It lasted 5 months!-
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  1. #1
    mtbr member
    Join Date
    Jan 2004

    Bonking ... not feelin' well It lasted 5 months!

    The SRAM dual drive internal geared disk brake 3 speed hub lasted 5 months. Which is 4 months longer than I expected. Failure point was NOT while doing a drop or a hop or anything else. I really was Just Riding Along the trail.
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    The axle broke at the C-clip on the disk side, probably the smallest diameter of the axle. I had noticed earlier in the ride that it seemed the hub bearings were getting loose, again, but as I was following Ken along a actually very smooth section, in middle gear (1:1 ratio) it suddenly went snap and got all wiggly (technical term for non-concentric bearing tracking). To the hub's credit, I was able to ride the 5 miles back to the gate, half of it in high gear. It was very unhappy in low gear.

    We will see if the LBS can get a replacement axle. This hub is designed similarly to the Sturmey Archer SW hub of old in that it uses three planetary gears for even loading vice the more common 2 planetary gears. If only SRAM would design it to have a longer shell and shorter "freehub" area and a stronger axle, this would be an excellent hub for all trail riding. Thats how I was using it.
    gearing note, it was running at 34:20 straight gear ratio.

    I know that some of you on the SS board were looking at this hub for many different reasons, that is why I post this post...

    bike ON


  2. #2
    Drinkin' Buddy
    Reputation: Blowout's Avatar
    Join Date
    Dec 2003

    Wow, I'm impressed!

    If you went through it in five months, I bet I can make it last at least a year. Maybe I'll break down and get me one now.
    Licking forehead to this coming weekend. I went out for a three hour ride today with Kevin and Ian to get my legs used to the pain and exhaustion I will feel on Saturday.
    Got Beer?

  3. #3
    semi-evolved simian
    Reputation: Mine'sAPint's Avatar
    Join Date
    Dec 2003
    Bravo Bob, we knew you could do it!!!

  4. #4
    The man who fell to earth
    Reputation: Ziggy-Stardust's Avatar
    Join Date
    Jan 2004
    Hey thanks for the update. I was looking at these internal geared hubs a few months back. Was on the verge of getting the SRAM (previously Sachs) 3 speed hub. There was a guy on here who had one and said it worked great.

    But after researching it for a while I found out the internally geared hubs actually eat up quite a bit of efficiency. A SS chain drive is about 98%-99% efficient (when clean and oiled), a derailleur/cassette setup about 95%, and the internally geared hubs ranged from the high 80%'s to maybe 94% or so. The internal geared hub efficiency dropped off the most for it's highest and lowest gears. As you moved to 1:1 the efficiency improved to the point it rivaled a derailleur setup. Another interesting thing was that the efficiency of all drive systems increased with power input...the harder you pedaled, the more efficiency you gained.

    Anyway, thanks for the info.

  5. #5
    highly visible
    Reputation: GlowBoy's Avatar
    Join Date
    Jan 2004

    Way to go Bob!

    Hope they can get that thing fixed for you.

    And looking forward to next week!

    I'm still debating what to do (if anything is possible) with the Sturmey AW hub I picked up at the swap meet back in November. Any idea if the axle (currently something like 115mm) can be re-spaced out to 135mm, or is that just too much difference?

    Ziggy, one thing I seem to remember about that efficiency study was that the figures for the derailleur drivetrain assumed a relatively straight chainline. So on a derailleur bike you'd achieve the measured efficiency if you were in one of the 3 or so cogs that are straight back from the chainring you're using. What they didn't quantify - but we all know is true - is that efficiency drops off real fast if you start using those bigger cogs with your big chainring or the smaller cogs with your small chainring. Even getting 2-3 cogs away from a perfectly straight chainline brings enough efficiency loss that you can feel it (at least on the road). In actual riding, the difference in efficency between a derailleur and an internal hub setup may be somewhat less than it appears.

    On an internal hub you get something like 94% in the direct drive (1.00) middle gear, 91-92% in the low gear and 88% in the high gear. That's the worst of the 3 systems, but ... these figures were all taken with a clean fresh chain.

    Add some mud or rust to the chain and the derailleur drivetrain is going to drop off in efficiency much faster than the SS or internal-hub drivetrains that don't have to snake that chain around through 2 pulleys. I bet with even a moderately dirty chain (which is unavoidable this time of year) the internal hub is at least competitive with the derailleur system for efficiency, and I wouldn't be surprised if it's actually slightly more efficient.

    - Dan (trying to justify a use for his internal hub)
    Last edited by GlowBoy; 02-22-2004 at 12:42 AM.

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