[KevRyd]

I agree, I am a little defensive if you take just this post into consideration, however the issue with this poster goes beyond this thread. These are trolling jabs to provoke a response. I will take your advice and not take the bait in the future.

I appreciate your post, my contention is that the controls of the care do a great job of eliminating negitive charactoristics for both AWD and RWD.

Kevin

Originally Posted by drob23

I think you're getting a little too defensive here, I don't read this as Elk attacking your car. What he's saying is a simple statement of physics regarding the tractive limits of the front wheels in a turn.

I don't think you'd argue that the engine generates more than enough torque on the F30 RWD to spin the wheels on a sharp turn in a low gear. So by deductive reasoning, xdrive will move drive torque to the front wheels in the same situation, which by definition will make the car understeer more if you are at the limits of the tires.

I think you're getting too hung up on the word "understeer", just because the car has more understeer doesn't make it inferior, it just changes the relative handling characteristics which might be less pleasant to certain people.

There are 3 basic ingredients that determine the handling characteristics - (1) suspension geometry/setup; (2) weight distribution; (3) drivetrain. Changing each in one way or another WILL change the oversteer/understeer characteristics, which are defined quantitatively relative to a "neutral" curve. A car can understeer slightly, or greatly, and can change depending on various vehicle inputs/states.

I can understand that you don't really care about the technical details of what all this means, but at least acknowledge that statements of physics are *facts", but how they are interpreted/feel might vary from driver to driver. A guy with a RR Porsche might hate driving a 50/50 BMW....YMMV

[Stan876]

Originally Posted by drob23

I think you're getting a little too defensive here, I don't read this as Elk attacking your car. What he's saying is a simple statement of physics regarding the tractive limits of the front wheels in a turn.

I don't think you'd argue that the engine generates more than enough torque on the F30 RWD to spin the wheels on a sharp turn in a low gear. So by deductive reasoning, xdrive will move drive torque to the front wheels in the same situation, which by definition will make the car understeer more if you are at the limits of the tires.

I think you're getting too hung up on the word "understeer", just because the car has more understeer doesn't make it inferior, it just changes the relative handling characteristics which might be less pleasant to certain people.

There are 3 basic ingredients that determine the handling characteristics - (1) suspension geometry/setup; (2) weight distribution; (3) drivetrain. Changing each in one way or another WILL change the oversteer/understeer characteristics, which are defined quantitatively relative to a "neutral" curve. A car can understeer slightly, or greatly, and can change depending on various vehicle inputs/states.

I can understand that you don't really care about the technical details of what all this means, but at least acknowledge that statements of physics are *facts", but how they are interpreted/feel might vary from driver to driver. A guy with a RR Porsche might hate driving a 50/50 BMW....YMMV

Sorry but you have kind of contradicted yourself what you have said is that if you go beyond the limits of the rear tires then the car will understeer which is different to the point being made by Kev who is saying that even driven up to the limits the car does not understeer just because it can put power through the front axle. The adaptive reacts in a tenth of a second so it will not oversteer or understeer until its past the limits of both axles when you will probably be in a full 4 wheel slide beautifully balanced slide into the undergrowth.

[drob23]

Originally Posted by Stan876

Sorry but you have kind of contradicted yourself what you have said is that if you go beyond the limits of the rear tires then the car will understeer

???

[300hp]

Guys you can come up with all sorts of logical explanations you want, the reality is the 335i xdrive DOES NOT understeer. The experts have already said the RWD 335i and the S4 understeer. I would challenge you to look for any expert who says the xdrive F30 understeers. If anything MT said the xdrive oversteers.

Let it rest.

[drob23]

Originally Posted by 300hp

Guys you can come up with all sorts of logical explanations you want, the reality is the 335i xdrive DOES NOT understeer. The experts have already said the RWD 335i and the S4 understeer. I would challenge you to look for any expert who says the xdrive F30 understeers. If anything MT said the xdrive oversteers.

Let it rest.

