It's all about mu
 

G isn't useful for understanding handling balance. Technically, g isn't even applicable as it is the acceleration of Earth's gravity which works only in a vertical plane. Certainly, when figuring out what's happening at each end of a car g is a pretty useless concept.

It's all about mu. Specifically static mu. Which is surprisingly constant for these purposes. Accident investigators successfully use assumed mu as well as experimentally measured mu.

The key to understanding how handling works is to understand mu.

Mu is the same for all four contact patches. In theory, all four contact patches develop the same frictional force for a given vertical loading. Size of the contact patch is not significant.

How a vehicle uses that total force determines how it handles.

Slip angle results from mu. The distortion of the tire exhibited as slip angle is the reason static mu is the only relevant factor unless and until the car is overdriven and slides. Kinetic mu is markedly lower than static mu, and, kinetic mu has nothing to do with slip angle. Only while the contact patch grips the road statically does the tire produce slip angle forces. Once the grip is lost, slip angles decrease as does total traction and cornering grip.

This is why oversteering cars are slower, they reach kinetic mu earlier than cars which understeer.

Technically, a car stops oversteering when the tires begin to slide. A sliding car also cannot understeer, by definition. It doesn't matter which end of the car slides, as soon as at least one axle slides then the car is technically skidding and going slower than it could if it were to return to static mu conditions.

Because mu is a constant and identical for all four tires (one reason you must never mix tires) all four tires have the potential to develop the same grip. Axle weight distribution isn't as important as people think because total force is proportional to vertical load. Total grip varies but so does the loading the grip is required to deal with. This is why lighter people don't slip and fall any more readily than heavier people. Were mu not a constant the world would be a weird place.

The more driving force you put through the drive wheel contact patches the less grip is available for cornering. The more powerful a car is the more it must be set up to understeer to be fast.

Mu on snow and ice is generally low. In fact it makes a big difference which it is. Driving on snow does not engage the mu between the rubber and the snow it engages internal mu in the snow layers. Mu on ice does engage the mu of the tread rubber. Tread design is critical for both surfaces but entirely different.

A car that is balanced on snow or ice will be well balanced on wet or dry pavement. A car that handles well on dry or wet pavement may not be so good on ice or snow.

Why?

The answer lies in the mu.

Now you know.

µ*

Hm... Thanks?

I'm having a hard time understanding what you're trying to convey. You're saying lateral acceleration using "G" as a base of measurement is absurd, instead we should be measuring the friction of the tire?

And how does tire friction (size of contact patch apparently irrelevant) magically tell us how well a car handles?

By definition I thought understeer was simply when the car doesn't turn or yaw in the direction of the turn and simply pushes toward the outside of said turn, whether the front or rear tires are under, at, or beyond optimal slip angle is completely irrelevant. For instance, a typical FWD car plowing into a turn, front tires sliding well past slip angle, is THE definition of understeer.

Also if axle loading isn't important, then by your logic a pickup truck should handle just as well as a Mazda RX8 because it has the same tire on all four axles....

Op for president of Canada.

I think he's trying to say that he got the wrong tires on the wrong car for his winter driving surroundings.

If a problem can be solved by money, then it's not a problem.

And this all brings me to one conclusion: bullshit baffles brains.

Just when I thought you couldn't be dumber...

There is far too many things fundamentally wrong with what you're saying, so here we go (again).

You clearly didn't take any physics classes I see... G is a widely accepted unit of measurement used to measure acceleration forces. The only relation to gravity is that 1G is the same acceleration force applied to an object by gravity. It's the same thing as using BAR to measure air pressure, 1bar is atmospheric pressure.

You are the ONLY person I've ever seen try to argue that G isn't applicable to anything except vertical acceleration. That shouldn't surprise me though, you're the only person trying to argue most things you argue.

source: http://wordnetweb.princeton.edu/perl/webwn?s=g-force

This is quite possibly the worst over simplification I've ever seen in my life. You're assuming that weight doesn't shift around in a corner (it does), that the tires stay flat at all times (they don't) and that heat held by each tire doesn't affect mu (it does).

No, wrong again. A car that is understeering broke traction at the front before the rear, a car that is oversteering broke traction at the rear before the front. Both could have broken traction at the exact same point in the turn.

