E46 M3 or M coupe or M Roadster?

[mPlasticDesign]

Originally Posted by Dammmittt

This statement is pure stupidity. You should be embarrassed. But then again, you don't know any better.

Are you sure? I Wikied this info on Cd/Kg/lbs per ft/lb.... It even came with a diagram. We all eat crow today!

[Dammmittt]

huh?

I understand that you're making fun of him but I don't get the crow reference.

[mPlasticDesign]

Originally Posted by Dammmittt

huh?

I understand that you're making fun of him but I don't get the crow reference.

SARCASM! Just trying to lighten the mood.

[DiscoZ]

Actually, I never insulted anyone. I simply stated that throwing a blanket *wrong* on most parts of a post and then putting a slapping smiley was idiotic behaviour. Which it is - with someone you don't know. Secondly, it is an insult.

As for being wrong, I simply stated kg over an area. Can you please tell me how that is wrong for measurement over an area?
If I am wrong elsewhere, please let me know - although I don't think this will happen. You are full of empty threats (about your supposed qualifications) and insults - you have effectively painted yourself into a corner.

That is all.

I need not have a pissing contest on the internet, I am far too old for that. In response to qualifications, I am not an enginner (my fiancee is) - however, I work with financial mathematics all day since I am in Investment Banking - and yes, I have a bachelors, a MBA (from a top 10 school)... and a few other charters in additon to more work experience than you have engineering schooling. I didn't want to bring it up as I don't want to sound like a braggart. There was no malice in my original post and I responded to the smack smiley which I felt was rude for someone you don't know.

Please tell me why my statement is pure stupidity. You keep referring to how stupid it is, yet you do not prove it wrong. Please do so. By now, you have likely realised that fuel economy is a consideration and have become conveniently quiet about it - choosing instead, to attack my choice of unit. Classic straw man.

So, unless you post anything worth refuting (i.e. a thesis that PROVES me wrong, and I know you can't), I will ignore you, as one does with indignant children. I never started this, but I am ending it now.

P.S. I don't think damnit (great name) or his buddy metak ever really understood what I meant, instead they typed away furiously, their hands quivering... proving their internet thugness. I really have wasted too much time on this.

[AtoB]

[Dammmittt]

Originally Posted by DiscoZ

Actually, I never insulted anyone. I simply stated that throwing a blanket *wrong* on most parts of a post and then putting a slapping smiley was idiotic behaviour. Which it is - with someone you don't know. Secondly, it is an insult.

As for being wrong, I simply stated kg over an area. Can you please tell me how that is wrong for measurement over an area?
If I am wrong elsewhere, please let me know - although I don't think this will happen. You are full of empty threats (about your supposed qualifications) and insults - you have effectively painted yourself into a corner.

That is all.

I need not have a pissing contest on the internet, I am far too old for that. In response to qualifications, I am not an enginner (my fiancee is) - however, I work with financial mathematics all day since I am in Investment Banking - and yes, I have a bachelors, a MBA (from a top 10 school)... and a few other charters in additon to more work experience than you have engineering schooling. I didn't want to bring it up as I don't want to sound like a braggart. There was no malice in my original post and I responded to the smack smiley which I felt was rude for someone you don't know.

Please tell me why my statement is pure stupidity. You keep referring to how stupid it is, yet you do not prove it wrong. Please do so. By now, you have likely realised that fuel economy is a consideration and have become conveniently quiet about it - choosing instead, to attack my choice of unit. Classic straw man.

So, unless you post anything worth refuting (i.e. a thesis that PROVES me wrong, and I know you can't), I will ignore you, as one does with indignant children. I never started this, but I am ending it now.

P.S. I don't think damnit (great name) or his buddy metak ever really understood what I meant, instead they typed away furiously, their hands quivering... proving their internet thugness. I really have wasted too much time on this.

I do suppose I was a little hard on you.

So...I'll try to end the night on a happy note...

When I first read your posts...I thought, this is some kid who thinks he knows everything, so I'll try to make him feel bad for sticking his nose where it doesn't belong...

In retrospective...I was probably a jackass for doing that but life goes on...

So, I'll make it up to you slightly...If you're that interested I can compute drag data all day long based on the available information...which is enough for an estimate albeit a rough estimate and tell you how I do it if you're that interested. But I think as I've stated over and over again, that the textual/ conceptual in the data in the threadshould be enough. The Z4M will have an edge, how much of edge would depend on some detailed schematics of both cars, that just aren't available to those of us without a job in the ///M division.

