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New stuff on the way.

It has been the longest fall I’ve ever experienced with very little snow here in the valley and warmish temperatures. This has really not done the skiing any favors but it’s been great winter riding weather and perfect for product testing. This soft and friendly weather has allowed me to move ahead on the testing of disc brakes on my road bike that I hadn’t planned on doing until spring.

So – I took the plunge and had the good guys at Joe Young Wheels build me up a set of wheels using DT rims and DT 6 bolt hubs – the rear being spaced at 135 mm. I then got to work and made some custom disc brake tabs to work with my frame and fork design. The designing of the tabs was the time consuming part as there are many considerations in getting it right – they need to be stiff enough both laterally and rotationally, they need to be light, they need to distribute the braking load well and they need to be attractive. After cutting them from steel plate I dove in and ruined an otherwise perfect paint job (sorry Joe Bell) and fillet brazed them in place. I didn’t bother doing any finish work or polishing as I just wanted to see how the set up worked and thought I may just end up removing them anyway.

Now I can hear the mix or reactions out there right now and imagine they range from “very cool!” to “no one needs disc brakes on a road bike!” and for what it’s worth I was thinking both of these things myself at first. Disc brakes have been around in the larger world for a very long time. They were first made popular by Dunlap on the Jaguar C Type of 1953 after having been proven on aircraft. Discs have been in common use on mountain bikes for a solid 15 years now and the bugs have been worked out of the system. So when the UCI approved discs for use on cross bikes recently I could very easily see a further cross over to road bikes.

What advantages does a disc brake have over a traditional rim brake and what are the disadvantages? I’ll jump right to the disadvantages -

* disc brakes add weight – how much depends on what type of brakes you are replacing. The disc caliper is a bit heavier than most rim brake calipers and there is a disc rotor for the caliper to grab that you otherwise don’t need. It’s not a lot of weight but there is some.

* disc brakes require ‘bedding in’ – when you first set up a disc brake in the work stand they seem to work well and then take it out for a test ride and to be frank they dont’ work very well…….at least at first. Disc brakes require heat to bed the pads to the rotors and until this occurs the braking power is just not there. It takes just a little bit to bed them in and I did it on my bike by going down a hill near my house dragging the brakes until they got really hot. Once this happens the braking is sublime.

* disc brakes require different skills to set up – when you think about it a rim brake is really a big disc brake with the rim doubling as the braking rotor. A disc brake works the same way but the braking force is applied to a small rotor bolted to the hub – you squeeze the lever and the disc pads clamp the rotor and the bike stops. The real difference in setting the two type of brakes up boils down to how one sets up the disc caliper on the frame/fork. This technique will be specific to the brand of brake used but with the Avid BB-7′s I’m using right now it could literally not be easier. You leave the two main caliper bolts a bit loose, squeeze the brake lever to align the caliper to the rotor and tighten the bolts and you are now 95% of the way there. All that’s left is to spin the two dials to set the pads the right distance from the rotor and you are done. I see this as less of a disadvantage and more of something new to learn. Once you learn it I think it’s as easy and quick as dealing with a rim brake.

Advantages -

* disc brakes are safer on long fast descents – The issue with rim brakes with long downhills is that they heat up the rim and this in turn heats up the air in the tire and increases the air pressure. Not a big deal on regular hills but a very big deal when riding in the high mountains. This increased air pressure can lead to the tire blowing off the rim or in the case of carbon rims can cause the rim to fail. This is rare frankly but it does happen. You can also have your rim glue holding on your tubular tires soften allowing the tire to roll off. We saw this a number of years ago in the Tour when Beloki hit a patch of goo on the road on a fast downhill that had lots of braking. His bike slid in the warm tar and when it hit the grippy stuff his tire rolled off and it effectively ended his career. Again – this is very rare but it’s something that those of us that ride in the mountains now have to keep in mind and manage.

* disc brakes work in all weather conditions – the issue with rims brakes in the wet is well known. The problem is that the braking surface is right down next to the wet road constantly being doused with water. Add road grit and oils and the braking can be downright bad. Discs on the other hand are up and out of the road slime and since they get hot almost instantly they burn the water off the rotor within a single rotation of the wheel and you get the same braking you get in the dry. Think of how well your car brakes work in the rain. Hit the pedal and stop. Bike discs are the same way, even in the wet.

