[T Bone]

Originally Posted by elucas730

For starters, it's in the article on the new xDrive system posted by catdog in post 53.

So you really have no data or any evidence. The article states the starting condition is 40:60 F:R with the ability in the cars to vary torque 100:0 and 0:100.

Have a read at this:

http://www.worldcarfans.com/2050714....l-drive-system

You will not see a document where it states the front wheels shut off because BMW is trying to convince everyone it is a permanent system. You can read between the lines, i.e. the benefits of AWD but without the burdens.

Also another hint is Xdrive is tied to DSC. DSC also shuts off at extreme speeds.


"xDrive in the BMW 3 Series is both innovative and convincing: Benefiting from the system’s inherent intelligence, the driver uses the advantages of four drive wheels whenever they really count. And at the same time the in­telli­gent system avoids the disadvantages of conventional all-wheel drive, the 3 Series with xDrive offering virtually the same agility and dynamic performance under everyday driving conditions as a 3 Series with rear-wheel drive."

[elucas730]

Originally Posted by T Bone

So you really have no data or any evidence. The article states the starting condition is 40:60 F:R with the ability in the cars to vary torque 100:0 and 0:100.

Have a read at this:

http://www.worldcarfans.com/2050714....l-drive-system

You will not see a document where it states the front wheels shut off because BMW is trying to convince everyone it is a permanent system. You can read between the lines, i.e. the benefits of AWD but without the burdens.

Also another hint is Xdrive is tied to DSC. DSC also shuts off at extreme speeds.


"xDrive in the BMW 3 Series is both innovative and convincing: Benefiting from the system’s inherent intelligence, the driver uses the advantages of four drive wheels whenever they really count. And at the same time the in*telli*gent system avoids the disadvantages of conventional all-wheel drive, the 3 Series with xDrive offering virtually the same agility and dynamic performance under everyday driving conditions as a 3 Series with rear-wheel drive."

From your article:

And when driving straight ahead under normal conditions, xDrive in general splits up drive power between the front and rear axles in a 40:60 ratio, thus maintaining that typical BMW style of rear-wheel drive and power.

It says it right there. Driving straight, no wheel slippage, you are sending power both front and back, leading to larger drivetrain losses than on a RWD car. There is no evidence that the xDrive goes 0:100 at "high speeds" (whatever 'high speed' means). All evidence points to the xi models having a 'normal' 40/60 power split.

[T Bone]

Originally Posted by elucas730

From your article:


It says it right there. Driving straight, no wheel slippage, you are sending power both front and back, leading to larger drivetrain losses than on a RWD car. There is no evidence that the xDrive goes 0:100 at "high speeds" (whatever 'high speed' means). All evidence points to the xi models having a 'normal' 40/60 power split.

Except fuel economy figures, dealer information and a document that I read at some point.

Here's a test, see if a regular RWD 335i pulls away from an 335XI from a roll. There will be a little difference because of the weight but the XI system will shut off.

If the front wheels don't cut off, the XI will have serious drivetrain losses and the RWD will walk it. You willing to bet on it?

[elucas730]

Originally Posted by T Bone

Except fuel economy figures, dealer information and a document that I read at some point.

Here's a test, see if a regular RWD 335i pulls away from an 335XI from a roll. There will be a little difference because of the weight but the XI system will shut off.

If the front wheels don't cut off, the XI will have serious drivetrain losses and the RWD will walk it. You willing to bet on it?

Too many variables, which is why I earlier suggested having two people with stock cars go to a dyno on the same day. Takes out most of the variability. I'm going to guess that the AWD version will show 10-15 less whp.

I'm also wondering if all this talk about torque split is the same exact thing we had with the STis. The STi has a "Driver Controlled Center Differential" (DCCD). There is a little knob on the center console that can be adjusted up or down to change the torque bias. At least, that is how Subaru kinda marketed it and that is how a lot of people think of it as. But that's not what it is at all. You can't change the torque bias one bit. What you can change is the lockup ratio. I suspect that that is the same thing we are talking about here - changing the lockup ratio, not the torque split. The difference between the Subaru and the BMW is that once set in the Subaru, that's where it stays, while the BMW's computer's can vary the lockup ratio infinitely.

