CVT Honda GXH50 + CVT Some questions

Discussion in 'Transmission / Drivetrain' started by alekor, Oct 9, 2009.

  1. alekor

    alekor Member

    I have bought X2 CVT the second type (where the transfer relation 7:1) and I wish to make with it a motor-bicycle with engine Honda GXH 50.
    In CVT FAQ I have found here this schedule.
    I want that the maximum speed was nearby 32 MPH. From schedule it is visible that between minimum RPM couplings (4000 RPM) and maximum RPM (7000) speed varies three times. Whether so it?
    If all is true, at my motor-bicycle at the maximum speed 32 MPH (7000 RPM) the minimum speed awakes 10 MPH (4000 RPM) and the motor-bicycle awakes itself to start without rotation of pedals - is my purpose. Whether my reasonings are true?

  2. loquin

    loquin Active Member

    That chart is an example one, to give you an ides as to how the CVT would work.

    For a specific application, we need to go through the steps. I'm going to assume that your wheel size is 26 inches. If this is not the case, you will need to adjust the calculations with your wheel size.

    First, you state that you want the bike to have a top speed of about 32 MPH, and you are using a Honda GHX-50. Per the engine curves, below, the GXH-50 has maximum torque output at about 4700 RPM, and maximum HP output at about 7000 RPM, and an upper RPM limit of about 7500 RPM. The first step is to calculate the gear ratio to achieve the desired upper limit for speed, at max RPM. With GearRat, I can calculate this required total gear ratio to be 18.13, to achieve 32 MPH at 7500 RPM. Let's round this off to 18.1 for the rest of the calcs.

    A ratio of 18.1, when you use the second type of X2 CVT (which has a gearbox with a 3.18 ratio) means that you still need a further reduction of 5.7. If you have a 12 T sprocket on the output of the CVT, you would need a 68 Tooth sprocket on the rear axle to achieve the required reduction. Note that either of these sizes of sprocket are hard to locate, and further, it is very desirable to have a freewheel sprocket in the final drive chain. You can't find 68T left-hand thread freewheel sprockets, but, you CAN find them down to about 16 teeth, in the standard english 1-3/8 inch, 24 threads-per-inch mounting.

    A 16 tooth drive sprocket would need a 91 tooth driven sprocket. Again, this would have to be a custom sprocket. And, it would be huge. The alternative is to add a jackshaft between the CVT and the rear sprocket.

    Lets assume a jackshaft, with a 16 tooth freewheel output sprocket, and a 14 Tooth sprocket on the output of the CVT. Playing around with the numbers on GearRat, and a 29T sprocket on the input of the jackshaft, and a 44T sprocket at the rear axle gets you the right ratios. (CVT1.JPG)

    With the gearing settled, we can calculate the upper 'bend' or breakpoint in the chart. This point is the speed, using a total gear ratio of 18.1 (per GearRat) and the max torque RPM of 4700. The speed is 20.1 MPH. (CVT2.JPG)

    Next, the lower breakpoint can be calculated, which is the max torque speed (where the CVT belt drive has it's maximum ratio (about 2.2:1) and the engine is at maximum torque (4700 RPM.) Plug in the 2.2 belt reduction in the CVT, to obtain this speed, which is 9.1 MPH. (CVT3.JPG)

    Finally, the bottom end of the system RPM-speed curve can be found, by plugging in the RPM when the clutch engages. If we assume this to be about 3000 RPM, the corresponding speed speed would be 5.8 MPH (CVT4.JPG)

    That's it then. It looks as if this approach should meet your goals...:cool2:

    Refer to the last image (Chart.JPG) for the RPM-Speed curve for your proposed configuration.

    Attached Files:

    Last edited: Oct 9, 2009
    Pezz likes this.
  3. alekor

    alekor Member

    Many thanks for so detailed clarification! I wish to translate CVT on a usual bicycle chain (as accessories for it at us more accessible) and as the maximum transfer relation at us on factory accessories nearby 4,6:1 I am compelled to use a wheel of 20 inches. Then, proceeding from your calculations, the transfer relation between CVT and a wheel should be nearby 4,3:1 (5,7 / (26/20)) - easily to receive it using 11t and 48t stars.