* disc brakes don’t wear out your expensive rims – normal rim brakes grab the rims with pads and grind what ever dirt and grit on them into the rims. This in time wears the brake track of the rims and can actually wear the rims out. This doesn’t happen often with aluminum rims but it’s all too common on carbon rims.

* disc brakes don’t care what size tire you run or if you want to use fenders – A rim brake has packaging issue around the tire. You can only run a tire so large under a short reach caliper brake and fenders can be difficult to fit unless the bike is designed for a long reach brake. A disc brake doesn’t care what size tire you use. If the tire fits in the frame/fork it will work. You also have the added benefit that you don’t need to quick release the brake to remove the wheel – just undo the skewer and the wheel drops out.

* disc brakes don’t care if your wheel is true – with a rim brake a broken spoke can be a minor pain or make for a long walk as the rim won’t spin between the pads. With a disc brake the wheel will turn as long at it clears the frame.

* disc rims can be lighter – this is an as yet unrealized advantage. Rims designed and made without the need to have brake tracks will end up being lighter. The rim brake type rim needs to have a flat surface for the pads, needs to be able to deal with the compressive force the brakes apply to them and needs to act as a heat sink. A rim designed to just hold the tire will be lighter and the word on the street is that we will see rims weights drop soon for disc wheels.

* disc brakes have the best modulation – this is the BIG one IMO and more than enough reason on its own to consider discs. Most types of brakes, rim or disc, will provide enough power to lock the wheel when dry but a disc brake will provide much better modulation. This may not seem to be a big deal until you try it for yourself. With a rim set up you can have a hard time feeling what the tire’s contact patch is don’t on the ground and how close it is to locking up. With a disc you get much better feedback and consistent braking power and this allows you to carry more speed ┬ádeeper into a corner and then brake later and harder. This means you’ve got a longer distance at a higher speed and in the end you will get to the bottom of the hill sooner than you would have with rim brakes. Cars and motorcycles have been working on brakes for a very long time in order to carry more speed deeper into a turn but it’s rarely talked about on a bicycle. I think we will see that change as road discs become more common. One thing I can’t over-stress here is just how much fun it is to do this – barrel into a corner and then drop anchor to get to your corner speed instead of feathering your rim brakes to keep speed in check all of the time. There are very few things that can actually make you faster on downhills and discs are one of them.

According to my word counter I’ve put down 1539 words so far and that seems like enough but I have a few things to add. I don’t think you are going to die in a great flaming crash using rims brakes the next time you go down a hill and I don’t think discs are for everyone. If you live in a place without steep long hills and you only ride in the dry then I doubt you would see much advantage to having discs. I spoke to a friend the other day who said he only needs enough brake to not his his garage door when he gets home from a ride and I understand that. But if you ride in the wet and/or in the mountains I think you would enjoy the advantage disc brakes give. I’ve been riding mine for a few months now and abusing them big time and I’m very pleased and can’t picture going back to rim brakes on either my road or cross bike. One thing I feel confident in saying is that Pro Tour guys will all be riding discs in the next few years. The advantages will so outweigh the downsides for them that it will be a done deal and we will see safer descending in the hight mountains of the grand tours. The strong rumors have it that both Shimano and Sram will be offering a high end disc set up that will be lighter and more simple this next model year. We should also see a move toward hydraulic actuation soon from both these guys and the already great modulation will only get better without cable stretch.

I will be offering disc brakes builds on road and cross bikes as soon as I can. It will no doubt be a few months down the road at least but I will offer them as an option as soon as I can. At this point I don’t know how it will affect the pricing but I expect it will be a slight upcharge. As soon as I know more I’ll pass it on.

1994 words – wow, that might be a record. Thanks for sticking with me.

Dave

28 Responses to “New stuff on the way.”

  1. SteveP says:

    Do disc frames/fork need to be constructed differently than rim brake frame/forks in order to handle braking stresses that are nearer to the hubs than the rims? Or is the stress shift so small that it doesn’t matter?

  2. kirks says:

    Hey Steve,

    I do think that the fork needs to be designed with a disc fork in mind and I suspect that there are many forks out there that would be ill equipped to deal with the different loading associated with a disc brake. That said I took my normal lightweight JKS fork and put the disc mount on it and it works very well.

