AWD vs RWD

S

solekeeper

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South Fla.
Besides the obvious here, I wanted to know which is faster if you had 2 cars with the same horsepower. Preferably 2 FX's one rear, one all wheel. I've heard being AWD, you will still lose some power.. I dont completely understand this too much and was wondering if you guys could provide some input... thanks!
 
you loose horsepower through the awd, it may take the drivetrain 45hp to spin a rwd while it may take 65 to spin the awd as a rough estimate, so you will have less available at the wheels. only time a 4wd would win would be in situations of low traction, the 2wd will loose more hp to wheelspin than the awd would
 
turbocad6 said:
situations of low traction
Click to expand...

If the FX35 came with 500 bhp, the AWD version would undoubtedly be faster as traction would always be an issue.

Since the FX35 is heavy and has 280 bhp, traction is rarely an issue (except in cases like you were alluding to such as snow or rain) and the RWD is undoubtedly faster.

The losses you're having a hard time grasping is the rotational mass of the drivetrain. Think of it like this... if you have two 45-pound plates on either side of a bar that's resting, let's say on a bench press, that's generally a 225 pound bar bell (assuming the standard 45 pound bar). Now if you spin this, your forearms will get a work-out.

Now put four 45-pound plates on either side and you have a 405 pound bar bell. Resting on the bench, this thing will be much harder to spin.

Likewise, your crank has to spin twice as much wheel weight, and slightly more rotating mass in the front axles and gears in the awd transfer case.

Back to the FX... Infiniti slightly makes up for these losses by changing the gearing. The AWD FX35 has I believe 3.69 final and the RWD has 3.3?

The shorter gearing in the AWD version improves acceleration.

(edited for spelling error)
 
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The awd will launch off the line much better than the rwd. The rwd will have to play catch up
 
Seeing is believing bro, take a look @ the track day vids, doc, ken & Bert kill me off the line. I know you're next arguement will be its my driving. So to that I'm gonna tell you to look at the vid of bert sleeping @ the light. Or go check out the vids I posted of the Syclones.
 
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the 18's are 35 lb's vs the 20's at 41. I think the 18" tire will be a few lb's heavier than a 20" tire in many cases so the 18"s are not going to be significantly lighter really... if light weight is a priority then aftermarket 3 piece wheels will be your best option, my 20's are almost 10lb's less each than the factory 18's...

I also want to get my rotora front brakes back on as the fx50 brakes I have on there now, the rotors are very heavy... the rotora's with there 2 piece design & aluminum hat is a big + in the rotating mass equation, stock 18's are not really the hot ticket for light weight wheels really...
 
doesn't the FX awd have the computerized system where it engages only when necessary so that it would have the efficiency of a rwd and launch traction capabilities of a awd.....

at least thats how it works in a murano.....
 
yeah, but, even when the front wheels aren't engaged, the transfer case is still in the drivetrain & it still takes hp to spin it weather it's directing power to the fronts too or just the rear. no matter how you look at it 4wd drivetrain will use more hp than 2wd & result in less available to the wheels...
 
it varies how much power it diverts to the front... it is rear biased so it will under normal conditions divert all power to the rear, but, it's still in the drivetrain so it still takes it's toll... & yeah, it does not transfer power to the fronts at higher speeds unless there is slip. it can divert 10%, 20%, 30%, 40% or up to 50% of the torque to the front wheels on demand & as conditions dictate...

when I first got my fx I kinda wished t was rwd instead of awd for performance reasons, but that's because I considered the awd setup to be similar to say a Yukon or a Tahoe or a 4 runner or something... now, after driving my fx a little over a year through many different conditions I am more satisfied that it is awd, it's not so much like a truck awd, it's more like an Audi quattro awd instead.

I drive fast & even in the rain I like to push it to see where it's limits are. the only car till now that I have been able to really go full speed in the pouring rain in the left lane where there can be huge spots of standing water was a v8 quattro that I had.. it was very stable even going through standing water in the left lane while under throttle... it may have hydroplaned a little, but it was very controllable & stable feeling, it reminded me of a jet ski, I mean when you hit heavy standing water in the left you just had to steer right slightly to compensate... there aren't too many cars that can do that, some cars will want to suck you into the guardrail or throw you around to the point of it not being stable, predictable & safe... well, the fx is like the quattro in that regard, it is very stable under power through standing water in the rain even at high speeds & under throttle... yeah, a lot of this is Dependant on the tires too, but the way the drivetrain transfers power to the wheels is also a factor when under throttle, the fx awd is a sick system & it works well when pushed to it's limits...

the added weight & the added drag of the transfer case will def make an awd a bit slower than a rwd in ideal conditions, but in less than ideal conditions the awd can def have the edge...
 
i read somewhere that the 2WD is like 300 lbs. lighter?? also has better weight distribution. still handles like an SUV to me though. i've scared myself a couple times already midturn. i still havent really got the feel for it yet, but i'd have to say it handles a bit better than the sled. BB
 
To chime in slightly OT, one poster suggested the weight difference between 18's and 20's. Weight difference is only nominal when comparing wheel sizes. The 18's will have less rotational inertia since the weight is distributed closer to the hub compared to the 20s.

A simple example of this is to take two 5 pound weights and hold them in your hands with outstretched arms...then try to spin in a circle. Take the same weights and put them in your pocket. Keep your arms outstretched, it will still take less effort to spin even though you're maintaining the same radius.

Just had to add my $.02.
 
true, but once you get rolling, you should have less resistance & greater momentum to add upon, . . so where is the breaking point from one theory being more beneficial than the other for acceleration. Someone wanna break out the calc?
 
gto-dave said:
true, but once you get rolling, you should have less resistance & greater momentum to add upon, . . so where is the breaking point from one theory being more beneficial than the other for acceleration. Someone wanna break out the calc?
Click to expand...

Dave, are you saying the 18's, or lighter wheel, will be better for acceleration from a dead stop...compared to the 20's will help make up the difference on the top end due to greater momentum?
 
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