RC Car Handling Basics


To start off anytime you run your car and are determining what to do with your set-up ask yourself these questions. 

1. What is the car doing in the initial second that I turn the steering? 
2. What does the car do entering the corner? 
3. What does the car do exiting the corner?
4. How far into the corner am I using the brakes?
5. How soon do I get on throttle and how fast?
6. What does the car do throughout the corner entering to exit? 

These questions will help you determine where to change your set-up or driving style. 


Definitions:

Understeer (aka push or tight): This is when a vehicle has the tendency to "push" toward the outer edges of a corner. 
Oversteer (aka loose): This is when the back end of the vehicle wants to loose grip and travel around the front of the vehicle. 
Camber: Negative - top edge of tire leans toward the centerline of the vehicle 
Camber Positive - top edge of tire leans away from the centerline of the vehicle 
Caster: The angle of the front upright relative to the ground plane, should always be negative. 
Toe: In - leading edge of the tires point toward the centerline of the car Out - leading edge of the tires point away from the centerline of the vehicle 
Squat: Same as caster only on the rear of the vehicle. 



I'll explain the basic effects of changes on certain settings and then give a couple examples of situations and possible solutions.

Camber -
Adjustments to this setting determine how much contact patch the tires have relative to the ground plane. Less contact Patch will usually cause less grip though this is not always the case. Tires have an optimum operating temperature (all do). This temperature dependance makes it tricky to set up camber since a full contact patch can cause the tire to run at a lower temperature than is necessary, In this case you need more camber, On the other end you could have to much camber centering the heat on a certain part of the tire which overheats the tire causing it to slip. In this case running less camber is better. If you are running a full contact set-up and are still overheating the tire or major camber and still under heating the tire it¹s time to run a different tire. By taking the tire heat into account you can reduce or increase grip by increasing or reducing camber. Though this is dependant entirely on the characteristics of your tire. Positive Camber is rarely used because it causes the outer edge of the tire to roll onto it¹s side which is not a good thing because you loose all traction. The only time positive camber may be used effectively is on certain oval tracks (usually less banking)

Caster -
This adjustment tends to affect the responsiveness and stability of the vehicle. The stability factor is usually eliminated in the RC cars because the steering is solid linked to the servo which centers the steering. The more caster the more the steering tends to self center creating stability, however it also causes the initial turn in to be less responsive and body roll to be greater due to the angle of the tires to the road. If you lower caster the car becomes more twitchy, less stable and has less body roll. The lower the caster angle the more the tire contacts the road when turning.

Toe -
Toe adjustments improve stability anytime they are greater or less than 0 or neutral. This is because it centralizes forces. But toe has a much more important roll in the handing of the vehicle. Toe out will cause the steering to become more responsive but due to the reduces steering angle of the outer front tire the vehicle will tend to understeer when coming out of the corner. Toe-in will cause the car to turn in a little less responsively but will allow the car to hold a tighter line coming out of the corner. Toe is an adjustment that can truly make you faster or slower because it determines when you are able to get on or off of the throttle.

Ride height -
Ride height will make minor adjustments to handling. An even ride height will do nothing to the handling of the car. Lowering the front relative to the rear will give more steering, Lowering the rear in relation to the front will give a little understeer

Shock settings-
I¹ll just overview the shock settings and give a little note on oil and springs. First oil does NOT determine stiffness of the vehicle, Springs do. Oils controls the springs and springs control the vehicle, oils DO NOT control the vehicle. Set the oil so that your springs can return your car to the ride height fast if you want a responsive car or so it returns slow if you want a more stable car and a little sluggish. If your car sags get harder springs, don¹t use spacers. If your car bounces get softer springs or run heavier oil. Try to use pre-load spacers only to determine ride height. This can make or break a set-up. 90% of the RC cars that I see are not correctly set-up in this area and that may be a generous figure. Remember the above and it will help you out.

