The contents of THE Guide is copyrighted © by JQ Products, but we thought it was rather brilliant and informative.

Parts: [1 Intro] [2 Electrics & Clutch] [3 Shocks] [4 Diffs] [5 Geometry] [6 Ride height] [7 Down travel] [Quick Reference Tips]

3. Shock Absorbers

The shocks on a 1:8 buggy are together with the tyres, the most important part of the car set up in my opinion. I base my opinion on the fact that all other set up issues are possible to drive around by changing your driving, by adapting. Of course a well set up car will be better, but I think all other set up features are of less importance, diffs are close, but shocks and tyres, if you got them wrong, it doesn’t matter what batman cereal you had for breakfast, you won’t win! You can’t make bad tyres fast by driving better, and you can’t make a car land, or go fast in bumps if the shocks are bad. Someone else will have their car dialled and will blow past you. So, in order to win races, you really need to understand how your shocks work, and how to set them up.

shocks

Shock absorbers. Simple stuff until you try making them work better than anyone elses.


3.1 Basic Stuff

The shocks on 1:8 buggies are quite honestly primitive. The shocks we have are pre-matches and lighters, or pre-cheese slicer. Old technology! Basically they are oil filled cylinders, with a piston with holes, attached to a shaft, that moves up and down inside them. As the shaft moves into the body (=cylinder), it takes up more and more volume inside the body, and pushes oil aside. This is why there is a rubber bladder in the cap of the shocks. Behind the bladder there is trapped air. As the shaft moves in, and displaces the oil, the oil compresses the bladder, to compensate for the reduced free volume in the body, and increases the pressure of the air. Then as the shaft moves out the bladder is pushed back out.

The suspension, or damping, is tuned by changing the viscosity of the silicon shock oil, by changing the size, or amount of holes in the piston, by changing the spring, or by changing the shock position on the arms or shock towers. Normally the damping has to be tested a lot on many different tracks and under different conditions in order to find a good set up. And most of the time a “pro” driver does all the hard work and then his mates just ask him “Dude, what do I put in these!”

 

pistons

Someone has to do THE Testing.


The process I go through to find a good set up that works everywhere for me, goes as follows:

I start off with something that I assume will work ok. Some sort of basic set up, in this case for example 1.4mm piston holes, 45wt oil, silver springs, and shocks in std positions, whatever is the norm. The first thing I do is find the right spring. Next I test as many different pistons as I can be bothered to test. There is an unlimited amount of pistons, or rather you can drill an unlimited amount of different pistons, so it is wise to figure out a system, and decide what you want to achieve, in order not to get lost. When changing pistons, if the car becomes better, one has to try and figure out the reason, and then continue heading in the same direction until it starts getting worse again. You can’t decide beforehand what pistons to try because you won’t know what works and what direction to head in. After I have selected the right piston, I fine tune the oil. Throughout the process I always try to run an oil that will make the car feel the same on the pit table. When I have my spring and oil, I then try 5wt thicker and thinner oils, and different combinations front and back, in order to find the best balance. It’s hard to put into words what the right oil feels like. I would say, feel top drivers’ cars to get an idea. But as for an explanation, when you move the chassis up and down on the pit table, you should feel that the oil is slowing down the movement slightly. When you drop the car from 30cm above the table, it should just land without much movement. Finally I also try some different shock positions. But one thing to remember is, that shock positions should be treated as a minor tuning aid. If you did all your testing with your shocks stood up, if you then lay them all the way down you will have to do it all over again. Most likely you will end up with a stiffer spring and smaller holes in the piston

When you find a good set up, you will know it’s good when you don’t have to change it from track to track. No matter what the track is like, the car will be good. The springs, pistons and shock positions are nearly always going to be the same. The oils are basically only tuned to suit the temperature. Cold weather will call for thinner oils, and hot weather for thicker oils, normally just 5wt. Sometimes a thicker oil can be used on high traction tracks, or a thinner oil for very slippery tracks.

Sometimes the set up can be close, but it’s great on some tracks, and not so good on others. It can be a case, where the car is great over bumps, specially the small bumps on the surface, but it bottoms out over the jumps, and flips over if you don’t land perfectly. Smaller piston holes (by 0.1mm) will help this, however, then you might face the problem that the car will not go over the bumps smoothly. In a case like this, the solution could be to just change the piston 0.05mm, but an even better way is to, if the piston is 6 hole, make just 3 of the holes smaller, or 3 bigger, try both. Then the car will be good in the bumps, and still land well. I will explain the reason for this later on.

Next I will attempt to explain separately, in more detail about the spring, piston, oil, and shock positions, how they work, and what changing them does.

 

3.2 Springs

Springs aren’t really changed very often. A stiffer spring reduces traction, and makes the car more responsive. The car will also jump better. Softer springs do the opposite. Short springs feel more progressive, and make the car responsive and jump well. Putting shorter springs on the front will help the car accelerate straight when exiting corners on a loose track. After finding a good spring, the piston and oil are tuned to work with the spring, so just changing the spring to get the car to handle differently doesn’t usually work very well.

 

spring

There are an unlimited amount of springs. Nice.


3.3 Pistons

First the very basics of what happens inside the shock and why different pistons change how the car goes round the track.