    There are a few reasons for this – first is that with a steel fork the blade cross section increases as it nears the crown and this increased cross section does a very good job dealing with the stress. In effect the blade near the crown is the part that handles the load and a steel fork blade, even the light ones I use, are more than up for the task. The other reason is that the disc tab is designed to focus the load to the larger part of the blade. That’s why it has the extended tang that goes up the blade.

    It’s interesting to note that I thought that putting the long tab on the one blade and nothing on the other might end up making the fork flex asymmetrically. To check this I did a load/displacement test on the two blades before doing anything and they measured exactly the same. I then added the disc tab and remeasured and was surprised to get the same number – the tab had not affected the stiffness of the blade at all. The reason for this became apparent when you watched the flex flex under load. Most all of the flex takes place in the upper 1/3 of the blade and very little at the bottom and since the top stays the same I get the same flex, road feel and handling.

    So I’m getting no pull, twist or chatter at all. Just rock solid straight and stable stopping.

    Thanks for the question.

    Dave

  3. Mike B says:

    Good for you for experimenting. Being ahead of the crush of diskee bikes (new term maybe) will be huge as cyclist love new technology.
    And I think it look better because now al the mechanics of the bike (drive train) are low on the bike so the frame is less cluttered.
    Yes, I probably will never have disk brakes except for my MTB but I love the evolution of our sport.
    Care to estimate how many bikes with disks will be at NAHBS??
    Mike B

  4. kirks says:

    Thanks for the note and the comments. I too like the way disc bring both the visual and actual weight of the bike lower – low center of mass is always good.

    I have no idea how many disc road bikes we’ll see at NAHBS. Lots I hope. I’ll be showing a fillet brazed (in the raw!) cross bike with discs and I’m finishing it up this week. Exciting stuff.

    Dave

  5. Tim To says:

    perhaps I can send my JKS Classic back for a retrofit ? :)

  6. Peter W. Polack says:

    I can think of 2 more benefits of discs:

    The lack of brake dust generated during braking, specifically wet braking, will leave bikes and wheels cleaner when ridden in the rain.

    With the calipers mounted so low relative to rim brakes, the bike will have a lower center of gravity, improving handling. I realize this might be such a small improvement as to be imperceptible for all practical purposes, I’ll bet salesmen won’t overlook it!

  7. Neil Fairweather says:

    Thanks for the pictures and report. Do you plan on staying with the cable pull disk brakes or do you envision moving to the hydraulic once that gets worked out. The clean lines of the cables versus the adapter box really make for a nice looking bike.

  8. kirks says:

    Maybe……. We’ll see how it all shakes out and if retrofitting is a practical idea.

    Dave

  9. kirks says:

    I agree……….Karin’s bike has some very nice white rims and they stay fairly clean in the dry but look pretty bad once ridden in the wet. I also agree with lowering the mass on the bike. It might be small but it all adds up and getting that weight as low as possible is a good thing.

    Dave

  10. kirks says:

    Hey,

    Thanks for the question. I think in the long run we will see hydro brakes taking over – they just make sense. Cars and motorcycles gave up on cables and rods to actuate the brakes a very long time ago for very good reasons and I think bikes will adopt hydro brakes for the same reasons. I’m not a big fan of the cable to hydro adapters. Word is they work well but I doubt I’ll be building around them and I see them as a short term work around. Once the SRAM/Shimano hydro brakes are out I’ll go that way and not look back. I think electronic shifting will leave plenty of room in the brake lever for a master cylinder and word on the street is that we should see wet brakes sooner rather than later.

    dave

  11. dave crane says:

    Maybe because of a dirt bike background, I agree with you that modulation is a huge advantage- Thanks for sharing
    DC

  12. parris says:

    Dave thanks for posting a super interesting thread. I don’t know anything about disk brakes so the questions thoughts may be totally wrong and if they are any correction is appreciated.
    I’ve seen concerns posted about a disk brake setup affecting the front end of the bike due to twist on one blade as well as the blade that holds the claiper having a different flex. You’ve stated that the blades flex the same would it make sense that the wheel in the fork would also tend to reduce or cancel out any torque due to braking forces?
    Although the wheels may be heavier overall, with the weight concentrated at the hub and the rims eventually being lighter could it make the bike ultimately handle quicker/better due to how the weight is distributed?
    Is there One mounting standard for the calipers or is this evolving? Thanks for putting this up.