Wait, so you're saying the 335i has more understeer than the xdrive version does?!? Dude...you gotta stop taking motor trend reviews as the holy gospel.

[300hp]

Originally Posted by drob23

Wait, so you're saying the 335i has more understeer than the xdrive version does?!? Dude...you gotta stop taking motor trend reviews as the holy gospel.

MT does not observe understeer, BMW states that with xdrive they made an attempt to ensure the car does not exhibit any understeer.

Each source seems to be corroborating the other. That's where I stand.

Why would MT/CD/RT lie about any of this stuff?

It just gets boring seeing the same arguments being made to support the thesis that F30 xdrive's understeers when per the experts this is not the case.

[drob23]

Quote me where Motor trend says the car doesn't understeer. All I see is

Kong noted that the BMW "feels ready to oversteer."

I also see in the suspension section

Oddly, the BMW features the laziest handling here.

Adding all that AWD hardware sure didn't help the 335ix out.

Its ride was the softest of the group.

If the first quote is your support that "the reality is the 335i xdrive DOES NOT understeer" then I'll tap out of this argument now.

[300hp]

Originally Posted by drob23

Quote me where Motor trend says the car doesn't understeer. All I see is

Kong noted that the BMW "feels ready to oversteer."

I also see in the suspension section

Oddly, the BMW features the laziest handling here.

Adding all that AWD hardware sure didn't help the 335ix out.

Its ride was the softest of the group.

If the first quote is your support that "the reality is the 335i xdrive DOES NOT understeer" then I'll tap out of this argument now.

Originally Posted by 300hp

Guys you can come up with all sorts of logical explanations you want, the reality is the 335i xdrive DOES NOT understeer. The experts have already said the RWD 335i and the S4 understeer. I would challenge you to look for any expert who says the xdrive F30 understeers. If anything MT said the xdrive oversteers.

Let it rest.

Oversteer is not the same as understeer (see my original post that I have reposted here)

Yes the handling is lazy, the ATS has the best handling of the bunch

I don't see any reference to understeer, do you?

[drob23]

Originally Posted by 300hp

Oversteer is not the same as understeer

Yes the handling is lazy

I don't see any reference to understeer, do you?

Oversteer and underteer are opposites, you can't have both, so the first statement indeed would support your claim.

http://en.wikipedia.org/wiki/Understeer_and_oversteer


Where do you see anything to the tune of

"We at MT have concluded that the 335ix does not exhibit understeer"

The lack of evidence to support a claim one way or another does not imply the claim is true/false.

[300hp]

Originally Posted by drob23

Oversteer and underteer are opposites, you can't have both, so the first statement indeed would support your claim.

http://en.wikipedia.org/wiki/Understeer_and_oversteer


Where do you see anything to the tune of

"We at MT have concluded that the 335ix does not exhibit understeer"

The lack of evidence to support a claim one way or another does not imply the claim is true/false.

I think the bold part is all we need to end this. The rest is just pure speculation.

[NISFAN]

Interesting.........it is well understood that the lighter engined 328i exhibits less under-steer than it's heavier engined 335i brother........

........yet there is amazement that 95kg's of mainly front mounted AWD equipment should make an F30 exhibit more under-steer.

[RPM90]

Originally Posted by Stan876

Regarding the understeer issue i think that it will probably be similar on the two wheel drive and 4 wheel drive cars. The electronics should transfer the drive as soon as they detect slip from the front wheels. It is true though that most modern mass produced cars have some understeer built in to give the numpties enough warning to prevent them crashing and i totally understand why they do it. As i said i did not feel any noticeable understeer but i was not on the limit and i am sure it raises its ugly head before the limit is reached.

However, with stability control being implemented even in lower priced cars, the idea that there MUST be under steer to "protect" the driving public has long past it's validity.
Stability control can easily help correct any over steer that a driver may induce when the system is on.

If the system is off, well then, the driver did it for a reason and must then WANT some neutral handling or a bit of power over steer.
Electronic assistance should allow makers of performance oriented cars to tune without the need to PUT IN under steer, imo.

