AdamDZ

The brakes were not adjusted properly.

Adam

Metaluna

Someone alluded to disc hubs having an effect on wheel strength a while back. I can understand this on the front, where the rotor mount requires the hub to have unequal flange spacing and thus a tension imbalance between the left and right-side spokes, but I'm wondering what the effect is on the rear. On the one hand, the rotor mount will reduce the flange spacing, which could make the wheel laterally weaker, but on the other hand, wouldn't pushing the left-side flange inward actually offset some of the dish caused by the freehub, which would tend to equalize the spoke tension?

I'm just curious since, if a non-disc rear wheel is stronger, it tends to argue that the "disc in front, rim brake in back" configuration might be preferable to an all-around disc frame.

AsanaCycles

facilitates ease of mounting the bike when loaded.

that is

the curve allows you to simply step across the top tube
rather than swing a leg over the saddle
and/or
the need to lean the bike some to get a leg over the bike.

curved tube lets you step across the top of the frame
while the bike can stay relatively stable.

electrik

Sort of, because i think the more perpendicular the spokes are with the rim the less lateral stiffness but higher vertical stiffness.

sehsuan

Nice!

I wish there was some brand with this kind of disc mounts, although I guess On-One is the only one - since they designed it...
https://forums.mtbr.com/showthread.php?t=301181

The mounting hole looks so much more sturdy - though it has to be ridden to be proven... hmm....

neil

There's plenty available with disc brakes, if that's what you want. But why do you want them? Disc brakes add weight, require special (expensive) hubs, strain your spokes, and because of where they're mounted, require a heavier fork that's stronger near the middle. Most importantly, I can skid my bike with cantis; regardless of whether discs offer more braking force or not, the weak point remains in the road-tire interface. Once you've skidded, you've exceeded your bike's maximum braking power. If you want to improve it, you should focus on new tires, not new brakes.

Tourers also tend to be a cheap bunch. Many would rather free camp than spend $12 for access to a toilet and shower. I can't see many spending extra money on discs.

cyccommute 

I'll add that nearly every bicycle already has disc brakes. A 'rim brake' is a hub mounted spinning disc that is clamped between two friction pads by some kind of hand actuated lever. The only difference is rotor size. Even in wet conditions, a rim brake is adequate. I've ridden in many rain storms with rim brakes. It takes a little longer to stop then dry conditions but not significantly so. In icy conditions, having a brake that can easily lock up the wheels isn't an advantage. Trust me.

Leebo

I love m BB7's, got them on two bikes. Disks stop better in the wet and mud. Those claiming rim brakes are better probably don't ride here in New England. Bring out the gloves.

jabberwocky

Most touring bikes use mountain hubs, so getting disc hubs is hardly exotic or expensive (in fact, non-disc MTB hubs are generally harder to find than disc ones as MTBs have almost totally switched to discs).

Spokes aren't really an issue. Any wheel built to handle touring loads will handle disc forces with no issues. A stronger fork (and frame) is definitely worth considering from a ride quality perspective, though I don't notice any ride difference between my disc CX bike and my rim brake fixies or tourer (the touring bike honestly has a heavier duty fork than the CX bike anyway, and I strongly suspect that modifying the design to put a disc mount on it wouldn't actually change it very much).

As for skidding and power, the advantage to discs is they generate power with less effort (you don't need to grab as hard), and more importantly, they are extremely consistent. Wet, dry, icy, hot, cold, it doesn't matter. You'll always get the same amount of braking for the same amount of lever pull. When you are in a situation where precise braking matters, that consistency is just fantastic. Discs also have a big advantage when it comes to heat. Rim brakes cannot take as much heating without adverse effects (on the rim, tire and pads) whereas discs can take an enormous amount of heat before performance begins to be compromised. On a long descent on a loaded touring bike, that may be a big advantage.

Definitely a consideration, but more expensive touring frames exist, so obviously some people are willing to spend money on equipment. Discs add at most 100 bucks (probably more like $50-60) to a complete bike build, so its not like its some massive cost.

