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Discussion By god they can go ....

Discussion in 'The Pub' started by trevorlatala, Oct 12, 2020.

  1. trevorlatala

    trevorlatala Active Member Contributing Member

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    I was out today with my wife Ann in her BMW Z3 sports car driving through the peak district in Staffordshire - Derbyshire This is a very hilly area When we were overtaken by a learner on his whatever 125 motorcycle ! Well bugger me these can really go up hill he was doing 50 plus and down hill 60 plus
    What are these new bikes doing my 250 ,s and 350 can only keep up at these speeds Come on guys what am i missing out on
    Trev
     
  2. jmw76

    jmw76 Well-Known Member

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    Not sure what bikes you have. An old Honda cbr250rr or any of the 250 4 cylinder sports bikes of that period are quite spritely and enjoyable to ride. If you are just interested in outright performance from a 250 then the 2 stroke pocket rockets are the thing, but they require a bit more maintenance.
     
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  3. trevorlatala

    trevorlatala Active Member Contributing Member

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    My bikes are listed as I can see so are yours
    This little thing was nothing more than a 125 single but by gum he was giving it some stick !
    I really enjoyed watching him go I could tell he was a learner though as he seemed to be ballet dancing on the brake pedal That is according to his brake light
    I really admire any one who gives it his all possibly getting a 100 miles to the gallon as well
    Trev
     
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  4. DannoXYZ

    DannoXYZ Well-Known Member

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    My wife's CB125T has 17bhp and gets 100mpg! Tops out just over 110kph! :)
    Such a fun bike to ride!
     
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  5. trevorlatala

    trevorlatala Active Member Contributing Member

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    I have always loved the concept of getting a lot out of a little I have even fantasised of getting 100 mph out of a 50 cc machine
    Fuel injection turbo and a slippy shape
    I cannot say how much I enjoyed watching the guy getting the max out of the minimum
    Trev
     
  6. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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  7. jmw76

    jmw76 Well-Known Member

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    Yes. There is real satisfaction out of getting the most out of little bikes. Anyone can go hard on a 1000.
     
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  8. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Just buy an NSR 150 if you want to play dragonslayer.
    Honda_NSR_150_L_1.jpg
    In fact, this would be the perfect track day bike, 40hp. Everyone passes you on the straight and you pass them all again before you finish the lap.
     
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    Last edited: Oct 13, 2020
  9. trevorlatala

    trevorlatala Active Member Contributing Member

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    there must be some kind of formula for the speed of yer bike against ist horsepower rating
    taking things like drag etc into account
    any one have any tables
    Trev
     
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  10. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Only thing which comes close to a formula I can think of is when Barry Sheene was commentating the 500 GP races.
    He'd always be lauding the speed and power of the Hondas and say that at those speeds each extra horsepower was one extra kilometre per hour by the end of the main straight
     
  11. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Err nope. Wind resistance is the killer. As with everything it will square with the speed so it only takes 40 or a little less to do 100mph and about 200 to do 200mph. After that it gets really crazy. The Ducatis have gobs more power than the Yamahas even though they might only be 12kph faster.

    You would think a simple comparison would be easily found on the internet of things but not so. Here are some links if you want to mess about
    https://www.omnicalculator.com/phys.../www.omnicalculator.com/physics/drag-equation
    http://elmoto.net/showthread.php?t=3400
     
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    Last edited: Oct 14, 2020
  12. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    You're disagreeing with Barry Sheene...always loved his comment - "like a rat up a drain pipe"
     
  13. DannoXYZ

    DannoXYZ Well-Known Member

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    While wind-resistance (aero-drag) goes up to square of speed, power-required to overcome that resistance goes up by cube-function of speed. So it requires eight times power to just double speed.

    For example, it requires about 9bhp go push bike through air at 100kph.
    To make it go 200kph, requires about 70-75bhp.
     
  14. DannoXYZ

    DannoXYZ Well-Known Member

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    He's not necessarily disagreeing with Barry, who's not talking about ultimate top-speed given unlimited runway, but acceleration to end of straight. So effects of extra power given extra speed at end of straight isn't as great as would be realised with more road.
     
  15. DannoXYZ

    DannoXYZ Well-Known Member

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    Hey, thanks!!! That list of bike cross-sections are very handy! Can plug into this equation to determine how much power is needed to reach any particular speed on any particular bike:

    TotalPower = aWS + (rho/2)CdCaS^3 where

    a = coefficient of rolling-resistance of tyres, and drivetrain (bearings & gears)
    W = weight of bike+rider in Newtons
    S = speed in meters/second

    rho = air-density (temperature and elevation dependent, so you'll have to expand on this)
    Cd = coefficient of drag, depends upon smoothness of body-shapes
    Ca = frontal-area of bike+rider in square meters, mirrors add surprising amount of area

    Notice that the 1st term (rolling-resistance) goes up linearly with speed while the 2nd term, power required to overcome wind-drag goes up to the cube-power of speed. When you go from 100 to 300kph, rolling resistance goes up 3x while power-required to overcome wind-resistance goes up by 3*3*3=27x !!! This is why you want to focus on aero-mods to improve top-speed. Easier than increasing gobs of power!
     
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  16. mboddy

    mboddy Well-Known Member Premium Member Contributing Member

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    On a push bike you provide all the power. Recumbents are faster because they have less frontal area.
    Around my local area I can pedal my recumbent trike up to 60kph.
    Once I fitted a small nose cone that increased to 80kph.

    I took a Trisled racing trike for a ride around the bike race track.
    It is fully enclosed with only a few cm of the bottom of the tyres exposed.
    The track has quite an uphill slope around the back of the circuit.
    When I got into it my heart sank when I saw that the only front sprocket had 80 teeth.
    I thought there was no way I would be able to get it up the hill.
    But when I tried it we just sailed up it really fast.
    The hill was nothing compared to wind resistance.
     
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  17. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I can think of one way to get more power on a bike, but I am uncertain as to the conversion between horsepower and sheeppower or if it's going to go any faster with that wind resistance

    Wallace-Gromit-sheep-bike.jpg
     
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  18. DannoXYZ

    DannoXYZ Well-Known Member

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    Now.... if all those sheep were to fart at same time....
    ... and we ignited it.... hmmmm....
     
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  19. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    That would probably have a level of difficulty on a par with tuning FZR250 carbies first go.. :)
     
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  20. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I think that has likely never happened, ever!

    They are worse than trying to play a game of Jenga whilst juggling three pins whilst balancing a plate on a stick on your nose with a hula hoop going on one leg whilst hopping over a skipping rope
     
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