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    • CommentAuthortypeDvorak
    • CommentTimeDec 17th 2010

    The pedals are skipping what feels like a link/groove/tooth when i apple heavy torque. I took my bicycle out for it's maiden voyage to a trailhead at a nearby park. As i reached the top half of the first hill I got out of the saddle and started to pull with the upstroke and felt the pedals skip. I duplicated the problem of flat ground by accelerating hard.
    Dumbfounded i went to a shop.
    The closest shop chalked up it up a biopace ring and that it is a poorly designed ring. At first I found this hard to believe as i ran a biopace ring on my first fg conversion at 48/17 and never had a problem with the chain skipping under stress. The more i consider the size difference between the chainrings on both bikes.
    My questions are:
    Are the number of teeth engaged during that part of the pedal stroke not enough to keep the ring and chain from separating for one link?
    How was this a non-issue when the bicycle was geared?
    What kind of solutions that don't involve losing the biopace chainring do you guys have to offer?
    So far the only thing i can think of doing is putting on one of those half-link chains to get the tension on the cog and ring tighter. the teeth on the freewheel could be wrapped more, i removed a link but the resulting chain was barely long enough to keep the rear wheel in the sort-of horizontal dropouts.
    • CommentAuthorAphex139
    • CommentTimeDec 17th 2010
    If the dropouts are semi-horizontal, why not just try losing the tensioner? My friend had a similar problem on a MTB conversion, and when he took the chain tensioner off, it was fine. He didn't have an ovalized Biopace chain ring up front, though...
    Is the ring oriented to the spider properly? I would try rotating it counterclockwise by one arm (as you're facing the drive side). It seems to me that the eccentric of the Biopace ring should be just trailing the crank arm instead of being lined up with it.
    Also, is there any way to install the tensioner so that it's pushing the bottom run of the chain up instead of pulling it down?
    Albeit without a biopace ring I had this same problem on my first ss cross setup and found the problem to be worse with over-tight chain tension, I finally realised the skipping was being caused by the chainline being slightly out. Check your chainline is completly straight before spending on new ring or chain, a few mm left or right could save you some ££s. Using a tensioner adds another factor into the chainline so its important to make sure everything lines up perfectly.
    Just noticed your using a bmx style screw on freewheel, it can be hard to get a straight chainline with those without respacing the hub and dishing the wheel accordingly, if you've used it as a direct replacement for a multispeed freewheel it probably isn't in the right place for straight chainline, other not ideal but possible options are to use spacers on bb or hub threads to move chainset or freewheel in or out as required.
    I hope this isn't all too obvious as I notice you also have fixed gear bikes so you may well have already done the whole chainline thing.
    • CommentAuthorncecchi
    • CommentTimeDec 17th 2010
    yeah, just get rid of the tensioner and run a straight chain. semi-horizontal is fine.
    I'm just gonna go on record and say that Biopace is one of the most (if not the most) asinine marketing gimmicks unleashed into the cycling ecosystem.
    • CommentAuthorpolitburo
    • CommentTimeDec 17th 2010
    i had biopace chainrings for a second with a geared set up. I dont think its completely asinine, but it wasnt particularly great, either.
    • CommentAuthorncecchi
    • CommentTimeDec 17th 2010
    Biopace is so fucking radical. So Epic. Amazing.

    anyone who says otherwise doesn't attend the Church of Sheldon Brown or hasn't ridden on much.
    • CommentAuthoravail86
    • CommentTimeDec 17th 2010
    The chainring is elliptical so some part of your pedal stroke the chain is tight, others loose you are not getting an even pull on the chain. On my fixed gear, I originally had a Biopace and about killed myself when I was pedaling fast and went over a speed bump which threw the chain off because of the ellpitical shape of the ring, my chain was in a loose part and thus got thrown off and my chain locked up around my cog. so in all, JUST GET A NEW CHAIN RING-THATS ROUND.
    I don't attend the Church of Sheldon Brown, and though I respect the faith and it's followers I must say that on this particular issue Reverend Brown (rest his soul) was full of shit up to his eyeballs. Here's why:

    round 48t chain ring + 17t cog = 2.82/1 ratio, or 74.2 gear inches

    ovalized 48t Biopace ring + 17t cog = 2.82/1 ratio, or 74.2 gear inches

    What Shimano and every other maker of ovalized rings wanted consumers to believe is that they've magically converted a constant in this equation into a variable. What riders feel and perceive as some sort of performance benefit from ovalized rings is simply nothing more than a wobbly ass drive train. When you turn the cranks, you're still pulling the same gear ratio throughout the entire rotation. Nothing about moving the chain away from and back toward the fulcrum can possibly boost performance because the number of teeth engaging the chain always remains the same.

