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  1. #1
    Addicted Cruiser MrBoard500's Avatar
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    Default Calculate a Predicted Average Speed?

    I'm 15 yrs old and was bored during math, so I started thinking about longboarding. I then started thinking about how to calculate an average speed I might get for a hill i'm dying to bomb within the next few days. I may have figured out an equation to figure out a predicted average speed.

    The current Speed Record is 89.41 mph set by Kyle Wester. I'm going to use the previous record set by Erik Lundberg at 81.17 mph because I found the % grade for his hill (18%). If you want to find the % grade of a hill, aswell as the length and location of roads...use Findhills.com

    Equation: y=x*4.5
    Y: predicted average speed
    X: % grade of a hill
    4.5: Erik's speed divided by 18%

    Let me explain: I took Erik's speed of 81.17 and divided that by 18, which is the grade of the hill where he once beat the previous world speed record. That gave me 4.5 mph for every 1% grade. So if you want to ride a 10% grade hill, you could expect to get around 45 mph. Now, this is only a prediction based on perfect riding conditions like the weather (no wind or wind at your back, dry) and road condition (smooth pavement, no dirt/gravel). And the speed will become closer to the predicted value as the length of the road increases at the same grade.

    To check this, I used a local hill me and a friend skate. I took the average % grade of 5, found on Findhills.com and multiplied that by 4.5 and i got 22.5 mph. Which is fairly accurate, the speedometer app i use says about 25 mph when i ride that hill.

    I'm not the best at math, but this makes sense to me. What do you guys think?


    Sent from my iPhone using Silverfish Longboarding


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  3. #2
    Addicted Cruiser WarrenS's Avatar
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    Default Re: Calculate a Predicted Average Speed?

    Why do I go 20 on some 2% grades then? Hmmm I'll hit up my Physics and check.

  4. #3
    A Heaping Helping Of Boner Pie Order of the 'Fish bucksaw87's Avatar
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    Default Re: Calculate a Predicted Average Speed?

    You're not taking into account several BIG factors... Length of the hill, wind or air conditions, the condition of the road itself, the rider's skill, the board setup (hard wheels vs. soft wheels). These things need to be accounted for...A wheel that's too hard won't roll properly over a rough, worn road; same as a soft wheel will be sluggish and gummy on a perfectly smooth surface (like in a skatepark).

    And, I myself have ridden some 8% grades and not broken 25 mph.

    The grade of a hill is the vertical drop over 100 lateral feet...in other words, a 100% grade would be 100 feet drop divided by 100 feet of lateral run-out, or a paltry 45°. There are banks steeper than that in every skatepark in America.

    Don't get me wrong, it's super cool that you did this! But, it's sort of incomplete.
    yes, an uber-grippy, square-lipped slalom wheel IS the best for sliding
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  5. #4
    Concrete Kahuna Momona Boe's Avatar
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    Default Re: Calculate a Predicted Average Speed?

    /\ agreed, very cool that you crunched some numbers

    maybe it's a good ballpark figure to start with
    "I knew Joe Iacovelli; Joe Iacovelli was a friend of mine. Senator, you're no Joe Iacovelli."

  6. #5
    Addicted Cruiser WarrenS's Avatar
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    Default Re: Calculate a Predicted Average Speed?

    This isn't new math, just wrong physics. I remember and forgot the correct way from Physics this year. Lol

  7. #6
    Stoked! Tahitus's Avatar
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    Default Re: Calculate a Predicted Average Speed?

    Your best bet would be to figure how much you weigh, use some trig and the % grade of the hill to find the forward force, take that and plug it into the equation

    Force = Mass x Acceleration

    solve for acceleration, take that, starting with an intial velocity of 0, take a guesstimate at length of hill, plug all those into the equation

    speed final (squared)= initial speed squared (0 m/s) + (2)(acceleration)(distance)

    which is just the kinematic equation that doesn't use time, and solve for final speed, which is do the calculation and then take the square root of it

    Then take that and plug it into the equation

    Acceleration = (Final speed - initial speed) all divided by time

    Solve for time

    Then take that and distance and plug it into the equation

    Speed = distance/time

    This, ignoring wind resistance will probably be the most accurate way to solve for average speed




    Sent from my mom


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