Doncaster Touring Cars

Camber

The Theory
Camber is the angle between the wheel's centerline (seen from the front of the car) and a vertical line. It is measured using a camber guage and can be positive or negative. Negative camber is when the wheels lean inwards towards the chassis, positive is when the wheels lean outwards.

Negative camber is used to combat the effect of chassis roll. Chassis roll is where a car enters a corner, the inside suspension lifts and the outside suspension compresses, causing the wheels to lean outwards (positive camber). This is a problem because now only the outer edge of the tyre is touching the track, causing a loss of grip. Putting on a few degrees of negative camber means that when the car leans into a corner there is a greater surface area of tyre in contact with the track giving more grip.

So, what's the catch? Well, although 2-3 degress of negative camber all-round will give you good grip and stability in the corners, it won't give the same effect at other times. To achieve maximum grip when the car is going in a straight line i.e. when accelerating or braking, you need zero degrees of camber.

So, like all other elements of chassis tuning, it's a question of arriving at the best compromise.

NOTE: Positive camber is almost never used, so it won't be discussed in this article.

The Effects of Altering Camber
FRONT
More negative camber Less negative camber
Lower centre of gravity Increased ride height
Quicker steering response Increased chassis clearance
More side traction Less side traction
Reduced chances of traction rolling Increased chance of traction rolling
REAR
More negative camber Less negative camber
More side traction Less side traction
More traction under braking Less traction under braking
Reduced chance of traction rolling Increased chance of traction rolling

May give more steering

  

Ride Hight

This is one of the simpler adjustments you can make and once you have found an exceptable height, don't 'play' with it unless you have a real problem.
Ride height is the distance between the bottom of your chassis and the ground. It is adjusted by putting small spacers in-between the top of the springs and the end of the shocks, or if you have threaded collars, by rotating these to raise or lower the car as desired. For on-road cars, the approach is simple: go as low as you can. The lower the ride height, the lower the centre of gravity, which generates grip and makes the car more stable.

BUT...
Set it too low and you risk bottoming-out either under accereration, braking or cornering, making the car slide. Set it too high and you will induce grip rolling.

Setting the height:

  • For smooth tracks sit the car lower, for bumpy tracks raise it slightly to prevent the car bottoming-out on the bumps.
  • If you want to tune the handling a little, set the front and rear differently . For instance, if you set the front slightly lower than the rear, you will gain grip at the front, to encourage oversteer. Set it lower at the back to get understeer.
  • One final point, whenever you adjust the ride height, you affect the camber on both the wheels at that end of the car. Similarly, when you adjust the camber you affect the ride height, so when you have finished setting the ride height always re-check the camber.
  • Recommended ride height: 4.0 - 6.0mm (at DTCC ride height is limited to at least 5.0mm)
  • Recommended maximum variation in height front-to-rear: 2.0mm

Guidelines for setting the ride height
Lowering Ride Height Raising Ride Height
Less body roll More body roll
More side traction Less side traction
Less weight transfer More weight transfer
More chance of bottoming-out Less chance of bottoming-out
  

Dampers

 The importance of damping becomes clear when you consider what happens to a spring when it is compressed. If you squeeze a spring with your hand it compresses, storing energy as it does so. Let it go and it returns to it's original state releasing that energy which you put in. If a car had only springs and no damping, it would continue to store and release energy uncontrollably, leading to an effect more akin to a space-hopper than a car!

Whilst springs store the energy put into them by bumps, acceralating, braking or cornering forces, dampers actually absorb or dissipate some of this energy, leading to much smoother and controlled suspension travel. Many people think that altering damping will alter how much the suspension travels, much like a change in spring selecton. If you only remember one thing from this section, let it be this;
your hand it compresses, storing energy as it does so. Let it go and it returns to it's original state releasing that energy which you put in. If a car had only springs and no damping, it would continue to store and release energy uncontrollably, leading to an effect more akin to a space-hopper than a car!

