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Touring Car Suspension 101

Tuning your touring car

The Internet's most comprehensive guide (under construction- last update 30 March 99)

This article is written in reference to the four wheel independent suspension commonly found on all 1/10 scale touring cars, but the occasional note to other types of cars has been included where appropriate. Sedan suspension is all about keeping the tires in contact with the track. The amount of tire in contact with the track is referred to as the contact patch.

Throughout the article keep in mind that the number of variables is vast, and each variable causes something else to change. This means that it is simply not possible to attain a perfect set-up. That is assuming we could define a perfect set-up. As R/C racers we have an advantage in that an R/C chassis is generally good for three to five seasons, so there is quite a lot of development time available. Of course if you change tires, your favorite springs go out of production etc you will have to redevelop the car.

Preliminary

The first rule is that the world's best suspension is useless without a rigid chassis. No matter how well sorted a suspension, it can all be thrown away if the chassis flexes and makes a mockery of all that fine tuning. The chassis must be stiff enough to cope with anticipated loads.

This also applies to the suspension arms themselves, as critical alignment settings will be altered through suspension flex. Tamiyas have very flexible arms and as a result the cars are pretty much always 80 percent dialled, but consistence suffers. Aluminuim arms from various manufacturers can remedy this.

Track/Wheelbase Ratio

Wheelbase divided by track is a basic but fundamental point to consider when trying to alter a vehicle's handling. Reduced track results in better aerodynamics because of a reduced frontal area, hence the car has a smaller hole to punch when it pushes itself though the air.

A short, wide car will be more twitchy and therefore more responsive on a tight track. Maneuverability is in part a function of polar intertia (Trinity's EV-10 went to great lengths to minimize polar moment- the first time the term had been used in R/C) which in turn is a function of the weight contained between the axles. A short wheelbase helps attain a lower polar moment, provided weight can be contained within the axles. This is why most agree that the TA-03R is better handling than the TA-03F, the front mounted motor means a lot of weight ahead of the front axle.

This is one of the few areas that Tamiya drivers are spoilt for choice. The TA-02 comes in regular, wide, and short/wide. The '03 also comes in regular, wide and short/wide. Mini's come in short, medium and long. Of course, there are quite a lot of parts required to make the changes. However it is certainly feasible to have different cars for long and short courses.

Roll Centre

The way a car rolls is fundamental to what a car does in a corner. There is little skill required to keep a car going straight (HPI Nitro Mini drivers exempt!), so the key to performance lies in a car's ability to corner.

At the heart of this is roll centre (RC). This is an invisible point in space around which the chassis rolls during cornering. This point is also prone to move about during cornering. The ideal system would be one where the roll center remained constant throughout the suspension's travel. Since this is not yet possible, we want to limit it as much as possible. By far the easiest way to do this is to reduce travel to a minimum (the same theory used in F-1!). For Tamiya sedans this means using two spacers (one small, one large) per CVA II shock.

Springs & Shocks

The primary function of the spring in a sedan application is to control weight transfer. Yes, it does absorb track irregularities (or corner dots!), but on most tracks this is secondary. The general rule is that soft springs give more grip, stiffer springs less grip but more response.

Most springs used in R/C are linear rate springs, meaning that the spring rate remains constant throughout it's compression. If the spring rate were 20 grams/millimetre, you would need to place 20 grams on the spring to move it one millimetre, and 40g to move it 2mm and so on. This means that the preload spacers (shock collars) are only there to adjust the cars ride height, not it's spring rate. Looking at the graph will make this clear. When you lower the spacers, the car will 'feel' stiffer, but you haven't changed the springs' stiffness, just loaded it with kinetic potential energy, making it feel stiffer. When you compress a preloaded spring it begins with more potential energy, so when the spring is released it releases more energy and bounces back as if it were stiffer.

This will make the car drive like it's more stiffly sprung. This is also because the ride height is higher and the wheels cannot drop into depressions, resulting in a harsh ride. I doubt whether a car set up in this manner can ever be fast.

A too stiff spring will result in a car that tends to dart around and be generally unstable. A too soft spring will result in excessive body roll and pitching under acceleration and brakes, & bottom out on even slight bumps. It will be slow to respond to driver input and hesitate in changes of direction.

Shock Leverage

The spring rate is rather academic if you don't consider the way it is mounted to the A arm. Unless the spring acts directly on the upright, the wheel rate will be lower than the spring rate. Acting on the up right, the wheel rate will be the same as the spring rate, because there is no leverage. If, like on most cars, the spring acts on the lower arm, then the closer to the centre line, the more leverage the wheel will have, reducing wheel rate. Most cars have extra holes in the lower arms to adjust leverage.

Shocks

The job of the shock (or damper to be correct) is to control the spring. Without shocks, the energy that is stored in the spring when it is compressed will all be released at once, causing excessive oscillations.

A too soft shock (thin oil) will not provide sufficient resistance to the spring and cause the chassis to bounce.

