The Mongoose Deception mountain bike has coiled spring shocks in the front fork. Shock absorbers reduce the impact of bumps and potholes and give the wheels better contact when landing jumps. Shocks should be set to suit the rider’s weight so that they do not compress too little or too much. If they are not adjusted correctly, the steering can feel unstable or the bike can sag too much. Adjusting the preload tension of the shocks is easier if you have another person to assist you.
Locate the shock absorbers that sit on either side of the front wheel. The shocks form the bike fork and look like one tube moving inside another. Measure the amount that the shock compresses when you sit on the bicycle -- this is the sag. Lean against a wall or get a friend to support you and your bike while you get on and sit on the seat and hold the handlebars in a riding position. Mark or measure the distance, then measure the amount of travel once you have removed your weight.
Measure the range of motion for your shocks in the fork by fully compressing it by applying your full weight to the handlebars until you feel it bottom out. Measure the amount of travel once you remove your weight.
Calculate the sag as a percentage of total range of motion. Check that it is about 25 percent for cross-country biking. For instance, if the total compression is 6 inches, you want the sag to be 1.5 inches, although for downhill riding, it can be more. If it is not around 25 percent, it will need adjustment.
Examine the top of each coil spring and locate the hex-head fittings on the adjustment rings. If the sag is more than 25 percent of the total range of motion, then the tension is too loose (unless you are a serious downhill rider). If the compression is less than this, then the tension is too stiff.
Turn the hex-head fittings with a metric hex wrench to adjust the tension. Turn each side of the fork by equal amounts. Turning the fittings clockwise lowers the adjustment rings to tighten the tension. Turning the fittings counterclockwise raises the adjustment rings and loosens the tension.
Take the bike for a test ride over bumps and mounds of different heights and take careful note of how it travels. If the shocks feel as if they are compressing too much on landing, your upper body will move forward in an unbalanced manner as you land, and you should tighten the tension a little more. If the front of the bike appears unstable and stiff, you should loosen the tension off. Retest until you are satisfied with the way your bike is handling.