Trials Bikes For Dummies

By Ron Milam

After all these months of discussing springs, geometry, conservation of energy, and the like, you guys probably wish I would just get down to the nitty gritty of adjusting your suspension. Well folks this is your lucky month, cause I’m-a-runnin-outta-stuff-ta-say. So here comes the nitty.

The most important thing is for you to keep the suspension at both ends balanced. This means that with your weight centered on the bike, you compress both front and rear suspensions the same amount. This should also happen while riding through a section. Sure you will hit bumps and such that temporarily affect one end or the other, but in general both ends should compress and rebound together. You might be asking yourself why this is so important. I’m glad you asked that question. ( If you did not ask that question, you might not have an inquiring mind. And you know what the National Inquirer says about that ). Any way, the reason is that you want the steering geometry to always be the same. We already discussed that a few months ago. Many knowledgeable or allegedly knowledgeable people suggest that when stand on a stationary bike, the suspension at both ends should compress about 1/3 of the total travel. This is about 50mm ( or 2 inches for the metrically challenged ).

Different bikes have a variety of adjustment methods on the forks. Most shocks adjust the same way. Lets do shocks first. The spring adjustment is easy to figure out. The damping adjustment will be a little harder to figure out. The reason for this is that most of them don’t make much of a difference. The suspensions of late ‘90’s bikes are faster rebounding than earlier models. If you want to duplicate this characteristic, you will probably have to replace the shock or have it modified. I have been told that Bob Ginder at B&J Racing is good at this. Non rebuildable type shocks can be rebuilt and the damping can be updated. If you are extremely handy, you can even do it yourself. Good aftermarket units are also available. Try the adjustment screw. It may be enough. If you speed up the rear be sure to do the same to the front. If your motive is rear wheel hopping, consider this. If you need faster rebound to hop, you probably aren’t doing it right. In that case, your scores may actually suffer from the change. Fast rebound is a hindrance in marginal traction conditions. And if you are attempting a splatter, you need the wheel to stick on the obstacle long enough to drive up it. I don’t mean to discourage anyone from experimenting. Just be sure to record your initial settings so you can get back to the original setting if you don’t like the changes.

Forks are a different matter. They have all kinds of adjustment. I will discuss the ones I know about. GasGas forks have both compression and rebound damping adjustment knobs on the top of the fork caps. Rebound is controlled by the right leg and compression on the left. If you need to change the preload, you do it by changing the spring spacers.

Conventional Paoli forks as used by Beta and probably Montesa, Scorpa, and others, work a little different. They only have one spring. It is in the left leg and it is adjustable externally via a hex key in the top of the cap. The adjustment is limited to about plus or minus 5 mm. If you need more, you can install a spring spacer. The rebound damping is in the right leg and is adjustable by a knob on the top of the cap. Compression damping is not adjustable except by changing oil viscosity or modifying parts in the left leg. Marzzochi forks as used on Fantics and others, work basically the same as the GasGas forks. All trials forks listed above use SAE 5W oil. Some month, I’ll get into oil viscosities, etc. But for now you should consider this point. An SAE specification for oil viscosity is not an absolute number. It is a number that covers a range of viscosities. This means that the 5W oil you get from one company may not have the same viscosity as the 5W you get from a different company. Once you find one you like, stick with it. Spring characteristics can be modified by playing with oil levels, but most trials riders stick with the recommended amount of oil. On the Paolis, this amount is 360 cc per leg. On a GasGas, the level should be 100mm from the top of the tube with the leg fully compressed and the spring removed. I don’t remember how much goes in the Marzzochis, but I do remember that they have air bleed screws in the caps and it is very beneficial to utilize them regularly. This really makes a difference to lighter riders.

One last suggestion for you guys that are fortunate enough to get a new bike and plan to keep it for a while. As soon as you have enough hours on it to get the suspension broken in, take the time to make some detailed observations and make notes. How much does each end compress at rest? With you on it? How fast does it seem to rebound? Is it very smooth or kind of jerky? Put numbers on as much as you can and write everything down. Even how much you weigh. That way you can review your notes a year or more later and compare the current condition to the new condition. Suspension deterioration is a gradual process. It is hard to notice the day to day changes.

Ron