Disc road bikes - your opinion

Discussion in 'Road Cycling' started by AyeYo, May 2, 2014.

  1. swampy1970

    swampy1970 Well-Known Member

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    I have a life. The wonders of portable devices and being able to type fast. A few minutes to write a longish post does not constitute "not having a life..." I spent 10 years racing bikes and 5 of those where nearly every waking second was about bikes - you could say I'm passionate about the topic. I'm of the opinion that anything that could constitute a technical advancement should be tried, tested, modified and tested again and then if it's good enough, it should be unleashed on the Pros to thrash - cause that's where all the gremlins are exposed. If it doesn't work take it back to the workshop and see if it can be improved using current technology. The road decides what works and what doesn't. My local bike shop is still of the opinion that Power Meters are a waste of time and that one should spend their money on fancy low profile very lightweight wheels. Cycling lore... Often so, so wrong. In reliable data I trust.
     


  2. Froze

    Froze Well-Known Member

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    Exactly, and it's the same thing that the tandem manufacture said who have studied various brakes systems because tandems carry a lot of weight yet have to stop using the just 1 brake on each wheel just as a regular bike has to with half the weight. This is why tandem bikes, touring bikes, clydesdale riders all (or should) use wider tires because it boils down to that nasty thing I said earlier...TIRE ADHESION. This is why a sports car used in racing events as as another poster wrote about uses wider tires and different tread design than a stock Miata all because of increasing tire adhesion to not only stop faster but to also handle better.
     
  3. Froze

    Froze Well-Known Member

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    I can accept your first paragraph because it's true!

    The second paragraph I cannot accept because I test rode many STI systems and a couple of Ergo systems both used but mostly new and none shift faster in the rear than SIS, they both, including friction shift darn near the same on the front. You should try an old bike with a properly adjusted SIS system and your eyes will open up.

    The third paragraph is what other forums I've read over the years is saying what they believe to be the life expectancy of STI systems and those that have reached those mileage figures were saying that they had to replace stuff but felt they got a lot of miles on the components too which I was laughing hysterically!!! The forums also are indicating that chains and gear clusters should be replaced every 3,000 miles or so which again I find to be extremely short. This is why I too take care of my stuff because I want it to last a long time which is indicative why I got 160k miles on my old Suntour Superbe components and they're still rideable. So I agree with you, this is why I too look after my own stuff.

    The fourth paragraph, no mechanical device will last forever, cars engines and transmissions will fail in time, yes taking care of the systems with proper and timely fluid change can extend that but in the end they will fail. Modern transmissions do not last as long as the older 3 speed autos due to extensive use of plastic and thinner steel components to cut weight, this is a known fact, and the more gears they put in the more long term issues have occurred. The 8 speed hasn't been out long enough yet for fair assessment, but if follows the same course as other more geared autos then we can expect more problems. Most older 3 speed auto trans were bullet proof, the GM's Turbo 350 and 400, Ford C6, and the most reliable and bullet proof trans EVER built was the Chrysler Torque Flite 727, all of those trans could take a redline neutral drop at a complete stop and just smoke the tires, but the 727 was so over built that it found it's way into many drag cars with up to 700 hp in stock form (a simple and inexpensive shift kit to any of these autos improved the quickness of the shift both in terms of firmness and manner of how the driver could shift it.) and up to 1,000 hp with minor mods. And a "quirk" with more geared autos is that the 6 and 8 (and the soon to be produced 9 speed) speed autos are almost constantly "hunting" for gears which will shorten their life even more due to the constant shifting, this is why too that trucks even with 4 and 5 speed autos when towing are requested to turn off the overdrive feature or put it in D instead of OD because if left in OD the trans is constantly "hunting" gears. Having said that about the differences in reliability with a 3 speed auto vs a 8 speed brings us back to bicycles because the older 5, 6, and 7 speed bikes the gears and chains lasted at least 3 times longer than todays 9,10, and 11 speed systems because they used thicker gears and chains, this is why you will rarely if ever see a chain or gears on todays bikes lasting 10 to 13,000 miles. My old bikes the chains would last about 10 to 13k miles and the clusters about twice as long as that and sometimes longer, and the chainrings even longer.

    By the way, of course a person should know about the cars they own and to make sure they put the right engine oil, transmission fluid, and even radiator fluid that the manufacture requests for that particular brand and sometimes even the model you own, doing anything different and you could ruin a component.
     
  4. CAMPYBOB

    CAMPYBOB Well-Known Member

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    Quote of a quote of a quote:
    "You shouldn't need to replace a transmission ever."


