Front sprocket size and drivetrain loss

Discussion in 'Performance & Technical' started by rock3r4life, Sep 28, 2016.

  1. rock3r4life

    rock3r4life Rides with no training wheels

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    Im curious, is it ideal to have a larger or smaller front sprocket, ratios the same?

    I ask because my bmw came with a 17t, and I use a 16t.

    My r1 has a 16t and I need to raise the ratio a lil, now the question is do I bump the rear up 2, or the front down 1?

    How small is too small of a front for high-pony high-rpm applications?
     
    #1 rock3r4life, Sep 28, 2016
    Last edited: Sep 28, 2016
  2. Roll Hard Racing

    Roll Hard Racing What's an apex?
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    Most people only go down 1 tooth in the front. If you go more, the chain tends to rub the living found out of the swingarm chain guide.
     
    rock3r4life likes this.
  3. sammPD4075

    sammPD4075 STT STAFF
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    i run -1/+1 on my r1
     
  4. rock3r4life

    rock3r4life Rides with no training wheels

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    New gen? the 14 and back had 17t
     
  5. sammPD4075

    sammPD4075 STT STAFF
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    2007 .. im broke so i dont get new stuff haha but ive always stuck to -1/+1 on any trackbike ive owned .. i dont change them for certain tracks .. i just run the same gearing and suspension for every track
     
  6. JTRC51

    JTRC51 The fast Juan

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    Going down 1 is less rotational mass vs going up 2. Lol
     
  7. rock3r4life

    rock3r4life Rides with no training wheels

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    I get that, but you are also asking the front of the chain to wrap VERY quickly around and even smaller radius, presumably requiring more energy. I guess my question is how to weigh the pros and cons of parasitic loss, and rotational mass.

    Heres an interesting article showing a notable parasitic power loss from changing the gearing. 153.9hp from stock. 149.1 from -1/+5. 150.6 on -1/+2

    http://www.superstreetbike.com/how-to/bigger-rear-sprocket-makes-more-horsepower-mythbusters
     
  8. JTRC51

    JTRC51 The fast Juan

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    I would have to think that going down 1 in front would be a minimal radius change. Going down 2 in the front....no way!

    I usually do -1/-1 or -1/+0
     
  9. sammPD4075

    sammPD4075 STT STAFF
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    screw it, go -5/+5 and let us know haha
     
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  10. rock3r4life

    rock3r4life Rides with no training wheels

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    I order a 2t front and an 49t rear. Should have better drive out of corners. May have to go 3t front for road America. Will report back
     
  11. rock3r4life

    rock3r4life Rides with no training wheels

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    For realsies tho, I ended up going with -1/0.

    Maybe one day, when im at a dyno, ill see which set of gears at an identical ratio produces more WHP
     
  12. sammPD4075

    sammPD4075 STT STAFF
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    im getting my engine rebuilt this winter and dyno tuned .. ill let yall know the results
     
  13. gkotlin

    gkotlin What's an apex?
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    Don't go smaller then 15 up front.
     
  14. Roll Hard Racing

    Roll Hard Racing What's an apex?
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    You will replace the swingarm also. As stated above, the chain has to follow the chain guide. Once it leaves the chain guide, the front sprocket sets a tad lower than the radius of the swingarm pivot. Once the chain leaves the guide, it has to get very small very quick to get down to the front sprocket. It will eat the swingarm on the top. Just heed that advice.
     
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  15. rock3r4life

    rock3r4life Rides with no training wheels

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    I don't think its physically possible to run a 2t front sprocket o_O like I said in the message after, I went -1/0

    Never had the intentions of dropping more in the front. In fact I didn't want to drop any. Except rotational mass, bigger radius... yada yada
     
  16. steve p

    steve p What's an apex?
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    Possible and doable. Done it on occasion to keep wheelbase where I wanted it when gearing for a track. I usually stick to -1 or stock though for the countershaft sprocket.
     
  17. tom@stewbar.com

    tom@stewbar.com Need4Speed

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    -1/+3 on Honda 600RR...perfect for Barber. Had to replace chain, obviously, to keep the wheel base in range. About 600 RPM below red line in 6th gear at end of front straight. Great drives coming off the corners. I guess it does make you a bit busy on the gear shift lever since you are usually in the close ratio top gears but I like it. You have to ride it like a dirt bike and keep the rev's up - which means be in the right gear... Been able to out run/out drive several litre bikes on acceleration coming off the corners...for a couple of gears anyway! Makes 'em work some at getting back around me at least! I can see them cussing behind their dark shields.
     

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