Understanding RC Car Suspension
A RC car suspension is what makes an RC car absorb the bumpy rides in rough terrain, landing jumps gracefully, and it is the system of linkages and springs or shocks that allows the wheels to move up & down independent of the chassis or body.
As the rc car suspension affects cornering, braking, jumping characteristics etc, it is important to understand how camber, toe or shocks affect the RC car handling. In fact, rc car suspension tuning is one of the most important way to decrease your lap time, thus allowing you to go even faster.
This guide will go through all the key components behind the rc car suspension: camber, toe, kick-up, caster, shock oil, shock spring, shock piston and shock position.
What is a camber?
The camber represents the vertical angle of your tires in relation to the ground, and are used to adjust the contact patch of the tires, because when entering a corner, the inner tires are leaning toward the chassis while the external tires are leaning away the chassis. A tire that is perpendicular to the racing surface has zero camber.
Hence, adjusting the camber allows you to have more contact on the track surface and thus have more traction.
Cambers are also classified as negative or positive camber.
A negative camber is considered when the top of the tires are leaning toward the chassis (like the letter A), and having more front negative camber will increase steering especially when turning into the corner. A front negative camber will also lessen the chances that the front tires will catch on ruts or bumps.
A negative camber in the rear tires will increase traction when entering corners, as well as navigate through rough sections of the track.
We recommend that you usually start with a little bit of negative camber in the front. Usually the front would be -2 to 0 degrees, while the rear would also be -2 to 0 degrees.
A positive camber is when the top of the tires are leaning away the chassis (like the letter V), and having more front positive camber will decrease steering when turning around corners. A positive camber in the rear will decrease traction when entering corners.
Running more positive camber in the rear reduces a bit of overall steering, but your RC car will handle more responsively. This helps to carry more speed through corners if the track is not bumpy and has good traction.
What is a toe-in/toe-out?
Toe represents the horizontal angle of the tires when compared to the centerline of the car. If the tires are pointing in, this is toe-in. If the tires are pointing out, this is toe-out. A tire that has zero toe is pointing straight ahead.
1/8-Scale Buggies almost always run toe-out in the front. To make the car smoother and easier to drive on big tracks, as well as to increase low-speed steering by decreasing the car’s turning radius, add more toe-out.
Decreasing toe-out (even to the point of running zero toe) will give the car more initial steering response. However this is usually only done on tight, low-speed tracks.
Running a front toe-in means your car won’t come out of the corner very well. If you run a front toe-out, your RC car will turn in and come out of the corner much smoother.
Toe-out is never used for the rear toe, as adding more rear toe-out will decrease overall rear traction, both in a straight line and during cornering.
Toe-out will also increase steering since the rear tires will have less traction. It will help on rough sections of the track as the rear suspension and driveshafts will be at less of an angle.
We do not recommend using toe-out for the rear. Usually the front would be -1 toe-in to 2 toe-out degrees, while the rear would also be -3 toe-in to 0 degrees.
What is a kick-up?
The kick-up is the angle between the ground and the lower inner hinge pins on which the rc car suspension arms swing. Altering kick-up will affect the steering and adding kick-up will make your bump higher and further. You should only decrease kick-up when the track has few or no jumps.
What is a caster?
The caster refers to the angle of the king pin or the steering block when viewed from the side of the vehicle.
The caster is broken down into positive and negative caster. A positive caster is when the top of the king pin or steering block leans toward the rear, whereas a negative caster is when the king pin or steering block leans forward the vehicle.
A negative caster increases off power steering but it also decreases straight line stability. A more positive caster increases on power steering and straight line stability but decreases off power steering.
What is a shock oil?
Using thicker shock oil helps the car navigate and absorb larger jumps and bumps due to a slower reaction of the shock from the oil. When the shock does not move fast enough, the tire looses contact with the ground and thus loses traction.
Using a thin shock oil means that the shock will not absorb sufficient bumps and can make your vehicle bottom out after landing jumps. The weight transfer when turning, accelerating and braking is also influenced by shock oil.
Since shock oil and shock springs work hand-in-hand, don’t forget to replace shock springs according to the oil used when you drastically change shock oil.
If you are racing in hot weather, you should increase the weight of your shock oil to maintain the same damping characteristics. During a change in season, if your RC car suspension works well in warm weather, you would want to switch to thinner shock oil once the weather turns very cold.
