confused about sprocket reasoning
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  1. #1
    Junior Member lagarto's Avatar
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    It has been advised previously that if I want to go faster with less rpms, I should raise the front (engine) sprocket to a 15T from the 14T on it--that makes sense to me. But I thought lowering the (getting a smaller diameter) back wheel sprocket size would do the same as well, but several have advised to go from a 45T to a 50T on the back--my present sprockets are 14T/45T ---> go to a 15T/50T for lower rpms at higher speeds? Doesn't make sense to me, i thought you put larger sprockets on the back for more hillclimbing, slower higher rpms/torque etc., not for highway use. (???)I'm confused! Wouldn't a 15T/<45T make more sense for what I want?!?!? (the more teeth the larger the sprocket, right?) I'm just trying to understand why...

  2. #2
    Senior Member RodneyReed's Avatar
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    Quote Originally Posted by lagarto View Post
    It has been advised previously that if I want to go faster with less rpms, I should raise the front (engine) sprocket to a 15T from the 14T on it--that makes sense to me. But I thought lowering the (getting a smaller diameter) back wheel sprocket size would do the same as well, but several have advised to go from a 45T to a 50T on the back--my present sprockets are 14T/45T ---> go to a 15T/50T for lower rpms at higher speeds? Doesn't make sense to me, i thought you put larger sprockets on the back for more hillclimbing, slower higher rpms/torque etc., not for highway use. (???)I'm confused! Wouldn't a 15T/<45T make more sense for what I want?!?!? (the more teeth the larger the sprocket, right?) I'm just trying to understand why...


    Just use this formula, whether you're changing one of the sprockets or both.



    (Number of teeth on rear sprocket / Number of teeth on front sprocket) = ratio

    The higher the ratio, the lower the gearing (the higher rpm at a given speed).



    For example,

    45/14 = 3.21

    45/15 = 3.00



    So the 45/15 will be geared higher, producing less rpms at a given speed



    50/15 = 3.33



    The 50/15 combo will be lower than what you have now, and in fact lower than your original gearing, producing more rpms at a given speed.

  3. #3
    Senior Member Dark Sol's Avatar
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    you must live somewhere where the stock rear is 45 - here in the US the stock gearing is 14/50, so when people refer to 15/50 it does reduce the speed a fair bit, because we're talking about 14/50 originally.



    if you were to go to 15/50, well, the engine would run faster. 15/45 would go slower, but I can't say for sure if you'll like such a tall gearing - the power really suffers. Try it if you want though.
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    * 2001 TW200 (Sold after 15k miles of fun)

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  5. #4
    Junior Member lagarto's Avatar
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    I think you're right, it must be 14/50 now because it is stock USA, I was told verbally it was stock at 45 sight unseen,I should have counted before posting-- now it makes sense--thanks...assuming I now have 14/50, how much of a difference will a front 15 make over the 14--at 55mph, it is revving waaay too high, I drive it on 40 mile round trips on a 60 mph highway, almost toally flat, but I would like to go around some fields in the dirt occasionally but nothing major--from what i've read, 15/50 has been discussed as ideal for 90% road use--do you have an opinion for me (please)? I guess I can try a 15 front and go from there!

  6. #5
    Senior Member uktw125's Avatar
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    According to the gearing calculator spreadsheet posted by petrus the difference at 60mph is 14/50=7683rpm, 15/50=7170rpm or 6%. So not a lot different.

    I use 15/50 gearing and it is still a bit low for me but I am very light and ride 90% street.

  7. #6
    Senior Member rm_hm's Avatar
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    Play around with



    http://www.sprocketcalculator.com/





    Enter in 14 / 50 then your alternative and it will give you an idea of torque & speed gains and losses.


  8. #7
    Senior Member elime's Avatar
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    It might be easier to get a cheap tachometer and see what your RPM's are at a given speed rather than start changing sprockets around based on the RPM calculator and your ear.



    The effect felt by changing the rear sprocket by one or two teeth I believe is largely placebo.
    When I changed my sprocket ration from 14/50 to 14/55 I barely noticed a difference. ( I don't know, maybe I am not sensitive enough.) Also, the red line is 9500 RPM and possibly even 10,250 RPM . With the 14/50 set up at 65 mph you are well within the operating limits of the engine. How much faster do you want to go?



    Whatever you decide the rear sprocket is easier / less scary to deal with. Don't forget to take into account you may have to lengthen or shorten your chain when you make your swap. Good luck!
    Long live the internal combustion engine!

  9. #8
    Banned qwerty's Avatar
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    I've run 15/47 and didn't care for the rpm drop between 3rd and 4th and 4th and 5th. Wind out a gear, shift up, and the bike slows down, even WFO. Very annoying. If that happens often, sprocket ratio is too tall. I've done 700+ highway miles in a day with 15/54 sprockets, holding 60-65mph tank-to-tank. The engine doesn't care. I currently run 15/50 because there is not much in the way of dualsport riding around here and the extra tooth on the countershaft makes 1st gear a bit more usable in town. Tdub is due for a new chain and I already have 15/51 sprockets on the bench. Why 51? Because 30mph in 5th in town is just slightly lugging going up hills. Also, 51 is un odd number.




  10. #9
    Senior Member RodneyReed's Avatar
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    I'm sticking with the stock 14/50. At my size, with a strong headwind, I'm not sure it would readily pull any higher gearing. Also, I feel like the first gear is low enough for any situation that might be encountered.

  11. #10
    Senior Member pgilles's Avatar
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    14/47 here. I like it for road use. My 2nd choice would be 14/50.



    14/44 sucked on the interstate. Bike couldn't pull that high of ratio.



    Let the engine rev



    My 2 cents.
    Sold bike.



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