    Somewhere...a village is missing its idjut.

    Dumbest statement I've read since the Germans bombed Pearl Harbor.
     
  5. swampy1970

    swampy1970 Well-Known Member

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    I currently have a road bike with Dura Ace 7900 and a tri bike with a 7900/XTR drive train running SIS (bar ends) - both shift as fast. While one can't expect tranmissions to last forever, it's not unreasonable to expect way more that 10 years heavy duty service from a truck transmission - heavy duty being the operative word. The "big rigs" that we use for testing lubricants (engine and transmission oil) get full engine and transmission rebuilds every 250,000 miles to check for wear and the original components are put back in - only gaskets are changed and typically more than 1,000,000 miles are the norm for a properly maintained engine and transmission.
     
  6. new_rider

    new_rider New Member

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    So much butthurt in this thread. :)

    It's over. Disc brakes are inferior to rim brakes:

    But, you might ask, aren’t motorcycle-style disc brakes more powerful?'

    Surprisingly, no. The engineers at Shimano and Avid (companies that produce both types) have confirmed Santana’s test results. Even the newest and most powerful bicycle disc brakes haven’t yet caught up the power of the best V-style (or linear-pull) rim brake.


    http://santanatandems.com/Techno/UnderstandingBraking.html

    All that's left is delusion and denial.
     
  7. AyeYo

    AyeYo Member

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    Everyone is ignoring that article and focusing on completely subjective and baseless claims that disc brakes are more powerful. Where is the testing evidence? There's been testing posted from multiple sites showing the superiority of rim brakes, but nothing showing the superiority of disc brakes beyond people claiming "they're so much better and more powerful!!!" with zero evidence to back it up.
     
  8. CAMPYBOB

    CAMPYBOB Well-Known Member

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    Some how...some way...all the bicyclists made it easily down the Gavia Pass and the Stelvio on today's Giro stage...in the rain...the freezing rain...the snow squalls...the frozen fog...with ice cold road spray flying.

    All...on caliper rim brakes.

    It's a miracle none of them kissed a house.
     
  9. swampy1970

    swampy1970 Well-Known Member

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    If it'd be 20 years ago, they wouldn't have swept the road for cowshit, gravel and diesel... ... But it looks like someone riding Campag might actually win something! Maybe...
     
  10. new_rider

    new_rider New Member

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    Still waiting on your "evidence" that disc brakes are superior.

    Oh wait, you don't have any. :)
     
  11. CAMPYBOB

    CAMPYBOB Well-Known Member

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    Quote by Swampy:
    "If it'd be 20 years ago, they wouldn't have swept the road for cowshit, gravel and diesel..."

    BZZZZT!

    Incorrecto!

    Your short memory is forgetting just a week or so ago when the ice skating rink stage in Bari and riders were still hitting the deck like their tires were manufactured by shimaNO.

    [​IMG]

    Do you even criterium, brah?

    Wide, open roads and they were still soaked with craptastic lubricants poorly engineered not to break down under rain and sunlight.

    Need more street sweepers from third world countries...I'm pretty sure they still make those crappy brooms out of twigs and crap over there.

    [​IMG]


    But, to beat a horse that's near death...disco brakes would not have helped a lick on these roads.
     
  12. maydog

    maydog Well-Known Member

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    There is a dearth of data supporting either sort of braking system. All I have seen is a lot of anecdote and opinion. Your assumptions / models ignore the fact that a rotor can tolerate much higher clamping forces and temperature ( as long as it does not get to the fluid and frame). Also clamping area does not direclty affect the frictional force. Your argument is that this one guy who builds tandems thinks so yet still puts disc brakes on all his tandems, is not convincing.

    Nor is is convincing to argue that the pros can descend without them - I'd guess that the pros spend a fair bit less time pulling on the brake racing down a mountain than the weekend warrior with a few extra pounds and a healthy fear of god.

    You are comparing a technology that is well established and has little room for further development to an emerging one that is undergoing continuous improvement. I am cheap and the difference in performance between systems is not great enough so all my road going bikes will be using rim brakes in the near future, but I am not going to fault the manufacturers for trying to innovate, not stagnate the market.

    There are a few beautiful disk designs coming out. A few weeks back I was in a shop and they were prepping a brand new Guru titanium framed cross bike with hydraulic disks and electronic shifting. It looked great - at 12K with electronic shifting I doubt that it would ever see mud or rain - but what a bike.
     
