Setup Explained (Detailed)
Setup Explained (RC F1 Setup Guide)
This section contains an explanation of common setup terms and how changing one setting can affect another. All of the terms explained are relevant to an F1 car however not all of these settings can be changed on an F1 car. Therefore the original guide has been split into:
- Setup Explained - Directly relevant to F1 (this page)
- Setup Explained (Advanced)
The following text was reproduced with permission of www.rc-setup.com a supplier of RC Setup Equipment. Some of the definitions found here were based on text found on wikipedia (www.wikipedia.com). Feel free to print these out and / or distribute this document as long as you do not alter this copyright notice.
1. M-Racing (RC-setup.com) Car Setup Guide
A setup system is an invaluable tool in helping you properly setup your RC race car to win races. However, being able to measure your RC car or RC truck's settings is just part of RC car handling tuning.
This guide is intended to introduce some concepts and explain how different RC car settings affect your RC car's handling. We are continually adding to this guide and hope that it will help beginners and advanced RC drivers alike.
2. Weight Transfer
Weight transfer refers to the redistribution of weight supported by each tire during acceleration (both longitudinal and lateral). This includes accelerating, braking, or turning. Understanding weight transfer is crucial for understanding vehicle dynamics.
For example, when a car accelerates, its weight is transferred towards the rear wheels. You can witness this as the car visibly leans to the back, or "squats". Conversely, under braking, weight transfer toward the front of the car will occur (the nose "dives" toward the ground). Similarly, during changes in direction (lateral acceleration), weight transfer to the outside of the direction of the turn occurs.
Weight transfer causes the available traction at all four wheels to vary as the car brakes, accelerates, or turns. For example, because of the forward weight transfer under braking, the front wheels do most of the braking. This bias to one pair of tires doing more `work' than the other pair results in a net loss of total available traction.
If lateral weight transfer reaches the tire loading on one end of a vehicle, the inside wheel on that end will lift, causing a change in the handling characteristics. If it reaches half the weight of the vehicle it will start to roll over. Some large trucks will roll over before skidding, while on-road cars usually roll over only when they leave the road.
Good setup is all about controlling weight transfer.
For the technically inclined:
Weight transfer occurs as the vehicle's center of gravity (CoG) shifts during automotive maneuvers. Acceleration causes the cars mass to rotate about a geometric axis resulting in relocation of the CoG. Front-back weight transfer is proportional to the ratio of the center of gravity height to the vehicles wheelbase, and side-to-side weight transfer (summed over front and rear) is proportional to the ratio of the center of gravity height to the vehicles track as well as its roll center (explained later).
3. Camber Angle
Above: A wheel with a negative camber angle
Camber angle is the angle between the vertical axis of the wheel and the vertical axis of the vehicle when viewed from the front or rear. If the top of the wheel is further out than the bottom (that is, away from the axle), it is called positive camber; if the bottom of the wheel is further out than the top, it is called negative camber.
Camber angle alters the handling characteristics of a car. As a general rule, increasing negative camber improves grip on that wheel when cornering (within limits). This is because it gives the tire that is taking the greatest proportion of the cornering forces, a more optimal angle to the road, increasing its contact patch and transmitting the forces through the vertical plane of the tire, rather than through a shear force across it. Another reason to have negative camber is that a rubber tire tends to roll on itself while cornering. If the tire had zero camber, the inside edge of the contact patch would begin to lift off of the ground, thereby reducing the contact patch. By applying negative camber, this effect is reduced, thereby maximizing the contact patch.
On the other hand, for maximum straight-line acceleration, obviously the greatest traction will be attained when the camber angle is zero and the tread is flat on the road. Proper management of camber angle is a major factor in suspension design, and must incorporate not only idealized geometric models, but also real-life behavior of the components: flex, distortion, elasticity, etc.
Most RC race cars have some form of double wishbone suspension which allow you to adjust camber angle (as well as camber intake).
4. Camber Intake
A certain amount of camber intake is desirable to maintain the face of the wheel parallel to the ground as the car rolls into a corner.
Note: the suspension arms should be either parallel or closer to each other on the inside (car side) than on the wheel side. Having suspension arms that are closer to each other at the wheel side than at the car, will result in camber angles that vary radically (and a car that behaves erratically).
Camber intake will define how the roll-center of your race car behaves. The roll center of your car will in turn determine how weight will be transferred when cornering and this will have an important effect on handling (more on this later).
