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I've made a photo of the actual "thing" as I find it very difficult to explain otherwise:

enter image description here

I'm wondering what this "thing" sets and how it actually works. So, what is "preload" and what happens when I turn it clockwise (plus) and anticlockwise (minus). I tried rotating it both ways to its maximum limit and I didn't notice any change in anything.

The bike the photo has been taken from is Merida Matts 40-D.

3
  • I always turn it to max(-) it fitted for me but I weigh 55kg.
    – user8102
    Sep 10, 2013 at 14:49
  • Expanding on what @freiheit has already said, the OP is asking what the preload setting does. Simply telling him or her that you like to set it to the max and your weight offers no context for the relationship between your weight and that setting.
    – jimchristie
    Sep 11, 2013 at 19:28
  • @freiheit and jimchristie and user8102 Please only post comments that answer the question or ask for clarification. No value comments will often get deleted. As for what the "preload" setting does, it's what ttarchala said in his answer. Mar 24 at 1:30

4 Answers 4

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This fork setting exists so that the fork can be customized to your weight (major reason) and riding style (minor reason). It's simply the initial compression of the internal spring in the fork. The more it's compressed, the stiffer the fork will feel.

Bigger preload compresses the spring more, and so it's best for heavier riders and/or people who need/prefer the stiffer ride (racers etc.) Lighter riders should use less(-) preload. Less(-) preload will also give you plusher ride, but the bike will e.g. dive more during braking.

Source: http://bicyclethailand.com/setting-the-sag-on-mtb-suspension-forks/

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  • So rotating it to the maximum of anticlockwise (maximum minus), it will be suitable for a lighter rider, is that right?
    – Frantisek
    Jan 23, 2012 at 21:14
  • Typically so, but just to be sure I would consult the manual for your fork to see if it adheres to the convention.
    – ttarchala
    Jan 23, 2012 at 21:18
  • I have a similar model, from RST, and @ttarchala explanation is perfectly exact and complete. BUT, in some models (like these RSTs), the difference is not so big, and you'll probably feel it only on the worst terrains (like roads with rocks or stones, or even slowly going down a stairway). Jan 23, 2012 at 22:47
  • For some riders the effect of the preload setting can be completely void specially if they are very low weighted, as their weight won't be enough to compress the suspension coil anyway, so tightening it won't make things much different. In a similar way a rider that is "too heavy" for the suspension will compress the spring to the bottom, so preload will simply do nothing.
    – Jahaziel
    Jan 24, 2012 at 17:33
7

@ttarchala's answer is awesome. But I thought I could provide a bit more info for anyone else looking for info.

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On a coil fork (fork with a spring inside), there are two ways to adjust preload. First off you should get a spring that is the right tension for your weight. For Rockshox forks there are 6 or 7 different spring tensions that are designed for different weight ranges.

See: Rockshox spring diagram.

Once you have the right spring in your fork you can adjust using the preload control (pictured in the question). See @ttarchala's answer for a good description of what this does.

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Air forks generally just have one way to adjust fork preload. Looks like this:

enter image description here

(That is a picture of an airpump adding air to an air fork. For more info see: http://bicyclethailand.com/setting-the-sag-on-mtb-suspension-forks/)

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An important thing to remember about the preload setting on a coil fork, is that it does NOT adjust the stiffness of the fork spring. The stiffness, also known as spring rate, is the amount of compression for a given amount of extra force on the fork, and it is fixed with a coil spring. The preload compresses the spring inside the fork, without the fork changing in length. The spring will not start compressing more until the force on the fork is more than the preload force. This means that you can use the preload to adjust how much the fork shortens if the fork is loaded only by the weight of a rider. The amount of additional fork compression by bumps or by movement of the rider is not affected by preload.

When doing a simple test of pushing on the handlebars, the fork may feel stiffer because it does not move until the preload force is exceeded. But unless the preload force is more than the weight of the rider on the fork (an undesirable situation typically), the stiffness experienced during riding will not be affected by the preload setting.

So if a fork is too stiff, or it bottoms out too easily, this cannot be adjusted with the preload, to adjust that you need to replace the spring with one that has the correct spring rate for the rider's weight and riding style. (you can also adjust how stiff it feels by modifying the damping but that is a wholly different can of worms)

The main purpose of the preload adjuster is to make sure the fork has the correct length when loaded by the rider's weight, and the geometry of the bicycle is as intended.

The amount of fork compression under the rider's weight is referred to as 'sag', and in forks with an air spring you usually adjust this with the air pressure. But air pressure actually changes the spring rate, not the preload. So any setup guide for air forks that refers to sag, should be ignored when working with coil forks.

The correct setting for the preload depends on the model of the fork and bicycle, but a good ballpark figure is for the fork to be compressed by 15% of its maximum travel when loaded by a stationary rider in a usual riding posture. Increasing preload will put the rider in a more upright position, decreasing preload will put the rider in a more forward leaning position. Be aware that increasing preload will also limit the fork's ability to follow depressions in the surface, since it can extend less.

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The way many of these work is by controlling the movement of the oil by adjusting the orafice size that the oil flows through.Small holes restrict the oil making the shock feel firmer.Larger holes allows more oil to flow through faster making the shock feel softer.That is how turning the knob such a small amount can make such a big difference.

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  • 4
    No. What you are talking about is the compression control, the preload is rarely anything more than an big screw - the more you turn it, the more it compresses the spring i.e. preloading it. Also the OP plainly stated for the control that he "didn't notice any change in anything".
    – cmannett85
    Feb 1, 2012 at 12:24

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