4WD M5/4WD VS 2WD/Turbo VS N/A Thread

[MitchZ06]

Traction doesn't equal mechanical grip. Tires equal mechanical grip.

Tires is chemical grip, traction is mechanical grip (tho chemical grip comes into it too).

And thinking a FWD car is fun? Gee you must love torque steer....

 

[niky]

Tires is chemical grip, traction is mechanical grip (tho chemical grip comes into it too).

And thinking a FWD car is fun? Gee you must love torque steer....

Educate us... What chemical reaction takes place between the tire and the road?

Whatever you choose to call it, tire grip is mechanical grip, for purposes of discussion when differentiating it from aero grip... as it directly relates to mechanical friction between the tire and the road.

My post was in response to the assertion that drive traction enhances mechanical grip. Which it does not.

-

Yeah. I love understeer. Which is why I love non-M BMWs... Because they understeer worse than my lowly front wheel drive sedan on the racetrack...

Oh, wait, you meant torque steer? Can't relate. My LSD is set too loose.

 

[///M-Spec]

Tires is chemical grip, traction is mechanical grip (tho chemical grip comes into it too).

Tires produce grip through both mechanical and chemical means. The two types of grip combined equal the total grip performance of the tire and are not mutually exclusive.

From an engineering perspective traction and grip are the same thing. They both describe the amount of friction between two solid surfaces.

But in common colloquial usage, most people use 'grip' to describe the amount of lateral friction a tire produces (the kind you generate on a skid pad) and 'traction' to describe the amount of longitudinal friction available to cope with forces produced by the driveline (the kind you unleash with your right foot).

Given those common definitions, it is correct say AWD improves overall traction, because drive forces can be distributed across double the amount of surface area, but not grip. Overall grip is unrelated to how many tires are distributing drive forces.

Put another way, AWD would not improve your peak gs but can possibly increase your track out speeds because you can get on the throttle more aggressively. I say possibly because there are so many other variables.

Educate us... What chemical reaction takes place between the tire and the road?

Mechanical grip would be the friction created by the interface between the physical features of the rubber and road surface. Chemical grip would be the bond temporarily created at the molecular level between the rubber and the road.

His choice of wording is odd though and doesn't really bolster his argument.

BTW, niky, I haven't been around much lately. Congrats on your mod status; well deserved and overdue


M

 

[MitchZ06]

Educate us... What chemical reaction takes place between the tire and the road?

Its not a chemical reaction, its called chemical grip because it refers to the chemical compound of the tire (soft, medium or hard just to make it simple to understand). Theres so much involved in tire engineering the last time I spoke to a tire engineer about compounds and make ups of different tires he was working on I really felt like the dumbest person on the planet.

Whatever you choose to call it, tire grip is mechanical grip, for purposes of discussion when differentiating it from aero grip... as it directly relates to mechanical friction between the tire and the road.

Tire grip is not mechanical grip....and if you try keeping on with using it as the point of argument you're leading yourself and everyone else astray.

- Mechanical grip is the grip created by the chassis, suspension and driven axles.
- Chemical grip is the grip created by the contact between the tire and the road surface.
- Aerodynamic grip is the grip created by the downforce acting on the body of the vehicle.

My post was in response to the assertion that drive traction enhances mechanical grip. Which it does not.

Sorry, but it does enhance mechanical grip. Talk to any race car engineer and they'll say they'd be running AWD if the system didnt add extra weight to the car and is allowed under regulations (some series allow it, others dont).

Yeah. I love understeer. Which is why I love non-M BMWs... Because they understeer worse than my lowly front wheel drive sedan on the racetrack...

Oh, wait, you meant torque steer? Can't relate. My LSD is set too loose.

You'll get torque steer in a front wheel drive car if accelerating hard (and the car has enough power, 150hp is enough depending on the car) as it really has nothing to do with the LSD, you'll notice it from the tugging on the steering wheel when putting your foot down.

Care to argue the point further?

 

[niky]

@M-Spec: Thanks. Haven't seen you for a while.

Always had issues with the separation of mechanical and chemical grip. Friction is friction, right? No matter how small?

@Mitch: As M-Spec has said, tires do have mechanical grip, whether you like to believe so or not. Part of the reason race cars run gummy compounds is to ensure maximum adherence between the tire and the road.

