AWD drivetrain loss

[Yaggus]

I was wondering what actually causes AWD cars to have more drivetrain loss than RWD or FWD cars.

obviously its because it has to spread the power between 4 wheels instead of 2. but i was wondering if you installed a 2WD swith if that would eliminate the loss. so you could get an AWD launch but change over to RWD once you get going.

just a thawt.

[YogsVR4]

You hit the nail on the head. More power is lost getting to all four wheels.

Yeah - the best of both worlds would be to have the AWD for launch and then RWD after the car reaches a certain speed. I don't know how practicle it would be, but it sounds cool.

[sLADe781]

I know this may be a dumb question....but when you guys speak of drivetrain loss, what exactly does that mean? ;o/

[Cro]

Originally Posted by sLADe781

I know this may be a dumb question....but when you guys speak of drivetrain loss, what exactly does that mean? ;o/

losing parts of the drivetrain....

but no, theyre talking about the power that is lost between the crank or flywheel and the wheels.

[sLADe781]

Oh okay....so is that like due to friction or what causes drivetrain losss?

[Igovert500]

Essentially anytime you hear of a hp rating, they are rating the engine, aka flywheel hp. However, what is important is how much of that hp gets delivered to the wheels. Horsepower is a kind of energy, I don't know how much you remember/know physics, but maybe this will help.
The engine's hp is like potential energy...the vr4 has 320, yet due to the circumstances of the real world...ie, friction, resistance, inertia, and all that junk, a fraction of the potential energy is lost throughout all the parts that connect the engine to the wheels...that energy has to get the driveshaft moving, the gears in the rear differential moving, and all those parts that go to the 4 wheels...and then it has to get those 4 wheels turning. So alot of power is wasted/lost in getting those parts to overcome inertia and start rotating, or rotate faster. The left over energy, that actually makes it to the wheels and that is transmitted to the pavement to get the entire car in motion is kinetic energy, or whp(wheel hp, aka bhp brake hp...hp the brakes would need to overcome to bring it to a stop)
Because AWD has 4 wheels to get in motion, not to mention our damn chrome wheels are quite heavy, so much energy is wasted in getting all this extra mass into rotation. Whereas a civic(FWD), or Supra(RWD) only have 2 wheels to get going. Hence we get amazing traction, yet it becomes our downfall around 100mph, because all this power is being channeled to 4 wheels, instead of just 2.

I hope I explained that well enough...it's been 4 years since physics.

[Musashi3000GT]

all Igovert!

[Italian Lunaticz]

Originally Posted by Musashi3000GT

all Igovert!

^ what he said

[sLADe781]

^

[Cro]

Sounds good except that hp isn't energy.
Its the rate at which energy is used.

[Hotshot8792]

one more thing to add, FWD has a less drivetrain loss than RWD because the FWD cars are directly connected to the tranny, where as the RWD has to go through the rear gears and differential, more moving parts, so a slightly greater loss.

[ikOnone]

unless the engine is in the back

but also, another point is that the energy is not lost, it is just converted from friction into heat and through various other methods. energy is neither created or lost unless it is converted into mass or vice versa through nuclear reactions.

what i think is a common misconception (and complete bull) is the universal 25% drivetrain loss figure that everyone allways quotes about our (AWD) cars. i would be much more willing to believe that you lose about 80 hp stock and 100 hp for a 600 hp (at flywheel) car. not 25% all the way around. i would believe a little more with more power but come on, 25% across the board... where does all that extra energy go then? true, hp is not energy but you know what i mean. so do you really think that a car with 600 hp at the flywheel only gets 450 to the wheels? i would guess a lot closer to 500. where would that extra 70 hp loss over stock go?

i remember gt-pro was building drag pro's engine and they were going to run it on an engine dyno as well as a wheel dyno to see what the loss really was but we all know how they are at producing results. (i know, i know, it is a customer car, i should not be so hard on them)

[ikOnone]

that first comment sounded dumb though lol. i have never heard of a car with an engine in the back that was FWD. but it COULD happen lol.

[youngvr4]

he meant if the engine is in the back the rwd wouldn't have less loss.

another thing is, i agree with pretty much every thing my buddy igovert500 said exept.

the loss of drivetrain logically imo, is that you loose the most only at the very beginnings. for instance, if your going 60 and downshift, you can dang near feel the lag from the jump because of the more parts bieng moved and the transfer bieng to all wheels instead of just 2. once it gets going i honestly don't see the loss. at speed as hotshot was saying fwd is closer to the tranny well our front and rear are getting power so, once your moving the diff in loss is basically nothing. and this is something that i not only think, but i feel it from driving a rwd vette to a awd vr4.
and after 100mph, i just dont see were we slow down at or loose any kind of speed, if anything that seems like our good point, not only is it more stable at high speeds because of awd but our gearing does wonders.
and last, drivetrain loss is overated, its really, really not that bad.


responses....................

[Igovert500]

Well I knew I was setting myself up the second I said the word physics
but thanks for clearing it up.

young, I definantly agree that while driving you really don't notice slowing down at higher speeds, but I've watched plenty of supras or ls1s or mustang cobras just come back with a vengance in 3rd gear. I guess it could be gearing...but I seriously think that it is the AWD hurting us. I love it, and do think drivetrain loss is overrated, but it is something to consider.

Ikonone, I've always heard 25% stock, but the number goes down as the car is modded, pretty much just like you said. I forget where I read that, probably on 3si, but I've never heard 25% across the board no matter what. I think your absolutely correct, and that would have been amazing if gtpro had actually produced some numbers for comparison.