The basic idea is that the car always feels the same when feeling it on the pit table, but then when changing the pistons it somehow magically changes on the track. The reason is that when moving the shocks slowly on the table small holes and thin oil, or big holes and thick oil will feel close to the same, but on the track, when the piston moves fast, there is a big difference. To understand this one has to understand some basic points of fluid dynamics. Simply put, a fluid flows in two ways, laminar or turbulent. When the flow is laminar the particles flow parallel to each other, in the same direction. Think of a river with water flowing calmly down it. When the flow is turbulent, the particles move randomly which creates eddies, and the friction between the particles increases. Think that the previous river hits some rocks and becomes a rapid. Flow in a shock is laminar when speeds are low, and when the speed increases enough, it becomes turbulent. When the car hits a bump at speed, the piston will move up in the shock, and oil will pass through the piston holes. Some will flow past the piston but let’s think of that as constant. If the piston moves fast enough, the oil flowing through the piston will cause turbulence, which increases the friction, and it will seem like the shock locks up. This is called “pack”. With small holes this happens more often, at lower piston speeds, so the car will bounce a lot in bumps, and with larger holes it will happen less often, at higher piston speeds, so the damping will absorb more of the bumps, and not bounce so much. If we think that the same amount of oil passes the piston in both cases, in the case of larger holes, the speed of the oil will be lower, than when compared to a piston with small holes. Furthermore, with thin oil (used with small holes) turbulence occurs earlier, and with thick oil, it occurs later, which makes the difference more pronounced. This is the basics, and all you need to know in order to understand how the pistons work in the shocks.

As far as how pistons affect the car’s handling, I will try to explain:

Larger holes gives the car more traction, it goes through bumps smoother, specially through ones you hit fast, and the small bumps in the surface of the track, the wheel follows the surface better. The downside is that the car doesn’t jump as well, and specially doesn’t land as well. When the holes are too big, the car bottoms out when landing off jumps, and will want to flip over. It will also feel unresponsive and slow.

Smaller holes reduces traction, it jumps and lands better, but it is generally worse in bumps. When the holes are too small, the car will feel like it gets unsettled by even the smallest bumps and it “stutters” over an uneven track surface, even with thin oil.

Increasing the amount of holes has an interesting effect. If you compare a 2×1.5mm piston, and a 4×1.4mm, assuming that the 2×1.5mm is good, you would be excused to think that the 4×1.4mm piston would have too many holes and the car would bottom out all over the place. However, this is not the case. When increasing the amount of holes, it’s possible to have more overall hole-area, than with 2 holes, before the negative points like bottoming out become a problem. This way, with many holes, it’s possible to set up the suspension to be soft, and plush, so it soaks up the bumps, yet it won’t bottom out too much on the jumps. Apparently the oil flow becomes turbulent more violently with more holes in the piston.

By using different size holes, for example 2×1.3 and 2×1.5 on the same piston, a similar result can be achieved. The car will have traction and be good in bumps, but will still land well, due to the flow becoming turbulent more aggressively than with all holes being the same size.

 

3.4 Shock Positions

Usually the basic set up from the manual is a good starting point. Shock positions are rarely changed. When a good set up is found that’s pretty much it.

 

shock

Shock positions are rarely changed a lot, as pistons, springs and oils need to matched to each position.

 

When standing the shocks up more, the car is more responsive, jumps better, doesn’t bottom out as easily, but can feel unstable in bumps. The rear of the car will slide in a controllable way, as it loses traction smoothly. Larger piston holes and softer springs are used when shocks are stood up a lot.

Leaning the shocks over, makes the car more stable, it will be easier to drive on bumpy tracks most of the time. It increases sidebite, but for example the rear end loses traction suddenly, and not as controllably as with the shocks stood up. You can’t slide the car as well. If you need to make the car more stable, and easier to drive, the first thing to do is to move the shock out on the front arm. It reduces steering and makes the car a lot easier to drive, and less prone to flipping over. When leaning just the front shocks over, the car is less responsive, but turns more while cornering, and when accelerating out of the corner. Leaning just the rear shocks over increases rear traction and reduces overall steering, although depending on the set up, you may get more steering into the corner.

 

3.5 Rebound

Rebound is the amount the shaft moves out, after you have pushed it in. It’s possible to build a shock so it is “dead”. The shaft doesn’t move out at all, or then full rebound, where as the shaft moves in the damping starts feeling harder, and the shaft moves back out all the way when released. I usually build my shocks to where the shaft moves about halfway out, slowly. More rebound will give more traction, and the car will jump and land a bit better. As for bump handling, some people feel that more rebound is better for bumps, and some people think a “dead” shock is best for bumps.

Rebound is a set up parameter which is often overlooked, but actually has a surprisingly large effect on the handling of a car.

 

3.6 Last Words

The shocks are definitely something everyone should take a look at. With a great shock set up a lesser driver can definitely kick a better drivers ass, if he happens to have a crappy shock set up. People easily overlook how important the shocks are! With a good set up, the shocks give the car more traction, the wheels spend more time on the ground, cornerspeed is increased, it jumps and lands better, and you can drive faster in bumps, and it’s all a lot easier. This is why I’m constantly trying new things. At the races I always use the same set up, but when I go testing, I try all kinds of different things. When I find something good, I try it on different tracks, take laptimes, see if I make less mistakes with it, and only then do I also use it in races.

One thing to remember is that driving style does affect the shock set up that will suit you. The way you use the throttle, how much, how aggressively, in what sections of the corners and bumps all effect the outcome. So just because someone’s car is great in their hands, doesn’t mean you will like it.