"calculated" speed

Discussion in 'General' started by grady anderson, Mar 19, 2015.

  1. grady anderson

    grady anderson Well-Known Member

    Just got back from Daytona and it seems like the first question from the Great Unwashed after "How did you do?" is "How fast did you go?"
    Given the wheel diameter, front and rear gears, final drive ratio in high gear and RPM.....anyone know the formula to determine mph?
    So far my answer is "Fast enough to win" but that is redundant after I answer their first question.
    Any engineers out there?
  2. ton

    ton Arf!


    or a radar gun to measure same.


    you'd need the coefficient of friction for the air, determined in your race position, on the bike, in similar atmospheric conditions, and the power to the wheel to calculate it the hard way...
    Last edited: Mar 19, 2015
  3. Mongo

    Mongo Administrator

    You should be able to actually get that from their scoring system if they put the proper mileage for the track in. Well, for average speed over a lap, not top speed.
  4. SamS

    SamS Well-Known Member

  5. SPL170db

    SPL170db Trackday winner

    I don't know what you've got but if that number is of particular importance to you a GPS lap timer will tell you that.

    I have a Starlane Stealth GPS that will display your top speed of each lap on the screen, and when you download the data to your computer it tracks your speed at any given point around the entire track. Easy way to tell, like I said if that number is particularly important to you.
  6. ryoung57

    ryoung57 Off his meds

    Just make something up. Doesn't matter what you say, they'll just reply with "Pssssh, dem Nascars go over two hunnert".
  7. peakpowersports

    peakpowersports Well-Known Member

  8. BigBird

    BigBird blah

    I would say about 201...definitely true in km, maybe not so much in mph. but what's a difference of measure between friends :)
  9. flyboy

    flyboy Well-Known Member

    +1 for GPS.
    I've seen data from one rider hitting just over 170 on his 600
  10. SethG

    SethG Well-Known Member

  11. OGs750

    OGs750 Well-Known Member

    You don't need those variables to calculate speed. The speed of the wheel is going to be the speed of the vehicle.

    In this case the wheel speed = angular velocity x tire circumference

    Since rpm is an angular velocity and you can make a good assumption of tire size, all you need are final drive ratio and gearing.
  12. ton

    ton Arf!

    good point.
  13. tzrider

    tzrider CZrider

    Engine rpm
    Primary drive ratio
    6th gear ratio
    Final drive ratio
    Rear tyre diameter
  14. metricdevilmoto

    metricdevilmoto Just forking around

    GPS timers can give you that data. Especially at Daytona, it's useful.
  15. grady anderson

    grady anderson Well-Known Member

    Average speed is easy
    Got that
    In fact the winner's average speed is posted on the race results
    And I get that most racers don't reLly care about the top speed number
    The question just got me thinking
  16. grady anderson

    grady anderson Well-Known Member

    Thanks Mike, I know that too
    Didn't have one
    Kind of a hindsight question
  17. SPL170db

    SPL170db Trackday winner

    Next time have someone follow you with their car and match you and take note of what speed it is. I used to do this when I was a kid and the speedometer in my POS beater car broke :)
  18. grady anderson

    grady anderson Well-Known Member

  19. grady anderson

    grady anderson Well-Known Member

    This one looks like fun but....
    Differential ratio need a little more explanation
    Must be a combination function of final drive (front and rear sprocket ratio) and 6th gear internal ratio
    Cool interactive chart though
    So far my guesses have me at 212 mph
    Woohoo but probably not
  20. grady anderson

    grady anderson Well-Known Member

    Great idea
    First let me find someone with a car that will top 150 and see if the track officials will let him follow me on track during the race
    Should not be too much of a problem

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