The good folks at NASIOC can explain it much better than I can: http://forums.nasioc.com/forums/show....php?t=1281101 see post #6

[Rips335iCoupe]

During a normal high speed run, xdrive will be at 40/60 ratio ... no cutting off front.

[ward]

Originally Posted by bnj

What might be RWD 60' times with those wider DRs in the rain?

I don't think you're supposed to drag race in the rain......

[Chowbow]

Enough technical specs and who cares if it turns to RWD at high speeds. Let's see some ACTUAL numbers. Somebody go to the strip already and rail out some 1.6x's!

[vs60r]

I really don't care if it's true or not regarding the cutoff, how many people here do daily highway passes (or even rolling starts) at 111MPH? That's what 180KPH works out to be. That's beyond the top speed of Procede 1.45 1/4 mile runs... So all that talk is irelevant 99% of time...

Stock for stock, given equal drivers, 335i with sports will out run/corner an XI on a race track because it has sports package and weight saving, except for the initial start. Without sports, the two will perform almost the same to 99.9% of drivers... I know that's not what the thread starter cared about since he was going to upgrade anyways, but all this argument is silly since real world physics still count...

RWD and new AWD differs in driving dynamics, it's a given. What AWD provides is still what AWD provided from day one, easier/more forgiving driving for your 99% drivers on the road as a daily driver.

Performance/racing wise, once you start modding, both cars will be so similar as to make any argument moot...

Frankly if there weren't an additional 4 month wait for the XI, I would have gotten it since I live in NE.

[T Bone]

Originally Posted by elucas730

Too many variables, which is why I earlier suggested having two people with stock cars go to a dyno on the same day. Takes out most of the variability. I'm going to guess that the AWD version will show 10-15 less whp.

I'm also wondering if all this talk about torque split is the same exact thing we had with the STis. The STi has a "Driver Controlled Center Differential" (DCCD). There is a little knob on the center console that can be adjusted up or down to change the torque bias. At least, that is how Subaru kinda marketed it and that is how a lot of people think of it as. But that's not what it is at all. You can't change the torque bias one bit. What you can change is the lockup ratio. I suspect that that is the same thing we are talking about here - changing the lockup ratio, not the torque split. The difference between the Subaru and the BMW is that once set in the Subaru, that's where it stays, while the BMW's computer's can vary the lockup ratio infinitely.

The good folks at NASIOC can explain it much better than I can: http://forums.nasioc.com/forums/show....php?t=1281101 see post #6

A think 3 rolling runs with the same variables will definitely show whether the fronts cut out or not. The results will be dramatic if AWD stays engaged.

[elucas730]

Originally Posted by T Bone

A think 3 rolling runs with the same variables will definitely show whether the fronts cut out or not. The results will be dramatic if AWD stays engaged.

I'm not stopping you from doing it, so if you want to, go right ahead. I'd rather see dyno numbers myself. Then there will be no question.

[e36jakeo]

Originally Posted by bnj

What causes the traction deficit in accelerating the car is too much power for the wheel considering the traction coefficient. Now if you direct the power via multiple wheels, the power will be less per wheel and the traction will be lost later. Where this is NOT necessary is at straight line (high speed). It IS beneficial in curves and at low speed (also in straight line).

Capability of a 4wd car is just amazing because of its ability to get grip a tad better than RWD.

I remember even 996 Porsche was faster in 4wd form than in RWD when tested. And Porsche is traditionally RWD and not front engine car. Front engine cars have weight distribution more front biased than Porsche and thus are able to get more grip through their front wheels. The Porsche test was in TV by Top Gear. The difference was not huge.