5. Toe-In and Toe-Out
Toe is the symmetric angle that each wheel makes with the longitudinal axis of the vehicle, as a function of static geometry, and kinematical and compliant effects. This can be contrasted with steer, which is the symmetric angle, i.e. both wheels point to the left or right, in parallel (roughly). Positive toe, or toe in is when the front of the wheel points in towards the centerline of the vehicle.
Front toe angle
In general, increased front toe in (i.e. the fronts of the front wheels are closer together than the backs of the front wheels) provides greater straight-line stability at the cost of some sluggishness of turning response, as well as a little more drag as the wheels are now driving a bit sideways.
Toe-out in the front wheels, will result in more responsive steering and quicker turn-in. However, front toe-out usually means a less stable car (i.e. more twitchy).
Rear toe angle
The rear wheels of your race car should always be adjusted with some degree of toe in (although 0 degrees of toe is acceptable under some conditions). In general, the more rear toe-in, the more stable your car will be. Keep in mind, however, that increasing toe angle (front or rear) will result in decreased straight line speed (particularly when racing stock electric motors).
One related concept is that the proper toe for straight line travel of a vehicle will not be correct while turning, since the inside wheel must travel around a smaller radius than the outside wheel; to compensate for this, the steering linkage typically conforms more or less to Ackermann steering geometry, modified to suit the characteristics of the individual vehicle.
6. Ackermann steering geometry
Ackermann steering geometry is a geometric arrangement of linkages in the steering of a car designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of different radii.
When a vehicle is steered, it follows a path which is part of the circumference of its turning circle, which will have a centre point somewhere along a line extending from the axis of the rear axle. The steered wheels must be angled so that they are both at 90 degrees to a line drawn from the circle centre through the centre of the wheel. Since the wheel on the outside of the turn will trace a larger circle than the wheel on the inside, the wheels need to be set at different angles.
The Ackermann steering geometry arranges this automatically by moving the steering pivot points inward so as to lie on a line drawn between the steering kingpins and the centre of the rear axle. The steering pivot points are joined by a rigid bar, the tie rod, which can also be part of the steering mechanism. This arrangement ensures that at any angle of steering, the centre point of all of the circles traced by all wheels will lie at a common point.
For a really good explanation of Ackermann check out the RC Tek explanation. When building a kit the manual will usually suggest a position for the Steering Arm Pivot Point (A in the RC Teck diagram) which is easy to drive. Use a hole closer to the front of the car to increase Ackermann and therefore increase Steering. The downside is the car may be harder to drive.
Understeer is a term for a car handling condition during cornering in which the circular path of the vehicle's motion is of a markedly greater diameter than the circle indicated by the direction its wheels are pointed. The effect is opposite to that of the oversteer and in simpler words understeer is the condition in which the front tires don't follow the trajectory the driver is trying to impose while taking the corner, instead following a more straight line trajectory.
This is also often referred to as pushing, plowing, or refusing to turn in. The car is referred to as being 'tight' because it is stable and far from wanting to spin.
As with oversteer, understeer has a variety of sources such as mechanical traction, aerodynamics and suspension.
Classically, understeer happens when the front tires have a loss of traction during a cornering situation, thus causing the front-end of the vehicle to have less mechanical grip and become unable to follow the trajectory in the corner.
Camber angles, ride height, tire pressure and centre of gravity are important factors that determine the understeer/oversteer handling condition.
It is common that manufacturers configure cars deliberately to have a slight understeer by default. If a car understeers slightly, it tends to be more stable (within the realms of a driver of average ability) if a violent change of direction occurs.
How to adjust your car to reduce understeer
You should begin by increasing the negative camber of the front wheels (never above -3 degrees in an on-road sedan or 5-6 degrees on an off-road car).
Another way to reduce understeer is to decrease the rear wheel negative camber (which should always be <= 0 degrees).
Yet another method to reduce understeer is to reduce the size or remove the front anti-roll bar (or to increase the size of the rear anti-roll bar).
It is important to notice that any adjustment made will result in a trade-off. Cars have a limited amount of grip that can be distributed between the front and rear wheels.
A car is said to be oversteering when the rear wheels do not track behind the front wheels but instead slide out toward the outside of the turn. Oversteer can throw the car into a spin.
The tendency of a car to oversteer is affected by several factors such as mechanical traction, aerodynamics and suspension, and driver control.
Limit oversteer happens when the rear tires exceed the limits of their lateral traction during a cornering situation before the front tires do, thus causing the rear of the vehicle to head towards the outside of the corner. More generally oversteer is the condition when the slip angle of the rear tires exceeds that of the front tires.
Rear wheel drive cars are generally more prone to oversteer, in particular when applying power in a tight corner. This occurs because the rear tires must handle both the lateral cornering force and engine torque.
