DIY-racetuning.net The ultimate tuning resource for Forza Motorsport 3

TERMINOLOGY - If you’re gonna tune, you gotta know the lingo.

Aerodynamic Load	The load on a wheel, wheel pair, or entire vehicle due to the vertical forces exerted on it by its passage through the air.
Aftermarket	When something is referred to as ‘aftermarket’ it means a part or component that is non stock, or a non-stock replacement. These parts are generally regarded as upgrades or improvements from the stock components. Aftermarket parts are pretty much what drives the tuning industry.
Alignment	Angles of the tire and suspension axes relative to each other and the ground: caster, camber, toe. Also, the adjustment of components to bring them into a predetermined position for the most efficient operation of wheel and vehicle for proper even tire wear.
Anti-Roll Bar	AKA: Sway Bar (acronym:ARB) A steel torsion bar, linking the left and right side of a suspension. It comes into play during cornering. As the car leans in a turn, the anti-roll bar resists this leaning by transferring more weight to the outside tire. It provides a means to achieve good handling from stiff roll resistance while maintaining a comfortable ride through soft springs.
Aspect Ratio	The dimensional relationship between tire section height and section width; section height divided by section width.
Axle Ratio	(AKA: ‘differential ratio’ or ‘rear end ratio’) is the number of revolutions required by the transmission’s output shaft to make the drive wheels revolve once.
Baller	When somebody says ‘That’s baller’, it usually means an expensive (and arguably overpriced or superfluous) item that looks great, but could probably be substituted by a less expensive item of comparable functionality. An item that has a huge ‘bling’ factor but doesn’t necessarily enhance performance. A good example would be a carbon fiber valve cover.
Backspacing	The measurement from the back of the bolt pad to the back edge of the rim; used to calculate offset and determine where the back of the bolt pad is located in relation to the rim width, sometimes referred to as rear-spacing.
Breakaway	The point at which tire cornering traction is lost.
Bumpsteer	A steering effect resulting from toe or camber changes as the suspension moves up and down.
Bump	AKA: bound, or compression of the suspension. Bump ‘stiffness’ is the measure of rate at which a shock absorber compresses.
Boost	When someone refers to ‘boost’ it is associated with forced induction, or compressed air that is forced into the engine by a turbo charger or supercharger. It is measured in PSI (pounds per square inch).
Camber	The angle that the tire is leaning measured from true vertical. The inward or outward tilt of the wheel/tire at the top. Performance cars run ‘negative’ camber (the tops of the wheels are tilted in).
Camber Thrust	The cornering force developed by a tire due to its camber. A force in the same direction as the leaning of the tire.
Caster	The angle between the tire vertical and the steering pivot axis; the backward or forward tilt of the steering knuckle pivot points.
Centerline	A plane dividing a tire, wheel, or vehicle into two symmetrical halves.
Centrifugal Force	The force that tends to throw a vehicle away from the center of rotation during cornering. Measured in lateral force, or lateral G’s.
Contact Patch	The area of the tire that is in direct contact with the road surface.
Co-efficient of friction	(Tires). The amount of force a tire can generate, measured in g’s. This includes cornering force (lateral acceleration), straight line acceleration, and braking.
Coil Springs	Suspension components of coiled spring steel that compress and expand in response to road pressure, permitting the up-and-down movement of a vehicle (and driver) as it goes over the irregularities of a road surface.
Compliance Steer	A steering effect caused by the deflection or compliance of bushings, joints, and other suspension components under loads and forces.
Control Arm	A device that acts like a hinge, used to connect the un-sprung components of a suspension to the sprung chassis, which allows suspension travel.
Cornering Power	(AKA: Cornering Force) The amount of force that a tire can generate in the lateral sense. Used to measure lateral acceleration.
Curb Weight	The total weight of a vehicle with no passengers and a full tank of gas.
Center of Gravity	(COG) - The center balance point of a vehicle; the single point where a car would be supported without tipping up or down. It is the three dimensional balance point of a race car.
Coilover	This is generally an aftermarket suspension component which is a combination of a shock absorber and coil spring. The defining characteristic of a coilover is usually the adjustability of both bump and rebound settings of the shock absorber component.
Deflection	The moving or bending of suspension parts. Usually results in camber loss during cornering.
Dive	The weight transfer of the sprung mass of a car from back to front under braking. More simply put, when you drive your car and hit the brakes hard, the feeling of the car (and your body) lunging forward is ‘dive’.
Dynamic Balance	Balance in motion. The balance of a wheel while it is rotating. A condition in which a tire and wheel assembly has weight distributed equally on both sides of the wheel's axis of rotation.
Dynamic Camber	Camber change that is a result of suspension travel.