    Shimano introduced Biopace in the eighties when technological prowess was limited to a select few. I just looked at the set I have here (yes, even I own a set of these stupid things), and the sticker on the large ring proclaims, "COMPUTER DESIGNED DRIVE SYSTEM". Sounds pretty high tech, huh? Back in the eighties people lapped shit like this up because most of them presumed that computers held some level of knowledge unattainable by mere mortals with pencils and drafting tables. Yet, in all of it's futuristic promise, Betamax...err......Biopace inexplicably never managed to take permanent hold in the marketplace.
    • CommentAuthoryeeyek8
    • CommentTimeDec 17th 2010 edited
    "delete - relatively useless post"
    • CommentAuthorfastfixie
    • CommentTimeDec 18th 2010 edited
    I ran a Biopace on a FG set up I had a couple yrs ago. Check my roadster set up. I had a problem with dropping the chain untill I took it to a shop. They checked retensioned my chain tightening it a 1/4 of a turn on ech axle nut at a time until it was completely straight and I never had a problem with it again.

    I will say that Biopace is the only chainring I ever had this problem with. Hope this helps.
    Michael, I'm afraid your reasoning is off.

    Counting teeth is only a constant on a circle. It's a measure of circumference. It's convenient because, in a circle, a given radius (the lever) always has the same circumference.

    But when you're not using a circle, that relationship is broken. Imagine an extreme case: a straight line with 24 teeth on each side, no wider than the spindle. Assuming that the tensioner can handle the change in chain length, you see how the leverage changes from extreme to near-zero?

    Similarly, imagine that the chainring is eccentric, with the spindle waay over by the teeth on one side. It would be hard, then easy, then hard to pedal.

    It's the radius from the center of the spindle that makes it easier or harder to pedal, not the circumference. Circumference is just a convenient measure when discussing circles.
    You're completely over-thinking it. Circumference is the sole determinant in how much power is needed to complete a full chain rotation under any given load, because it determines the distance that chain has to travel. If anything, what you described would be detrimental to efficient power transfer, since the best path for the chain to take is one of least resistance; in this case, a circle. There's a reason that we're not all riding Biopace right now, and it's not because the technology is too advanced for us knuckle dragging proles to appreciate.
    • CommentAuthorlatron
    • CommentTimeDec 18th 2010
    Posted By: Michael PerzIs the ring oriented to the spider properly? I would try rotating it counterclockwise by one arm (as you're facing the drive side). It seems to me that the eccentric of the Biopace ring should be just trailing the crank arm instead of being lined up with it.

    +1. The Church of Sheldon also says that you can run biopace on fixed gear with only slight variation in the tension, and thus no tensioner. It's worth giving it a try.
    • CommentAuthorSkidMark
    • CommentTimeDec 18th 2010 edited
    But why run a Biopace ring at all? Just get an Origin 8 chainring, they are inexpensive. I rode Biopace when it came out, it would make the bike sort of lurch forward when you stood up to pedal in a low gear. Every MTBer I knew replaced at least the granny if not the middle ring as well with round rings. However I do like Biopace for the big ring.

    Chainline is suspect. Are you still using the bb that goes with that Deore crank? What is it like 115mm? I had to use a 105mm bb to get chainline on my Fixed/Free mtb.
    Right now it is set up with the stock length spindle and a 32t granny gear and a 16t cog.

    And about this rear hub, is it a dedicated singlespeed hub or a hub meant for a multispeed freewheel? Riddim track has a valid point.

    Time to start measuring, Sheldon can help you.
    • CommentAuthortypeDvorak
    • CommentTimeDec 18th 2010 edited
    Hey all, thanks tons.
    To answer chainline questions, it is a shorter spindle in the bb and I had help re-dishing/spacing the wheel over so I could use a bmx freewheel on the hub the cassette was on and the tensioner is dead on with feeding the chain to sprocket. Reversing the tension is something I hadn't thought about, I'll try that.
    • CommentAuthorpeazweag
    • CommentTimeDec 19th 2010 edited

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