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Thread: Spring Rate Calculator

  1. #1
    Car Addict MAYcar's Avatar
    Join Date
    Aug 2006
    Sunny Arizona!

    Spring Rate Calculator

    Awhile back Lee asked me to post some of the stuff that I have found out about spring selections. Here are a couple of links that I use to figure out what my wheel rates for the BMod car are. Now, understand that wheel rates are not necessarly the same as spring rates. Wheel rates are the effective rate of the spring as measured from the wheel. This takes into account the leverage advantage that your suspension has on the spring.

    Typical MacPherson strut type suspension has a leverage ratio of 1.1 to 1. Other types of suspension you will need to calculate the leverage ratio. At the Strawberry Hill Cobra website ( ), click the link "Tweaks", then select "Measuring the Motion Ratio". They give a very good description of how to measure and then calculate your Motion Ratio.

    Once you have calculated your Motion Ratio's (front and rear) then you can go to:

    There are a few things that you'll need to know before you can calculate your wheel rate.

    1) Corner weight
    2) Unsprung weight
    3) Spring rate

    Once you have those values you can plug them into the calculator.

    In box number 2) Suspension Leverage, select "I know this value" and enter the leverage ratio that you calculated earlier.

    Once you have entered this information it will calculate your:

    1) Efective Coil Rate
    2) Wheel Rate
    3) Static Deflection
    4) Wheel Frequency
    5) Natural Frequency

    Below the results is a general guideline on types of cars and Wheel frequencies.

    From the Competition Car Suspension book.

    60 - 80 cpm Comfortable road car.

    80 - 100 cpm Sports road car.

    100 - 125 cpm Racing cars without wings or ground effects.

    200 - 350 cpm Current racing cars with downforce.

    - 500 cpm Ground effect era cars.

    Another note to keep in mind when selecting springs is to keep the front to natural frequency about 10% higher towards the front.

    Hope this is helpfull!

    Mark Yakich
    Casa Grande, Arizona

    Proud recipient of the 2012 Paul Weidner "Spirit of the Sport" award.

    '09 Demon F500 - FMod Baby! (Beumer's car in my possession)
    '03 PCR Red Rocket - KMod Baby! (my car in Beumer's possession)

  2. #2
    No mention of farnorthracing's calculator?
    David Nichols
    2001 Grand Prix GT #569 SMF
    //// TrackTimeAudio - Speed sounds awesome.

  3. #3
    07-09 Driver of the Year washburn's Avatar
    Join Date
    Jun 2002
    Wausau, WI
    (Calender day number * (Average daily temp / historic ave. temp)) * the Puxatawny Multiplier ("1" if he did, ".25" if he didn't) - snow depth = Spring Rate. meant *car* springs. Never mind.
    Patrick Washburn
    Lucky Lugnut / SoloPro / Red Eye Brewing
    Member of Team One Out
    Very proud recipient of the 2010 Paul Weidner Spirit of the Sport award!!!!!

    "Drives like a drunken one armed crack monkey"

  4. #4
    Quote Originally Posted by washburn View Post
    (Calender day number * (Average daily temp / historic ave. temp)) * the Puxatawny Multiplier ("1" if he did, ".25" if he didn't) - snow depth = Spring Rate. meant *car* springs. Never mind.
    Can somebody in nothern Wisconsin drive over to Pat's house and check if he's OK? I suspect a severe case of cabin fever.

    "Get out your guitar, sing two cheerful songs and call me in the morning."
    Phil Ethier West Side Saint Paul Minnesota USA
    1973 Triumph Stag LE22439UBW "uncle jack", Sapphire Blue
    2004 Suburban 8.1, Sport Red, the only automatic of the bunch
    2005 Lotus Elise, Bordeaux Red Pearl
    2005 Subaru Legacy GT Limited, Regal Blue Pearl
    pethier7 [at] gmail [dot] com

  5. #5
    Thanks Mark

    I thought you forgot

    Lee F.
    SSK Miata

  6. #6
    One great thing about owning a miata is most of the hard work has been done already.
    2013 Scion FR-S Build Thread

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