Trials Bikes For Dummies

By Ron Milam

This is Part 4 of suspension basics. Last time we discussed how to make spring preload adjustments. There is plenty to cover in upcoming columns, but we now have enough information to decide if adjustments are necessary and what adjustment to make.

First, you want your suspension firm enough to not bottom severely, but it should be soft enough so that it does bottom on the very hardest impacts. If you try to avoid bottoming altogether, you will not have the compliance to keep the tires on the ground in some conditions. When you go to make your changes you may find different possibilities depending on your bike. Next month we will cover various bikes.

This time I want to talk about steering geometry and how it is affected by suspension settings. Once you have adjusted preload and damping, you will need to make further changes to get your bike to steer properly. There is a great deal of advice and debate about things like bar position and such and how forward positioned bars can help you turn sharper and etc. Furthermore, some folks think they can affect steering by moving their weight forward or back to compensate for bike deficiencies. This can help on up / down hills, but in an average turn, it is likely to make matters worse. I finally learned a lesson that has been taught by many people, but took me a long time to adapt to. When you are turning, you should have practically no weight on your arms. Next time you continually have trouble in a turn, think about this and make a point to keep your arms light. You will probably find the turn wasn’t so hard after all. You will also find that since you do not have you arms propping you up any more, you are forced to balance yourself on the pegs. Now your mass is pushing downward on components located a foot above the ground and much closer to the contact patch of the tires instead of on the bars which are located much higher and which will probably be located on the inside of the tire contact patch if the bike is leaning into the turn. Since you are positioning your body so that you are nearly balanced with little arm pressure, you cannot do things like the typical go-fast guy does and slide your weight forward in turns. And also, since your bike probably doesn’t have an adjustment for steering head angle, you must have your suspension set up properly to be able to carve that tight turn.

Basic rules are as follows. If your front wheel is “plowing” or not turning tight enough, you need a steeper steering head angle. If it is “knifing” or digging in and causing itself to turn sharper than it should, the angle is too steep. You can affect the angle in several ways. One is to slide the fork tubes up or down slightly in the clamps. Another is to change the spring preload. A third is to change the ride height in the rear by changing the rear preload. All of these methods change the angle of your steering stem with the ground. I finally learned that even small changes can have a dramatic effect. A year ago if some told me that a 1/8 in adjustment in fork preload could even be felt, I would think they were crazy. After all, I could make bigger changes than that simply by moving my weight forward or back. But now since I have learned to keep my weight off the handlebars, I can’t affect the suspension in that way. So I made adjustments until the steering was satisfactory. If your bike is more than a couple of years old and has some wear and/or bad adjustments caused by you or a previous owner, this can be a very satisfying discovery. It can be like getting a whole new bike. Don’t forget the fact that if you change your tire pressures you can affect the steering angle. If you drop the rear pressure a couple of pounds for example; you will make the rear end ride a little lower. This effectively increases the rake angle of the front end and can allow the front tire to plow. If you did this for muddy conditions, you may attribute the plowing to the mud, but it may be partly caused by the rake change. It would probably be a good idea to experiment with suspension settings for an alternate tire pressure at home. That way, when you get to a muddy event and drop your tire pressure, you can slide your fork tubes up a little to compensate.

Ron