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Pre-loading of suspension springs

  • Nutty
    Nutty
    6 years ago
    At the urging of another member I'll have a go at explaining pre-loading.

    Firstly, pre-loading doesn't affect the spring rate. Spring rate is a mechanically fixed value determined by the physical properties of the spring. Adding pre-load changes ride height but DOES NOT affect the energy required to bottom out the suspension.

    For example, a SGS I'm revalving now has Ohlins 1.0kg/mm x 277mm long springs pre-loaded by 17mm. There's 2x 17mm (34kg) preloaded into the fork. The bike has 31mm or so of sag at that spec.

    31.5mm of sag requires 63kg of static load. Add the 32kg already stored in the preloaded springs and you have 95kg  of sprung weight on the front end. 

    Now the math. 95kg/2 legs = 47.5kg per leg. Total spring compression is (17+31.5) 48.5mm.

    Preloaded spring rate is mass/distance...47.5/48.5, close enough to 1.0, the rating of the unloaded spring. 

    Preloading springs changes static ride height but not bottoming resistance because a preloaded spring is just that...it had energy already loaded into it before the suspension operates. 

    Because pre-loading stores energy in the spring it effectively makes the rebound damping softer in the top of the stroke, giving that 'ejector seat' feeling. 

    Hope that helps. Cheers.
  • Nutty
    Nutty
    6 years ago
    Pretty long winded there old mate...it's not that you "weren't clear enough", what you posted was blatantly incorrect. Also, it was YOU who asked me create my own post to offer input to the site. It's a bit tough chasing me over to another thread to continue your tirade..

    Look on the up-side. At least we all now know that pre-load doesn't change spring rate or stop bottoming. It changes static ride height only. 

    Over time the opposite actually occurs, the spring rate falls  because the modus of elasticity drops off. Then, often extra preload is added to maintain ride height over an even softer spring. The result is increased bottoming. 
    Quality Harley springs are really cheap, about $160 pr. Riders can gain a lot in handling and ride quality by proper spring selection. 

    p.s. I did a nice 612km loop on Monday, surely this site's about riding, not saving egos and Internet  pissing competitions. 
  • steelo
    steelo
    6 years ago

  • JFE
    JFE
    6 years ago
    You are all acting like a bloke on the rebound near a Swedish beach volleyball team.
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