Race engineers would love to use AWD not because of the enhancement of mechanical grip... No matter how many tires are driven, the amount of grip remains the same... but because distributing the power evenly across all four wheels means that no wheel is overwhelmed by the amount of power being put through it. In other words, AWD doesn't subtract as much from the grip when you put your boot down in the corner as 2WD does. But in steady-state cornering, the amount of mechanical grip available is exactly the same.

-

You get torque steer from front wheel drive partially due to the imbalance between unequal length halfshafts. You get similar in AWD, but the effect is understandably less pronounced. And you get it in rear-wheel drive, too... although you feel it more with your behind than through the steering wheel, since the rear tires aren't connected directly to the steering column.

That said, my car doesn't really torque steer appreciably. At higher torque inputs (which, on my naturally aspirated car, occur very high in the rev range), there is an effect, but thanks to good tires and an LSD, the torque tends to pull me into the turn rather than in some random direction. I've never had to wrestle to get my car through a corner, thank you.

Yes, torque steer is a pain in my other car (a diesel), but it doesn't detract from the fun. Handling purity? Yes. Fun? No.

 

[NLxAROSA]

get torque steer in a front wheel drive car if accelerating hard (and the car has enough power, 150hp is enough depending on the car) as it really has nothing to do with the LSD, you'll notice it from the tugging on the steering wheel when putting your foot down.

Not so much a matter of LSD rather than suspension/combination of the two. My Renault Megane III RS has no torque steer with 250hp/340Nm, even at full throttle, any gear. Though granted, I have never seen any FWD car with similar power pull that off.

 

[MitchZ06]

Not so much a matter of LSD rather than suspension/combination of the two. My Renault Megane III RS has no torque steer with 250hp/340Nm, even at full throttle, any gear. Though granted, I have never seen any FWD car with similar power pull that off.

That says it all, Renault has the hot hatch down pat.

 

[Bones Brigade]

The SVT Focus handles about as neutral as any car I've driven. My RWD experience is limited to Mustangs, Z's and Miatas, but I would still rate the SVT very highly. Given the age of the Miata chassis (all NA cars) and safe engineering baked into the Z, the Focus is right up there with them. Torque steer is really only a factor in a straight line. But it takes less work to hold the 170hp straight as it does the 280 of a Z.

 

[Eric.]

Fun fact: There are two Google hits for "chemical grip" relevant to tires. You're looking at one of them.

 

[MitchZ06]

Fun fact: There are two Google hits for "chemical grip" relevant to tires. You're looking at one of them.

And the other is on the technical subforum of Autosport talking about Formula 1....

 

[C-ZETA]

Which one? The new one? I doubt the new TT V8 sounds as good as the old manic V10.

I meant the last one that was on sale, the V10. Because of the new 4WD it won't be able to slide as much and you won't be able to hear the full revs of the V8 while driving the thing.

 

[MitchZ06]

I meant the last one that was on sale, the V10. Because of the new 4WD it won't be able to slide as much and you won't be able to hear the full revs of the V8 while driving the thing.

Any AWD car can get sideways....you've just gotta try. And you wont be able to hear the V8? WTF

 

[Eric.]

Coefficient of friction is a physical property, not a chemical one. Grip is friction. What I found regarding "chemical grip" online is just that "chemical grip" is considered to be how much grip a tire has due to how soft the rubber is, and the physical grip of a tire results from its construction such as sidewall stiffness, etc.


When you get down to it, all of a car's grip is mechanical grip. Aero grip results from downforce which is just more weight pressing down on the tires to make it possible for more friction before slipping. Before this thread, I've never heard the term "checmical grip".

 

[C-ZETA]

And you wont be able to hear the V8?

I mean you won't be able it hear it at full revs as often (while driving). And sliding, if you manage to pull it off in a 4WD car would be shorter than it would be in a RWD most of the time.

 

[MitchZ06]

I mean you won't be able it hear it at full revs as often (while driving).

Why?

And sliding, if you manage to pull it off in a 4WD car would be shorter than it would be in a RWD most of the time.

Tell that to Ken Block, Jeremy Clarkson, etc.

 

[C-ZETA]

Why?
Tell that to Ken Block, Jeremy Clarkson, etc.

Because you won't be sliding as long and therefore won't get to rev it up as much through corners.

And Ken Block is an expert. Most of us aren't. Although Jeremy Clarkson isn't really one but even so he's done it enough times with a million cars that we haven't driven.