Whilst springs store the energy put into them by bumps, acceralating, braking or cornering forces, dampers actually absorb or dissipate some of this energy, leading to much smoother and controlled suspension travel. Many people think that altering damping will alter how much the suspension travels, much like a change in spring selecton. If you only remember one thing from this section, let it be this;
 

Damping does NOT affect how much the suspension travels, but it DOES affect how fast it travels.

So, a car with soft springs will always have a lot of travel and a car with hard springs will always have a lesser travel. But, if you couple soft springs with soft damping (when compressed) it will rebound quickly. Use hard damping and it will rebound slowly. The level of damping needs to be matched to the choice of springs i.e. don't match soft springs with hard damping, but to better understand the effects, we will consider some extreme examples;

A car with soft springs and hard damping (lots of travel, slow to rebound) makes a turn. On entering the corner, the weight is transfered to one side and the car begins to roll, but the hard damping restricts the speed at which the springs can react. This reduces the initial body roll, especially at the front, thus reducing the amount of grip generated. The effect, understeer. A similar effect can be experienced when exiting the corner: When you start to straighten-up the car settles as the shocks uncompress, the speed at which this occurs is again limited by the hard damping, so the car wants to keep on turning -oversteer. In other words, the car will feel slow to respond, but easy and smooth to drive.
At the other extreme (hard springs, soft damping) the suspension will react much faster, but not travel as far, leading to very responsive, even twitchy car with less than optimum levels of grip.

Shock Pistons
Until now I have just talked about soft or hard damping, which is basically achieved by using hard or soft oil. However, just to make matters more complicated, there is another variable - pistons. Choosing pistons is all about altering when the pack effect occurs. Simplified, this is when the oil flowing through the holes in the shock pistons changes from a smooth flow (called laminer flow) to a turbulent one. At this point the level of damping is suddenly amplified. Manipulating the pack of your shocks is more useful for off-road cars, so I will keep it simple. Making your shocks pack-up quickly prevents the car from bottoming-out when landing from a big jump, whilst packing-up too soon will make the car bounce on smaller jumps.
Small holes and thin oil will pack-up quickly (but only when the shocks are forced at speed i.e. in fast corners). Large holes and thick oil will pack up more slowly. For on-road racing pack is generally an unwanted effect, so I will leave it there.

Springs 

In order to decide which springs to select, you need to understand a little bit about the effect they have on the car.
A car with soft springs will exhibit a lot of body roll when cornering at high speed which is good, because this generates high levels of grip. However, it will also dive a lot when braking and squat excessively when accelerating, making the car unpredictable when entering or exiting a corner. It is difficult to consider spring selection in isolation, without taking into account all the other settings on the car, so for now just bear in mind that your choice of springs has the following effects:

  • Grip level: As a general rule, softer springs give more grip, but go too soft and the car will grip roll.
  • Weight transfer: Springs control the amount of body roll, both left-to-right and front-to-back. Harder springs lessen the effect, softer springs increase it.
  • Bump handling: Springs (coupled with damping) have the greatest effect on how your car handles bumps in the track. Too hard and the car won't absorb them, too soft and the car may bottom-out causing a loss of control.

Guidelines for spring selection
FRONT
Softer Springs Harder springs
More grip Less grip
More body roll Less body roll
More steering Less steering
More chance of grip rolling Less chance of grip rolling
REAR
Softer Springs Harder springs
More grip Less grip
More body roll Less body roll
Less steering More steering

Sway bars 

Introduction
The purpose of anti-roll bars or sway bars, as they are sometimes known is often mis-understood. Like all other aspects of vehicle dynamics, you need to consider their effects in a logical manner.

What is an anti-roll bar?
A roll bar is essentially a spring, just like the ones over your shocks, but without the helical shape.A straight spring like this is known as a torsion spring. You can appreciate its effects by holding a rule firmly at one end and twisting the other end (gently). When twisted it bends, when you let go it returns to its original position - just like a helical spring.