Technically, you're wrong again, by definition. Understeer (by the real definition) is when the yaw angle of a car is less than it should be for the given steering input, if you want to talk slip angles it is when the front wheels are at a higher slip angle than the rears. Oversteer is when the yaw angle of the car is greater than it should be for a given steering input, relating to slip angles it's when the rear tires are at a greater slip angle than the fronts. It's actually impossible to be under or oversteering without one end of the car sliding.

I'll agree on the first part, but the second part is flat out wrong again. In your magical world that would mean a car like a Ferrari 458 would have to be an understeering nightmare to put power down, but it's not even close. That's why to PROPERLY drive fast you have to balance braking/throttle inputs with steering inputs. If you just floor it mid corner while at maximum cornering force any RWD car is going to spin, regardless of how much it naturally understeers off power.

You really can't wrap your head around the difference between a chassis that oversteers off power and power oversteer, can you? I'll make it VERY simple for you.

If you enter a corner coasting and the car wants to spin that's power off oversteer, if it wants to push that's power off understeer.

If the car is neutral off power it's VERY easy to predict if it will under or over steer under too much power. Is it RWD (or rear biased AWD), it'll oversteer. Is it FWD (or front biased AWD), it'll understeer.

It doesn't matter how well the chassis is set up, if you can't drive properly it will ALWAYS slide under power.

Remember when you tried to bring up the friction circle? If you actually understood them you would also understand that the key to maximizing grip is that you're always balancing lateral and forward grip. Entering a corner you're hard on the brakes while going straight, then as you start to feed in steering you're backing off the brakes until you're at the apex, at which point you start to release the steering angle and feed in power. You can't be at full braking and full steering angle or full power and full steering angle, there simply isn't enough grip available for that unless you're driving WAY below the limits.

And the single biggest flaw with what you're saying, mu is actually a really useless number to bring up when talking about chassis balance since it is, like you said, constant on all four tires. A different mu will change the ultimate grip provided, but it's not going to change the chassis balance at the limit at all.

I hadn't checked this site since I put my car away for the winter, my first day back...

And all I see is you braying about the same thing as you were in November. Either you're complete rubbish at explaining yourself to an entire forum full of people, or nobody cares what you have to say. Teacher or troll, you've lost your audience.

Time to get a new schtick or move on.

Actually, the grip tires have with pavement is not entirely Newtonian.

Asphalt is not smooth for the same reason that rubber makes a good tire. The rubber forms to the pits of the asphalt aggregate. In physics, this is called conjoined surfaces. It's the reason why a larger contact patch can allow for more traction.

If the physics of a road tire was as Suberman says, we'd all be running on skinny little tires because it classic Newtonian physics, pressure and mu dictate the amount of force transferred normal to the force (of gravity in the car example). However, drag cars, and most race cars that put the majority of their rear tires run a staggered (wider rear than front tire)

It's also the major reason why lighter cars corner harder than heavier cars, why roll bars work etc. etc. etc.

What Suberman said above is purely academic, dumbed down "Magic physics world" BS, that doesn't really explain anything about how our cars work and doesn't prove why an understeering car would actually be better (even though it isn't).


Suberman.... if you are really desparate for so much more understeer, why don't you just go out and put the front tire pressure up to 40-45psi, and drop the rears to 28psi or something to achieve maybe a 30-31psi operating temp?

I've blocked Suberman so that I don't have to read his BS in other threads... but I just feel the need to make sure Canadians specifically aren't reading his non-sensical tirade against the 86's, and spewing of miss-information on a forum dedicated to cars.

Moderators: Please change thread title to "It's All About Me" LOL

Hi Everyone,

This is my first post here so I figure I should introduce myself. My name is Sean. Last year I finished my masters in mechanical engineering studying vehicle dynamics and tire modelling. I have attached my thesis for the curious reader and to hopefully have somebody actually read the damn thing since I spent 2 years developing it! I have been participating in grassroots racing for nearly 10 years driving a wide variety of cars including a Hyundai accent, Toyota mr2 Spyder, Toyota Celica GT4, Mazda Rx-7 and now the BRZ.

I would certainly not say I am an expert, but I do have some insight on this topic and after reading several posts from suberman I would like to clarify some of the false information.

First I would like to make something abundantly clear

THE COEFFICIENT OF FRICTION IS NOT CONSTANT UNDER ANY CIRCUMSTANCES!