Unlike other oils that don’t offer a stable damping response over a wide temperature range, and may even damage the plastics and o-rings used, silicone shock oil doesn’t have this risk and has a stable viscosity over a wide temperature range.
Silicon shock oil comes in many thickness ratings, expressed in CST, CPS or WT. However, the problem is their relation is not the same across different brands of silicon shock oil. Even with the WT (weight) standard, one brand’s 30 WT might not be as thick as another brand’s 30 WT. Since CPS/CST doesn’t have this problem, it’s easier to stick to CPS/CST instead. It is good to note that soft, thin oils are up to 350, you have the medium thick oils from 350 to 700, and up till 1000 are the “hard” oils.
What is a shock spring?
As mentioned, shock springs and shock oil go hand-in-hand. You should normally use firmer springs if you are using thicker oil.
Make sure that your shock spring is firm enough to fully extend the shock when fully compressed in a reasonable amount of time. If you use thicker shock oil and the spring is not firm enough, the spring will have not enough time to fully extend the shock before the next shock compression.
Lighter springs and thinner oil should be used when the tracks are slippery in order to create more body roll and slow the car’s reactions. Firmer springs with thicker oil should be used on asphalt, grass or Astroturf tracks with tons of grip to resist traction rolling.
When changing the shock springs, be sure to change both the front and rear springs at the same time to maintain the same balance front to rear.
What is a shock piston?
A shock piston is used to delay or activate the damping action, and thus is similar to using thicker or thinner shock oil.
In order to slow down the damping, you would want a smaller piston hole because less oil will pass through the piston. Increasing/decreasing the size of a piston’s hole is used when you can’t find the right oil density. For example, if the 30 weight oil is too thin and 40 weight oil is too thick, hence you would need to use the 30 weight oil with smaller piston holes or 40 weight oil with larger piston holes.
When used in the front, bigger holes increase front traction on bumpy surface and body roll on high traction surface. When used in the rear, bigger holes increase rear traction on bumpy surface and body roll on high traction surface.
When used in the front and rear, smaller holes decrease front traction on bumpy surface and body roll on high traction surface. It also makes the RC car less prone to bottoming out and allow the RC car jump better and higher. Additionally, smaller holes decrease the rear end to squat under hard acceleration when used in the rear.
What is a shock position?
The angle of the shock is called the shock position, and can be adjusted by changing the shock location on the shock tower and/or the a-arm. This is particularly helpful when you can’t find the correct shock spring/oil combo.
Changing the shock position also alters the rc car suspension damping and you may have to adjust the shock spring/oil according to your new shock position. The ride height will also be affected by the new shock position.
A less inclined shock position will make the initial shock damping stiffer, decrease lateral traction, makes the vehicle more responsive but less stable.
A more inclined shock position will soften the initial shock damping, make shocks more progressive, increases lateral traction and make the vehicle more stable.
How do I know which oil shocks to buy?
If your current shocks are worn, broken, or your car currently has friction shocks or simple springs, you will need new shocks. There are different types of shocks to choose from.
Metal vs Plastic Shock
Metal shocks are better than plastic shocks. There is always a risk of the shock caps popping off on a big impact with a plastic shock, whereas a metal shock body tends to have less friction between it and the piston. Some metal shocks also are coated insides for even further reduced friction, like the “velvet” coating Kyosho uses, or Titanium Nitride coating etc.
Regular Shocks vs Big Bore Shocks vs Piggyback Shocks
RTR cars that come with oil shocks are often fitted with regular shocks. A 1/10 scale RC car will need a shock body diameter of around 12 mm.
Big Bore shock body is bigger in diameter than regular shocks. Big Bore shocks supposedly improves damping, and it usually does, but sometimes the label Big Bore is just used for marketing by a brand, and are the same as another brand’s regular shocks.
Piggyback shocks have a second oil reservoir, on top on the main cylinder and are supposed to have an advantage over regular and big bore shocks. The oil in the shock can get warmer during heavy action and will get thinner as a result, even though silicone oil has quite a consistant thickness over a wide temperature range. Since the Piggyback shock has more oil in the shock, it takes longer for it to heat up.
That said, the advantage of using a piggyback shock over regular or big bore shocks is limited. Piggyback shocks are also harder to refill properly, and it also take up more space thus limiting mounting options.
Hopefully this guide will help you understand the RC car suspension better and how you can improve and adjust to improve your lap times.