    And still a question - time at Honda GXH50 coupling turns are equal 3000, single turns should be nearby 2000 RPM?
    Last edited: Oct 10, 2009

    TREEWK Member

    Alekor, I Have Some Post Of My Cvt With The Titan 4 Stroke In "Cvt`S and Comet Drives" , I Think It Is Started By "nutsky" I Thought I Came Up With The Idea On The Other Forum. I Came On Here And He Was A Few Months Ahead Of Me. His Is Left Hand Drive, Which Is Fine. Mine Is Right Hand Drive With Free Wheels. My First Cvt Build Was With A Cag 2 Stroke . The Titan Has A 11 Tooth On The Cvt Out Put Shaft And A 54 Tooth On The Rear Wheel, weigh Over 300 Lbs, It Starts Off With Out Pedal Assist. I Give It 1/4 Throttle And It Takes Off With Ease, As If There Is No Rider, It Is Smooth. It Go`s 25 Max, But The Throttle Is Not Fully Opening. I Will Correct The Throttle And Am Going To Try A 17 Tooth On The Tranny. I Have Pics On The Thread Around Posts 56 Thru 67. Ron
    Last edited: Oct 10, 2009
  5. alekor

    alekor Member

    It is interesting to see photos, Ron - Can give the reference?
  6. alekor

    alekor Member

    Today I at last have received mine CVT - I have bought it here -
    That is interesting - the general fall CVT equally 8,25:1. Thus reducer fall 3,75:1. These characteristics do not approach neither under the first, nor under the second kind CVT(in FAQ CVT) - that will tell?

    Foto by my CVT:

    Last edited: Oct 10, 2009

    TREEWK Member

  8. alekor

    alekor Member


    TREEWK Member

    Alekor, Is That A 35cc Motor? Good Motor. Harder To Mount Than The Titan When Using The Cvt. It Should Be A Good Set Up. Just Gear It To Suit That Motor. Happy Riding To You. Ron
  10. alekor

    alekor Member

    Yes, it is the engine 35 cc. But I have resulted work with CVT together with Honda GX35 only as an example - I am going to use Honda GXH50 with CVT.
  11. TREEWK

    TREEWK Member

    Alekor, Do You Know That The Honda 50cc Needs Adapter To Bolt To Cvt? Makes It Wider Also. The Titan Bolts Up And Less Money. Just Trying To Help. Is It Hard For You To Get Parts, Motors, Cvt And Other Parts?? Ron
  12. alekor

    alekor Member

    That that the adapter I is necessary I know. While precisely has not decided what to choose - original Honda GXH 50 or its Chinese clone. Smaller capacity at a clone and a twisting moment confuses.

    To receive spare parts and engines for me it is not difficult - we have firms intermediaries which forward the goods from American the Internet of shops in Russia. It costs additional money, but expands possibilities on construction of motor-bicycles. In America spare parts much more. And frequently with delivery the goods cost cheaper than if to buy from us (for example Honda GXH 50 at us costs 533$ - and if to buy in America - nearby 400$ with delivery).
  13. loquin

    loquin Active Member

    Have you verified that the gearbox on the CVT is 3.75:1 ?
    And, when the CVT is at low RPM, that the total reduction is 8.25 to 1?
    this makes the CVT speed range = 2.2 (8.25/3.75=2.2)

    If so, using 20" tires, with 11T to 48T, the overall gear ratio is 3.75 * 48/11, or 16.4, and the resulting top end speed is about 27.3 MPH at 7500 RPM.

    Carrying the rest of the calculations out, the upper breakpoint is therefore 17.1 MPH at 4700 RPM, the lower breakpoint is 7.8 MPH at 4700 RPM, and the first point is 5.0 MPH at 3000 RPM
  14. TREEWK

    TREEWK Member

    There Is Additional Gear Reduction On The Back Side Of The Cvt. Ron

    Attached Files:

    Last edited: Oct 11, 2009
  15. loquin

    loquin Active Member

    Yup. The gearbox is accounted for in the calculations.

