AWD vs FWD vs RWD.
Aug 15, 2007, 06:29 PM
#1
AWD vs FWD vs RWD.
For a long while I've heard that the AWD cars are not much for top end, but never really got the answer to why. The Bugatti is AWD and goes 256! So, I'd like to know why RWD and FWD have the advantage over AWD at high end speed or if it's just a load of crap.
Aug 16, 2007, 07:16 AM
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If the cars with AWD, RWD, and FWD have the same amount of power at the crank they will have different power to the wheels because of different amounts of drive train power loss each drive train set up has.
The front wheel drive car will have the most at the wheels, because it will have the least amount of drive train power loss due to the least amount of drive train components.
With RWD it will have the second most amount of power to the wheels due to the addition of a drive shaft to send power to the rear wheels.
As for AWD it will have the least amount of power to the wheels because it's the most complex out of the three set-ups.
Basically the more complex/more parts a drive train has the less power it has to the wheels.
The front wheel drive car will have the most at the wheels, because it will have the least amount of drive train power loss due to the least amount of drive train components.
With RWD it will have the second most amount of power to the wheels due to the addition of a drive shaft to send power to the rear wheels.
As for AWD it will have the least amount of power to the wheels because it's the most complex out of the three set-ups.
Basically the more complex/more parts a drive train has the less power it has to the wheels.
Aug 16, 2007, 07:31 AM
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Top end as in top speed or high speed acceleration?
Given the same engine with components (same amount of crank horse power and the powerband), transmission with same gear ratios, same aero dynamics, same size and weight of the wheels, tires, brakes and suspension bits, ie basically the same car with just different powering wheels, then as the guy mentioned above, due to the extra drivetrain loss, its gonna put less wheel horse power thus having lower top speed. MR or FF (possibly RR as well) layout will theoretically have the least loss.
Usually 4wd counterparts (for cars like 3 series, A4 etc) tends to sit half inch to an inch taller as well which will affect the aerodynamics. They generally tend to weigh about 100lbs more tho this won't really affect the top speed, theoretically if the wheels dont have friction, added weight wont affect the top speed, even if there is friction, like in real life, it would affect top speed probably by tiny fractions of an mph on a 150-250mph car so you can consider it nil.
Major variables that affect a car's top speed are: engine power, aerodynamics and gearing. Why you see Veyron reaching almost 250mph but you don't see 2000hp drag Vipers never reaching that speed? Because their aerodynamics and gear ratios are not set to reach that speed.
If you want better acceleration, you need shorter gearing, which will reduce top speed. Also whenever you try to add more downforce to your car, the car tends to become not as slippery although not always. Thats why a lot of race engineers are working hard to find solutions for more downforce while not harming aerodynamics of the car, or at least little enough for a good trade off.
If you don't have any downforce at high speed, or even worse, have lift at high speed, then your car will become unstable and eventually take a flight/flip. Most companies will make sure to put a speed limiter well below the point the car will do such thing. Also, tire choices and materials for it are very limited. You'll have hard time finding tires for 220mph, let alone 250mph+
I think the 'rumors' you are hearing is usually based on 1/4 mile runs. 4wd cars will get a good jump and a really nice 1/8 mile time compared to its competition (say STi vs. Pontiac GTO), then kind of loses steam and eventually GTO will catch up by the time you reach the 1/4 mile mark. Thats why RWD/FWD car with same 1/4 mile time slip tend to have higher trap speed than AWD cars.
Given the same engine with components (same amount of crank horse power and the powerband), transmission with same gear ratios, same aero dynamics, same size and weight of the wheels, tires, brakes and suspension bits, ie basically the same car with just different powering wheels, then as the guy mentioned above, due to the extra drivetrain loss, its gonna put less wheel horse power thus having lower top speed. MR or FF (possibly RR as well) layout will theoretically have the least loss.
Usually 4wd counterparts (for cars like 3 series, A4 etc) tends to sit half inch to an inch taller as well which will affect the aerodynamics. They generally tend to weigh about 100lbs more tho this won't really affect the top speed, theoretically if the wheels dont have friction, added weight wont affect the top speed, even if there is friction, like in real life, it would affect top speed probably by tiny fractions of an mph on a 150-250mph car so you can consider it nil.
Major variables that affect a car's top speed are: engine power, aerodynamics and gearing. Why you see Veyron reaching almost 250mph but you don't see 2000hp drag Vipers never reaching that speed? Because their aerodynamics and gear ratios are not set to reach that speed.
If you want better acceleration, you need shorter gearing, which will reduce top speed. Also whenever you try to add more downforce to your car, the car tends to become not as slippery although not always. Thats why a lot of race engineers are working hard to find solutions for more downforce while not harming aerodynamics of the car, or at least little enough for a good trade off.
If you don't have any downforce at high speed, or even worse, have lift at high speed, then your car will become unstable and eventually take a flight/flip. Most companies will make sure to put a speed limiter well below the point the car will do such thing. Also, tire choices and materials for it are very limited. You'll have hard time finding tires for 220mph, let alone 250mph+
I think the 'rumors' you are hearing is usually based on 1/4 mile runs. 4wd cars will get a good jump and a really nice 1/8 mile time compared to its competition (say STi vs. Pontiac GTO), then kind of loses steam and eventually GTO will catch up by the time you reach the 1/4 mile mark. Thats why RWD/FWD car with same 1/4 mile time slip tend to have higher trap speed than AWD cars.
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Aug 16, 2007, 10:32 AM
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I remember watching a top speed comparison on TV. They brought in a bunch of high powered cars and motorcycles. But, the most interesting car was a high horsepower supra with a giant wing. The driver ran a good top speed, but then took off his wing and ran again. He was able to get a higher top speed... but at the risk of completely loosing control. The aerodynimics of a car are so important when considering top speed. There is a fine line between having enough aero to keep a car on the ground at 200+mph... and having too much downforce limiting your top speed. Interesting stuff!
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4wd, awd, driveterain, drivetrain, faq, fwd, horsepower, loss, lower, mile, quarter, rwd, speed, top, vehicles
