Author [NL] [FR] [ES] [DE] [SE] [IT] Topic: Gearing question - speed vs RPM  (Read 5825 times)

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  • Offline thogland   us

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    Offline thogland

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    Gearing question - speed vs RPM
    on: Jun 12, 2017, 10.03 pm
    Jun 12, 2017, 10.03 pm
    So, odd question that I can't seem to find an answer to. I have an Excel spreadsheet that takes input of tire size and gearing, and computes out a table of speeds per gear and rpm. I plugged in the bevel box gearing, the final drive gearing, and the gears themselves (all from the handbook), and was pleased to see that it came up with a 130mph top speed (which I've read is the Trophy's actual top speed). But, it shows that 4000 rpm in 6th is 52mpg, when I know for a fact that 4000 rpm in 6th is 70, as that's most of my ride to and from work two days per week... Watched things this morning - for 4k rpm, 3rd is 35, 4th is 45 and 5th is 55 (or very close to those). Computed is 31, 39 and 44, so it's not a simple "you typo'd 6th gear".

    Thought maybe I'd gotten the bevel box ratio backwards - divide instead of multiply - but a front 1.042 and rear 2.455 = 2.3561. Then I saw that if you do it the other way it's 2.558:1 and they show a final drive of 2.557:1. Thought maybe I should have ignored the bevel box and just used the final drive. Nope - taking the bevel box's 2.3561:1 out, you end up with 4k rpm in 6th being 122 mph... I even dug around to see if maybe I had plugged in Euro-market gears, and there was US-specific gearing (nope), or maybe a typo in there and an errata sheet I wasn't seeing (couldn't find that either).

    Anyone have any idea what I might be missing? I guess this is useful info in an esoteric way - if you know that a certain rpm in a certain gear should be a certain speed, you can tell if the clutch is slipping or something like that; or, it might answer questions like "if I switch to a 195/55 rear tire, will it correct my speedo error?"... Probably not worth all this head-scratching, but once you get started on a problem...

    Thank,
    Tom

  • Offline Lamin

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    Offline Lamin

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    Re: Gearing question - speed vs RPM
    Reply #1 on: Jun 12, 2017, 10.21 pm
    Jun 12, 2017, 10.21 pm
    Tom, no idea what you've said there, if there is anything else I can help you with......

  • Offline trophied   us

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    Offline trophied

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    Re: Gearing question - speed vs RPM
    Reply #2 on: Jun 13, 2017, 12.18 am
    Jun 13, 2017, 12.18 am
    Relax, put your feet up, and take a long pull on a nice single malt, and the world will be fine.  I'm too old to work on anything like this.  :821:
    One of the Founding Members of the Twisted Trophies

  • Offline HACKLE   au

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    Re: Gearing question - speed vs RPM
    Reply #3 on: Jun 13, 2017, 01.31 am
    Jun 13, 2017, 01.31 am
    thogland. And I thought I had lots of free time. Old story on clutch slip.
                      1. Revs rise.
                      2.  Forward motion is reduced.
                      3.   Swear words start to be emitted.
                      4.    Hip pocket is suddenly affected.

       Long story, short version. Just ride it, and above all else enjoy it. Don't stress what you can't change. :169: :169:
    HACKLE     I'm too young to be this old.

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  • Offline Coconut   gb

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    Offline Coconut

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    Re: Gearing question - speed vs RPM
    Reply #4 on: Jun 13, 2017, 07.13 am
    Jun 13, 2017, 07.13 am
    If you're using the Analogue Speedo for your comparisons,
    be aware that it is NOT totally accurate, and will generally read too slow by around 3 or 4 %

    If you're travelling on a flat road, the indicated speed of a GPS Unit will usually be more accurate.

    Here's another comparison table :

    1st Gear =  :001:
    2nd Gear =  :001:
    3rd Gear =  :001:
    4th Gear =  :001:
    5th Gear =  :001:
    6th Gear =  :001:

    Neutral =  :030:


    Cheers  :821:

    Last Edit: Apr 25, 2020, 05.49 pm by Coconut

  • Offline thogland   us

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    Offline thogland

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    Re: Gearing question - speed vs RPM
    Reply #5 on: Jun 13, 2017, 05.27 pm
    Jun 13, 2017, 05.27 pm
    So, all interesting replies...  :008:

    My speedo is off about 3% (compared to my Garmin 660). Excellent, in my opinion. I'm really filling this spreadsheet in because it's sitting here, and once I plugged in all the gear ratios, and the speeds were completely off, it started to irritate me. More of a "why do all of the given gear ratios not equal observed speeds?" than "I shouldn't ride until I get this right" kind of thing.

    If anyone wants the sheet for their own use, let me know. I used it previously when I was looking at a front drive pulley change on my V-Star and wanted to know what the actual difference would look like. Would be equally useful for figuring out sprocket changes on chain-driven bikes... Not as useful for the Trophy, but interesting data to have. Also have a similar sheet for time/speed/distance calculations - plug in trip length, time to complete, tank capacity and speeds, and it shows stops and averages. Useful for "I'm riding 550 miles and have 10 hours to do it in, the tank is 6.9 gallons and I want to get gas after 75% is used. How many stops will it take and how many hours at these speeds?"

    And adding a nice single-malt to the mix didn't help, although it was enjoyable in it's own right  :001:

  • Offline atrophy   us

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    Offline atrophy

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    Re: Gearing question - speed vs RPM
    Reply #6 on: Jun 13, 2017, 07.05 pm
    Jun 13, 2017, 07.05 pm
    Thogland, what kind of engineer are you?   :001:
    2016 Tiger 800XR  Black
    2013 Trophy Lunar Silver

    Exclusively using recycled electrons since 2004
    IBA 24605

  • Offline Coconut   gb

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    Offline Coconut

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    Re: Gearing question - speed vs RPM
    Reply #7 on: Jun 13, 2017, 08.03 pm
    Jun 13, 2017, 08.03 pm
    I'll guess he's a "Thou" type !  :038:

    Last Edit: Apr 25, 2020, 05.46 pm by Coconut