    The steps involved in calculating the gearing and speeds for your bike are as follows:
    1. Calculate the max RPM gearing/speed.
    2. Using the same gearing as in step 1, calculate the speed at Max Torque RPM.
    3. Apply the CVT Belt reduction ratio, to calculate the maximum torque speed.
    4. Using the clutch pull-in RPM, calculate the pull-in speed, using the gear ratio from step 3

    The one, final bit of tuning you may need to do is to adjust the CVT sheave weights. These weights move outwards as the RPM increases, and this pushes the drive pulley sheaves closer together, which increases the drive pulley diameter.

    The ideal RPM for this to occur is just about at the max torque RPM, or, maybe just a little lower. (This is the 'flat' portion of the RPM/Speed charts above) If you need to shift the flat portion up, you increase the weights; if you need to shift it down, reduce the weights.

    Remember though, this step should be the LAST one you take. The gearing needs to be correct first, else you may never be able to get the most out of your CVT. Also remember that adding a CVT will reduce the total amount of power to the rear wheel by 10-15%. The trade-off is that you should be able to get faster acceleration, and better hill-climbing ability, but, this may be come the expense of maximum top-end speed.
  16. TREEWK

    TREEWK Member

    Thanks Lou. Ron
  17. alekor

    alekor Member


    Thank you. As I understood it is optimum to set cruising speed on the upper breakpoint at 4700 RPM ?
  18. TREEWK

    TREEWK Member

    Lou, Just For The Heck Of It, What Is My Starting Ratio - 26 " Wheel, 54 Tooth On Wheel, 11 Tooth On Cvt?? I Figured About 29 To 32:1 Starting Ratio. But I Aso Think There Is To Much Slack In The Belt. (CAUSE`S IT TO LOSE SOME STARTING RATIO) BUT IT STARTS OUT NICE (ON TAKE OFF. LOL) NO OVER REVING OF MOTOR. MY BROTHER CLOCKED ME WITH CAR FOR QUITE A DISTANCE = 25 MPH. MY THROTTLE IS NOT FULLY OPEN. THAT FITS YOUR TOP SPEED FOR ALEKOR, OUR RUSSIAN FRIEND. Ron
    Last edited: Oct 12, 2009
  19. loquin

    loquin Active Member

    Which version of the CVT is it, Ron? (Ref the CVT FAQ) (there are two 'flavors' of pocket bike CVT commonly available - each has a different gearbox gear ratio...)

    What engine are you using? The pocket bike moter in the photo above? They can wind out to 8000 RPM.

    Assuming the newer, type 'B' CVT, you would have a top end gear ratio of about 15.6:1, which, IF the motor has enough power, (and max RPMs) could push you to nearly 40 MPH. However, if you don't have enough engine power for this, the CVT belt drive never really reaches the high end, and you lose some of the CVT speed range. (plus, your belt will probably wear faster.) It's very important that you don't try to push a CVT based system to this point. A 50CC honda may be fine with this ratio, but I doubt that a 35CC Honda/R-S has the 'oomph' to make this work.

    At a first guess, the newer CVTs used with a Honda or R/S 35cc, or the Mitsubishi TLE 33/43, shouldn't be geared past 30-32 MPH at their max rpm.

    Since they can reach 8000 RPM, you're talking about a 68 tooth rear sprocket, if no jackshaft is used. The older CVT type, with it's 4:1 gearbox, should be fine with a 54 tooth sprocket, though.

    When you accelerate, your RPMs should rise fairly quickly to a plateau, then run at roughly the same RPM while the bike continues to speed up. Finally, when the belt drive has achieved a 1:1 ratio (the drive pulley is fully 'expanded') the RPMs will start to rise again, as the bike continues to speed up. If you never get to the point where the RPMs start to increase again, the gearing is definitely too low a ratio.
    Last edited: Oct 13, 2009
  20. alekor

    alekor Member

    Last edited: Oct 22, 2009