So what does it do?
To see what the effect of adding a roll bar is, let's consider what happens when a car enters a corner with a rear roll bar attached; Normally (without roll bars) the car begins to roll, i.e. the outer suspension begins to compress and the inner suspension begins to lift. However, because we've linked the two sides with a roll bar, when the outer suspension compresses, (some of) the force is transferred to the inner suspension which prevents it lifting, even compressing it slightly (depending on the strength of the roll bar). In this way the roll bar reduces lateral roll, making the car less likely to roll-over. This is the first effect.
Secondly, due to the effects described above, as you enter the corner the suspension compresses more than normal, because the inside is being compressed as well as the outside. This makes the car sit lower, generating more grip.
Thirdly, when you reach the middle of the corner and the suspension has equalised, it is compressed less than normal, as some force has been absorbed by the roll bar itself, hence you have less grip. However, the weight is distributed more evenly over the wheels, so the car is better balanced, giving a smoother feel.

So in summary, you have less body roll, less rear grip (more steering), but a more consistant motion through the corner.

Putting a roll bar on the front has a similar, but opposite effect i.e. less steering, but more consistant cornering.

You can choose roll bars of different thicknesses, whereby a thicker roll bar has a more pronounced effect. See the table below for guidelines.

Guidelines for choosing anti-roll bars
FRONT: Increased thickness REAR: Increased thickness
Decreased steering response Increased steering into corners
Decreased front-end grip Decreased rear-end grip
Decreased chassis roll Decreased chassis roll

 Shock positions

Shock positions are possibly the easiest thing to change on a car to change it's handling characteristics,

 but you do actually know what effect these changes will have on your car before you try? This article is designed to give you an insight into how you can get the most out of setting up your car.

The basic rule for shock positions is that the greater the shock leans in towards the car, the more grip will be generated. This works like this because it has the effect of softening the suspension, but the changes aren't quite as drastic as changing the stiffness of springs.

Shock positions should be used to fine tune the handling of the car, so basically, if your car has a touch of understeer you can dial this out by "laying" the front shocks down a bit more to give the front end a bit more grip, and vice versa if you have slight oversteer.

As well as changing the balance of the car by altering either the front or back shock positions, you can change the way which the car responds by changing both the front and rear shocks. Generally speaking, because when the shocks are more laid down they have the effect of softening the suspension, the car tends to be slower in the corners and have more body roll although this obviously depends on other settings you have on the car also. When the shocks are stood up fully you would get the opposite effect of this, which very quick direction changes and good cornering speed, however, if the grip is not there between your tyres and the track then the car may slide about more, and it's finding the good balance which is the real art to setting up a car.

Roll Centers 

hanges in roll centres probably aren't very common, as a lot of people don't fully understand what a change in roll centre means. Basically, to change the roll centre means to raise, or add or remove spacers underneath the suspension arms and upper links. Obviously, a high roll centre would be where the suspension arms and upper links are raised on the car, and a low roll centre would usually be without any spacers whatsoever.

A higher roll centre will normally make the car more responsive, and maybe even a little bit "twitchy" and some people may find this way hard to drive, but in essence, it is normally the quickest way to go. However, if the surface is low traction then it can often be beneficial to use a lower roll centre generate that little bit more grip and make the car easier to drive.

In this section I will also include the effects of kick-up, anti-dive and anti-squat. Now these words sound very technical, but all they refer to is whether there is a difference between the heights of the front and rear mounting blocks for the suspension arms.

Kick-up is where on the front of the car, the front pivot block for the suspension arms is higher than the rear pivot block. This will improve front end response and can be used for bumpy tracks.
Anti-dive is where on the front of the car, the rear pivot block for the suspension arms is higher than the front pivot block. This should be used for smooth surfaces but may make the front end of the car unstable, or understeer slightly.
Anti-squat is where on the rear of the car, the front pivot block for the suspension arms is higher than the rear pivot block. This will help give the rear end more traction and grip, but could affect the absorption of bumps.