  13. jhuskey

    jhuskey Moderator

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    I told you to let that one go, after all Hitler wanted the pineapple concession. I do agree that all transmissions are not created equal. Ford made a real turd for a while(early 2000s) that would systematically go out at 60 -70 K miles and start slipping,. Some components are just junk but with good service even a turd can last longer. Operator error is generally equated to " it's not my fault".
     
  14. CAMPYBOB

    CAMPYBOB Well-Known Member

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    Quote by JH:
    "...after all Hitler wanted the pineapple concession."

    So...he was on the dole?


    "Ford made a real turd for a while(early 2000s) that would systematically go out at 60 -70 K miles and start slipping,. Some components are just junk but with good service even a turd can last longer."


    I work with several manufacturers of automotive and light truck transmission components. Shafts are so lightly engineered it is ONLY through the engine management system reducing engine torque during shifting that keeps the splines from being ripped off the damn pieces of shit.

    Bearings are replaced with craptastic bushings. Clutches are undersized. Pump flow and pressure are marginal. No safety factors designed in.

    Basically, they are programmed to fail in a way that would do shimaNO proud. NO lubricant can save the FAIL and no frequency of change or transmission-overhaul-in-a-bottle can undo the piss poor designs that sacrifice power handling abilities to the gods of weight, NVH and fuel economy.

    It isn't just Ford. Nor is it limited to the fail found in cars and light trucks. Class A trucks are going through a rash of failures not seen since Road Ranger became a trade name. Eaton...Allison...at least those are rebuildable. See what rebuilding your 6-speed FERD slushbox costs as opposed to just replacing it with a sealed, factory fresh unit. Hell, it was cheaper to just stuff a new Hydro-Gear under one of my only 5-year old garden tractors that buy the rebuild parts and overhaul the piece of trash, myself.

    Now...if Hitler WAS on the dole...was it because of non-Aryan hula girls or because the shimaNO parts in the Zeros kept them grounded and he he had to do the job himself?
     
  15. CAMPYBOB

    CAMPYBOB Well-Known Member

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    I forgot to mention...all the major automotive playas share the same transmission component pieces parts and FERD and Goobermint Motors share actual transmissions...with some small parts tuned to their particular applications.

    No Snake Oil has been developed that can replace the longevity designing with real engineering know how of how to make a mechanism that lasts long enough that your grandchildren could proudly drive that vehicle. Much like polymer frame firearms, modern vehicles and the sub-assemblies from which they are assemble are disposable landfill fodder.
     
  16. jhuskey

    jhuskey Moderator

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    I always suspected those guys like to share their parts.
     
  17. CAMPYBOB

    CAMPYBOB Well-Known Member

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    It all goes back to the grass skirts. And the days when disc brakes were just a gleam in Hitler's eye's.
     
  18. swampy1970

    swampy1970 Well-Known Member

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    I've ridden more crits than I'd like to admit despite hating events that went around in circles and featured nothing interesting of note. Think back about 15 years - do you remember Pros falling off their bikes like Lemmings on a regular basis? No, neither do I. Maybe the modulation issue with carbon rims and rim brakes is more of a concern than ultimate braking and heat dissipation. The riders union will be calling for all races to be neutralized unless race day is 75F, no wind or rain. Disk brakes are hardly new technology. Their application for road bikes might be fairly new but if they're so crap it's a wonder why work so well on race cars - with no vacuum assist. 250mm seems to be big enough to haul a ~950lb with driver Formula Ford race car to a halt pretty damned quickly. Shifter Karts use pee-wee brake rotors and anyone that tells you that SuperKart brakes don't try and eject your eyeballs out of the front of your helmet needs to reconsider their grasp on reality - the last time I looked, they weren't much bigger than 8". Sure they have more "tire" for grip but that's not the discussion here. That someone can't apply the lessons learned elsewhere and apply them to a tandem really doesn't provide evidence that disk brakes are crap - it tends to suggest that their implementation is rather naff.
     
  19. AyeYo

    AyeYo Member

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    Quote: Maybe the modulation issue with carbon rims and rim brakes is more of a concern than ultimate braking and heat dissipation.

    Probably true, for carbon rims at least.

    But then suddenly you're back to talking about braking force...

    Quote: Disk brakes are hardly new technology. Their application for road bikes might be fairly new but if they're so crap it's a wonder why work so well on race cars - with no vacuum assist. 250mm seems to be big enough to haul a ~950lb with driver Formula Ford race car to a halt pretty damned quickly. Shifter Karts use pee-wee brake rotors and anyone that tells you that SuperKart brakes don't try and eject your eyeballs out of the front of your helmet needs to reconsider their grasp on reality - the last time I looked, they weren't much bigger than 8".

