I've always read that 4x4 vehicles consume more petrol, but never understood why. Can any sifu teach me?

transmission power loss... the engine needs to push a bit harder to move four wheels instead of two

You mean the transmission of the engine pull to rear wheels is highly ineffecient and causes a very significant loss in energy?

Heavier chassis cause needs to be stronger.
Larger chunky tires got more rolling resistance.
Lousier aerodynamics.
Heavier transmission cause of transfer case.
Mechanical losses cause of 4 wheel drive.

i heard there someting below like a exhaust 'tabung' which keep a 4wd engine from water entrance.. if emove tat thing the car FC can improve alot... anyone heard tis before??

Bigger tyres mean more rolling resistance, heavier bodies, big aerodynamic drag.

You can remover the one way valve at the exhaust or try any of the usual tips and tricks that you hear of to increase power but there is no escaping the fact that a 4x4 is heavy. So it needs more power to move it

The fact that is the aerodynamics of a matchbox doesn't help during the highway cruise and engaging the 4 wheel drive makes it worse by increasing the rolling resistance that is already bad with the wide tyres.

Why does the discussion tend to assume 4x4 means heavy vehicles?

There are small cars with 4WD also right? E.g. the evolution...

Does the same rules apply?

coz 4 wheel drive
more tayar contact on the road

more drag

haha it sounds wrong... coz all cars have 4 wheels mar...

Like some people say in this thread, it is because of transmission/powertrain loss. You have more components to drive all 4 wheels. The engine has to transfer power through all that differentials and stuff.

There is a difference between the terms 4x4 and AWD. Go check it out.

But ultimately, the extra mechanical components like gears and shafts etc., do increase the amount of drag on the system.

Its like having paying 2 workers to fix a window. You may get double the productivity but you also have to pay double the wages. So its how much more efficiency you can get out of having 2 workers that make the difference.

The same goes for 4x4s and all wheel drives. You get more traction from 4 driving wheels but then the amount of stuff you have to turn increases. Thats why they tend to weigh more.

aiseh.......wrong argument there......

you say 4 wheel drive --> more tayar contact on the road
then 2 wheel drive --> not all 4 tayar contact the road ah?

that is right.

more FC because more mechanical parts to move all the 4 wheels.

also because the Laws of Thermodynamics tells me so.

First Law of Thermodynamics: Energy can be changed from one form to another, but it cannot be created or destroyed. The total amount of energy and matter in the Universe remains constant, merely changing from one form to another. The First Law of Thermodynamics (Conservation) states that energy is always conserved, it cannot be created or destroyed. In essence, energy can be converted from one form into another.

4X4 has more power. power has to come from somewhere. so come from petrol combustion lah. 4X4 has more power than 2 wheel drive. so naturally 4X4 uses more petrol than 2 wheel drive.

This post has been edited by tester1979: Dec 8 2006, 11:52 AM

tester seems to give a very scientific answer for u.........hope it's good enough hehe...........

btw i would like to add some ........... 4x4 pickup is usually quite heavy (1.6 tonne >) and uses a large diameter wheel, with lots of tyre surface to roll around ......... the 4wd mechanism with center and some differential also give out quite a lot of loses due to viscosity effects of the lubricant inside....... constant movement would give u very high efficiency but not in the mode of stop and go.........so all of these sums up......u make the figure urself.....

as for sedan like subaru (all models are AWD supposelly), the drive train need to push a lot of extra mechanism too........even the drive train itself would simply add around 100kg already....... imagine thats..... if it come with differential........more is lose but scarifice for better control is out weighted for that little increase in FC rite.......

so lets take a very simple car subrau impreza 1.6 TS come with AWD produce about 100hp and 14.5kgm or torque.......it does not make a lot of power, (this would be explain better with a torque curve)......... so usually in order to make up AWD cars has lower final drive ratio in the final drive even all the gear ratios are simliar with 2wd brethrans........more torque is need to drive the AWD drive train for daily usage rite..... so the engine needed to be working harder in order to move the car, which ends up FC ++ situation.......

anyway about the tyre surface thing, drag is about the same for 4wd or 2wd car as long as it has 4 wheels, but weight does kill on FC here........... tyre are meant to provide low rolling resistance while maintaining sufficient side and some forward grip for control and speed..........

but accelerating make a different story > 4wd accelerate better and does need more torque to get all of the 4 wheels tyre surface to break surface grip to move......... 2wd car just need to move 2 while the other 2 merely mean for supporting.......rolling resistance is rather low..........

Thanks for all the replies. Very good info. Understooded now.

but the best about 4x4.....more traction control.

This law not the Newton First Law lai de meh?