By: Nicholas Wong
Geometry plays an important role in our lives that sometimes we do not notice or overlook. For example, the cars that we ride in are designed with the help of geometry. Geometry is used to improve the aerodynamics of a vehicle. The aerodynamics effects stability of the car at high speeds, safety, and wind noise that filters into the cabin. Geometry also is involved in engine designs. For example, some engines are angled, like a V6 engine while others are line segments, like a straight 8. Geometry is present in transmissions too. The diameter and ratio of the gears must be correct to match the engine capabilities. The tires of the car also involve geometry. The treads form a continuous pattern that repeats over and over. In suspensions, geometry plays an important role in the car's handling characteristics.
Geometry in Aerodynamics
Geometry is very important to the aerodynamics of a vehicle. The aerodynamics affect the car's handling, stability, safety, and wind noise at high speed. The angles and shapes of certain parts of a car can produce positive or negative effects on the vehicle.
Aerodynamic Aids: Spoilers, Wings, & Airfoils
Aerodynamics is most important and evident in a race car. Race cars have large wings, spoilers, or airfoils to help them stay on the road and allow them to go faster. Spoilers wings, or airfoils all do the same thing. They are inverted wings, such as those on a bird or airplane. The ones on planes and birds are angled to produce lift to allow them to fly. Wings on race cars produce negative lift to insure that they stay on the ground. They alter the airflow over a car to increase downforce, which in turn, occasionally causes drag. The angle of the spoilers can be adjusted for specific races, conditions, or tracks. In the front of the race car, there are front spoilers, which add downforce to the front and optimizes the angle the air will flow in. The downforce helps to keep the car planted during the race and from having too much understeer, which leads to a faster, better handling car.
Spoilers can also reduce drag. Drag is the force of the air resisting the motion of the vehicle. Less drag equals a faster and more efficient vehicle. Less drag is important to race cars as it is to regular cars. Streamlined vehicles produce less drag and have better fuel economy and better top speed capabilities because less air is displace when the car is in motion. Streamlined cars must have the correct angles and correct shapes to have low coefficient drag (expressed as Cd) numbers. The angle or rake of the winshields effects drag and wind noise. The shape of the sideview mirros can also effect aerodynamics. If they are designed with correct angles, their effects on aerodynamics can be improved.
The angles and shapes of bad spoilers can add drag to a vehicle, which slows it down and slightly worsens fuel economy. These spoilers are merely for aesthetic looks. Even sports cars can sprout these just for the looks. For example, the De Tomaso Pantera GT5 had a large rear wing, but it actually slowed the vehicle's top speed down.
Aerodynamic Aids: Underbody Ground Effects
Ground effects are planes or panels under a car used to suck a car to the ground. The Ferrari 360 Modena may not have any large visible spoilers but its underbody has panels shaped to aid its aerodynamic efficiency and to add stability at high speed. Its coefficient of drag is reduced from its predecessor's (the F355) 0.34 Cd to 0.33 Cd and it has a lift coefficient of minus 0.24, which translates to about 400 pounds of downforce at 180 MPH. This is all thanks toits aerodynamics, ground effects, geometry, and 5400 hours of wind tunnel testing. The fastest production and road legal car in the world, the McLaren F1, which costs about $1,000,000, aslo has o visible wings or spoilers. Instead it uses ground effect to maintain stability at its 231 MPH top speed. When braking, a small spoiler pops up and it is angled to increase rear end stability, reducing the effects of weight transfer to the front of the car.
Geometry in Automotive Engines
Geometry is used in the designs of car engines. V6s or V8s have a certain degree between the banks of cylinders. Most V8s have a right angle (90 degrees) that is formed between the two banks and most V6s have either a 90 or 70 degree angle. Engines can also be in the form of a line segment, such as an inline 6.
In racing engines such as CART and Formula 1, the choice of angles for an engine's V is weighed between two factors. With a lower center of gravity for the engine, a car's handling is better. To do this, you would make the angle large. But, the narrower the engine, the stiffer it will be and there will be more room for aerodynamic subtleties around and below the engine. To do that, you must make the angle small.
Most engines use cylinders and pistons to harness the power of combustion. The curvesof the intake manifold, the part of the engine that channels air into the combustion chambers, must have the correctly shaped curves to move the air with the least resistance possible. Another example of geometry in engines lies in the degress of the crankshaft. The new Ferrari 360 Modena has a 180 degree crankshaft to enable it to obtain a 112 horsepower per liter power to engine displacement ratio.
Geometry in Automobile Transmissions
The teeth of the gears in a transmission must be cut in very specific angles so that they mesh correctly. If cut improperly, the transmission can be ruined when attempted to be used. The ratios between the gears must be matched to the engine's capabilities. Various diameter cogs are used to create these gear ratios. A small gap between gears is especially important in racing. They allow an engine to stay in its power band, the range of revolutions per minute (RPM) in which an engine produces the most power.
Geometry in Tires
Geometry also plays a part in the tread pattern of tires. The Rubber Manufacturers Association uses the geometry of a tire's tread pattern to rate the tire's mud and snow designation (M+S). For example "...the M+S designation depends purely on the geometry of a tire's tread pattern.Multiple pockets or slots muts extend inward at least 0.5 inches, measured from the footprint edge of the tread centerline. These gaps must have a minimal cross section width of 1/16 inch. They must be angled at between 35 and 90 degrees from the direction of travel. And, last, the tires sea/land ratio (i.e., open area to rubber) must be at least 25 percent."* The 1999 Saab 9-5 Aero has wider tires than the standard 9-5. The tires create more drag but the spoilers have been tweaked to maintain the low 0.29 Cd of the car.
*Road and Track Magazine, June 1999
Disc Brakes and Geometry
The diameter of disc brakes will effect a car's stopping power. The larger the diameter that brake discs, the faster and less distance it will take to stop the moving vehicle. When more performance-oriented models are made based upon standard cars, sometimes manufacturers may upgrade to better brakes to cope with the added power of the vehicle. The Mercedes-Benz E55 AMG, for example, is a performance version of the regular E-Class. Upgraded brakes were installed to cope with the 349 horsepower and 391 pound feet of torque. The car is able to stop from 60 MPH in 114 feet, same as a Ferrari 550 Maranello. The upgraded brakes are 13.1 inches in diameter in the front and 11.8 inches in the back.
Suspensions in Vehicles and Geometry
In front a arm suspensions, the wheel moves in arcs or curved paths instead of going straight up or down. During hard cornering, the car's body roll can lift up an inside tire (usually the front). You can improve a car's suspension geometry (the curves and way it moves) so that the full width of a tire can be kept on the ground no matter how much the car's body rolls. In rea suspensions, geometry causes the rear axles to move in certain curved paths. When the car is accelerating and/or when it exhibits body roll during cornering, the suspension's geometry will determine at which angle the axle of the car will move.
