What is Wheel Horsepower?
Wheel horsepower is the actual power available at the driving wheels of a car. Unlike the engine or crank horsepower, which manufacturers often highlight, wheel horsepower accounts for energy losses in the drivetrain during power transmission.
Bhp to whp Calculation Formula:
The formula for wheel horsepower (WHP) is given by:
WHP=ηdvtr⋅EHP
Where:
- WHP is the wheel horsepower.
- ηdvtr is the efficiency of power transmission of the drivetrain.
- EHP is the engine horsepower (also known as crank or brake horsepower).
Drivetrain Systems:
Cars can have different drivetrain systems:
- Front-wheel drive (FWD)
- Rear-wheel drive (RWD)
- All-wheel drive (AWD) or Four-wheel drive (4WD)
Drivetrain Loss Calculation
The drivetrain introduces losses in power transmission due to various components. Drivetrain loss depends on the efficiency of these components.
Front-Wheel Drive Efficiency Formula:
ηFWD=ηgbx⋅ηdif⋅ηfdrs
Where:
- ηFWD is the efficiency of the front-wheel drive system.
- ηgbx is the efficiency of the gearbox.
- ηdif is the efficiency of the differential.
- ηfdrs is the efficiency of the front drive shaft.
Rear-Wheel Drive Efficiency Formula:
ηRWD=ηgbx⋅ηprs⋅ηdif⋅ηrdrs
Where:
- ηRWD is the efficiency of the rear-wheel drive system.
- ηprs is the efficiency of the propeller shaft.
- ηrdrs is the efficiency of the rear drive shaft.
Drivetrain Loss Calculation Formula:
Drivetrain Loss=1−ηdvtr
Drivetrain hp loss=(1−ηdvtr)⋅EHP=EHP−WHP
Efficiency of Drivetrain Components
Gearbox Efficiency Formula:
ηgbx=Nbrgηbrg⋅Ngrmηgrm
Where:
- ηgbx is the gearbox efficiency.
- ηbrg is the bearing efficiency.
- Nbrg is the number of bearings.
- ηgrm is the gear mesh efficiency.
- Ngrm is the number of gear meshes.
Propeller Shaft Efficiency Formula:
ηprs=Nujηuj⋅Nbrgηbrg
Where:
- ηprs is the propeller shaft efficiency.
- ηuj is the universal joint efficiency.
- Nuj is the number of universal joints.
Differential Efficiency Formula:
1ηdif=Nbrgηbrg⋅1ηgrm
Where:
- ηdif is the differential efficiency.
- ηbrg is the bearing efficiency.
- Nbrg is the number of bearings.
- ηgrm is the gear mesh efficiency.
Drive Shaft Efficiency Formula:
ηdrs=ηtrp⋅ηrzp
Where:
- ηdrs is the drive shaft efficiency.
- ηtrp is the tripod joint efficiency.
- ηrzp is the Rzeppa joint efficiency.
How to Calculate Wheel Horsepower?
- Determine Drivetrain Efficiency:
- Use the wheel horsepower calculator to find the drivetrain efficiency.
- Multiply with Engine Horsepower:
- Multiply the drivetrain efficiency with the engine horsepower to obtain wheel horsepower.
- Verify with Calculator:
- Confirm the result using the wheel horsepower calculator.
How to Use the Wheel Horsepower Calculator?
- Select Drive Type:
- Choose between Rear-wheel drive or Front-wheel drive.
- Enter Engine Horsepower:
- Input the vehicle’s engine horsepower.
- Enter Component Efficiencies:
- Fill in the efficiencies for gearbox, propeller shaft, differential, and drive shaft. Advanced mode allows entering individual efficiencies.
- Get Wheel Horsepower:
- The calculator will provide the calculated wheel horsepower.
FAQ
Q: What is the wheel horsepower of a 660 bhp rear-wheel drive vehicle?
A: The wheel horsepower is 539.4 hp. Multiply brake horsepower by the assumed drivetrain efficiency (0.8173).
Q: What is the drivetrain loss of a 118 bhp car if the wheel horsepower is 95 hp?
A: The drivetrain loss is 23 hp. Subtract wheel horsepower from brake horsepower.
Q: Which drivetrain system has maximum efficiency?
A: Front-wheel drive systems generally have the highest efficiency due to fewer power transmission components.
Note: This information is provided in simplified terms for better understanding. For precise calculations, the wheel horsepower calculator is recommended.
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