Uh, no. Generally speaking, they are both "disc brakes", but there are big differences between rim brakes and disc brakes as used on bikes. Rim brakes are squeezing a thin, hollow object (a rim) with much less force than a disc brake. They use soft, rubber pads with a long profile to compensate for the fact that they can't squeeze with much force. Disc brakes are squeezing a solid steel disc, and grab with considerably more force than a rim brake, using a solid resin (or sintered metallic) pad. They have very little in common in terms of function, other than that they are both, broadly speaking, brakes grabbing a disc.

Don't know about that, but I'm guessing most people who claim rim brakes are better haven't actually ever used discs. There is this perception that they are somehow new, immature technology, but they've actually been around a long time and proven themselves very reliable in the MTB world. Heck, BB7s have been on the market for almost a decade now, pretty much totally unchanged, and problems with them are almost unheard of. They are the definition of a bulletproof component.

To answer the original question (why they aren't seen on more touring bikes), I'd guess that its a combination of tradition and the fact that most touring bikes evolved from road bikes (where lighter-weight wheels/bikes and a lack of interest in absolute braking performance make discs less attractive). Theres a lot of market inertia as well (if the LHT sells well with cantis, why bother updating it to run discs?). And theres a bit of retro-grouchery as well.

I wouldn't be very surprised to see discs start appearing on more touring bikes in the next few years though, at least as an option. They definitely make a lot of sense on a touring bike.

Metaluna

Indeed, the Deore LX M585 front hubs are a great value right now (you'll need a Center Lock adapter for Avid rotors though). In fact JensonUSA is selling them for a couple of bucks less than the non-disc version.

https://www.jensonusa.com/store/produ...rlock+Hub.aspx
https://www.jensonusa.com/store/produ...+M580+Hub.aspx

chipcom 

Isn't that what stand over clearance is for, which is what I said?
Sorry, maybe I should have said step-over clearance.

neil

The whole point of my post wasn't that rim brakes are better. It's that there are tradeoffs and in the end you will not increase your braking power because the brake is not the restricting factor. Essentially, to paraphrase your post, you are adding weight and expense in order to not have to squeeze as hard. If you have arthritic hands, this might make sense, but for the rest of us?

And no, I have never owned a disc brake bike. I have test ridden one or two, but have not been convinced that there is a benefit for riding on a road, touring bike or not. Trail riding may be different, as knobby tires may have enough friction to take advantage of any increased power provided by the disc brake. Mud on the rim would also be far more detrimental to braking performance than water (generally I find that it's actually easier to skid when my rims are wet because I've lost more traction on the wet road than I've lost on the braking surface.) Different technology is appropriate to different applications.

KonAaron Snake 

This thread makes me really want to try a pair of discs on a long ride. I was looking at rack set ups and lot of the companies have lines specifically designed to work with disc brakes. I can definitely see not having the rim overheat on decents as a huge advantage.

I had a MTB where I was using v-brakes and ceramic rims and pads...I saw a notable increase in stopping power, especially in wet conditions. Would that work for a touring rig?

jabberwocky

To add fade resistance during extended braking, to add braking consistency in all conditions, to eliminate rim wear... Don't discount the power factor, either. Trying to bring a loaded bike to a stop in a hurry at speed takes a fair bit of force on the lever with rim brakes. There is plenty to appreciate about the extra power even if you aren't "arthritic".

Now, I'm not arguing that there is anything wrong with rim brakes (FWIW, my touring bike has rim brakes, as do two of my road bikes). Just that there is a lot of misinformation out there regarding discs for some reason. On a road bike, there are really three disadvantages to discs: they require heavier fork/frame construction, they require 3-cross laced wheels (or at least a lacing pattern with trailing spokes) and they weigh more than caliper brakes. They are also hampered by the fact that roadies generally don't ride in bad weather, and certainly don't ride heavy, loaded bikes. However, on a touring bike, weight is a non-issue (seriously, who cares about an extra 1/4 pound of brakes on a bike with 5 pounds of fenders/racks and 30 pounds of gear hung on it?), the frame and fork is already pretty heavy (to handle racks and touring loads) and the wheels probably aren't 20 spoke radially laced jobbies.

