Ask DH – A Primer on Suspension

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Sometimes there are questions you have about RC you’ve always wondered, but for one reason or another, never asked.  Whether you’re a seasoned veteran or brand new, we’re going to bring you up to speed. Have a question you’ve been wanting to ask? Let us know in the comments!

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So you want to tune your suspension – maybe you can’t quite hit that corner, maybe you’re landing on those jumps isn’t quite feeling right, or maybe you’re just a tinkerer. Either way, once you’ve got the right tires and fit them correctly, tuning your suspension can make a huge difference for each kind of track you’re on.

We’re going to break down the key components of your suspension set up and the pros and cons of each so you can determine what makes sense for you.

Shock Angle

There are multiple mounting points for shocks, both on the arms and towers, and each position has its advantage.

A helpful concept to keep in mind is leverage and mechanical advantage. For example with the lower mounting positions, the closer the mounting position to the wheels (outer mount holes), the shorter the “lever” is, and more force is required to compress the shock. The farther the mounting position is from the wheels (inner mount holes), the longer the “lever” is, and despite the now increased ride height, the easier it is to compress the shock.

Here’s a quick run down of each option:

Front/Rear Lower Mount | Outer Holes:
Firmer feel, less cornering at low speeds / more cornering at high speeds

Front/Rear Lower Mount | Inner Holes:
Softer feel for rough terrain, more cornering at low speeds

Front/Rear Upper Mount | Outer Holes:
Quicker steering and shock response, but if the rear is set to the outer holes, the back end could swing out partway through the turn.

Front/Rear Upper Mount | Inner Holes:
Less steering but smoother handling and shock response

Shock Oil

Oil thickness will determine how slow or fast your shock reacts. Thicker oil will react slower and help navigate large jumps and bumps. Thinner oil will react more quickly and soak up little bumps and ruts in the track. Ambient temperature can play a big part in performance – cold weather will thicken your oil, while heat will thin it. Change your oil accordingly to make sure you have the performance set up you need.

Changing oil viscosity can help maximize performance, but a “middle ground” will work if you’re just running in your backyard. Make sure to check your oil levels as leaks can negatively affect performance. Pitting and rust on the shock shaft can tear shock seals, so make sure to clean them especially after mud, snow or salt. Oil or WD-40 comes in handy for preventative maintenance.

Shock Pistons and Spring Stiffness

For shock pistons, you need to consider the size of the holes that the oil will pass through. Shocks are velocity-sensitive, meaning quickly compressing a shock is exponentially more difficult than doing so slowly. The rate of how difficult it gets, along with how soon a shock acts completely firm is often expressed as “Pack”. Large/more-holed  pistons are great for bumpy tracks since they react quickly and have less “pack”. Smaller/fewer-holed pistons are great for smooth tracks since they offer stability, but since they have more “pack” and can’t react quickly, small holed pistons will treat small/quick bumps the same way a truck with no suspension would. Think of it this way – more oil needs to quickly run through a smaller hole, and now there is only one of them, which means a lot more resistance.

There are a few different schools of thought on spring stiffness. Some prefer to keep stiffness the same across both front and rear for the sake of predicability. That is definitely one option, and all you need to do is increase stiffness across the board for greater direct responsiveness, or softer springs to soak up bumps in the road.

You can also have the front stiffer or softer than the rear. A stiffer front compared to the rear can increase jumping and stability while keeping traction in the rear, while a softer front compared to the rear offers better steering at the risk of understeer. Keep in mind that with high powered trucks running something like 6S LiPo, the back end will “squat” down under heavy acceleration. You may want firmer springs in the rear to keep things level for maximum traction.

More Info

Want a printable cheat sheet of the pros and cons from different set ups? Check out this awesome resource.

Want to change your shock oil? This video from Ultimate RC will guide you through.

Here is a great Q&A with Losi that walks through some benefits of different set ups

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