The car's tendency toward oversteer is generally increased by softening the front suspension or stiffening the rear suspension (or adding a rear roll bar). Camber angles, ride height, and tire temperature ratings can also be used to tune the balance of the car.
An oversteering car is alternatively referred to as 'loose' or 'tail happy'.
How do you differentiate Oversteer and Understeer?
When you turn into a corner, oversteer is when the car turns more than you expected and understeer is when it turns less than you expect.
9. To Oversteer or to Understeer , that is the question
As mentioned before, any adjustment made will result in a trade-off. Cars have a limited amount of grip that can be distributed between the front and rear wheels (this can be enhanced through aerodynamics, but that's another story).
All race cars develop a greater lateral (i.e. sideslip) velocity than is indicated by the direction in which the wheels are pointed. The difference between the circle the wheels are currently tracing and the direction in which they are pointed is the slip angle. If the slip angles of the front and rear wheels are equal, the car is in a neutral steering state. If the slip angle of the front wheels exceeds that of the rear, the vehicle is said to be understeering. If the slip angle of the rear wheels exceeds that of the front, the vehicle is said to be oversteering.
Just remember that an understeering car goes into the boards nose first, an oversteering car goes into them tail first, and with a neutral-steering car, both ends hit the boards at the same time.
10. Spring rate
Spring rate is a component in setting the vehicles ride height and its location in the suspension stroke. Spring rate is a ratio used to measure how resistant a spring is to being compressed.
When do you know you have the best spring tension combo?
By Andy Cooke - TFTR Newsletter March 2002 (but still very relevant)
The springs will determine the total amount of chassis roll you will get.
If the car is rolling a lot it will create a lot of grip due to more weight being transferred onto the outside tyres in the turn, which is good for slippery tracks. But on grippy tracks this will decrease the corner speed and slow the 'change of direction' responsiveness. At an extreme it could even make the car traction roll.
A characteristic of too hard a spring when the track has high grip is the car seems to hop or chatter across the track when cornering.
A characteristic of too hard a spring when the track does not have sufficient grip is the car will grip initially, but part way into a corner, well before the apex, the rear end will break away suddenly and substantially.
What I aim for usually is to limit the chassis roll as much as possible by using hard springs without the car chattering or the rear end breaking away unexpectedly.
To take this to the next level, torsion bars can be used to limit the chassis roll while also running slightly softer springs than would otherwise be possible, giving more steering going into a corner, more rear grip coming out of the corner and better stability and directional responsiveness.
11. Suspension Travel
Travel is the measure of distance from the bottom of the suspension stroke (when the vehicle is on a stand and the wheel hangs freely), to the top of the suspension stroke (when the vehicles wheel can no longer travel in an upward direction toward the vehicle). Bottoming or lifting a wheel can cause serious control problems. "Bottoming" can be done by either the suspension, tires, chassis, etc. running out of space to move or the body or other components of the car hitting the road.
Damping is the control of motion or oscillation, as seen with the use of hydraulic shock absorbers. Damping controls the travel speed and resistance of the vehicles suspension. An undamped car will oscillate up and down. With proper damping levels, the car will settle back to a normal state in a minimal amount of time. Most damping in modern vehicles can be controlled by increasing or decreasing the thickness of the fluid (or the size of the shock valve holes) in the shock absorber.
13. Finding the Zen (or at least a balanced car)
A car that tends neither to oversteer nor understeer when pushed to the limit is said to have neutral handling. It seems intuitive that race drivers would prefer a slight oversteer condition to rotate the car around a corner, but this isn't usually the case for two reasons. Accelerating early as the car passes the apex of a corner allows it to gain extra speed down the following straight. The driver who accelerates sooner and/or harder has a large advantage. The rear tires need some excess traction to accelerate the car in this critical phase of the corner, while the front tires can devote all their traction to turning. So the car must be set up with a slight understeer or "tight" tendency. Also, an oversteering car tends to be twitchy and ill tempered, making a race car driver more likely to lose control during a long race or when reacting to sudden situations in traffic.
Note that this applies only to pavement racing. Dirt racing is a different matter.
Some successful drivers do prefer a bit of oversteer in their cars, preferring a car which is less sedate and more willing to turn into corners (or inside their opponents). It should be noted that the judgment of a car's handling balance is not an objective one. Driving style is a major factor in the apparent balance of a car. This is why two drivers with identical cars often run with rather different balance settings from each other. And both may call the balance of their cars 'neutral'.
Thank you to www.rc-setup.com for granting permission to reproduce the above.
14. Wheel Offset