Bike Spring Rate Calculators

Bike Spring Rate CalculatorsCoil springs have always been the best suspension and they're making a come-back.  But they have one big downside: you've got to get the spring-rate right.

The methods for getting spring rate right have historically sucked.  You can spend a fortune on springs (up to $300 each) and swap them out until you find happiness, or find someone else and copy them.  But this isn't guaranteed either.  If your damping is wrong even the right spring will feel wrong.

Many have attempted spring-rate calculators; based on sag, leverage ratio or straight out hocus-pocus.  No two would agree.

Here at Shockcraft we do things differently.  We brush aside all the black art BS and apply physics and maths the way it should be.  It's called Engineering and it's amazing that this hasn't been done before!

Working from the ground up we calculate sprung and unsprung weights and the spring rates required to drive those leveraged weights at the frequencies that bike suspension needs.  Both fork and rear shock spring rates are delivered.

From all this work we have published two spring-rate calculators.  The first is very simple and it's free to use.  Simply enter your weight and it spits out front and rear weights.  This calculator is based around a 160 mm Enduro/Trail bike using a 56 mm stroke shock with a 65 deg head angle.

If you want to get serious, pay a small amount and you get into our advanced bike spring rate calculator.  It lets you tweak everything from wheelbase and head-angle through shock stroke and unsprung weight.

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  1. This is a complex spring rate calculator to determine front and rear spring rates for Trail and Enduro MTB.

    Enter rider weight, bike weight and unsprung weight as well as bike geometry numbers to get the most accurate starting point for bike setup.
    IFP force is the shaft force your rear shock presents due to the internal gas charge.  It can greatly change sag numbers.
    A stock Cane Creek Double Barrel will exert about 5kg force, a Fox DHX2 about 7kg, a Manitou Swinger/Revox or Fox DHX/Vanilla with 1/2" shaft about 18kg and a Fox DHX/Vanilla with 5/8" shaft about 27 kg force.

    This calculator is frequency based and operates in a different way to every other spring calculator.
    It has been configured to work well for most XC through Enduro bikes in the 120-180 mm travel range.
    It has not been verified on DH bikes yet.  That work is still in progress.
    Sag numbers are based on the rider in the attack position.  Sag is difficult to measure, is affected by dozens of other variables and doesn't really matter unless your numbers are out enough to affect geometry and bike handling.

    You must purchase a voucher code to use this calculator which will be emailled to you.  Each voucher code can only be used once.  Simply click add to cart and proceed through the checkout process.  Your results (fork & rear shock spring rates & sag approximation) will be emailled.

    Note for International Customers: Price is in NZD and includes New Zealand GST of 15% for NZ customers.  International is approx $US12.

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  2. This is a simple spring rate calculator to ball-park bike setup and provide front and rear spring rates.

    It makes several assumptions to reduce the user input down to just one variable (rider weight).  If you want a more complex calculator then use this one here.

    This calculator is frequency based and operates in a different way to every other spring calculator.
    It has been configured to work well for most trail and Enduro bikes in the 140-160 mm travel range.
    Rear shock leverage (average) is fixed at 2.8:1 which represents 160 mm of travel on a 57 mm stroke shock.
    Bike geometry is based around a 65 degree head angle and rider in the attack position.

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