 

[MitchZ06]

I was asking why you wont hear it at full revs while driving (like you said), not drifting....

 

[C-ZETA]

I was asking why you wont hear it at full revs while driving (like you said), not drifting....

I meant full revs as in past the redline BTW...

 

[MitchZ06]

Question stands, why?

 

[C-ZETA]

Question stands, why?

Of course you'll be able to hear them while 'driving' (because you don't count drifting as driving) and I didn't just say 'won't'. I said 'won't as often'.

If you mean before the redline then obviously you would. If you mean beyond it, then that'll be harder I think without a manual since slides won't occur as often with all the extra grip. Obviously the exception is when you just rev it up, which is not 'driving' in any shape or form.

 

[MitchZ06]

you won't be able to hear the full revs of the V8 while driving the thing.

I got the gist from that that you mean driving (as in on the street) not while drifting. You did say won't too not 'won't as often'.....Your starting to lose me man, what your saying is getting hard to follow.

 

[C-ZETA]

You did say won't too not 'won't as often'.....Your starting to lose me man, what your saying is getting hard to follow.

I was mentioning my other post after you quoted that one, I kind of forgot about how this all started.

So for everyone's assistance, let me rephrase everything I've said.

The new 4WD system will have more grip than the RWD so sliding will be less occurent and harder, and when you do get into a slide, it will probably be shorter. Therefore, you won't be able to rev it up through corners as often, which was a strong point of the RWD M5 where you could wheel spin out of corners and listen to the epic sound of the V10.

 

[Eric.]

In other words, it'll be faster.

Case closed, make an AWD one.

 

[Clark]

I've never understood why something needs to be faster to be better. They're not racing cars they're about enjoyment. Otherwise everybody would drive Radicals.

 

[MatskiMonk]

I've never understood why something needs to be faster to be better. They're not racing cars they're about enjoyment. Otherwise everybody would drive Radicals.

I blame the interwebz, fan bois only speak in numbers..

 

[Eric.]

I never knew I was a BMW fanboi.

 

[MatskiMonk]

I never knew I was a BMW fanboi.

Well nobodies perfect... welcome to the club

Actually, my comment wasn't particularly directed at you, simply a possible answer to Duffers question.

 

[Eric.]

I mean its only natural for a high performance luxury sedan to increase in...*drumroll*...performance and luxury.

 

[///M-Spec]

@M-Spec: Thanks. Haven't seen you for a while.

I duck in and out these days, mostly lurking. Bought NFS Shift 2 a few weeks ago, the (little) time I spend here these days is in that subforum.

Always had issues with the separation of mechanical and chemical grip. Friction is friction, right? No matter how small?

Aye, friction is friction. I think the only people for whom the distinction between mechanical and chemical grip truly matters is a tire engineer. And not just any, but specifically the guys who sweat over the compounds. Chemical grip makes mechanical grip possible, so at the end of the day, its all mechanical grip, like Eric. said previously.

As for the original topic at hand, ie, the M5, I can only say that some people are afraid of change. Maybe its because they can't see the forest for the trees and are stuck in a philosophical comfort-zone where arbitrary details are what defines something for them, rather than seeing the big picture.

The primary mission of the M5 has always been to carry four people and their things in comfort over vast distances at blazing speeds. How fast and how comfortable has always been subject to the prevailing expectations of the day, not some chiseled in stone edict about engine configuration or drive wheels.

I don't know about the GT-R, but I'd wager the AWD version of the car will be ultimately quicker on a track than the RWD version. RWD M5 will probably have the advantage in top speed and fuel econ...

(just realized I said fuel econ and M5 in the same sentence, lolz.)

I've never understood why something needs to be faster to be better. They're not racing cars they're about enjoyment. Otherwise everybody would drive Radicals.

Some people enjoy going faster than X, whatever X may be. It is human nature to want more than what we already have and cars are a natural expression of this. While I don't necessarily subscribe to that creedo personally (for a daily driven street car, objective performance has diminishing returns), I don't see anything inherently wrong with it.

I mean its only natural for a high performance luxury sedan to increase in...*drumroll*...performance and luxury.

Too much sense-making in that post, Eric. Knock it off.


M

 

[E28]

If it was part time 4WD that could be switched off for sideways idiocy, would that please everyone?