A too stiff shock will not allow the spring to do it's job. The wheels will bounce over bumps.

Spring/shock angles

Strictly speaking, the spring/shock assembly should be within 10 degrees of vertical to the suspension arm. The reason for this is that an inclination of 10 degrees or more results in the spring/shock becoming softer as it approaches the limit of it's travel. This is why the TA-03 has such upright shocks. If you think about the arc scribed by an A arm, this is not possible to have the spring/shock at exactly 90 degrees to the arm through out suspension travel with a simple linkage.

Anti Roll Bar or Sway bar

The anti-roll bar is a torsion-bar that operates between opposite ends of an axle. It's function is to resist (to a certain degree) large differences in movement between the left and right wheel to make the car corner flatter. To demonstrate how it works remove the shocks and springs and move one side of the suspension up and down. The opposite side should move nearly as much. The Anti-roll bar can be of greatest advantage where the car needs to have soft springs but still retain minimal body roll for the faster sections of the track. Keep in mind that the Anti-roll bar needs to be matched to the springs or it will be counter productive. A too soft bar will not provide sufficient resistance to the springs, while a too stiff bar will do nothing but cause the inside wheel to lift.

Camber

Refers to the angle of the wheels when viewed from head on. Negative camber means that the tops of the tires lean in (toward each other). Negative means they lean out. To adjust camber you need to adjust the camber link (upper suspension arm). On most Tamiya cars this requires optional parts. If you shorten the camber link you gain negative camber. Lengthen it and you gain positive camber.

So why do we need camber? When a car corners, it inevitably has some degree of chassis roll. This roll makes the wheels lean. To keep them parallel with the track surface, camber is added. Of course, only the outside wheel will be level with the track, the inside wheel will be leaning the wrong way (oval racers take note).

Many people will tell you that more camber equals more traction, but too much is worse than not enough, and will only result in increased tire wear on the inside of the tread. How much camber is dependent on the amount of chassis roll the vehicle exhibits. Therefore softening the springs or removing a sway bar will change the 'ideal' amount of camber.

FF cars are particularly sensitive to camber changes, because more than 1-2 degrees on the front won't allow the wheels to pull the car out of turns.

Camber Change

As the suspension arm moves up and down, there will inevitably be some degree of camber change, normally, as the suspension is compressed, negative camber increases. This serves to keep maximum contact patch by allowing the suspension to increase camber during cornering, but run little or no camber when at rest. On Tamiya cars there are no adjustments for this, but some cars like HPI have extra holes in the shock tower, bulkhead or hub carrier (or a combination). If you can see extra holes for the camber rod then this adjustment is available to you.

Placing the camber rod closer to the chassis centerline (you will have to lengthen it) decreases negative camber change so that the tire stays more parallel to the side of the chassis when the suspension is compressed (less vertical to the track), so cornering traction is reduced. At the front, this causes a loss in steering. At the rear, this will gain steering. Placing the camber rod further from the chassis centerline increases negative camber change so that the tire stays more vertical to the track when the suspension is compressed, so cornering traction is increased. Generally, the camber rod should always be shorter than the lower A arm (this is referred to as an 'Unequal Length Double Wishbone').

Caster

Refers to the angle of the kingpins (lean back). More caster results in more high speed and on power steering , but decreased low speed and off throttle steering. Too much caster will result in savage low speed understeer because the front wheels lean over and come off the ground as the steering is turned.

So, going into a turn, more caster will let you turn in tightly and quickly, but as the car scrubs speed in the middle and exit, you will loose steering accordingly. Less caster will do the opposite, the car will "push" coming into the turn, but you will gain steering towards the middle and exit.

Again, in FF cars, too much caster limits front wheel traction and acceleration.

*In off road cars caster is sometimes referred to as "kick up".

Toe-in/ Out

This is the easiest adjustment on any car. Toe in is when the front of the tire points towards the center of the chassis. Toe out is when the front of the tire points away from the center of the chassis. Toe in: Up front, toe-in increases stability but decreases initial turn in traction. At the rear, toe-in increases traction out of a turn, to stop spins. Most cars come with about 3 degrees toe-in each side. Rear toe is not adjustable on Tamiya cars.

Toe-out is only used up front. Toe-out in the front will increase steering aggressiveness, decreasing stability. This is a good way to add steering to FF cars. Don't go overboard, usually, 2 degrees or less per side will suffice.

* Whenever toe is not set to zero, the vehicle will scrub speed in a straight line.

Who is Ackermann?

Ackermann is the difference in steering angle between the left and right sides. Take your car and turn the wheels to full lock. See how the inside is turned in sharper than the outside? That's Ackermann. Some cars let you adjust Ackermann, but Tamiya don't. To adjust Ackermann all you have to do is adjust the length of the central steering rod, this changes the distance between the inner tie-rods, and alters Ackermann. More Ackermann makes a car smoother during cornering. Less makes it more aggressive.

