TECH TUESDAY – SUSPENSION PRELOAD

Shaun George Mechanics

The fun part of the sport of Mountain biking involves riding over rough and uneven terrains – often at a fun, fast pace! Hence a vast majority of mountain bikes come with suspension forks. Many of these also have some basic adjustability to improve the suspension effort.

Coil forks are the most common these days and available on entry-level bicycles as they are usually quite cheap. Air forks, on the other hand, are usually only found on mid-range to top-end bikes, end up being a lot more advanced and lighter too.

Knowing how to adjust the various knobs and dials on your suspension is not only geekily exciting, but it also allows you to improve your overall ride experience by playing around with some basic settings.

Today we’re going to talk about Preload and its importance.

The preload dial is usually seen on budget forks on only one side. Usually the left hand side – some forks have it on both sides. The preload dial looks like a circular knob with a “+” on one side and a “-” on the other side (pictured above).

What is preload?

The preload refers to the amount of sag the shock will allow when the bike is at rest with the rider’s weight bearing down on it.

Determining the correct preload is important because if it’s too high, it takes more energy to move the shock and compress the springs, resulting in a harder and desensitized shock system. If it’s too low, your shocks won’t be supportive when you need them to be. You will also experience what is called “brake dive” when you get on the brakes hard. Preload pre-compresses your spring so that it takes more/less force to begin compressing the fork. Increasing the preload will increase the stiffness of the fork (like increasing air pressure in an air fork). Decreasing preload will decrease the stiffness of the fork, similar to decreasing air pressure in an air fork.

Why should I adjust my preload?

Hard braking, landing hard after a jump and pedaling to accelerate suddenly have the potential to bottom or top out the suspension through its travel. Bottoming or topping your fork out isn’t a great idea especially if you’re out on a trail riding hard. Either of the extremes will cause you to lose traction. Under less intensive usage, the preload will determine how plush or stiff your forks responsiveness to bumps is.

Adding preload to the spring will increase the force required to start compressing the spring. Similarly, too much preload will keep the fork from reacting to small bumps, making it harsh.

POSITIVE PRELOAD SPRINGS

Positive preload springs are the mainsprings found in coil shocks and are responsible for keeping the bike level while you are riding over rocky terrain. When you increase the preload on the positive fork, the positive spring will have more load on it than the negative spring. It will result in a lower sag. It’s important to keep these two springs balanced or your bikes shock system will become uneven and potentially dangerous if you’re biking on really rough terrain.

NEGATIVE PRELOAD SPRINGS

Negative preload springs on a fork are responsible for repelling the force generated by the positive preload shock spring. Keeping the two balanced and keeping the sag from becoming too great or from the shocks compressing too quickly. Negative preload springs can also be found in air shocks, but they have a different role than with coil shocks. A Negative air chamber in an air shock is similar to the negative preload springs on a coil shock

How do I set the preload on my bike?

Coil sprung forks have a way to compress or relax the spring by turning a knob on the fork. Adjusting the forks preload requires measuring the sag -how much the fork compresses when the rider is sitting on the bike. Typically you want the fork to sag about 30 – 40% of its travel. This allows the fork to extend into depressions and absorb all minor trail chatter.

Turning the preloaded dial towards the negative symbol will decrease the preload on the spring. On the other hand, if you find the fork to be too stiff, backing off the preload will soften the fork. 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.

SUMMARY

Adjusting preload can play a pretty big role in how your mountain bike rides. A 30% preload on MTBs and a 40% preload on DownHill bikes are standards most riders gun for. Having said that, find a good balance on your fork according to your riding style and body weight is quite important.

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