    Again, you're comparing vehicles with leg actuated, long lever travel brakes that offer hundreds of pounds of force at the master cylinder to bike brakes with a two inch long, 1/4" throw lever actuated by two fingers that offers a couple pounds of force at the master cylinder. Multiply those initial forces out by the hydraulic advantage and then tell me about how it's an apples to apples comparison. You're also ignoring two other very important parts of the equation which are piston size and clamping area, and those are two more points on which tiny road discs fail. You can put a 300mm rotor on the bike, but that's only going to do so much when clamped with a 5mm diameter single piston.

    Here's a really good article by StopTech on braking physics that'll help you see how many variables in the braking system you're overlooking.
    http://www.stoptech.com/docs/media-center-documents/the-physics-of-braking-systems

    Quote: Sure they have more "tire" for grip but that's not the discussion here.


    But it is the discussion when you start talking about race cars and go karts ejecting your eyeballs. That has everything to do with tire grip and nothing to do with their braking systems. As already stated many times, any bare minimum braking system capable of locking the tires cannot be improved upon for single-stop performance. If the coaster brake equiped bike I had as a kid could maintain tire traction instead of skidding all over the place, that would have ejected my eyeballs too. A Kia with worn out drum brakes on warm slicks will out-stop a Ferrari with 15" carbon rotors and six piston calipers on plastic tires. If I didn't go airborn over the bars and into the trees when hammering my crappy rim brakes at speed, those would eject my eyeballs too. It's a traction and weight transfer issue, NOT a brake power issue.


    What is continuously overlooked is the simple fact that rim brakes ARE disc brakes. They have a really, really big disc, which is why they have the stopping power advantage. Road disc brakes are a massive compromise towards the bare minimum of stopping power and heat handling required to stop a bicycle. Every article about their development demonstrates this as manufacturers strive to find the smallest possible rotor and least caliper mass that won't result in boiling fluid on a long downhill. It's not about performance, it's about new tech for the sake of new tech and the struggle to make that new tech reach the bare minimum of safety and usability already offered by the current tech. We've seen this same phenomenon with MTBs. "OMG 29ers are the best bikes ever! How could you ride anything else??... oh wait, no, 29ers are too big, 650b is the best bike ever! How could ride anything else??? OMG more gears is better!!! Double, triple, quadruple, 10x front gearing!! NO wait, fixed speed is better!! Oh wait, no it's not then you can't climb hills!! 1x11 is better!! How could you ever ride anything else???" It's marketing hype and separating people from their money. It's not about performance.



    Relevant part of above linked article. I've highlighted all the variables you keep overlooking.

    Quote: The Brake Pedal
    The brake pedal exists to multiply the force exerted by the driver’s foot. From
    elementary statics, the force increase will be equal to the driver’s applied force multiplied
    by the lever ratio of the brake pedal assembly:

    Fbp = Fd ×{L2 ÷L1}

    • where Fbp = the force output of the brake pedal assembly
    • where Fd = the force applied to the pedal pad by the driver
    • where L1 = the distance from the brake pedal arm pivot to the output rod clevis
    attachment
    • where L2 = the distance from the brake pedal arm pivot to the brake pedal pad

    Note that this relationship assumes 100% mechanical efficiency of all components in the
    brake pedal assembly. In practical application, the mechanical deflection of components
    and friction present in physical interfaces prevents this condition.

    The Master Cylinder
    It is the functional responsibility of the master cylinder to translate the force from the
    brake pedal assembly into hydraulic fluid pressure. Assuming incompressible liquids and
    infinitely rigid hydraulic vessels, the pressure generated by the master cylinder will be
    equal to:

    mc
    bp
    mc A
    F
    P =

    • where Pmc = the hydraulic pressure generated by the master cylinder
    • where Amc = the effective area of the master cylinder hydraulic piston

    Note that this relationship assumes 100% hydraulic efficiency of all components in the
    master cylinder assembly. In practical application, fluid properties, seal friction, and
    compliance the physical components prevents this condition.

    Brake Fluid, Brake Pipes, and Hoses
    It is the functional responsibility of the brake fluid, brake pipes, and hoses to transmit the
    hydraulic fluid pressure from the master cylinder to the calipers located at the wheel ends. Out of necessity, part of this subsystem must be constructed from flexible
    (compliant) materials, as the wheel ends are free to articulate relative to the vehicle’s
    unsprung mass (most commonly known as the body structure). However, again assuming
    incompressible liquids and infinitely rigid hydraulic vessels, the pressure transmitted to
    the calipers will be equal to:

    Pcal = Pmc

    • where Pcal = the hydraulic pressure transmitted to the caliper

    Note that this relationship assumes 100% hydraulic efficiency of all brake fluid, brake
    pipes, and hoses. In practical application, fluid properties and the compliance inherent in
    flexible brake hoses prevent this condition.

    The Caliper, Part I
    It is the first functional responsibility of the caliper to translate the hydraulic fluid
    pressure from the pipes and hoses into a linear mechanical force. Once again assuming
    incompressible liquids and infinitely rigid hydraulic vessels, the one-sided linear
    mechanical force generated by the caliper will be equal to:

    Fcal = Pcal × Acal

    • where Fcal = the one-sided linear mechanical force generated by the caliper
    • where Acal = the effective area of the caliper hydraulic piston(s) found on one half
    of the caliper body

    Note that this relationship assumes 100% hydraulic efficiency of all components in the
    caliper assembly. In practical application, fluid properties, seal friction, and compliance
    the physical components prevents this condition.

    The Caliper, Part II
    It is the second functional responsibility of the caliper to react the one-sided linear
    mechanical force in such a way that a clamping force is generated between the two halves
    of the caliper body. Regardless of caliper design (fixed body or floating body), the
    clamping force will be equal to, in theory, twice the linear mechanical force as follows:

    Fclamp = Fcal ×2

    • where Fclamp = the clamp force generated by the caliper

    Note that this relationship assumes 100% mechanical efficiency of all components in the
    caliper assembly. In practical application, mechanical deflection and, in the case of
    floating caliper bodies, the friction in the caliper slider assembly components prevents
    this condition.
    The Brake Pads
    It is the functional responsibility of the brake pads to generate a frictional force which
    opposes the rotation of the spinning rotor assembly. This frictional force is related to the
    caliper clamp force as follows:

    Ffriction = Fclamp ×µbp

    • where Ffriction = the frictional force generated by the brake pads opposing the
    rotation of the rotor
    • where µbp = the coefficient of friction between the brake pad and the rotor

    Note that this relationship assumes 100% mechanical efficiency of all components at the
    brake pad interface. In practical application, mechanical deflection (compressibility) of
    the brake pad materials and friction found between the brake pad and the caliper body
    components prevents this condition. In addition, it should be noted that the coefficient of
    friction between the brake pad and the rotor is not a single fixed value, but rather changes
    dynamically with time, temperature, pressure, wear, and such.

    The Rotor
    While the rotor serves as the primary heat sink in the braking system, it is the functional
    responsibility of the rotor to generate a retarding torque as a function of the brake pad
    frictional force. This torque is related to the brake pad frictional force as follows:

    Tr = Ffriction ×Reff

    • where Tr = the torque generated by the rotor
    • where Reff = the effective radius (effective moment arm) of the rotor (measured
    from the rotor center of rotation to the center of pressure of the caliper pistons)

    Because the rotor is mechanically coupled to the hub and wheel assembly, and because
    the tire is assumed to be rigidly attached to the wheel, the torque will be constant
    throughout the entire rotating assembly as follows:

    Tt =Tw =Tr

    • where Tt = the torque found in the tire
    • where Tw = the torque found in the wheel

    Note that this relationship assumes 100% mechanical efficiency of all components at the
    wheel end. In practical application, mechanical deflection and relative motion between
    the rotating components prevents this condition.
     
  20. maydog

    maydog Well-Known Member

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    These armchair analyses are ignoring a lot of aspects of the brake function and include poor assumptions.

    You are not fully understanding what you are reading here - frictional force is not proportional to the contact area. Engineers have a wide latitude to play with the mechanical advantage to multiply the the force applied at the levers. Last I checked, most people can easily generate more than a few pounds of grip force. Fifty+ pounds per hand is a better low end estimate for men and women.

    In a disc system the force could be multiplied many times over since the disk will not crush as a rim would. The pad travel required is also much less since the disk should be more true than a rim.

    In the cable actuated caliper systems that I have used, there seems to be a point of diminishing returns where additional brake force at the levers no longer results in a proportional stopping force. This could be due to flex in the levers, pads, calipers, rims, cable stretch or my own fear of breaking something. I'd imagine that a hydro or even mechanical system could be made much more rigid hence the better modulation and potentially more reliable peak braking force.
     
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