Roll Bars-
As far Is I will get into roll bars at this moment is to say that they are secondary springs that are used only during cornering. In many cases with RC cars they are not needed unless you cannot get your car stiff enough in the corners while keeping it from bouncing down the straights. Or you are having a problem with a tire lifting off the ground. If you are having a problem with a tire lifting put a roll bar on the opposite end of the car. OK now for a couple of examples: You can test your skills a little by trying to determine the solution before reading it. (BTW all solutions may not be the best for all cases since there are other factors that can be induced)

Example 1
You enter a sweeper, everything seems ok. Turn -in was smooth, cornering grip seems to par, you start accelerating coming out of the sweeper and your car goes loose and spins out. 
Solution: Since your car has adequate turn-in response and grip off power it would tend to indicate that your camber, caster, and toe settings are correct. The problem is induced when you start to accelerate. This would tell me that it is a weight induced oversteer. This means that the acceleration momentum is placing to much weight on the outer rear tire causing it to break loose. To solve this I would stiffen the rear suspension or add a rear roll bar.

Example 2
You enter a hairpin and your car progresses toward the wall at a rapid rate. 
Solution: Slow down sooner you entered the corner to fast (Driving problem). Many understeer characteristics are caused more often by driver error than set-up.

Example 3
Again entering a sweeper. Your initial turn in is satisfactory, though as you go further into the corner your car starts drifting toward the wall, you slow down enough to keep it in line and accelerate out of the corner, as you accelerate out your car starts drifting once again toward the outer wall. 
Solution: There can be multiple solutions to this problem. Toe is probably not a problem in this case because the car didn¹t change characteristics throughout the corner. Since you like the initial turn in I wouldn¹t change the caster either. If the push is minor I would try changing the camber on the front of the vehicle to cause the front to grip again, if it¹s a very minor push then I would change ride height on the front. If the push is more major I would soften the front to allow it to grip further or possibly stiffen the rear. If you are to stiffen the rear you may induce a loose condition in other corners.

Example 4
You enter a corner and the car turns in very fast, holds the line, then under acceleration the car drifts off line toward the outer edges and you have to let off the throttle. 
Solution: This is completely a toe issue. You have to much toe out which is not allowing the car to hold the line effectively while exiting the corner. Reduce toe-out or give the car more toe-in

Example 5
You enter a corner and your car turns in really fast grips and sends the tail around immediately. 
Solution: There are again more solutions to this problem but the most obvious one would be that you have to little caster (this cannot be changed on all cars). This is indicated because the car had a very responsive turn in and then went immediately into oversteer. The oversteer is induced because of the limited lean in the chassis with the massive grip given the front because of the lowered caster. Other minor causes could be Brake turning or to much toe out (but this would usually result in immediate push). You can also get a less grippy front tire, Stiffening the front suspension will not help in this case (early HPI cars had this problem)

Example 6
Your car goes through a corner perfectly but it feels a little sluggish (slow responding). 
Solution: Stiffer tire Inserts, Stiffer Suspension, or Less Caster

Example 7
Your car drifts like on sand through a corner. 
Solution: Some people like this but if you don¹t you can get softer tires or harder tires in some cases (depending on heat), or Soften the suspension overall to gain more grip.

Example 8
You enter a corner and your car feels to responsive, and twichy, it doesn¹t break loose but you feel you are scrubbing off speed.
Solution: This is a rare problem but it can happen, You have to much grip. At this point you need to either learn to drive very smoothly so not to scrub speed. Other methods that are usually more practical are To Stiffen the suspension evenly, reduce camber, reduce caster, purposely overheat the tires (though not recommended), anything that you can do to reduce the grip. Usually just a tire change may do the trick. Don¹t adjust toe here since it is not inducing grip.
 

Example 9
The dreaded high speed chicane you go throughout the first half fine, everything is Ok and then your car gets loose coming out of the second half.
Solution: You are causing a transfer induced oversteer which can be caused by may things. One of these problems could be a weight imbalance in the chassis which causes the weight to transfer unevenly from side to side. Another can be suspension that is to soft or overdampened, which doesn¹t allow weight to transfer quick enough. You could also be underdampened which may cause the car to respond to quick and bounce. This is one of the hardest things to solve, one more solution might come from a different body but this may only mask a problem. You can also be over reacting in your driving. This problem has so many solutions and minor issues that can cause it that it takes experimentation.

copyright 1997 Penguin r/c