Considering gearing changes...

Discussion in '1st & 2nd Generation 1983-1989' started by Outlawz24, May 7, 2008.

  1. Outlawz24

    Outlawz24 New Member

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    My bike is pretty much overdue for a chain and sprocket swap. I am considering altering the gearing when i do this however im not sure how much it will impact the bikes low end power. The combination im looking at running is 17/39 which with a stock size rear tire would net me about 257 km/h top speed in 5th. But im not sure how much low end power im giving up in the process of which...

    Suggestions?
     
  2. Lgn001

    Lgn001 Member

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    The easiest way to figure out the approximate impact on torque reduction or increase through gear ratio changes, is to figure out the percentage of change. Say that your standard gearing was;

    15/45. 45 divided by 15 = 3.0

    Modify it to;

    15/43. 43 divided by 15 = 2.86

    Now divide 2.86 by 3.0 = .955

    The ".955" is the percentage of relative torque multiplication you now have, so you would have about a 4.5% reduction in torque multiplication. Again, this is a rough comparison, but it will give you a baseline to work with. In the real world, it works pretty well.

    Hope that helps somewhat. From a practical perspective, gearing changes that reduce torque can be disappointing from a performance point of view. If you spend a lot of time on long straight roads at moderately fast speeds, you might see a decrease in fuel consumption, but not always. Generally speaking, the bike will not have a higher top speed, simply because it does not have enough power to overcome the aerodynamic drag.
     
  3. Outlawz24

    Outlawz24 New Member

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    So in the long run i would be better off changing the gearing to a set up that increases low end torque to overcome said drag. I loose some top end but gain it back in low end acceleration.
     
  4. Lgn001

    Lgn001 Member

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    Yeah, pretty much. But it does depend on where and how you like to ride. One of the "gotchas" about changing final drive ratios becomes apparent if you have particular roads you like a lot. Say you have a few corners that third gear is perfect for. You lower your final drive ratio, and now third gear is winding the motor a little too high, but fourth gear is a little too low.

    The rule of thumb, for me anyway, is what my intended use for the bike is and how much power is available. If I am going to use it mostly for around town and twisties, I can live with higher RPM. If I use it primarily on longer rides, I'll live with a bit less power if it does not lug the motor too much.

    Part of the reason I finally bought the VFR was that my SV650 does not work well with gearing changes for highway use. I went from a 15/45 to a 14/45, and then a 15/44. The 14/45 really hurt it around town, but calmed down the motor at highway speeds. However, my fuel consumption got worse at highway speeds because I was having to use more throttle to hold the same speed (75 - 80 MPH). The 15/44 is more livable, but I'll go back to 15/45 next chain replacement.

    But then again, my slightly modded SV only has about 45 lb/ft of torque and 70 HP. Even though it is relatively light at about 430 pounds wet, it is sensitive to gearing changes. Trying to make it a long distance highway bike just took it out of it's element.

    There will be those who argue this, but it might be worth getting a stock countershaft sprocket and a one tooth smaller version just to try for a few hundred miles. If you don't like it, put the stock size back on. A few hundred miles should not drastically affect the wearing process between chain and sprockets.

    In general, using a smaller countershaft sprocket increases wear on the chain because it has to make a tighter bend to get around it. The neat thing is that a one tooth difference on the countershaft sprocket has a relatively large impact on the final drive ratio, compared to the rear sprocket, and you can usually use the standard chain length.

    So, my friend, as these things ALWAYS go, pick your poison and see how it tastes. Sorry for the long-winded reply; gearhead stuff brings out the lecturer in me...
     
  5. Outlawz24

    Outlawz24 New Member

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    Most of the riding i use my Interceptor for is around town riding with a bunch of other sport bikes. So in all reality im looking for a lil more top end speed in each gear.
     
  6. koorbloh

    koorbloh New Member

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    with more top end on each gear, you'll lose accelleration
     
  7. Outlawz24

    Outlawz24 New Member

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    Does anyone know what the stock gear combo is on the VF750? Some sites i have read state its 17/45 others state its 17/44. Either way it seems like the optimal combo for enhanced performance may just be 17/42.
     
  8. James Popp

    James Popp New Member

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    I kept the rear stock (not sure if its 42 or 44 but I'm pretty sure I could check that in the manual tomorrow) and switched to a 16-tooth front. The 16-tooth is what comes stock on the 700cc bike while the 750cc came with a 17-tooth front. The extra torque is nice. However, the main reason I did this is because I'm running a 140/80-18 rear tire, so I was giving up a little torque already.
     
  9. Outlawz24

    Outlawz24 New Member

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    Just wondering would i gain anything by regearing to get max speed at the bikes torque peak?
     
  10. James Popp

    James Popp New Member

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    If your bike has max torque at redline that means there is no overrev in the design. Most modern sportbikes have only a small amount of overrev.
     
  11. Outlawz24

    Outlawz24 New Member

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    the 1st gens make max torque at 7500...while the redline is 10500.
     
  12. Lgn001

    Lgn001 Member

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    You might be over-thinking this a bit, no offense intended. Basically, if you want better acceleration, go for about a 5% increase in the final drive ratio (numerically, that is). If you want less acceleration but a higher speed in each gear, go for about a 3% - 4% reduction.

    If you just are not sure which direction to go, get the stock back sprocket and two countershaft sprockets; one 1 tooth smaller than stock and one 1 tooth bigger than stock. Try them both. That will at least give you an indication of what you like better. Oh, make sure to check that the chain clears the case and surrounding area of the countershaft sprocket.

    Most bikes, with the exception of the Hayabusa-class and the literbike RR's, really take a noticeable hit when you gear them for higher speeds. Too much weight, not enough horsepower.
     
    Last edited: May 13, 2008
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