Most people, when they get some RC experience, develop a pretty good understanding of how a suspension works. Understanding, however, may not be the ideal word to use as it implies they know exactly what’s going on and are tuning correctly. Read on and see if you’re getting things right when tuning the suspension on your monster truck.
There are a lot of moving parts in a RC suspension system, but the key component is the shock. And, almost all RC monster trucks use what is called a coil-over shock design—a coil spring is fitted over the shock body. The shock and the spring work together, but they have very different functions. The spring’s main job is to support the weight of the vehicle. The shock, in turn, is there to absorb energy. Technically, the shock converts kinetic energy (motion) into heat, but the real point is it keeps the truck from bouncing like a pogo after every bump or jump. In addition to the basic functions of the shock and spring, this key component of the suspension greatly influences how a truck handles.
Changes in pre-load are achieved either via an adjustable collar on a threaded shock body or by clip-on spacers. It’s important to note that increasing pre-load does not increase spring stiffness. Again, if you’re looking to increase your suspension’s stiffness, pre-load will not achieve that result. Pre-load is used to adjust ride height. If you have determined your truck is sitting too low, adding some pre-load could be a good fix. So, pre-load is used to set the ride height, and it is often used to compensate for ride height changes that occur when the shock position is changed.
While the main function of a spring is to support the weight of the truck, springs also greatly influence how weight is transferred while the truck is moving and thus have an important impact on handling. Springs also influence traction even more directly by impacting how easy the suspension moves. That is why it is common to install softer springs on the rear of a race vehicle that needs more rear traction. In contrast, it is common for racers to install softer front springs if more steering is desired.
As was said previously, the main job of the shock is to absorb energy. Without the piston inside the shock body having to pass through the shock fluid, your truck would just bounce and bounce after a bump or jump. The thickness of the shock fluid greatly impacts the handling of the truck. If the fluid inside is too thin, the piston will move too freely and the truck will still bounce. It will also most likely have other negative handling characteristics such as excessive body lean in the corners and bottoming out when landing from even small jumps. In the same way that springs impact handling, shock fluid does the same. Racers will often switch to thinner fluid to get increased traction or do switch to thicker fluid at the opposite end that more traction is needed (i.e. thicker front shock fluid for increased rear traction).
How shock mounting positions or locations influence handling is extremely interesting and yet simple. The suspension arm is a simple lever. If the lower shock mount is moved in on the suspension arm toward the center of the truck, the shock will feel softer much the same as installing a softer spring. This is because the suspension is now applying more leverage on the shock. Keep in mind that when moving the lower position in will also impact ride height. In this case, it would increase ride height and this is best compensated by adjusting pre-load.
While shock position is pretty straightforward and easy to understand, shock angles get a little more complicated. A shock that is straight up and down operates in a linear manner. Huh? This means as the suspension compresses, the shock’s feel doesn’t change. If the shock is angled in at the top, the shock will feel progressively stiffer as it is compressed.
On a monster truck that is being run for fun on a variety of surfaces such as dirt, pavement and grass, you shouldn’t have to get too crazy with the suspension tuning and should leave the never ending search for the perfect setup to the racers. That said, if your truck isn’t handling exactly how you would like, you can probably easily fix it with a little shock tuning.
> If your truck is bottoming out when landing from jumps, first check to make sure the ride height isn’t set too low. If the truck doesn’t seem to be sitting too low, try adding thicker shock fluid.
> If your truck is sitting low after adding a lot of aluminum hop-ups, do not add pre-load, use stiffer springs to properly compensate for the added weight of the new parts. You may also need to slightly increase the shock fluid weight.
> If your truck is bouncing excessively over small bumps, try slightly thinner shock fluid to allow the shock to react faster. This should be a minor change.
About the Author: Matt has over 25 years of experience in RC and has worked professionally in media for over a decade. Matt enjoys everything from racing to rock crawling to bashing, and he believes RC should be all about having fun. Matt is as at home covering a world championship in an exotic country as he is showing a new hobbyist how to set gear mesh. His desire to share the hobby with as many people as possible inspired him to create RC Truck Stop and RCTruckStop.com.