is more effective due to the more efficient method of transferring force from the lever to the brake pad.

I don't get paid by the character...:twitchy: so rather than argue with you I'll leave you to read a few brief words from Sheldon Brown:

"Hydraulic brake actuation comes naturally with the demand for a high mechanical advantage. The need for such a high ratio made cars switch to hydraulics in their early days and is why they are essential to disc brakes that require a higher mechanical advantage than other brakes. In addition, hydraulic lines, in contrast to cables, allow small bend radii and access to narrow space. However, as long as rim brakes serve well with the current mechanical advantage, hydraulics will probably remain with disc brakes."