Note: Roll centre changes may not be available on all makes and models of car.

 Chassis flex

Chassis flex probably isn't the easiest thing to change on a car, but pretty much every manufacturer offers either a super stiff chassis and top deck combination, or a super flexy chassis and top deck combination, so why?

I'm into full scale racing where it is taught that the stiffer the chassis the better, why isn't this so for R/C cars?
Well...without getting too technical, the forces endured by our R/C cars are much greater than the scale forces endured by full size cars. Think of it this way, for a 1/10th scale car, you would expect a top speed of around 20mph, as this is a 10th of 200mph, a pretty typical top speed for Formula 1 cars. However, most R/C cars go beyond this speed, and some may even double it, even in the confines of a sports hall! This means that you cannot compare like with like, just because they are 1/10th of the size of full scale cars, they are different.

So when should I use a stiff chassis, and when should I use a flexible chassis?
When looking at team drivers setup sheets the general trend is that they use stiff chassis' when using foam tyres on carpet, and they use flexible chassis' when using rubber tyres on either tarmac or carpet.
Although it is not understood fully why they do this, it is clear that it works, as if it didn't then numerous ex-world champions would not follow this trend. The basic idea is that on high traction surfaces stiffer is better because there is plenty of grip and it's best to let the suspension do it's work, and on lower traction surfaces it's best to have flex in the chassis to make the car more forgiving to drive, and generate more traction.

When changing between different chassis and top deck combinations on the same surface setup alterations will be needed, in general, a stiffer chassis requires stiffer springs to stop the car rolling in the corners as the chassis can no longer flex as much.

  DIffs

When it comes to the type of drive you want in your car you have a few options, most cars will have options for replacing the front differential with either a spool (locked axle) or a one-way differential. These both have the same basic aim, to increase corner speed, but they work in different ways and will make the car handle differently.

One-way diff - A one-way diff consists of two one-way bearings, which mean that the front wheels are able to "free wheel" but will not slip backwards. This means that instead of the inside wheel slipping when going round a corner, the outside wheel will speed up, and this is how this type of drive will increase corner speed over a normal differential. There are, however, a few problems with this tyre of drive, and the first is the price, it's not unknown for a one-way diff to cost in excess of £40. Another disadvantage is that because the front wheels are able to free wheel, under braking they will want to carry on turning, meaning that you are reduced to two wheel braking, which can also mean that on low grip surfaces the car is liable to swap ends quite drastically if the brakes are applied too hard or whilst turning. This can make the car very difficult to drive, but most of the time it is ultimately the faster way around, but not always. Another problem with the one-way diff over a normal diff is that there is no "give" when you crash, meaning that the drivetrain of the car is more liable to wear or breakages (especially on a shaft driven car).

Spool - A spool is basically a locked axle, it will drive both front wheels at exactly the same speed, so effectively there is no differential action at all for the front wheels. This means that a spool is inheritly understeery because one of the wheels has to give way on the track for it to go around the corner. For this reason it is unlikely that a spool will work well on a very high traction surface, but not impossible. However, a spool can also increase corner speed over a normal differential, and is often seen as a compromise between a differential and a one-way diff because it allows the driver to use the brakes as normal. The disadvantages of running a spool are that there is absolutely no "give" in it meaning that you could end up breaking various parts in your drivetrain.

Setting a ball differential - Most top end touring cars come with ball differentials instead of gear differentials, despite gear differentials often having a much free-er action. This is because ball differentials allow adjustment, by tightening or loosening the thrust screw, which allows for more setup options. Generally, a looser diff will give more grip, but often the front differential is run tighter than the rear to give more corner speed because of less slippage and loss of power. This will give a very mild "spool effect" and is useful for fine tuning.

Note - always check the tightness of you differential by holding one wheel and the spur gear and trying to turn the opposite wheel. If you can turn this with ease you will lose power as the pulley/gear will just spin between the two outdrives and not turn the wheels. If this is the case you need to tighten up the thrust screw and re-check the tightness.

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