Since it's late and I'm tired I'm not going to go into the whole where you were wrong issue too much...But as far as the units are concerned I'll say this. kg is a unit of mass. Period. All matter has density, from air, to water to trees...everything. The density of the material you're looking at multiplied by the volume it encompasses is mass. Now, if you want to look at force or pressure, that's the acceleration or change in momentum of mass (see Newton's laws)...and pressure is the integral over an area that the force is acting on. For fluids, normally you'll look at mass as mass flow, or mass*velocity*Area. Usually mass flow is for internal flow, so it's not something you think of for external flow...like drag on an object in a homogenuos fluid...such as a car driving down the highway/track whatever.

For a car...normally...Cd (which is the coefficient of drag per unit length) is determined by experimental wind tunnel tests. You can estimate it through CFD, but to get a real value, you need a wind tunnel and a car. A scale model will work just fine for this, provided you can isolate the viscous(friction) drag. Anywho, for this test, the Drag force can be measured one of two ways, either, by measuring pressure along the surface and integrating it, which can be a pain in the ass or by fixing the car to any number of instruments that'll measure the force in the X-direction from the affect of drag on the car. Now, this force will be the total Drag measured in Newtons. A total drag coefficient is normally denoted by C_D. Since auto manufactures list C_d as the drag coefficient, it means that this is the coefficient of drag per unit length (span) of the car. Which would be N/m or some other length unit...doesn't really matter, as long as the units are consistant.

So...it turns out that the drag force being felt can be transformed into a unit-free constant that has no dimensions...so that it will be good for any fluid that the object is immersed in. So, the car will actually have the same drag coefficient in air as it does in water...cool, huh?

So, where was I? Oh yeah, if you'll note, I didn't mention kg or mass anywhere in my drag discussion...so yeah, that's wrong. Here's wiki to tell you more if you really want to know...

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

So, I hope we can all just get along now. If you want to discuss it more, feel free to PM me. But I think we'll consider the war over for now.

Good night.

[RussRamz]

Originally Posted by DiscoZ

The lower the drag, the less fuel efficient the car will be on an equal basis(given that it has the torque to overcome the drag). Thus, if the MZ4 and the E46 M3 were of equal weight and equal size, then the E46 M3 would be faster up top, given it's lower Cd. However, the E46 M3 is 6% heavier than the MZ4, generally makes less whp, has more lbs per ft/lb of torque, and a larger frontal surface area - so these thoughts are all conjectures until someone does the math. In which case, even given the MZ4's 2% longer 6th gear (3% shorter 1st gear - effectively), it should be faster than the E46 M3 in any situation.

The drag force on either a MZ4 or M3 should not be significant in terms of kgs till 120kmph at the very least.

I believe your reversed on your drag/fuel efficiency statement. Reducing drag will only increase efficiency.

Torque doesn't overcome drag--power does. Torque is the feel of acceleration, but it will only apply while there is POWER to accomplish the acceleration. Believe it or not, with a tent pole long enough, I can apply 450 foot pounds of torque on a nut and did when I was a young helicopter mechanic many years ago. I am well under 1 hp.

Weight of the car will affect acceleration and top speed no matter what the forward velocity is. That weight applies a force on the tires which is--additional drag.

The total drag force on the car is a combination of the Cd (shape of the car) and the size of the car. You can have a car with a Cd or .00004, but if it's as big as the Empire State Building, it will still generate more drag than a little M3.

Nothing is free in life. I hope I am sincerely able to help clarify this a bit.

[Irish Bimmer]

Originally Posted by Hawkeye

It's all about preference... would you rather wear sweat pants and a sweat shirt or khakis and a button up?

Some people prefer to feel good while others prefer to look good.

Haha, awesome way to put it... I never liked the Z4 until the coupe came out... but again - its up to you...

[Dammmittt]

Originally Posted by RussRamz

I believe your reversed on your drag/fuel efficiency statement. Reducing drag will only increase efficiency.

Torque doesn't overcome drag--power does. Torque is the feel of acceleration, but it will only apply while there is POWER to accomplish the acceleration. Believe it or not, with a tent pole long enough, I can apply 450 foot pounds of torque on a nut and did when I was a young helicopter mechanic many years ago. I am well under 1 hp.

Weight of the car will affect acceleration and top speed no matter what the forward velocity is. That weight applies a force on the tires which is--additional drag.

The total drag force on the car is a combination of the Cd (shape of the car) and the size of the car. You can have a car with a Cd or .00004, but if it's as big as the Empire State Building, it will still generate more drag than a little M3.

Nothing is free in life. I hope I am sincerely able to help clarify this a bit.

You're mostly right, but I bolded out the comments that need more research my aviator brother.

[DiscoZ]

Cheer mate.

I used Kg as I did some quick googling and found an engineering page where the guy had computer different drag forces at varying speeds on a Honda Civic and had posted the results in kg (which, I knew from my college physics days was a unit of mass, but I checked around and it seemed to be ok to use in specific circumstances).

