key terms

Terms to define:

Horsepower(HP):

Torque:

Horsepower and torque are the two measurements that are used to tell customers how powerful their cars are. But what do they mean? In the simplest terms torque is the measure of force over a distance and horsepower is a measure of force over time. For cars torque is measured in ft-lbs and HP is actually a unit that is equivalent to 33000 ft-lbs/minute. The unit of HP was developed by James Watt towards the end of the 18^th century when he needed a way of letting his customers know how powerful his new steam engines were. To help this make sense, think of a 1 pound weight. If you lift it 1 ft then you just did 1 ft-lb of work. If this were to take you 1 minute then it would be 1ft-lb/min or if it took you 1 sec then it would be 60 ft-lb/min. Or if an engine were to exert the force need to move 33000 lbs 1 ft in one minute then it would have 1 HP.

I posted a link to another site that goes into more detail if your interested

Drivetrain: This includes the engine and the wheels and everything in between. IE: the engine, transmission, transfer case, differentials and axles.

Vehicle Curb Weight: This is the weight of an unloaded vehicle.

GVWR: Gross Vehicle Weight Rating: This is the maximum weight that the vehicle can support including its own weight. IE: vehicle curb weight plus passengers and cargo

Payload capacity: This is the maximum cargo weight that a vehicle can carry. This statistic can be manipulated in how the manufacturer measures it. For example the manufacturer could simply subtract the vehicle curb weight from the GVWR or they could figure the weight of the driver and passengers into the figure.

Fuel type (flex fuel): Flex fuel refers to the ability of an engine to run on a blend of multiple fuels. In the U.S. this typically refers to gasoline and ethanol. The standard for flex fuels in the U.S. is E85 or 85% ethanol 15% gasoline.

Wheel base: the distance from the center of the front tire to the center of the rear

Ground clearance: the distance from the ground to the lowest part of the chassis

http://www.lcool.org/technical/diffs/diffs.html http://auto.howstuffworks.com/differential.htm These sites help to explain differentials and lockers.

Open Differential: a gear mechanism that allows a single input and dual output. The driveshaft is the input power and the differential sends that power to the wheels on the axle. When turning the wheel on the inside of the turn travels less distance then the one on the outside. The differential is designed to allow the tires to spin at different speeds in turns. However with open differentials, the amount of torque available is equal only to the least amount being produced at either tire. This means that when one tire loses traction it loses torque and therefore neither tire receives any torque.

Center differential: Just as the inside tire rotates at a different speed as the outside tire in a turn; the front tires rotate at different speeds than the rear. When a vehicle has power going to all 4 tires (4WD or AWD) then this becomes an issue. Trucks and SUVs that are only designed to operate in 4WD at low speeds and on slippery surfaces don’t usually need to compensate for this but vehicles that operate in 4WD at high speeds on dry surfaces (pavement) often use a center differential to allow for this.

Limited slip differential: is designed to prevent the loss of torque to both tires when one loses traction. These types of differentials are found mostly on SUV’s and trucks.

Locking differential: This type of differential uses essentially locks the axle together so that the same amount of force is sent to both tires. This way if either tire loses traction then the other tire remains unaffected. If used at high speeds on surfaces with good traction then this can damage the axle, tires, and drivetrain.

Locking hubs: Since many part time 4WD vehicles do not have center differentials and are designed to only use the 4WD in low traction low speed situations, locking hubs were developed to give operators the ability to disconnect the wheels from the driveshafts which allows the tires to spin independently of each other.

Final drive ratio: This is the ratio of the input gear to the output gear. This means that in a truck with 4.10 gears the driveshaft must turn 4.1 times to turn the tires once. The chart in the following post shows ideal gear ratios and tires sizes.

Suspension travel: This is the measured distance that the wheel can travel.

Tow rating: The maximum weight that a vehicle is capable of towing