Dynamic Load Transfer	The shift in vehicle weight from one tire to another when the vehicle is accelerated in one sense or another. Vehicle gross weight is not affected, only its distribution.
Dynamometer	*(Acronym: Dyno)*. This is a machine that measures force or power. In cars, it measures horsepower from the engine by calculating both torque and RPMs. Dynos, outside of plotting horsepower / torque, can be used for a much wider variety of functions, like measuring an engine’s fuel/air ratio
Dyno ‘pull’	Is a single run on a dyno. Generally the car is strapped on the dyno, with the driven wheels on a set of rollers. The car is then accelerated through the entire RPM range (at full throttle) until it hits the rev limiter. The horsepower and torque are measured and displayed via a line graph known as a ‘curve’.
Forced Induction	*(Acronym: FI)* is the connection of a turbo charger or supercharger to the air inlet (intake) of an engine which utilizes the production of compressed air. This air is forced into the engine at high pressure to produce additional power.
Fore and Aft	(weight transfer) - A load factor where weight is transferred from the front tires to the rear tires during acceleration and from the rear to the front tires during braking.
G-force	A unit of acceleration. "g" is a symbol that represents the acceleration of gravity. Acceleration at 1g equals 32 feet per second.
High-End	(Power) refers to available horsepower and torque at the high side of the RPM range. On a car with a 9000 RPM red line (limit), high end power is considered 6000 RPMs and above.
Independent Suspension	A suspension system in which the front or rear pair of wheels of a car are independently connected to the frame or underbody. In this system, deflection of the wheel on one side will not affect the wheel on the other side.
Inertia	The tendency of any mass at rest to stay motionless, or any mass which is moving to remain moving. Inertia is the measurement of the mass’s resistance to said changes in movement. Inertia is also a measurement of a vehicle moving in a straight line’s resistance to turning.
JDM	Means ‘Japanese Domestic Market’. For many tuners JDM parts are synonymous with ‘authenticity’ and ‘quality’. To others, JDM means overpriced aftermarket components that although are of good quality, are more for show, (the ‘Bling’ factor).
Laden	(Wheel) – The term ‘laden wheel’ refers to the outer wheel of a pair that bears increased lateral loading during a turn.
Lateral Weight Transfer	A load factor in cornering where weight is transferred from the inside tires to the outside (laden) tires.
Longitudinal Load Transfer	Transfer of weight fore and aft (forward and back) as a result of the forces of acceleration and braking. (See: ‘Dive’ and ‘Squat’)
Lean	When an engine is said to be running ‘lean’ it means the mix of air to fuel is out of balance, with too much air and not enough fuel.
Load Index	A numerical code which specifies the maximum load a tire can carry at the speed indicated by its speed symbol, at maximum inflation pressure.
Loading	(AKA: Vertical Load) The amount of weight put on tires. Increased load will increase cornering force to a limited extent, as indicated by a tire’s performance curve. The amount of traction available from any given tire is dependent upon how much weight is on it.
Loose	When a driver says his car is ‘loose’ it means it’s oversteering. In NASCAR lingo it means, 'Rear hits wall first'.
Low-End	(Power) refers to available horsepower and torque at the low side of the RPM range. On a car with a 9000 RPM red line (limit), low end power is considered 1000-3000 RPMs.
Mid-Range	(Power) refers to available horsepower and torque in the middle of the RPM range. On a car with a 9000 RPM red line (limit), mid-range power is considered 3000-6000 RPMs.
Negative Camber	Is when the top of the tire is tilted inward from perpendicular to the road surface.
Negative Caster	A setting where the steering axis is inclined forward at the top as viewed from the side; a condition which tends to cause instability.
Negative Offset	(Wheels) When the back of the bolt pad is closer to the inside of the wheel; when the mounting face in inboard of the rim centerline; extends assembly away from vehicle resulting in wider tracking.
Offset	The distance from the centerline of the wheel to the mounting face of the wheel. Wheels can be offset both inside and outside of this centerline.
OEM	(Original Equipment Manufacturer) - Refers to parts sold to or produced by automobile manufacturers for equipping their new cars.
Oversteer	Car doesn’t have enough rear grip. A cornering condition where rear tires operate at a greater slip angle than the front tires. Generally speaking, it’s the tendency of a car’s rear end to rotate more sharply than the driver intends while negotiating a turn.
Plowing	The loss of cornering capability of the font of the vehicle. The car tends to go straighter than the desired driving line through a turn: understeer.
Positive Camber	Is when the top of the tire is tilted outward from perpendicular to the road surface.
Positive Caster	A setting where the steering axis is inclined rearward at the top, as viewed from the side; makes possible the self-centering force that tends to return the wheel to the direction the vehicle is traveling.
