Advertise on Bikeforums.net



User Tag List

Results 1 to 15 of 15
  1. #1
    Charles Ramsey
    Guest

    Predicted life of heavy duty spokes.

    Wheelsmith fatigue tested 76 spokes 68 of them broke at the elbow and 8 of them broke at the threads. They also came up with a formula that relates stress to life the math will be at the bottom. If wheelsmith's test applies to the real world an if I did the math right then a 2.0mm spoke will last 2.01 times as long as a 1.8mm spoke and a 2.34mm spoke will last 2.84 times as long as a 2.0mm spoke. How much longer will a spoke longer will a single butted spoke last compared to a plain spoke? The problem is wheelsmith combined the two types of breaks into one formula but it looks like a 2.34mm/2.0mm spoke is effectively as strong as a 2.34mm plain spoke. Here is the formula Log(stress)=-.3xLog(cycles)+4.12 all logs base 10 the stress is in megapascals. For a given stress the formula gives the number of cycles where half of the spokes fail. The Log of the stress forms a normal distribution with a standard deviation of .072 and the Log of the cycles forms a normal distribution with a standard deviation of .24

  2. #2
    Senior Member Retro Grouch's Avatar
    Join Date
    Feb 2004
    Location
    St Peters, Missouri
    My Bikes
    Rans Enduro Sport, Hase Kettweisel Tandem, Merin Bear Valley beater bike
    Posts
    24,010
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Don't mean diddly. You can pretty much throw that formula out of the window so far as real life use is concerned because you can't normalize the quality of the wheel assembly. Arguably, that's the most significant factor.

  3. #3
    Senior Member mtbikerinpa's Avatar
    Join Date
    Dec 2004
    Location
    PA
    My Bikes
    92 Giant Sedona ATX Custom
    Posts
    1,672
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    The thing is, a spoked wheel should not permit enough spoke flex to achieve a fatigue issue. Ultimate strength can be a concern to a truely hardcore hucker, but to calculate how many cycles a spoke can withstand excludes too many variables. Spoke tension, force applied, inconsistent spike loads, etc.
    I am all for engineering data however, so don't let me quash the fun.
    Aviation Mechanic, Bike racer, Fitness Equipment Restorer

    http://pedalmybike.com/userTrackies/myTrackie4758.jpg[/url]

  4. #4
    Not So Senior Member
    Join Date
    Dec 2004
    Posts
    59
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    As others have said, there are to many variable and unknowns to fully predict how durable a spoke would be. I think that if some one were to try to fully calculate this, it would have a wide margin of error, and simply wouldn't apply to some situations. A road wheel would probably be the easiest to figure out, as there is possibly the lowest number of variables on that style of riding/wheel. A mountain bike prediction, throw everything out the window. There is simply no way to add into the calculation (at least practically) things like maintenance, rider style etc., and give these a number. An experienced wheel builder may be able to guess to the durability, that probably won’t involve math.

  5. #5
    Senior Member
    Join Date
    Sep 2004
    Posts
    328
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I think the formula could be reasonably used to compare one spoke to another assuming a given riding style. It's interesting they got two somewhat equivalent break points which suggests a near optimum design. I'm not sure I know anyone who actually counts wheel revolutions, except indirectly by mileage so the numbers them selves are somewhat academic

  6. #6
    Senior Member mtbikerinpa's Avatar
    Join Date
    Dec 2004
    Location
    PA
    My Bikes
    92 Giant Sedona ATX Custom
    Posts
    1,672
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Could do it like landing gear. That is if you did jumps a lot
    cycles(landings)
    Aviation Mechanic, Bike racer, Fitness Equipment Restorer

    http://pedalmybike.com/userTrackies/myTrackie4758.jpg[/url]

  7. #7
    The Red Lantern Rev.Chuck's Avatar
    Join Date
    Apr 2003
    Location
    Raleigh NC
    Posts
    5,967
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    There should not be any failure difference between butted and unbutted as long as the J-hook and threaded end are the same dia. A butted spoke might even last longer because they are a little stretchy and remove some of thefatigue from the other more prevalent failure points. I have never seen a spoke fail at the butt.
    Spoke quality is so high I never consider failure rates(Excepting straight 15g spokes, they breal to often for my taste) when picking them. My concern is ride and total wheel durability(OK, maybe weight )
    Are you a registered member? Why not? click here to register. Its free, and only takes 27 seconds!
    Help out the forums, abide by our community guidelines.

    I am in the woods and I have gone crazy.