    Parris

  13. Vitaly B says:

    Hello Dave,

    thanks a lot for very interesting post. Basically I agree with advantages of disc brakes, but I have very often a couple of problems with them:
    - brake pads are grinding the disc. Especially by hydraulic brakes where you do not have a possibility to adjust a brake pad position manually. But also BB’7 I would not mark as problem-free. For rim-brakes I did not have this problem if the wheel is true.
    - it is true that disc brakes are much more friendly to ride in rain and snow, but I have a couple of time a situation in winter when the pads just didn’t go back from the disc and the wheel was almost blocked. This issue is for instance recognized by Magura and they suggested a procedure to make the brakes working.
    These should not be a problem if you have a service team, but if you just own a bike and must maintain it, you have to be prepared for eventual problems with disc brakes.

    Regards from Germany,
    Vitaly

  14. Patrick says:

    I am surprised at how much it didn’t change the look of the bike. Even with all of the positives of disc brakes, I wouldn’t switch if it changed the look of the road bike into something less beautiful. Win/win: improvement in brakes and still a great looking bike. Thanks for speaking english (vs techno blab) when you write about the pros/cons of the disc brakes.

  15. kirks says:

    Hey Vitaly –

    I agree that setting the pads is crucial to prevent the pads from rubbing the disc. I haven’t worked with all the different calipers out there but the ones I’ve worked with each have a way to set pad clearance from the rotor. With the BB-7 this is very easy but one still needs to be sure to have the preload on the cable set properly. Avid now ships the calipers with in-line adjusters and using them to set the brake up really is the ticket IMO. My brakes run rub free and make zero noise.

    I can see where certain designs might have issues with pad retraction in wet and freezing weather and there is no doubt room to improve here. To be fair if it’s wet and below freezing I doubt your rim brakes would be worth much so every system has its down side.

    From what I’ve seen SRAM will offer a hydro road disc that has independent pad settings and retraction so this should make set up even more simple.

    Overall I see the road discs as being relatively new technology with much room to improve over the very slim number of choices available now……..so I think we will see things just continue to improve. Again – I don’t think discs are for everyone nor do I think they will replace rims brakes in the general market but I do think they will offer a good alternative to those that would benefit greatly from them.

    Thanks again for your comments.

    Dave

  16. kirks says:

    I agree – I too wondered how the bike would look with discs and I think it looks great – purposeful and focused. It looks like the real racing machine that it is.

    Thanks again for reading.

    Dave

  17. kirks says:

    Hey Parris –

    Yes the front axle does help stabilize the package but I would not want to rely on it. The interface between the hub and for is too small to really be effective. I’d rather be sure that the two blades behave in a similar fashion independent of one another and then the problem takes care of itself.

    You are right – the added weight on a disc wheel is near the axle so the energy needed to get the wheel spinning is low. Once disc-specific rim weights come down there should be a performance advantage to the disc type wheel.

    Yes there is an industry standard for disc mounting so most any brake will bolt right up to most any disc frame.

    Stay well,

    dave

  18. Vitaly B says:

    Hi Dave,

    thank you very much for your explanation. Here in Germany I saw a lot of hydro disc brakes (Hayes, Formula, Hope, Magura) and none of them provide a possibility to adjust a pad position. And this is a “feature” that I’m really missing. But I’m pretty exciting about a development of road disc brake and hope, they’ll do things in a right way.
    I just want to ask, why did you braze rear disc tab between chain and seat stays? Is there any advantages again brazing just on the seat stay?
    Thanks for your answer.

    Vitaly.

    PS:
    Sorry, I forgot to say in my previous post that I found all of your bicycles very beautiful from both, technical and aesthetic, points of view :-)

  19. Eric says:

    Darnit — now must fine room in garage for one more bike.

    Dave: I may have lost this in the shuffle as I don’t know the topic well, but was the bike you did in the photos a cable-brake setup, and from the discussion I infer you may go to a hydrolic setup when-if SRAM-Shimano come out with a system you trust. If that is the case, and taking advantage of your patience with my ignorance, could you remind me why hydrolic may be preferable to cable (meaning, I take it, non-hydrolic). I’ll try to do a search and find photos of both types. Thx. Yrs, Eric

  20. Jayme says:

    Looks great Dave! Do you think we’ll ever see carbon discs, a la F1 cars, on bikes?