On the other hand, I do have a disc-equipped road bike (A Lemond Poprad Disc) and have had another before (Redline Conquest Disc-R, which I had for 6k miles before selling). Both served as general purpose road/commuting bikes. I also have a rim-equipped tourer and two rim-equipped fixies that get used for the same purposes. The discs are flat-out superior brakes, even compared to the koolstop-equipped v-brakes on the tourer (which are excellent). I honestly don't see much in the way of downsides with them aside from weight (obviously, if you're building a weight-weenie machine, discs need not apply). I don't see them catching on in the roadie realm anytime soon, but I think they're an excellent solution on a touring bike.

Leebo

Neil, I have to disagree with you, disc brakes will increase your stopping power. I have four bikes with discs and 3 without. They are great for wet and dirty conditions. This is often what I ride in when I'm on trail, commuting or touring. I'm 230 lbs plus bike and gear, that's a whole lot to slow and stop. Ride one for a while, you will come to see the light. Be not afraid.

cyccommute 

Um, yes. There is functionally little difference between the two systems. Rim brakes may be squeezing a hollow object but there are two walls with a solid structure between them. In effect, the rim is like an I-beam and as strong a steel hub mounted rotor. I doubt that anyone using hand power alone could apply enough force to crush a rim. Both systems operate the same way using the same principles, i.e. frictional deceleration by squeezing a rotating disc between two pads.

Rim brakes use long rubber pads to keep erosion of the rim to a minimum and extend the life of the wheel. Replacing rims isn't a cheap proposition and the rim serves not only as a braking surface but as an integral part of the wheel structure and we want them to be as light as possible. You could use solid resin (rubber isn't exactly a liquid resin) or sintered pads for rim brakes you'd just have to replace the rims more often or use a harder material for the rim surface. There are ceramic rims out there that will take far more abrasion than aluminum will. If you used steel rims and sintered pads but no one would like the weight.

As for force, I doubt that you can squeeze the brake levers with much more force when using a 'disc' brake than with a rim brake. The advantage for the disc comes from less lever travel because the pads are set closer to the rotor. Most rim brakes I've seen are set too far from the rim for the best braking in the first place. Some advise that the brake lever should travel half way to the bars before the brakes engage...to prevent pitchover I suspect. That is far too much lever travel and is likely the major reason that people complain about rim brakes.

The amount of force that you can put on the rim or on a rotor hardly matters anyway. The maximum deceleration available for any bicycle braking system is limited by the tire's contact patch, by the rider's position and by the possibility of pitch over. Nearly every single bike out there is capable of enough deceleration to skid the rear wheel and rotate the bike around the front axle independent of whether it is a rim or 'disc' brake.

Leebo

When I want to skid the front and rear wheels, I use disk.

cyccommute 

I have both disc and rim on mountain bikes and I don't find any difference in braking power between them. Both are capable of locking the rear wheel...not really a good test of ultimate braking ability but it's the gold standard that everyone uses for how powerful their brakes are It takes slightly less lever movement to achieve the same result using discs over rim calipers but it's not like my fingers can't move an extra 1/2" when using the rim brake equipped bike.

I can even skid the tire on my touring bike with a full load but even then skidding a tire isn't the test of ultimate braking power. Slide forward on any bike and you can skid the tire until the cows come home...ask any 10 year old kid to show you how if you don't know.

Mud and water on the rim aren't even that detrimental to decelerating a bike if you know how to deal with it. It take longer to stop but if you are riding in wet or muddy conditions, it's a lesson you learn pretty quickly (and possibly painfully).