  8. #8
    Banned.
    Join Date
    Feb 2003
    Location
    Fort Wayne, Indiana
    My Bikes
    84 Trek 660 Suntour Superbe; 87 Giant Rincon Shimano XT; 07 Mercian Vincitore Campy Veloce
    Posts
    4,766
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Charles, are you bored? Why in the world would you fuss over such drible? I ride DT Competition double butted spokes that have over 30,000 miles on them...do you think I care about how much more life I would have gotten had I opted for thicker spokes? NO!!

  9. #9
    I drink your MILKSHAKE Raiyn's Avatar
    Join Date
    Jul 2002
    Location
    St. Petersburg, FL
    My Bikes
    2003 Specialized Rockhopper FSR Comp, 1999 Specialized Hardrock Comp FS, 1971 Schwinn Varsity
    Posts
    15,071
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by froze
    Charles, are you bored? Why in the world would you fuss over such drible? I ride DT Competition double butted spokes that have over 30,000 miles on them...do you think I care about how much more life I would have gotten had I opted for thicker spokes? NO!!
    He's trying to trump 53-11 in the minutiae dept.

  10. #10
    Charles Ramsey
    Guest
    Look at the economics a 2.34/1.8/2.0 spoke weighs less than a 2.0 spoke and at 25 cents more will pay for itself in spoke replacement costs. Good spokes have rolled threads this makes the threads larger than the shaft this means the spoke holes have to be drilled too large. A double or triple butted spoke fits better in the spoke hole and should result in less stress to the flange. A perfect spoke would have an equal chance of breaking at the elbow or the threads. If any one is using these spokes let me know where they are breaking. Wheelsmith makes a 2.34/2.0 called a DH or a downhill. DT makes a 2.34/1.8/2.0 called the alpine and a 2.0/1.7/1.8 called super comp. The formula came from http://www.duke.edu/~hpgavin/papers/...heel-Paper.pdf or if that doesn't work look for it on damonrinard.com

  11. #11
    Licensed Bike Geek Davet's Avatar
    Join Date
    Oct 2002
    Location
    Los Barriles, Baja Sur, Mexico
    My Bikes
    Kirk Terraplane, Serotta Ottrott, Spectrum Super Custom, Hampsten Carbon Leger Tournesol
    Posts
    955
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Still doesn't mean much. A properly-built wheel, for the job at hand, will last for tens of thousands of miles and more. A butted spoke will last longer than a straight-gauge spoke.

    Jobst Brandt, who has ridden well over 200,000 miles, and wrote arguably the definitive book on Wheel building, uses the same spokes when his rims wear out! Spoke breakage is not a problem, again, with properly built wheels.

  12. #12
    Senior Member mtbikerinpa's Avatar
    Join Date
    Dec 2004
    Location
    PA
    My Bikes
    92 Giant Sedona ATX Custom
    Posts
    1,672
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I agree, I have reused a ton of spokes through the years and to date I have only had 2 broken(not even a wheel I owned or made).
    Aviation Mechanic, Bike racer, Fitness Equipment Restorer

    http://pedalmybike.com/userTrackies/myTrackie4758.jpg[/url]

  13. #13
    Charles Ramsey
    Guest
    People are breaking spokes they are tandems tourists and working bikes. Say you have a 40 spoke wheel and you break your first spoke at 4000 miles then your next break will be due at 4762 miles and your third at 5333 miles and your forth at 5820 miles. Now I tried to answer a specific question what happens if you build the same wheel but with stronger spokes. In the above example if you go from 2.0mm spokes to 2.34/2.0mm spokes then your first break will be due at after 10000 miles. This is what people are reporting stronger spokes seem to be indestructible. My first thought was a plain guage spoke was near opimum but it looks like all the breaks at the threads were at the highest cycles. It looks like a spoke needs to 1.48 times stronger at the elbow to get equal breaks at the elbow and the threads.

  14. #14
    Get the stick. darkmother's Avatar
    Join Date
    Nov 2004
    Location
    Toronto, ON
    My Bikes
    12 Y.O. Litespeed MTB, IRO Jamie Roy fixie, Custom Habanero Ti 'Cross, No name SS MTB, Old school lugged steel track bike (soon)
    Posts
    1,544
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Spoke breakage like this can be completely eliminated if the wheel is properly stress releived, and built with adequate spoke tension-assuming good quality spokes, and a properly designed hub flange. If the cyclical stress is low enough, the spoke will last indefinately.

  15. #15
    Senior Member mtbikerinpa's Avatar
    Join Date
    Dec 2004
    Location
    PA
    My Bikes
    92 Giant Sedona ATX Custom
    Posts
    1,672
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Agreed. As I said before, if it is tensioned propperly fatigue life will not arise.
    Aviation Mechanic, Bike racer, Fitness Equipment Restorer

    http://pedalmybike.com/userTrackies/myTrackie4758.jpg[/url]

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •