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Gear Ratios

This is a discussion on Gear Ratios within the Technical forums, part of the Caferacer.net Forums category; If you want to have closer ratio gears but wanted the same final ratio, could you make a smaller primary gear and then run taller ...

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Thread: Gear Ratios

  1. #1
    Senior Member aaron's Avatar
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    Gear Ratios

    If you want to have closer ratio gears but wanted the same final ratio, could you make a smaller primary gear and then run taller sprocket gearing or would that bring you back to the same as you started?

    Aaron


    mvdusa.com

  2. #2
    Moderator jbranson's Avatar
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    Wow, dude, good question.

    I once went loopy for a few days trying to figure out a similar scenario.

    Here's the basic situation we want.

    An undeniable fact is that the engine is going to have to turn a certain amount of turns per revolution of the rear wheel to be geared properly for a track.

    Ok.

    Here's where it gets tricky. We want to make the gearbox the "smallest" part of the various reductions between engine and wheel..right?

    So....if our primary ratio was bigger, meaning higher, then the gearbox would represent a smaller overall "chunk" of the reduction.

    Here's the problem I think...

    In order to the bet the rear wheel back up to speed you would have to run a taller (larger) front sprocket...that would multiply your gearbox "effect" right back up to where it started from.... I think. I could be wrong.

    Aaron, it's a really tricky problem... I actually discovered that running different final drive ratios...affects the "percentage" jump by each gear in the gearbox, of the total reduction if you know what I mean...but once again I think it all get's canceled out. I gotta write a spread sheet or program to figure this out.

    JohnnyB


  3. #3
    Senior Member aaron's Avatar
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    At Loudon not so much but some of the bigger tracks would benefit greatly to having a 2nd, 3rd, 4th, 5th, and 6th gear. The first gear (the new 2nd) seems to be used for such a short amount of time. If you could give up some of the start to have better ratios every where else would be ideal. I shouldn't really be complaining coming from strangly seperated British four speeds, but I read something about a Yamaha that did something of the sort at Daytona back int he late 60's so essentially gained a gear on the top but one on he bottom. I think their wording seemed a little more scientific but concluded with what I said.

    Also how much does the PVL system weigh and how much does the part weigh thats on the crank?

    Aaron


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  5. #4
    Moderator jbranson's Avatar
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    Aaron,
    I'm trying to make a spread sheet to figure this out... I can almost see the solution in my head but I'll have to plug it all in and graph it cause me eyes keep going crossed trying to figure it out.
    However.... I've learned this...don't think too much about things you can't do. Changing the primary ratio would be an impossibility unless the the parts are plug and play from another model. And honda isn't huge on interchangability between primary drives..hell the 160 primary gears have different splines than the 175 sloper. Primary gears have to have an exceptional fit or they will destroy themselves.

    PVLs.... ours wouldn't weigh much as it would use only one stator winding. Rotor probably weighs around 7 oz.
    I'm hoping the whole system only weighs less than 1.5 lbs not including coil (since we already have to use a coil). The rotor will have little effect due to it's small diameter... in fact I'm hoping it might help dampen some of the harsh crank vibrations.

    We'll save the weight of the battery and any components used to mount the battery...hopefully about three pounds on my bike.
    JohnnyB


  6. #5
    Moderator jbranson's Avatar
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    Aaron,
    Just did the math.
    If you change the primary ratio, and then change the spockets to achieve the same top speed (which you'd have to do) then your speed in any particular gear is still the same.

    Luckily the ratios on the 175 are pretty freakin good. They are better for a place like NHIS than they are for a place like Daytona or Mosport though.

    The yamaha you read about probably was able to swap some tranny gears too, and between that and the primary ratio was able to find another usable gear.
    JohnnyB


  7. #6
    panic's Avatar
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    Changing primary ratio or any sprockets has no effect on transmission ratios.

    Need help with your Mikuni VM? Click here:
    http://victorylibrary.com/MIK-BT.htm

  8. #7
    panic's Avatar
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    Changing primary ratio or any sprockets has no effect on transmission ratios.
    I'm not sure of how the internal parts work on japanese boxes, but quoting in part from my own article on british:
    "Ratio Calculations
    Triumph 4 speed transmission’s intermediate gears (1st through 3rd) are the result of power transmission through two pairs of mating gears, one of which is the mainshaft high gear being turned by the layshaft (countershaft) high gear. The gear ratio is the product of multiplying the two pairs’ tooth count ratios together: the high-gear ratio times the ratio of the individual gear pair selected (1st, 2nd or 3rd).
    In 4th gear the mainshaft high gear, which turns the transmission sprocket, is locked to the mainshaft, so the ratio is 1-1. No power is transmitted through the intermediate gears. Although they still turn, they’re only idling.
    The high-gear ratio is the ratio of the tooth counts of the high-gear pair for the transmission type selected (see “high-gear pair” in the header of the Table below). For example, the std. transmission (the most common model) has 26 teeth on the mainshaft high gear and 20 teeth on the layshaft high gear, so the high-gear multiplier will be 1.30000 for this transmission.
    The 2nd number is the ratio of the tooth counts of the pair of gears (mainshaft & layshaft) for that ratio: 1st, 2nd or 3rd. In general all 1st and 2nd gear pair ratios will be above 1.000. Some 3rd gear pair ratios will be above and some below 1.000.
    The std. transmission has 26 teeth on the mainshaft 1st gear and 20 teeth on the layshaft 1st gear, so the gear ratio for the 1st gear pair is 1.6875 for 1st gear in the std. transmission. To get the actual effective ratio of 1st gear, multiply those two numbers together:
    High-Gear Multiplier × 1st Pair Ratio = 1st Gear Ratio
    1.30000 × 1.68750 = 2.43750-1
    The overall governing component for all ratio selection is the high-gear pair, which determines the “range” of ratio spread between 1st gear and 4th gear. The selection of which high-gear pair to use must be made first, since this limits the number of choices to a specific range."

    Read the article here:
    http://victorylibrary.com/tech/trans-ratio-tri.htm











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  9. #8
    Senior Member aaron's Avatar
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    Panic, thanks for the info.

    Aaron


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