Positive Offset	When the back of the bolt pad is closer to the street side of the wheel; when the mounting face is outboard of the rim centerline, draws assembly towards the vehicle resulting in narrower tracking.
Power to Weight	(Ratio) – Expressed in pounds per horsepower, it is obtained by dividing the vehicle’s gross weight by its maximum horsepower. Is used to roughly measure a vehicle’s linear acceleration capacity.
Push	When a driver says his car is ‘pushing’ it means it’s understeering.
Rebound	AKA: extension; the movement of the suspension as the springs expand or stretch. Rebound ‘stiffness’ is the measure of rate at which a shock absorber stretches up or ‘rebounds’ from a compressed state.
Red Lining	A car is red lining when the RPMs go all the way to the top of its available rev limit.
Rev matching	Matching revs is a term used when a driver downshifts to a lower gear, and pulses the accelerator during the shift to bring the RPMs up to match where they need to be to make the shift seamless.
Ricer	A person who makes unnecessary modifications to their car to make it look faster. The cars are usually Japanese imports, which is where the slang ‘rice’ comes from. The cars are often FWD economy cars that were designed to go slow in the first place. Common ricer mods are: Huge exhaust that serves no purpose other than to be loud and attract attention. A huge spoiler made of carbon fiber which is supposed to produce downforce, but can’t, because the car has no power. Lots of after-market company stickers they don't actually have parts from. And expensive rims that usually cost more than the car itself
Ride Height	The distance between the frame of the vehicle and the road.
Roll	The lateral transfer of weight from a car’s sprung mass, from side to side during cornering (turning). Body roll is generally measured in degrees.
Roll Axis	The straight line that joins the front roll center with the rear roll center.
Roll Center	Is the point in the transverse plane of the axles, about which the sprung mass of that end of the vehicle will roll under the influence of centrifugal force.
Roll Stiffness	The amount of resistance a vehicle has to body roll. Roll stiffness is controlled by spring rates and anti roll bars.
Rotational Inertia	Inertia specific to the rotational components of the internal combustion engine. The inertia created by the mass of the crankshaft, flywheel and driveshaft (for example) must be overcome by the engine’s power before the remainder of the car’s horsepower can be utilized at the driven wheels.
Slip Angle	The difference (in degrees) between the path a tire is traveling and the direction the rim pointing.
Spring Rate	The measurement of a spring’s stiffness, measured in inch/pounds (in/lbs). For example, a (non-variable rated) spring rated at 300 in/lbs means that 300 lbs of force will be required to compress the spring 1 inch. As such, 600 lbs of force would be required to compress the spring 2 inches.
Sprung mass	All parts of the car that are supported by the suspension including chassis, engine, transmission, body, driveshaft, passenger cabin, (and passengers, too).
Squat	The weight transfer of the sprung mass of a car rearward under acceleration. More simply put, when you’re at a stop light and hit the accelerator, the sensation you feel of leaning back as you speed up is ‘squat’.
Static	Having no motion.
Static Weight Distribution	The amount of vehicle gross weight supported by the rear wheels when compared to the weight supported by the front wheels when the vehicle is at rest.
Steering Response	Reaction time between driver input at the steering wheel and the directional change of the vehicle.
Tight	When a driver says his car is ‘tight’ it means it’s understeering. In NASCAR lingo it means, 'Front hits wall first'.
Time Attack	A ‘time attack’ is a driving competition where cars do not race wheel to wheel like in a conventional race, but drive to post the fastest lap time.
Torque	The measurement of the force applied to produce a rotating or turning motion. In an engine, torque is the amount of force with which the crankshaft is rotated. Torque can also be used to measure rotational force at the driven wheels.
Track	(width) - The distance between the front tires on the front axle and the rear tires on the rear axle.
Traction Capacity	The amount of force a tire can generate in the longitudinal sense. Used to measure straight line acceleration.
Understeer	Car doesn’t have enough front grip. A cornering situation where the front tires generate more sip angle than the rear tires. It’s the tendency of a car to turn less sharply than the driver intends and compensated for by the addition of more steering input.
Unsprung Mass	All the parts of the car ‘below’ or unsupported by the suspension. Generally it’s the wheels, wheel spindles, tires, lower control arm, half the shock weight, and brakes that comprise the bulk of the car’s unsprung mass. The most common way to reduce this is by mounting lighter wheels.
Vertical Load	(AKA: Load) The amount of force applied to an individual tire in the direction perpendicular to the road surface.
Wheels	Rims (without, and not to be included with tires). Generally, wheels and tires are not used interchangeably or in combination. Tuners like to keep the terms separate to maintain the distinction between both components.
Wheelbase	The distance between the contact patch of the front tires of a vehicle and the contact patch of the rear tires.