In­stant ex­pert: PRO­GRES­SIV­ITY

Mountain Biking UK - - KYRGYZSTAN -

What is it?

A bike’s lever­age ra­tio is how far the rear axle moves for ev­ery mil­lime­tre the shock shaft moves. ‘Lin­ear’ sus­pen­sion set-ups main­tain the same lever­age ra­tio through­out their travel, so the ef­fec­tive spring rate of the bike (how hard it is to com­press the sus­pen­sion at any point in its stroke) is dic­tated en­tirely by the spring rate of the shock. On ‘pro­gres­sive’ frame de­signs, the lever­age ra­tio de­creases as the sus­pen­sion moves through its travel, mak­ing it pro­gres­sively harder to com­press the shock, ir­re­spec­tive of the spring rate of the shock it­self. This ‘ramp­ing up’ to­wards the end of the stroke is known as ‘pro­gres­siv­ity’.

What af­fects it?

Not only do sus­pen­sion sys­tems have dif­fer­ing amounts of pro­gres­siv­ity built in, but rear shocks do too. Coil-sprung shocks are nat­u­rally lin­ear, while air springs are nat­u­rally pro­gres­sive and can be made even more so. So, a bike with a lin­ear sus­pen­sion de­sign, such as a sin­glepivot, can be made pro­gres­sive by us­ing an air shock. And bikes de­signed to be com­pat­i­ble with coil shocks tend to have pro­gres­sive link­ages.

What ef­fects does it have?

On a lin­ear bike, the sus­pen­sion doesn’t ramp up to­wards the end of its stroke. This can lead to harsh bot­tom-outs un­less you in­crease the spring rate (by up­ping the air pres­sure or fit­ting a heav­ier coil), which re­duces small-bump sen­si­tiv­ity and grip. On a pro­gres­sive bike, the firmer end to the stroke means you can main­tain the same spring rate with­out bot­tom­ing out – or even re­duce the spring rate, for a softer feel ear­lier in the travel with­out bot­tom­ing out any more than a lin­ear bike.

Lin­ear TRAVEL

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