[RPM90]

Originally Posted by BruceOmega

I would be interested in seeing a comparison of two F30 335i's that are identically equipped except for one variable - RWD versus BMW's implementation of AWD on the F30. For example, two 335i MSport cars, one RWD and the other xDrive, where they both have the same wheels and tires, DHP, and Sport AT.

Would like to see a comparison of lap times / figure 8 times. Don't recall ever seeing anything like this.

Bruce

Would be great to see.

Of the bat my money is on the RWD.
Why?
Because historically BMW's AWD has not done as well as the RWD spec.
X drive offers advantage off the line, but for handling not so much.

I do have an open mind though and would love to see if BMW did achieve better handling out of the new 3 using X drive.
If they did, then their whole RWD handling supremacy goes out the proverbial tailpipe.

[drob23]

Originally Posted by RPM90

However, with stability control being implemented even in lower priced cars, the idea that there MUST be under steer to "protect" the driving public has long past it's validity.
Stability control can easily help correct any over steer that a driver may induce when the system is on.

If the system is off, well then, the driver did it for a reason and must then WANT some neutral handling or a bit of power over steer.
Electronic assistance should allow makers of performance oriented cars to tune without the need to PUT IN under steer, imo.

There's a large difference between a BMW 3er and a Ford Fusion. I've spoken to some suspension engineers and the majority of mass produced cars on the road are designed to understeer just based on passive suspension geometry. The simple reality is most drivers don't have limit handling training and by the time they swerve a car to avoid a deer it might be too late for the TSC. Although roll-stability control is pretty impressive on SUV's, but that's not the same as the steering behavior.

On the other end of the spectrum is the corvette, which someone told me (albeit in jest) was the most "unsafe" car on the road based on how easily the car can break out and fishtail. In that case TSC probably has quite a large work load

[NISFAN]

Originally Posted by drob23

There's a large difference between a BMW 3er and a Ford Fusion. I've spoken to some suspension engineers and the majority of mass produced cars on the road are designed to understeer just based on passive suspension geometry. The simple reality is most drivers don't have limit handling training and by the time they swerve a car to avoid a deer it might be too late for the TSC. Although roll-stability control is pretty impressive on SUV's, but that's not the same as the steering behavior.

On the other end of the spectrum is the corvette, which someone told me (albeit in jest) was the most "unsafe" car on the road based on how easily the car can break out and fishtail. In that case TSC probably has quite a large work load

Agreed, ASC can't react to some situations for example pendulum effect.

[Stan876]

Originally Posted by drob23

???

You said

"I don't think you'd argue that the engine generates more than enough torque on the F30 RWD to spin the wheels on a sharp turn in a low gear. So by deductive reasoning, xdrive will move drive torque to the front wheels in the same situation, which by definition will make the car understeer more if you are at the limits of the tires."

Sorry saying you contradicted yourself was the wrong description I should have said your argument makes no sense. The electronics detect the slip from both ends and balance it out in a fraction of a second. The car isn't going to oversteer for a bit then understeer for a bit like some old tractor with very worn steering so saying that rear tyre slip causes understeer is not a valid statement IMO.

[Stan876]

Originally Posted by NISFAN

Interesting.........it is well understood that the lighter engined 328i exhibits less under-steer than it's heavier engined 335i brother........

........yet there is amazement that 95kg's of mainly front mounted AWD equipment should make an F30 exhibit more under-steer.

Is there any published data about the xdrive under steering or is it all anecdotal that's a genuine question not a dig by the way. I know there is an extra 100kg but its not a lot in the scheme of things and its very low slung weight as well. I appreciate any weight increases lateral force which does not help but it would be less detrimental surely than having a average sized passenger sat up in the seat. Have you driven one in anger and experienced understeer or for that matter have you seen the understeer some have mentioned in the RWD car.