I am very pleased with my RWD 335. (xi was not in the market, and if I'm in a hurry I can take my fast A to B AWD car ) But dissing xi does not make sense. My 4wd car is almost 20 years old, but still some car mags claim it to be the best handling car ever built. It's classic (World Rally Champion 6 times in the row) and all "best handling" claims are subjective. But there is nothing wrong in 4wd handling. E.g. if driving Mitsu EVO, you notice that it is very fast in the curves. Sport Auto just had a comparison test of EVO, STI and 335i. Evo was rated the best and to be the best driver's car. And this was in dry tarmac. Have some rain, snow, gravel, whatever dirt in the pavement and there is no need to even have this discussion.

I am not dissing AWD, just giving my personal preferance. I have an E36 M3 track car with race suspension, fancy diff, cams, etc. My buddy has an Evo XIII with race suspension, reflash (340 BHP) and front and rear LSDs. His car turns ridiculous times at Nor Cal tracks due to a great driver, excellent handling, and about 60 more HP and torque than the M3. But we both agree the M3's handling is consierably better than the very well set up Evo because of the RWD separation of steering and power and BMW's amazing E36 chassis (BTW, he is about 0.5 seconds faster per lap than the M3).

I am not saying you CAN'T set up AWD to handle very well, but the at-the-limit nature will never be as balanced because when you ask the front tires to corner at the limit AND steer it will usually ultimately understeer. So you have to set up the car very aggressively with an oversteering nature that is corrected with throttle to make it neutal. Essentially you are "fixing" the inherant understeer this way. This can be very fast on a track, but no stock AWD car is going to be set up like this on the street (too dangerous off throttle for novice drivers).

So my bias towards RWD has to do with balance, feel, and the ability to do doughnuts and smokey-burnout uturns! AWD can be amazing, and what owners of the Xis have said about how great the handling is has peaked my interest.

TIme for a test drive!

[bnj]

Originally Posted by e36jakeo

I am not dissing AWD, just giving my personal preferance. I have an E36 M3 track car with race suspension, fancy diff, cams, etc. My buddy has an Evo XIII with race suspension, reflash (340 BHP) and front and rear LSDs. His car turns ridiculous times at Nor Cal tracks due to a great driver, excellent handling, and about 60 more HP and torque than the M3. But we both agree the M3's handling is consierably better than the very well set up Evo because of the RWD separation of steering and power and BMW's amazing E36 chassis (BTW, he is about 0.5 seconds faster per lap than the M3).

I am not saying you CAN'T set up AWD to handle very well, but the at-the-limit nature will never be as balanced because when you ask the front tires to corner at the limit AND steer it will usually ultimately understeer. So you have to set up the car very aggressively with an oversteering nature that is corrected with throttle to make it neutal. Essentially you are "fixing" the inherant understeer this way. This can be very fast on a track, but no stock AWD car is going to be set up like this on the street (too dangerous off throttle for novice drivers).

So my bias towards RWD has to do with balance, feel, and the ability to do doughnuts and smokey-burnout uturns! AWD can be amazing, and what owners of the Xis have said about how great the handling is has peaked my interest.

TIme for a test drive!

E36 M3 is a great track car. It was still light enough.

I agree with you totally. Rwd handles extremely well. What is phenomenal in AWD is the grip by which you an e.g. use full throttle a bit earlier out from the corner and you are still able to steer the car forward in the road. And yes, at the limit it is more demanding and even with having experience with AWD it takes a lot more to drive it to its full potential. Thus at the limit rwd is more controllable, while AWD tries to have a mind of its own. You can say that being "more controllable" is what is "handling". Then Rwd has better handling. On the other hand if one thinks "handling" is "making wonders using the grip", AWD has a great handling.

Talking about my AWD, having some turbo lag complicates the things further. Assume a corner, let's say we are on gravel, understeer, the car pushes towards the curve and then seemingly straight out, you apply throttle, wait through the lag and see the fast approaching ditch in front of you, all four wheels are spinning of which none of them has a good grip alone and the car is impossible to steer for a short while, finally the thrust takes place, oversteer takes over and the thrust throws you along the curve keeping you at the track and catapulting you out of the curve at an unbelievable speed. Scary. Since you thought ending up in the ditch cannot be avoided. But with experience also enjoyment for being able to control the beast that seems to have a mind of its own. And extremely fast if you got the guts and don’t lift the throttle (which would get you to the bottom of the ditch). Then again my RWD Bmw is under control all the time, which is just great. Best of both worlds..

