F650 Twin sprocket choice

Discussion in 'Parallel Universe' started by Ash, Jul 28, 2012.

  1. Ash

    Ash UFO Pilot

    Joined:
    Feb 25, 2007
    Oddometer:
    469
    Location:
    Berkshire England
    i would like to make the gearing taller from the stock 17 tooth front and 41 tooth rear.
    could i go to 39 tooth on the rear , so it's smoother or would it kill it ?
    or would a 40 tooth rear be wiser ?

    :thumb
    #1
  2. bobobob

    bobobob IN HOC SIGNO VINCES

    Joined:
    Feb 11, 2011
    Oddometer:
    7,490
    Location:
    On a hill
    What is your split on road/dirt use percentage wise?
    Do you want faster acceleration and better 1st gear grunt for tight trail situations?
    Or do you prefer more relaxed freeway high speed cruising and better mpg?

    Your answers will help with a suggestion.
    #2
  3. GH41

    GH41 Been here awhile

    Joined:
    Oct 19, 2011
    Oddometer:
    822
    If you weigh 90 lbs and travel light you might get away with the proposed change. Are you prepared for less acceleration and possibly lower fuel milage?? Taller gearing doesn't always get better milage but it always means the engine has to work harder to maintain a given speed. I am actualy going the other way with my 658. I am dropping a tooth on the front for better power down low but I never ride faster than 70mph. GH
    #3
  4. Ash

    Ash UFO Pilot

    Joined:
    Feb 25, 2007
    Oddometer:
    469
    Location:
    Berkshire England
    90% roads use and i prefer more relaxed freeway high speed cruising and better mpg?

    :thumb
    #4
  5. markymcd

    markymcd Been here awhile

    Joined:
    Sep 18, 2008
    Oddometer:
    890
    Location:
    Vancouver, BC, Canada
    I know it's an odd combo but 18 / 44 works really well.

    the 18 is very hard to find and a bitch to get on because it's just a tad too big for the space up there but i've used this combo for about a month now and love it. You get the versatility to put a 17 on for your off road adventures.

    so far i've tried 17/41 (stock) 16/41, 17/42, 16/42 and now 18/44

    cheers,
    Mark
    #5
  6. Johnnyboxer

    Johnnyboxer Long timer

    Joined:
    Oct 23, 2003
    Oddometer:
    1,146
    Location:
    Yorkshire, UK
    I think the OP wants to to reduce the revs, for a given mph on the highway

    He's not at all interested in offroad as he never ventures off tarmac, so lowering the gearing is of no interest

    So he's considering fitting 17/40 or 39 to reduce the revs & so vibes at say 70 or 80mph

    Would this work?
    #6
  7. JRWooden

    JRWooden Long timer

    Joined:
    Jul 5, 2008
    Oddometer:
    4,631
    Location:
    The great state of confusion
    Mark:
    You're a better man than I am :clap I'm pretty sure that at least with some of those combinations if someone sneaked into my garage and made them I'm not sure I would notice the difference ... I'm just not that good at fine detail....

    41/17 is 2.41

    42/17 is 2.47

    44/18 is 2.44

    My sprockets are almost due for a change so it's a good time for me to try something else...
    What were the differences you felt across these changes?

    Thanks,
    Jim
    #7
  8. Maxacceleration

    Maxacceleration Off the grid

    Joined:
    Oct 9, 2009
    Oddometer:
    2,419
    Location:
    Wa
    The stock gearing is so nice on the 658. As is a relaxed rpm at highway speeds.
    Tall enough IMO because some headwinds & mountain passes whiled loaded (touring gear silly) will have you going down to 5th or 4th at times.
    1st gear is usually low enough for most situations. I have done very technical two track trail and the 658 works well at idle through those situations.
    If you are dog paddling through technical stuff a -1 countershaft sprocket could be advantageous.
    Over gearing it will have you going a gear or two lower (than normal) on the passes and you will be doing the same rpm's anyway...
    IMO from idle to top speeds the 658 is geared well and gets good fuel mileage doing it.
    From my experience cruising from 70-90 kills mpg's (upper 40's). 55 to 70 and the 658 pushes 60 mpg (57-58 for me)
    YMMV
    #8
  9. markymcd

    markymcd Been here awhile

    Joined:
    Sep 18, 2008
    Oddometer:
    890
    Location:
    Vancouver, BC, Canada
    the 18/44 is slightly slacker than the stock for the 650 twin. When I first installed this combo it was for a 3 day trip. 1,300KM with 800 of it on gravel, dirt and double track. on our second day which was more technical I was going to swap out the 18 for my 17 but couldn't get the 18 off. Thought it was going to be a crappy day as I remember the original stock ratio not being great for off road but it was just fine.

    http://www.bikecalc.com/gear_ratios

    with the 18/44 it was pretty rare that I even had to get into 6th gear. I think it might be my favourite overall combo yet.

    Mark
    #9
  10. markymcd

    markymcd Been here awhile

    Joined:
    Sep 18, 2008
    Oddometer:
    890
    Location:
    Vancouver, BC, Canada

    Hey Jim,

    Where you notice the differences are at over 70mph on the road and off the road on anything slightly technical and slower. With the off road the differences are with the twitchiness of first gear and how much you have to mess around with the clutch.

    I've also got the HiTechCoonass WukaKing Power Commander which makes everything much smoother in the lower gears too.

    cheers,
    Mark.
    #10
  11. markymcd

    markymcd Been here awhile

    Joined:
    Sep 18, 2008
    Oddometer:
    890
    Location:
    Vancouver, BC, Canada
    On a side note a couple of other things that help with the vibes.

    1) Do not use the BMW hand guards. They use a very light handlebar weight which makes the vibrations worse.

    2) I know lots of people would be against it but you can fill your bar with #9 lead shot. Works awesome and unless your a gram counter I wouldn't sweat the difference. The benefit outweighs the detriment in my mind. No difference in steering feel.

    Mark
    #11
  12. vtbob

    vtbob wanderer

    Joined:
    Jun 20, 2009
    Oddometer:
    653
    Location:
    Western Vermont
    FWIW

    I have a F650GS with the std sprockets....I have essentially NO vibration from 40 to 75mph. At around 85 there is a slight buzz. I do have throttle Miester installed...ie stainless steel bar end weights.

    While I normally use Tourance EXPs

    For my Alaska trip I put Hideneaus on....they have a significant front wheel resonance at around 20mph. But after the 1st 1000 mile( worn in a bit) nothing on the hiway....they do sing to you though.
    #12
  13. JRWooden

    JRWooden Long timer

    Joined:
    Jul 5, 2008
    Oddometer:
    4,631
    Location:
    The great state of confusion

    Thanks mark!

    I have the IICE mod. on my bike.
    I'll get out my crystal ball and re-read your posts and pick out a new ratio!
    Likely it won't be a big deal ... I don't get to do lots of technical stuff nor much over 70 mph....

    I do have the BMW guards ... I did not realize the bar end weights were lighter............
    that really pisses me off ...
    1) why did BMW do that
    2) why didn't I notice that when I installed them .......... :cry
    #13