Anti-squat

The perpose of Anti-squat is to optimize weight transfer under acceleration. Anti-squat can't actually alter the amount of weight transfer, which is defined by CG height, acceleration, wheelrates wheelbase etc. The centre of rotation is the imaginary point around which the suspension rotates. It is also the point at which the suspension 'pushes' on the chassis to move the car forward. Note that in a R/C double wishbone system the point of rotation is on a line scribed by the hinge pin, and is an infinite distance forward.

0 anti-squat is when the rear lower arms are parallel with the bottom to the chassis, 100% anti-squat is when the line of the hinge pin goes directly through the CG. As load is applied to the rear wheels, the anti-squat causes the rear wheels to be pushed away from the chassis, thereby planting the tire to the track. At 100% anti-squat, no body squat would occur.

However, it tends to 'lock up' the suspension when accelerating, which is why 100% (or greater) anti-squat is rarely used. Because anti squat is geometric, it is capable of producing unwanted effects when loads are reversed, such as reducing weight transfer to the front wheels under brakes.

You can adjust it by putting shims under the front of the hinge pin mounting blocks. Tamiya cars and others with integral inner wishbone mounts are not adjustable.

*On pan cars there is no anti squat. The line of action would run from the centre of the axle to a point on the T bar, which means somewhere around 100% body squat. However, because these cars have the motor mounted transversely across the motor pod, the motor torque has a tendency to lift the front of the motor pod, mimicking anti squat, but because it is a function of motor torque, cannot be considered anti squat. This point is rather open to debate since it is unique to R/C cars- perhaps we can refer to it as 'torque squat'. The closest full-size cars get to this phenomenon is axle wrap on leaf sprung vehicles, where it is unwanted because is angles the uni joints.

Weight Distribution

The more load is placed on a wheel the more traction it will have, because of increased contact pressure. If you ever scratch build a car you will realize how important weight distribution is. If it isn't correct, nothing will help the car handle right. On many cars there is little way of making weight distribution changes. The placement of the ESC is usually governed by the shortest path between motor and battery, the servo is pretty much fixed and that only leaves the receiver and battery. The receiver will only make a small difference because it weighs so little. The battery can only be moved on a handful of cars. The ideal front to rear bias ratio is generally around 35:65 (RWD) 45:55 (4WD) or 65:35 (FF).

It should be noted that the while a heavily rear biased weight will give heaps of rear traction, when the G forces build up (because of the weight) the rear will step out very quickly and be very difficult to control. Conversely, a heavy front end will make the car reluctant to change direction because of the momentum carried at the front. A 50:50 car will corner very progressively and will tend to four wheel drift when the car's mechanical grip limit is exceeded. Off road cars need the weight biased further rearward to help the car keep it's nose up over jumps.

* Keep in mind that lowering the front suspension in relation to the rear will increase front weight bias and vice versa. This is the easiest way to change weight distribution, but may alter geometry exessively.

Aerodynamics

Several factors influence the downforce generated by a wing. Wing area, aerofoil shape and wing angle. Most tourers only have tiny rear wings, so the downforce generated is minimal. Most are also not adjustable. A steeper angle produces more downforce.

Item	Adjustment	Effect
Springs & Shocks	Softer	More grip, more weight transfer, less response
	Harder	Less grip, less weight transfer, more response
Shock Angle General	Upright	Higher CG, More Downward Travel, More Pack (Higher Piston Speed), Wheel Rate Stays Constant
	Laid down	Lower CG, Less Downward Travel, More Pack, Wheel Rate Becomes Progressively Softer
Shock Angle Front	Upright	Smoother High Speed Steering, Increased Low Speed Steering
	Laid down	Smoother Steering
Shock Angle Rear	Upright	Better on bumpy tracks
	Laid down	increased High Speed Steering, Smoother changes of direction
Ride Height Front	Lower	Lower CG, Less sensitive steering
	Higher	More sensitive steering
Ride Height Rear	Lower	More rear traction, smoother transition
	Higher	Less traction more weight transfer to front wheels
Anti Roll Bar	Stiffer	Less Low Speed Traction, Better Response
	Softer	More Low Speed Traction, Lower Low Speed Response
Camber	More Negative	More cornering traction
	Less Negative	More straight line traction
Camber Change	Holes closer together	More camber change
	Holes farther apart	Less camber change
Caster	More	More high speed steering
	Less	More low speed steering
Front Toe	In	More stability in a straight line
	Out	Better turn in
Rear Toe	In	More stable under power
	Out	Rarely Used (Never On FF), Less Stability, more steering
Ackermann	less	More Agressive Steering
	more	Smoother steering
Anti-squat	More	increased rear traction under acceleration
	less	less rear traction under acceleration
Weight Distribution	More Forward	More Front traction and weight transfer, less weight transfer to rear
	More Rearward	More Rear traction and weight transfer, less weight transfer to front
Aerodynamics	Larger/Steeper Wing	More traction at respective end of car, traction increases with speed
	Smaller/Less Steep wing	Less traction at respective end of car, traction increases with speed