rdenis
6/3/2007 9:19:44 AM
Uhhm, I don't think MB is speaking based on "his own theories". He happens to know the mechanics inside out for a very good reason. His whole point is there is no actual difference between 4WD and 2WD mechanical load. As he rightly states, there is no significant difference in fuel economy under identical test conditions.
However, here is MY theory on why there may be a perceptible difference for a lot of people:
1) People believe they have two different systems, 2WD and 4WD with most people believing from past history and knowledge of 4WD systems that there is additional load.
2) Because people believe there are two different systems they instinctively select 2WD for most "normal" driving and 4WD for when environmental conditions warrant. These conditions typically contribute more to the poorer fuel economy not the drive system.
3) Older 4WD systems were perceived to have noticeably less power than 2WD so driving habits are affected as well - i.e. more lead foot syndrome.
4) Mitsu's statement in the owners manual that you will experience better fuel economy in 2WD I think has more to do with Mitsu understanding the consumer's built in habits and mindset, at the present time. Perhaps they should have considered something like:
"We at Mitsubishi understand that you as the consumer do not have the capability to understand new technology. Even though we have built one of the most technologically advanced all wheel drive systems in the world, we have given you the option of shutting down the rear wheel drive system to satisfy your ignorance rather than expecting your pea-sized brain to rationalize how a vehicle could get the same fuel economy and ride in 4WD versus 2WD. However, because you are a loyal customer we will agree that in certain conditions, you may experience better fuel economy in 2WD versus 4WD. For example, if you drive in 2WD when it is a cool summer day you will likely experience better fuel economy then when you drive in 4WD in the middle of a blizzard in December. Another example would be, if you drive in 2WD at 55mph for one hour you will likely experience better fuel economy then if you drive in 4WD at 80mph for one hour. At Mitsubishi, we care. Even though we have some really smart engineers, you can be rest assured we always try to adhere to the laws of physics." 
BoldlyGoingNowhere
6/3/2007 5:56:42 PM
I have a question, doesnt running it in 4WD lock generate more heat and possibly damage the transfer asm running 70mph on the freeway?
I have a 93 Chevy 4x4 I know it will damage the 4WD with extended driving on dry pavement. I know the newer systems are different but basically my Chevy is turning the entire time but when 4WD is engaged it actuates a large solenoid that moves the drive to the front axle. I do notice a difference in performance however to burn enough gas to know mileage dif I havent been able to but I can tell from engine RPMs that it is using more gas.
rcpax
6/4/2007 7:34:25 AM
That's right. Mitsu doesn't recommend 4WD Lock mode on dry pavement. But they speak more of tire wear than mechanical damage. I'm pretty sure the mechanical stress on the transmission is going to be high. And that's why on dry tarmac I drive 2WD always, especially in twisty areas.
BoldlyGoingNowhere
6/4/2007 4:01:32 PM
Actually in the twisties we have here, low speed 10-15 mph and super tight the 4WD makes the handling even more superb in fact it rocks. It latches into the turn and flies.
The roads are so bad I have to take them easy on the sport bike but in the outie I get to really enjoy them.
If you want to have some interesting fun and can handle a vehicle slightly out of control take off the traction control and put it in 2WD it squeals the tires and slides around in the gravel thats piled in the road.
Manybrews
6/4/2007 5:15:49 PM
Manybrews
6/4/2007 5:24:55 PM
quote:
1) People believe they have two different systems, 2WD and 4WD with most people believing from past history and knowledge of 4WD systems that there is additional load.
exactly. this is NOT a "shift on the fly" 4WD system. this is an AWD system with a computer controlled clutch. The more amperage sent to the clutch, the less it slips. At a certain amperage, it slips no more (until its maximum torque is reached, and I have no idea what that is.. Im sure its will into the thousands of ft/pounds, though.).
the componants are always in motion. The clutch just determines the amount of torque transferred from the propshaft (being spun by the transfer case) to the rear differential/axles (being spun by the tires).
No amperage = no transfer of power. Like reving your car engine in nuetral.
quote:
2) Because people believe there are two different systems they instinctively select 2WD for most "normal" driving and 4WD for when environmental conditions warrant. These conditions typically contribute more to the poorer fuel economy not the drive system.
quite possible. I did think of one potential therory, though.. its POSSIBLE that the transfer of torque through the propshaft and rear differential is LESS efficient than through the front tires. So instead of 100 percent going to the front wheels with a lesser degree of parasitic loss, 50 percent (or whatever the ECM decides) of the power will go to the rear, but suffer a slightly larger loss of energy. As such, the engine will need to create more torque equal to the percentage of parasitic loss associated with torque transfer though the rear. Friction losses dont change, but energy losses may.
quote:
3) Older 4WD systems were perceived to have noticeably less power than 2WD so driving habits are affected as well - i.e. more lead foot syndrome.
really, that could just be the case.
BoldlyGoingNowhere
6/4/2007 8:40:55 PM
rtrackr99
6/5/2007 3:28:28 AM
Hey Manybrews!
You're a "Good Sport"!
But I still believe that the difference in MPG exists!