Btw awd car you can spin at its place without moving. If you want to turn 180 degrees, the turning circle is the length of the car Just lock the steering at one end and drop the glutch. (Preferably at somewhat slippery ground to prevent any damage.) Nice in between the cool RWD doughnuts

[catdog]

Integrale, thank you for the words of wisdom. I think tey are different driving experiences and for myself, this is a second car and daily driver so it's perfect for all weather with a nice engine and AWD; i have a RWD for a different dynamic when i want. Nonetheless, i think people are treating the xi and xdrive in bmw specifically unfairly because people on this forum are mostly rwd users/modders and or have previous AWD in more estblished platforms i.e. wrx/evo/quattro. It kind of detracts from the 335xi for what it is, a 335i with no traction issues and handling to explore that is diffferent from the excellent bmw RWD although mind you not so excellent without lsd. Had the 335i been offered with an lsd from the factory then it would have been a really tough choice. Seeing how adding a few HP/Tq with a JB stage 2 has transformed the car, i am very happy to have gone with the xi, it's the perfect compromise for me at this point.

[e36jakeo]

Originally Posted by bnj

E36 M3 is a great track car. It was still light enough.

I agree with you totally. Rwd handles extremely well. What is phenomenal in AWD is the grip by which you an e.g. use full throttle a bit earlier out from the corner and you are still able to steer the car forward in the road. And yes, at the limit it is more demanding and even with having experience with AWD it takes a lot more to drive it to its full potential. Thus at the limit rwd is more controllable, while AWD tries to have a mind of its own. You can say that being "more controllable" is what is "handling". Then Rwd has better handling. On the other hand if one thinks "handling" is "making wonders using the grip", AWD has a great handling.

Talking about my AWD, having some turbo lag complicates the things further. Assume a corner, let's say we are on gravel, understeer, the car pushes towards the curve and then seemingly straight out, you apply throttle, wait through the lag and see the fast approaching ditch in front of you, all four wheels are spinning of which none of them has a good grip alone and the car is impossible to steer for a short while, finally the thrust takes place, oversteer takes over and the thrust throws you along the curve keeping you at the track and catapulting you out of the curve at an unbelievable speed. Scary. Since you thought ending up in the ditch cannot be avoided. But with experience also enjoyment for being able to control the beast that seems to have a mind of its own. And extremely fast if you got the guts and don’t lift the throttle (which would get you to the bottom of the ditch). Then again my RWD Bmw is under control all the time, which is just great. Best of both worlds..

Btw awd car you can spin at its place without moving. If you want to turn 180 degrees, the turning circle is the length of the car Just lock the steering at one end and drop the glutch. (Preferably at somewhat slippery ground to prevent any damage.) Nice in between the cool RWD doughnuts

Great points, bnj! I am jealous that you have rallied - that is something I have yet to do but would love to!

Racing is a crazy thing. For a novice it is MUCH easier to get the most out of AWD because if you get in trouble, flooring it will bring you out of an oversteering situation and save the day. However, once you become an "expert" driver able to turn laps within a second or two of the car's real potential AWD does seem MORE difficult to drive (esp with turbo). The significant lift-throttle oversteer, and slight throttle delay due to the turbo spool, in my buddies Evo makes it trickier than I would have thought. Meanwhile eeking out all the available traction in the M3 is much easier.

The GPS data logger told the whole story of our laps. My exit speeds were consistently faster due to a bit less weight and the amazing variable ramp diff that allow you to modulate the amount of rear-end drift. But after that the Evo would quickly hit higher speeds on the straights due to its major torque and HP advantage.

Time to switch to stickier rubber