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  1. #1
    Bronze Member
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    Jun 2008
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    71
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    earth
    Tractor
    JD 770

    Default Calculating ground speed

    We recently picked up a 3 pt sprayer and I am trying to figure out my ground speeds at different RPM's in different gears.

    So the question I have is;

    Lets say on a gear tractor, like my JD 770, if 2nd (high) gear is rated at 4.4 mph when at 2600 RPM.

    Does that mean 1500 RPM's would be would be 58% of 4.4 MPH or 2.5 MPH?

    Thanks for any input,
    Bill

  2. #2
    Veteran Member
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    Aug 2005
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    Guernsey Co. Ohio
    Tractor
    Ford 3000

    Default Re: Calculating ground speed

    Beg, borrow, or steal a GPS. Well, don't steal one, but it's much better than guestimating. The percentage guesses won't work, and you need to be pretty accurate to calibrate properly.

  3. #3
    Platinum Member rjkobbeman's Avatar
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    Apr 2010
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    USA
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    Kubota M8540HD-12 2010

    Default Re: Calculating ground speed

    Quote Originally Posted by wcpeabody View Post
    We recently picked up a 3 pt sprayer and I am trying to figure out my ground speeds at different RPM's in different gears.

    So the question I have is;

    Lets say on a gear tractor, like my JD 770, if 2nd (high) gear is rated at 4.4 mph when at 2600 RPM.

    Does that mean 1500 RPM's would be would be 58% of 4.4 MPH or 2.5 MPH?

    Thanks for any input,
    Bill
    Although there are factors that can lead to inaccuracy, yes, your thinking is correct. 1300 RPM (IN THE SAME GEAR) will be 50% less speed of 2600 RPM (IN THE SAME GEAR).

    However, here are some factors that you have to consider:

    Are the published speeds accurate?
    Are you using the same wheels and tires as the published speeds?
    Are you in terrain that is causing your tires to slip?
    Is your tach accurate?

    The GPS comment is a good recommendation if ground speed in critical.

  4. #4
    Platinum Member
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    May 2005
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    596
    Location
    Rochester, NY
    Tractor
    FarmTrac 270DTC

    Default Re: Calculating ground speed

    A 300' tape measure from HF and a timer works just as well and cheaper. Make some measurements in a couple gears then put all the data into Excel and you can pick you gear and rpm for the desired speed.

  5. #5
    Elite Member gwdixon's Avatar
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    Jul 2009
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    Northern CA

    Default Re: Calculating ground speed

    A GPS device is fairly accurate in the short run and very accurate in the long run.

    If it has a logging feature you can run for 10 - 20 minutes and it will be able to record average speed, top speed (in case of hilly terrain slowing or speeding the tractor), distance traveled, time traveled, and more.

    Using different gears and RPMs will enable you to make a chart or graph of the tractor's response.

    I am partial to Garmin products but any should work.
    2009 Kubota M7040, R1s, LA1153 FEL, fork lift, 3 rear remotes, T&T
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  6. #6
    Super Star Member
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    Aug 2001
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    Upper Midwest USA
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    JD 4300, JD X485 JD 4x2 Gator, JD 425, JD455

    Default Re: Calculating ground speed

    Bill

    Many ways to do it as have been mentioned.

    Which way seems most appealing to you?

    I'd set up a course (100' or 200' ) and use the second hand on a watch to time the seconds it takes to traverse the distance laid out. That will give you distance/time for each gear and rpm. You can lay out the course with a 10' tape or whatever you have handy. And can convert to mph easily.

  7. #7
    Bronze Member
    Join Date
    Jun 2008
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    71
    Location
    earth
    Tractor
    JD 770

    Default Re: Calculating ground speed

    Thanks again for the input.

    I put together a spread sheet for figuring it all out based on published speeds. I will verify the accuracy of the speeds and adjust the sheet.

    Bill

  8. #8
    Veteran Member
    Join Date
    Sep 2004
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    2,419
    Location
    Kansas, Butler county, Just east of DooDah
    Tractor
    Kubota L4200 GSTCA

    Default Re: Calculating ground speed

    Quote Originally Posted by wcpeabody View Post
    Thanks again for the input.

    I put together a spread sheet for figuring it all out based on published speeds.

    Bill
    Bill:
    Your math and percentage will work perfectly.
    As silly as it seamed at the time I got it, my phone has an application for this.

    I guess it is the future... I can even plot my exact path with speed and elevation variations on a map and have it uploaded to my computer with more telemetry than I care to track.... Plus my phone is in the cab with me if someone needs to call me... What a deal. KennyV

  9. #9
    Super Member
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    Feb 2006
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    VA
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    JD2010, Kubota3450,2550, Mahindra 7520 w FEL w Skid Steer QC w/Tilt Tatch, & BH, BX1500

    Default Re: Calculating ground speed

    Quote Originally Posted by rjkobbeman View Post
    Although there are factors that can lead to inaccuracy, yes, your thinking is correct. 1300 RPM (IN THE SAME GEAR) will be 50% less speed of 2600 RPM (IN THE SAME GEAR).

    However, here are some factors that you have to consider:

    Are the published speeds accurate?
    Are you using the same wheels and tires as the published speeds?
    Are you in terrain that is causing your tires to slip?
    Is your tach accurate?

    The GPS comment is a good recommendation if ground speed in critical.
    Yes for groundspeed. Also, If your sprayer pump is pto driven you will need to be sure delivery pressure remains the same at the chosen rpm.
    larry
    This side of 40
    JD2010, Kubota L3450/FEL w SK QC, L2550 w FEL
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