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Thread: 16:64 or 20:80

  1. #31
    4 Cycle Advanced User
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    my though is... adding teeth to the driver increases the diameter of the diver percentage wise, is greater than adding or subtracting teeth from a larger rear sprocket... I'm sure someone has done the math... and I'm sure i'm wrong but thanks for answering, I'm still tring to wrap my mind around... "does it create more friction wrapping a chain around a small gear with greater load on each link... or wrapping a chain around a larger gear with less load on each tooth"

  2. #32
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    yes I am using #219 chain.......perhaps this is why I'm finding the 16 driver is a little slower on dyno acelleration time, like you say, a little small.

    Love the previous thread on the matter......7 pages of bashing away with Alvin and his 2-strokes, I could think of nothing worse!......a very interesting read though B-)

    On my dyno I can plot and overlay curves of angular acceleration in Rad/sec^2......with the 20:80 ratio, its a no brainer, it gives noticably more angular acceleration at the bottom end, around 3000rpm than the 16:64 ever does......at the top-end, its the same......hence I'm taking a sabbatical for a while regarding the 16T, and will use a 19T driver for the rest of this year.

  3. #33
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    What is your angular acceleration measured from and how is your software computing it ? Not doubting what your seeing on your screen /data but ya need to know how its coming up with them # to determine if they are real or fake. Earlier you did not know if it was wheel speed or engine rpm. Start with the basics

  4. #34
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    Its measured from the 99 teeth on the wheel speed sensor, i checked with the dyno manufacturer and software writer.

  5. #35
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    If it was an inertial loss issue I would expect the loss to be consistant through the range. If it were a friction Issue I would expect it to be higher in upper rev range. Carefully check the chain slack is identical in each scenario. When you are swapping drivers is it just the gear only or the whole drum?

  6. #36
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    I did not arrive at the number, a bicycle race team that did massive research on this topic actually measured the number. They found the number was never consistent, the statement less 5% was accepted as true. How did you arrive at 1.6% frictional change?

  7. #37
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    Quote Originally Posted by Kart43 View Post
    I did not arrive at the number, a bicycle race team that did massive research on this topic actually measured the number. They found the number was never consistent, the statement less 5% was accepted as true. How did you arrive at 1.6% frictional change?
    I thought you were quoting the original post of being .05 seconds faster in a 3 second pull.

    Not even sure that the gain or loss would be equivalent to that number in the output.

    Sorry, I didn't have your frame of reference.

  8. #38
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    Quote Originally Posted by Oman View Post
    If it was an inertial loss issue I would expect the loss to be consistant through the range. If it were a friction Issue I would expect it to be higher in upper rev range. Carefully check the chain slack is identical in each scenario. When you are swapping drivers is it just the gear only or the whole drum?
    Yes, the chain slack was as identical as I could make it, within reason......for sure the trend I have seen does not make sense, but the numbers are the numbers, admittedley I'm scratching my head too, my dyno is not a crude item, quite a professional piece of kit, and I myself have been in and around dynos for 20 years for a living.....I dont know it all, but I'm not a beginner either!

  9. #39
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    You said .05 in 3 sec run, that has to be an average of the ten runs you made on that gear set, compared to an average of the other set. This being such a small difference When you compare all of the runs instead of the difference of the average, what is the range of the times were any of the 16:64 pulls quicker than the 20:80? Does your dyno have a controlled throttle or are you manually controlling it?

  10. #40
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    I will have a look at the data again tonight.......the engine idles at 2000rpm, the acceleration duration was measured from 2600-6100rpm, my dyno is inside a ventilated dyno cell, with a cable throttle control on a lever outside the cell......it feels like we are splitting hairs now!......yes 0.05 seconds is a small amount but over a 3 second run its 1.66%, which on the track could equate to a substantial amount of lap time, I remember it was quite repeatable......I have since changed my gearing to load up the wheel more and runs are taking 4.5 seconds or so.

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