Sunday, 1 February 2015

Shocks and Springs

(Image source: Yeah Racing)

This is a BIG subject, shocks (also known as shock absorbers or dampers) and/or springs can be the hero of the moment or the complete failure of chassis. It's all do to with the oils, pistons, springs, positioning etc.

(Image source: Mack Web)

Seriously though, shocks and spring DO make a big difference, this post will be about the different parts/sections and what they do. First off, components.

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Here I have taken apart my personal shocks and springs. This is an Eagle Racing set and comes with piston and springs options but no oil.
  1. Top hat
  2. Top hat cover
  3. Shock body (damper body)
  4. Upper spring retainer
  5. Oil seal / bladder / diaphragm
  6. Piston and rod
  7. O rings (x 2)
  8. Rod guide
  9. Rod guide cap
  10. Lower spring retainer
  11. Ball link end
  12. Spring
Most of these components are pretty self explanatory, I am going to explain some of the other basic components that can be tuned for a better handling chassis and usually come in a set of shock gear. Before getting into it, lets talk about oils.


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(Image source: Ultimate RC)

Oils can differ a lot by manufacturer and by type of measurement of density but can also give varying results depending on use.

The two means of measurement in use are Centi-Stroke (cSt) and Weight (WT); cSt being the recognised world standard. WT differs from brand to brand so it can be difficult to compare and evaluate different oils. For example; Losi, Associated and Fastrax all use the WT rating system but if you were to compare a 30WT oil from each brand, you would find a difference in performance.

(Image source: Team Durango)

All these numbers also have meaning whether it's a 30WT or a 350cSt. As a general rule, the lower the number, the thinner the oil. A 50WT or 700cSt oil will be thicker than a 10WT or 100cSt oil. You can use oils to tune your chassis whether you need a thin or thick oil depending on chassis layout and surface. That takes us onto pistons.

As I always mention, choosing any type of setup is completely down to driver choice and feel. If you were to do a quick check online for what oil to run, a lot of forums/websites etc will suggest a thicker oil at the rear with a thinner oil upfront. My advice would be do initially go by manufacturer specifications and play with springs first as they are easy to adjust and change.

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Pistons are another tuneable item but can be annoying and time-consuming to change. They sit inside the body and move up and down with suspension movement and are held in place using 2 E or C clips onto the shock shaft.

As pistons move up and down, they displace the oil inside the shock body. The standard pistons used/supplied is 3-hole. This means that regardless of oil thickness, the oil will flow through the holes with suspension movement. Another general rule, more holes equals more flow.

Take into account that thicker oils will take longer to flow through the 3 holes compared to a thinner oil. Also, a thinner oil will take longer to flow through a piston that only has one hole. This can be useful information if you run on a rough surface or a smooth surface or the layout of the track. A rough surface will require a thicker oil and a polished surface will be thicker still. Also, if you have a front mounted or rear mounted motor, there will be excessive weight present and the shocks will have to be filled to operate accordingly.

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First off, why all the colours? Even the solid black springs can have a marking or splodge of colour on them. Whether the whole spring is one colour or has a colour marking, it is to identify spring rate.

Spring rate is the amount of weight it takes to compress the spring a certain amount. For example, a real car has a spring rate of 500 lbf/in. This means that it'll take 500 pound (lb) force (f) to make the spring move an inch (in). You can get equipment to measure spring rate for real cars AND RC cars. In RC though,  they are measured as soft, medium hard etc. If you really want to get a precise measurement, get your wallet out!




Now that we have recognised which spring is soft, which ones are hard, which ones are medium etc, we can install them on the shocks and test them on the chassis for performance. Similar to the oils, install the recommended springs, play with the settings and only change springs if you really need to.

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So, you've built your shock absorbers, you've installed the springs, what next? Shock positioning. This is a complex, time consuming, advanced tuning method so proceed at your own risk...

All those holes on the shock tower and lower arm have different effects in handling when coupled with shocks and springs.

(Image source: Broadtech)

You'll notice on the shock tower that there are 3 sets of holes. We can ignore the inner ones for now as they are for mounting the shock tower making it higher or lower and the other set is for the camber arms. The set of holes on the outer shoulders is where the shocks will be mounted using ball joints/ends but the choice you make will depend on your preference.

The rule to remember with shock positions is: more angled = less grip, more upright = more grip. As I always say, go by manufacturer's recommendation, try it and then change if necessary and only change ONE thing at a time. Either change the front OR the rear, never both. Change ONE position along the top, don't jump 2 or 3.

According to Mizunaga San from Japan, relayed to us by Mitto at Soul RC, you should set the front shock angle for the most difficult corner first. That means try the chassis round the track for a few laps, find the most difficult corner and only adjust the front upper shock position by one point and then go for another few laps. Better? Leave it. Worse? Change it back. Try again and move it the other way. It is time consuming but when you get that sweet spot, it's totally worth it.

Once you've set the front, go to the rear. The rear shock angle should be set to balance the front, not by position but by traction (grip).

(Image source: Broadtech)

Good, you made it this far. Next is the settings on the lower arms but this time you do the rear arms first.

The holes along the bottom will allow you to control the roll speed of the chassis. As weight transitions from side to side through steering and direction changes, one shock will compress and the other will extend giving the chassis its roll. How much roll will depend on the positioning. Unlike the top shock mounts, the further out you are on the lower arm, the more roll you'll get.

Once you're happy will the amount of roll, move on to the front.

The front is slightly different; you're adjusting "on lock" roll. How the chassis will roll with the front wheels steering in one way or the other will depend on the positioning on the front lower arm and how much steering lock you actually use. It's great seeing all the cars with major amounts of steering lock but unlikely that they use to full swing on every turn. Find the "average" amount of lock you use on the track and adjust the front roll with the wheels set at that position.

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That was a big one! Hope this all helps and always have fun doing it! If you're not having fun, you're doing it wrong!!