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I've got an SR Suntour XCM HLO 27.5" 100mm travel that comes with my bike. It has preload adjuster on the left and lock on the right.

What I wonder is how to properly adjust the fork softness/stiffness as I encountered some bumps with stiff feelings on the fork.

Also, if I lock it and turn the preload adjuster, I can turn it more than if I let the fork open. What causes this and should I lock it before adjusting the preload?

3 Answers 3

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Turning the preloaded dial towards the negative symbol will decrease the preload on the spring. Therefore if you find the forks are too stiff, backing off the preload will soften the fork. Alternatively if you wish to firm up the fork, turn the preload dial towards the positive symbol. This will compress the spring and stiffen up the suspension.

I would adjust the preload with the lock out off, though I don't believe it would make any difference beside allowing you to compress the fork as you dial preload on/off to see what affect it has on the fork.

Hope that helps!

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Preload does not change the stiffness of the fork. A coil spring is quite linear, so the stiffness does not change with preload. You can only change the spring stiffness by exchanging the spring. What will change with preload is how much the fork compresses under the weight of the rider, also known as 'sag'. The preload compresses the spring without shortening the fork. The fork will only start compressing once the load on the fork exceeds the preload, and the compression of the fork will be (load - preload)/(spring rate). This allows heavier riders to have the same geometry of the bicycle as lighter riders. A much more correct way to achieve this would be to use the right spring rate for the rider weight, but different stiffness springs are often only available aftermarket for high end, expensive forks. In fact, a more cynical explanation for the presence of preload knobs on budget forks is so it looks like they could be adjusted to the rider. The correct amount of sag to aim for by adjusting the preload depends on the fork model and a good manual should list it, but a good ballpark figure is about 15% of the total travel of the fork.

Many setup guides for forks are written for air springs. With air springs, the sag and stiffness are usually coupled, and sag is used as a placeholder measure for stiffness, which I suspect is one reason for the confusion.

See also here: https://www.singletracks.com/mtb-gear/whats-hot-with-mtb-coil-shocks-and-forks-we-asked-the-suspension-experts/

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I do not know the inner workings of this particular fork, but in general preload and lockout should be independent, unless you adjust the preload while the fork is loaded, since the lockout would prevent the fork from moving. I would open any damper settings (switch off lockout) while adjusting preload, since to set the spring correctly you want it to be as unimpeded as possible

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