The biggest single factor that you can use to influence how the bike brakes in any condition is to know how to move your center of gravity and how it influences the deceleration of the bicycle. Sitting on the saddle in a normal riding and applying the brake will allow you to get to around 0.5g of maximum deceleration before the bike rotates around the front axle and puts you on your face. Move your CG back and down a few inches and you can double that deceleration without the risk of hitting your face

jabberwocky

He is correct, actually, in that no brake can exert more force on the pavement than what the tire is capable of. The difference is that, if it is easier to get to and hold the maximum proper braking force (i.e. immediately before the tires being skidding), the brake will certainly feel more powerful. The advantage of discs isn't necessarily raw power, its consistent power. I certainly agree that I can consistently stop faster on my disc bikes, because its easier to lock the maximum force in without skidding.

sstorkel

So, you seem to be siding with the disc-brakes-have-no-advantage crowd... but you admit that rim brakes take longer to stop in wet/muddy conditions?

FWIW, wet weather riding is one of the reasons that I installed a disc brake on my touring bike. In the rain, my rim brake-equipped bikes take a noticeable amount of time to clear water/mud/sludge off the rim before they provide any significant stopping power. The disc brake-equipped bike, on the other hand, begins to slow almost immediately and stops in a significantly shorter distance. Don't know if the disc-equipped bike really has more absolute stopping power than a rim brake, but it does provide more consistent braking and better modulation than any of the rim brakes I've used...

electrik

Where is this disc vs v-brake discussion going anyways... i see a lot of arguments about the features of either systems but not much in the way of stating why fewer touring bicycles have disc brakes. The only real problem i ever heard about disc brakes was some guy dropping his bicycle into a fire-pit and the rotor being bent, but if he carried a spare rotor or a rotor truing fork(both wise ideas) he would have been rolling quickly. On the flip side i have heard a few stories about machined rim-brake sidewall failures ending trips and causing delays. Smashing a rim on a tree so it will become true enough to go through your brake stays is less than idea. Sand and grit grinding through expensive rims is not cool. If anything disc brakes increase the longevity of your equipment at a modest cost in weight(sounds good for touring) - does anybody have some real weight numbers here?

Finally, nobody here is trying to force certain people to use disc brakes, stick with the rim brakes if you want, but their are those of us always looking for a better fit.

Metaluna

From the Avid website:
BB7 caliper + rotor: 329 g
Single Digit 7 (V-brake) + hardware : 185g (a common mid-range linear cantilever. Most of the other models were within 20 g give or take)

I also looked at a few Shimano hubs and the disc and non-disc versions were usually within 5-15 grams, with some having no stated weight difference (e.g. XTR freehub). You may also need center lock adapters so add a few grams there.

So by my math, the difference for 2 brakes is: (329*2 + 15*2) - (2*185) = 318g, or about 12 ounces.

electrik

Hmm, yeah... there is more to it though, for one the rim can be lighter since one doesn't need a braking surface but then one also needs a stronger fork...

Metaluna

Yes I forgot the fork...that could be pretty significant (also the left rear triangle). Not sure how to figure that one. I think there are a few cyclocross forks that are sold in disc and non-disc versions that might be useable to get an idea of the weight difference.

cyccommute 

It takes longer to stop in muddy and wet conditions with any brake system...on any vehicle be it a car or a bike. Simple physics. Again it comes down to where the deceleration is taking place...at the tire, not at the brake. Moving your center of gravity rearward in slick conditions (water, mud, ice, snow, boiling oil...if you happen to be attacking the castle) does more for slowing the bike then what kind of brakes you have.

As for better modulation, I haven't experienced it on the two disc brake systems I've owned. Both have been digital...either being on or off...and don't offer the kind of braking and speed control that I get from a rim brake . The hydraulic system I have on a mountain bike turns the bike into a skidding machine but the ability to skid the rear tire (or front) isn't a measure of deceleration ability of the bike. It's just indicative of bad braking. A rolling wheel will stop a bike faster with more control than a skidding one.

You can surely put me in the 'disc don't offer any advantage crowd'. I'm proud to be there