AWD drivetrain loss

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.

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.

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

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.

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

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.

all :worshippy Igovert!

all :worshippy Igovert!



^ what he said :werd:

^:1:

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

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.

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)

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.

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....................

Well I knew I was setting myself up the second I said the word physics :biggrin:
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.

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

funny, i've had the opposite effects. whiile racing a ls1 trans am, with just exhaust, i completely realed him in at 135mph and was 2 car lengths ahead by 150.

and also 3rd gear seems to be the strongest gear for me.

we do have diff gearing and this is may be the difference

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....................



I dont see what exactly you mean with "loose the most only at the very beginnings". Since most of the power is lost at high revs. When youre at say 5000 rpm and you set go of the gas, you will see the rpms drop quickly suggesting that a lof of power is being lost somewhere. When youre at 1500 rpm however you wont see the rpms drop as quickly. Thus the whole concept of using the engine to slow down.

The more power the engine makes, the higher the amount that is lost will be. I'm not too sure about how the whole % thing works, so the % might go down or stay the same (ill have to think a bit more about that). However in no case can you say that you will lose a set amount of power no matter how much power the engine produces. Like saying that once you have lost 80 or 100 hp, you wont lose anymore.

Oh and i'm pretty sure that the precentage for fwd & rwd is around 15% or 16%.

not to sound like an a-hole, but your not making sense to me

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.

cheers. i was wondering that, given the current discussing on what causes drivetrain loss, if it would be better to switch to FWD rather than RWD given that this apparently has less loss?

ive seem numerous GTR's with a 2WD/AWD switch and i was just wondering why no one has thought of trying it in a 3kgt if they want to get good 1/4 mile times.

Fabrication is probably the answer, but that is an interesting concept. The downside of FWD is a complete lack of traction as you probably knew. But having a switch like that is a pretty interesting concept...it would add more weight to our cars, which of course isn't the most desirable thing...but I wonder if this would be possible.

but with the added weight do you think it would make much difference?

surely the switch woulldnt weight more than a kilo.

im not sure of this as i havent driven a high powered FWD car before. At what speed does traction not become an issue? i imagine it would be hard to get wheelspin in 4th gear even if the car is running on FWD or even 3rd. I would have thought that after the car has launched that it wouldnt need the AWD. or would 2nd gear still have problems? though that is a guess as im not lucky/rich enough to own a GTO myself to find out.

or would that 2%(approx) sacrifice of drivetrain loss be worth it to have it switched to RWD?

And given that skylines have it done i imagine that it wouldnt be too hard to do it on a 3kgt. but i have no idea what the switch would turn off/disconnect to stop power going to one set of wheels.

and at the same time, what about the handling. fwd instead of awd or rwd.

it doesn't sound like its for me, but it does sound interesting :)

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.


lol, look closer, i was talking about myself, but thanks for the support :p

i agree with what igovert said too, i just wanted to go off an my little rant about drive train loss % being flat acroos the board. i seem to hear people say things like "wow my car has 600 hp to the wheels so i must be making 800 at the crank" and i seriously doubt it, more like 700 probably.

as far as the switch goes, it can be done, anything can be done, but it would be real hard and real expensive. i think even though fwd has less drive train loss, most would prefer to switch to rwd after a launch but it would probably be easier to "diable" the one drive shaft rather than the two axels. then again, say you unattached everything connected to the transmition from the back (for example, you somehow unattach the driveshaft on the transmition side and let it spin freely, this being a very hard task by itself) you would STILL be wasteing almost as much energy because the back wheels would still be connected to everything and to get them to spin (from the power delivered at the front) you would have them spinning the driveshaft etc.

********* DAMN a 360 modena just drove by my window and it sounded sweet!!! it just cruzed by about 25 feet away, no other cars by it so i could hear and see it perfectly :) **************

anyway back to what i was saying lol. all in all, i think it would be very very hard to pull off and cost a whole lot and would really not be worth it in the long run. you would also want awd on corners as someone mentioned so you would want a "smart" system rather than a switch unless you were only concerned about drag racing. anyway, just my .02

well we almost got a nickel i cause i second that