Then I asked my fiancee and she said I could express it in kg as long as it was acting upon an area and I got into the equation and it seemed algebrically possible (given the speed and conversion, etc). My initial assertion was that the Z4M would have a slight edge, but it's hard to tell.

Anyway, I appreciate the candor and I hate i-wars (and don't have the time for them either).

[DiscoZ]

Originally Posted by RussRamz

I believe your reversed on your drag/fuel efficiency statement. Reducing drag will only increase efficiency.

Appreciate the clarification, I made a typo there and corrected it in a subsequent post.

I get the torque/hp bit. However, hp is work done, right? HP is not multipled at the wheels, it is torque - as you mentioned in your 450 pole argument. So, wouldn't it be the torque that is accelerating? A = F/M (adjusted for other opposing forces, of course)? Perhaps someone else can clarify?

Cheers.

[ianbiz]

Roadster ftw.

[Dammmittt]

Originally Posted by DiscoZ

Cheer mate.

I used Kg as I did some quick googling and found an engineering page where the guy had computer different drag forces at varying speeds on a Honda Civic and had posted the results in kg (which, I knew from my college physics days was a unit of mass, but I checked around and it seemed to be ok to use in specific circumstances).

Then I asked my fiancee and she said I could express it in kg as long as it was acting upon an area and I got into the equation and it seemed algebrically possible (given the speed and conversion, etc). My initial assertion was that the Z4M would have a slight edge, but it's hard to tell.

Anyway, I appreciate the candor and I hate i-wars (and don't have the time for them either).

Seems odd that anyone would use kg for any type of drag or force analysis at all. Definately not the standard unless you're comparing to some sort of standard acceleration like gravity and have factored it out.

Originally Posted by DiscoZ

Appreciate the clarification, I made a typo there and corrected it in a subsequent post.

I get the torque/hp bit. However, hp is work done, right? HP is not multipled at the wheels, it is torque - as you mentioned in your 450 pole argument. So, wouldn't it be the torque that is accelerating? A = F/M (adjusted for other opposing forces, of course)? Perhaps someone else can clarify?

Cheers.

Torque is just a measure of leverage or "moment" and means nothing more than force * length.

Power is the ability to do work over time. (See Power and work for all the basics.) Basically the drag force does work on the car, and in order for the car to continue to accelerate it needs to over come the work being done on it. Think of it as an energy balance. The car moving at a certain velocity has kinetic and potential energy, and if the car is moving at a constant speed the gradient of work being done on it is the same as that of the kinetic and potential energy (See Lagrange) If the car needs to accelerate you need to increase the car's ability to do work on the fluid around it...which mean it neads more power...so that it can do work over time on the fluid...it's kinda complicated, but you gotta look at it in terms of energy rather than force on force.

This is basically why, cars with high torque can accelerate well up to about 30-40 mph when the drag force is low, but you need high hp to overcome the work the drag is doing on the car. So cars that have BOTH can attain high speeds and accelerate well at low speeds as well. Make sense?

[DiscoZ]

Ok... makes sense, I always thought that the torque made more of a difference in terms of drag (opposing force), compared to HP.

Have a couple of questions: if there are two cars with 290whp, both have the same aerodynamics and they both start accelerating in a speed contest from 50mph - drag limit. Which one will be faster (hand-grenade accuracy, just curious) given that:

A) Both weigh the same and car A has 220 lb/ft at the wheels and car B has 190?

b) Both have the same torque (220), but Car A weighs 200lbs less than car B?

[Dammmittt]

Good questions...at first glance...I'd say the following.

A. All other things being equal...same car same weight, different engines...I'd say the one with more torque would get there faster...but it might be the same...I'd have to do some math to be sure.

B. All things being equal aside from the weight..lighter car gets there faster. How much faster, would again be determined by the math. The only thing that might affect this is inertia of the car...the heavier car might be able to use it's inertia to its advantage.

But, I gotta run to class. Maybe later provided I don't get HW (either from class or the wife).

[vachss]

A friend of mine who raced pretty seriously for a while (national champion in his class for a couple of years) once told me that torque was for people who don't know how to shift. In other words, HP is really all that matters. It's just up to the driver to keep the motor near the HP peak. High torque just makes it easy to stomp on the gas and go without thinking about revs.

[rc'Z]

....which mean it neads more power, "neads"? Did some one also mention run on sentences and head aches?

[Dammmittt]

Originally Posted by rc'Z

....which mean it neads more power, "neads"? Did some one also mention run on sentences and head aches?

One typo. Thanks for noticing. I'll leave it there just for you!!!

[rc'Z]

Originally Posted by Dammmittt

One typo. Thanks for noticing. I'll leave it there just for you!!!

I always claim 'inadvertent clerical error' vs typo. But thanks for making my day anyhow, it doesn't take a lot.