[drob23]

Originally Posted by Stan876

You said

"I don't think you'd argue that the engine generates more than enough torque on the F30 RWD to spin the wheels on a sharp turn in a low gear. So by deductive reasoning, xdrive will move drive torque to the front wheels in the same situation, which by definition will make the car understeer more if you are at the limits of the tires."

Sorry saying you contradicted yourself was the wrong description I should have said your argument makes no sense. The electronics detect the slip from both ends and balance it out in a fraction of a second. The car isn't going to oversteer for a bit then understeer for a bit like some old tractor with very worn steering so saying that rear tyre slip causes understeer is not a valid statement IMO.

No, you are not understanding. The rear wheels brake out ----> xdrive routes torque to front wheels -----> less lateral grip for front wheels that steer the car ----> understeer. I am saying that the xdrive car understeers RELATIVE to the RWD setup. The RWD would spin out the rear tires and the back-end would slide out and you would have power induced oversteer. Once the tires are spinning the contact patch essentially becomes a hockey puck and lateral grip no longer exists. I'm not saying that one is optimal to the other, maybe you don't want the rear tires to brake out, so understeer is desired if you want to be faster

Your interpretation that the "fraction of a second controller balances out the car during oversteer or understeer" sounds like marketing dribble to me. There is no conceivable scenario where an AWD car can induce oversteer relative to the RWD car, like Elk said, go look at the friction circle.

[Stan876]

Playing devils advocate a bit can I ask another question. If the extra weight of the Xdrive system promotes understeer does that mean that in the 330/ 335 with that big lump of engine in the front surely they must understeer like crazy compared to the 320D xdrive.

[NISFAN]

Originally Posted by Stan876

Is there any published data about the xdrive under steering or is it all anecdotal that's a genuine question not a dig by the way. I know there is an extra 100kg but its not a lot in the scheme of things and its very low slung weight as well. I appreciate any weight increases lateral force which does not help but it would be less detrimental surely than having a average sized passenger sat up in the seat. Have you driven one in anger and experienced understeer or for that matter have you seen the understeer some have mentioned in the RWD car.

100kg is not a lot? ...seriously? The 330d is about that heavier than a 320d and you can for sure feel it. Much more under-steer mid corner.

I have driven just about every F30 engine combo and you can definitely feel the difference in handling between the 4 pot and 6 pot engines. Night and day is how I would describe it.

I haven't driven an xDrive, but 100kg in the front half of the car IS absolutely going to make a difference to the handling. True it will be something you get a feel for straight away and become 'normal', but it will be present.

[NISFAN]

Originally Posted by Stan876

Playing devils advocate a bit can I ask another question. If the extra weight of the Xdrive system promotes understeer does that mean that in the 330/ 335 with that big lump of engine in the front surely they must understeer like crazy compared to the 320D xdrive.

Yes they do, but unlike xDrive they have power to make up on the straight bits

[Stan876]

Originally Posted by drob23

No, you are not understanding. The rear wheels brake out ----> xdrive routes torque to front wheels -----> less lateral grip for front wheels that steer the car ----> understeer. I am saying that the xdrive car understeers RELATIVE to the RWD setup. The RWD would spin out the rear tires and the back-end would slide out and you would have power induced oversteer. Once the tires are spinning the contact patch essentially becomes a hockey puck and lateral grip no longer exists. I'm not saying that one is optimal to the other, maybe you don't want the rear tires to brake out, so understeer is desired if you want to be faster

Your interpretation that the "fraction of a second controller balances out the car during oversteer or understeer" sounds like marketing dribble to me. There is no conceivable scenario where an AWD car can induce oversteer relative to the RWD car, like Elk said, go look at the friction circle.

The electronics wont allow understeer like they wont allow oversteer there is no difference in the measurement of the slip that brings the traction control into action (the electronics don't completely eliminate either admittedly) your friction circle principal only holds water when there are no electronics interfering to stop the torque overpowering the front wheels again your argument does not stand up and as for marketing dribble you will find that sensors have come on quite a lot in the last few years ones capable of doing this job on both axles are a few pound to buy and yes they work in fractions of a second.