  21. kirks says:

    Hey Eric,

    I do think we will see a move toward hydro set ups and with good reason. Brake cables stretch and brake cable housing compresses and this can give any brake a mushy feel and compromise modulation. On the other hand fluid will not compress so you end up with more braking power and even better modulation. I’ve had hydro brakes on my MTB for about 16 years and they are wonderful.

    Be well.

    Dave

  22. kirks says:

    Good question – I like to think so. If I have a concern with them it is will they be able to handle the side load of a tip over crash? A steel disc is pretty tough and can handle a pretty good hit but I just don’t know how well a carbon disc could handle the impact. That said a carbon braking surface ring attached to an alloy spider could be the shit……………….

    dave

  23. Don4 says:

    Ever since experiencing an early Shimano mechanical disc brake (rear only) on, of all things, an AMF “10-speed” (my first road bike) back in the mid-70′s, I’ve been convinced that disc brakes were unbeatable. Glad to see they seem to finally seem to be coming of age.

    The three key items that appeal to me are braking on descents, braking in the wet, and the potential to offset the extra weight of the brakes themselves by going with lighter rims. To me, that last one is the perfect match for carbon rims, even clinchers. Take the heat of braking out of the equation, and suddenly, you are talking something I would consider!

    Interestingly, I found myself riding the Apple Cider Century this year, in a steady rain, with 5500 of my new found closest friends. I spent every moment of the decents, some of them 20+ mph, just because of the terrain, with my hands lightly on the brakes, to keep them clear of road grit and somewhat dry. I’ve done the same thing autocrossing in the rain, although that’s a bit harder! With discs, I would have been a lot happier, and a lot more confident.

    Nice work, Dave. I don’t have a Kirk yet, but I’m betting when I do order one, it’ll be with disc brakes.

    – Don

    P.S. Joe Young does makes nice wheels. I have a set on my bike!

  24. kirks says:

    I agree completely. I don’t think that discs will completely replace rim brakes any time soon but I do think they will become a viable option for those who would benefit from them. I look forward to seeing what comes down the pipeline.

    dave

  25. jeff says:

    Good work.
    Are you familiar with the ejection issues associated with front disc brakes? http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/
    Solution for you is simple enough; braze your tabs and mount the caliper on the RH (drive side) of the front fork.

    jeff

  26. kirks says:

    Yes I am aware of this. There are a few ways to handle it and mounting the caliper on the driveside of the bike is one way to go. The other is to use a front dropout with a slot angled such that the slot won’t let the wheel get pulled by brake torque – I’ve opted for the later and have custom front dropouts made with this in mind. The fillet bike and prototype I’ve been riding were both done before the new front dropouts were done so that will not reflect the design change.

    Thanks again,

    dave

  27. Jason says:

    Hi Dave,
    I have been reading back though your blog and it has been super informative, and inspiring; I am at the very beginning of my framebuilding learning curve. Your work is clearly very well designed and executed. Anyway, your response to SteveP above made me curious how you applied the load to your fork for the load/deflection test. Did you apply the load in the same direction as the force vector the brake imparts on the fork or did you try to apply the load in such a way that would mimic the “average” force vector under braking while the fork is being ridden? It would be challenging to determine the “average” force vector since it is certainly always changing in real life but, if this is what you did, and you combine that with your finding that most of the flex occurs in the upper 1/3 of the blade that would seem to be a data point for the argument that straight and curved bladed forks don’t really behave differently; since the curved section of the blade didn’t flex in your test (wow, that was a run on!). If you applied the load in the same direction as the force vector of the brake though, my point is moot. Again, I am thoroughly impressed with your design and testing process and your work in general. You have inspired me to try to come up with my own testing rig. There is lots to learn!

    Thanks,
    Jason

  28. kirks says:

    Hey Jason,

    I applied the load such that it would simulate the braking loads exclusively. The vertical and lateral loads are well understood and this is reflected in the design of a ‘normal’ lugged for and I wanted to see what would happen when the disc brake load was introduced.

    Interesting stuff.

    Dave

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