final drive ratio

Discussion in 'Transmission' started by medechant, Jul 12, 2011.

  1. medechant

    medechant New Member

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    I would like to change my final drive ratio, ex; if I was going 60mph. in 6th. gear, what would it take to go 55mph. at the same rpm. I am thinking of a larger rear pulley, but not sure how many teeth it would take to get where I want to be? or I could change the front to a smaller pulley, but again , how many teeth? The reason for the change is the conditions where I ride ,are that I am always going from 5th to 6th, and 6th to 5th, so.
    with a little change I could always be in 6th. Thanks!
     
  2. Dr. Dolittle

    Dr. Dolittle Experienced Member Staff Member Moderator Contributor

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    Just my opinion but it's not worth the expense and time of doing what you suggest for the reason you state. I'd leave it alone and simply ride in 5th gear. As long as you're below the redline you're not hurting anything. Upshift to 6th if you encounter a downhill stretch or big tailwind where your engine would be loafing anyway.
     
  3. Breeze3at

    Breeze3at Well-Known Member

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    I agree that it is not worth the trouble/expense. Speedo and odo will be affected also. You can figure it out. Stock 2007 pulleys are 34 front 66 rear = 1.94. Just play around with numbers until you come up with something greater than 2.00. Dropping a couple of teeth on the front can probably still use the stock belt, getting the same ratio by increasing rear requires a longer belt.
     
  4. ahern25

    ahern25 Active Member

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    Final drive x speed x 336 divided by tire diameter = RPM. I believe this is the formula.
     
  5. BOWHIKER

    BOWHIKER Junior Member

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    You can ride all day in 5th gear at 60 mph , you're only turning 2650 rpm's, better to run a little higher rpm then to lug the engine . The guys on this site convinced me of that a long time ago .
     
  6. Slo-Ryd

    Slo-Ryd Junior Member Contributor

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    Not to contradict anyone, but hopefully I'm following along correctly. Increasing the rear drive pulley tooth count would lower the final gear ratio and increase rpm's and decreasing the front would have the same effect.

    The reason I question is when I raced dirt bikes, I would change the rear up or down to compensate for different track conditions. Bigger rear sprocket gave me more bottom end (torque) and less top speed.

    My softail has a 70T rear, if I dropped down to a 66T it would lower my highway rpm's. Corrrect me if I'm wrong:p
     
  7. biscuit

    biscuit Junior Member

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    BigAL;

    You are quite correct in what you say.
    Just recently,i've been trying to do exactly the opposite with my 6 speed.For the life of me i cannot understand having a 6 speed box when only the first 5 are useable.

    My stock gearing is 32 front/66 rear.I can buy a 30t front pulley which will increase rpms in top gear by about 6%,but it is a HUGE task to fit the thing.
    I've searched hard and long for a 70t rear pulley to fit my bike,but they just aint available.I have now given up.

    Only two option left to me now (1)make my motor bigger
    (2)lose weight.-better power to weight ratio.
     
  8. wilks3

    wilks3 Junior Member

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    Would a shorter diameter rear tire be a option? 1" less diameter might do what you want.
    I woundn't think it would hurt riding performance. Just a thought.
    wilks3
    :USA
     
  9. Slo-Ryd

    Slo-Ryd Junior Member Contributor

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    Yes, but are there alot of low profile tires available? I've included a link to tire size explanations if it'll help the OP if it's an option for him.

    DennisKirk.com - Tire Sizes Explained
     
    Last edited: Jul 14, 2011
  10. wilks3

    wilks3 Junior Member

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    BigAl66, Yes, after looking around some didn't find anything. Was just a thought. Could probably be done ,"if" wheel was changed also but $$$$$$$$. You would think somebody would make different size rear pulley though.
    wilks3
    :USA