The effective coefficient of friction for a given tire is a function of not only temperature, pressure, age, and road conditions, but most importantly normal load. That's right the coefficient of friction is dependent on the normal load

MuFn = Ft
Where, Mu f(T,P,t,Fn)

Where Mu = coefficient of friction, T = temperature, P = Pressure, t = time, Fn = Normal load, and Ft = Tire lateral force

I have attached a typical plot of lateral tire force response as a function of slip angle. Each line represents a different normal load. starting at a normal load of 200 Newtons and incrementing by 200 Newtons up to 1000 Newtons. (The maximum normal load is relatively low because this is a 13" FSAE tire)

Several things can be determined from this plot.

1) The peak lateral tire grip occurs at a different slip angle depending on normal load
2) The reduction in performance after the tire is fully saturated is more dramatic at higher normal loads
3) The increase in lateral grip with increased normal loads is a situation of diminishing returns. This is most easily seen by looking at the right side of the graph after each tire has saturated, but this is also true when comparing the peak lateral force at each normal load.

The third point is very critical and is the reason roll bar tuning allows for the designer to change the balance of the vehicle between oversteer and understeer.

As the vehicle corners, weight is transferred from the inside tires to the outside tires due to the roll moment generated at the center of gravity. Now if the coefficient of friction were the same than it wouldn't matter how much weight transferred since the sum of the lateral grip between the left and right sides would always be equal.

Since the coefficient of friction diminishes with increased normal load, we can tune the amount of relative weight transfer between the front and rear axle in order to force one end of the vehicle to generate more lateral force and thus generate a yaw moment. This diminishing coefficient of friction is also why a lower center of gravity increases overall grip.

Assume every tire is exactly the same at the same temperature,age, etc.

Also assuming the chassis is a perfectly rigid body, the roll angle must be the same between the front and rear axle of the vehicle. This means that if the roll stiffness of the rear of the vehicle (roll bar plus spring) is higher than the front of the vehicle than more weight transfer will occur on that axle. Because of the diminishing coefficient of friction, the rear axle will generate less force overall and cause the vehicle to yaw into the turn. The opposite is also true, more front axle roll stiffness will cause the vehicle to yaw away from the turn.

This is only one of several factors that affect the handling of the vehicle, but to attribute the handling characteristics to one factor as suberman has in regards to the rear wheel geometry of the vehicle is utter non-sense. The overall vehicle handling is a factor of all of these things and the relative weight of the suspension characteristics, tire characteristics and environmental characteristics on the system response must be evaluated in each handling situation in order to understand how much one of these factors contributes to the purportedly undesired oversteering tendency of the vehicle.

suberman if you feel the vehicle has too high a tendency to oversteer this can easily be remedied by changing the roll stiffness of the vehicle, changing tires, wheel alignment, or rear differential tuning, depending on the situation you find the vehicle oversteering too greatly in.

I can assure you the suspension is not set up from the factory to oversteer inherently as this would result in too many accidents and lawsuits.

The one thing Subaru did to allow a bit of fun with the car is put on those skinny tires so that the car can power over with its chassis twisting 150 ft-lbs of torque.

I hope this post was informative. Here is a link to my thesis for anyone interested.

http://137.207.14.230/vdc/downloads/...loney_masc.pdf

Sean

^^ GREAT information, but don't worry... Suberman will claim you're wrong too.

In the meantime, Suberman should give this video a watch and try to say that this car is understeering, or that it would be faster if it was understeering:

[ame="http://www.youtube.com/watch?v=xgKjp1pq7iI"]Ferrari 458 vs Ferrari 430 - Top Gear - BBC - YouTube[/ame]


You can CLEARLY see that at turn in (except maybe the hammerhead) there's some rotation (mild oversteer), and at every exit there is also mild oversteer. Not drifting with the tail out 20*, but there's at least a couple degrees of rear slip. That's the fast way around a track, and the fast way to set up a car. You can control oversteer without slowing down, the only way to control understeer is to slow down.

To add to what Sean said above, if you want to test out how little traction you'll gain in snowy corners with more understeer, disconnect one of the end links on the rear sway bar. The chassis will be balanced way towards understeer in that state, but it's still going to oversteer VERY easily if you get on the gas like before.

Another thing he fails to realize... he keeps making comments about the torque, but doesn't seem to think about common sense. Take an Audi S4 (his previous favorite sports car), it puts about 230lb/ft to the wheels stock, these cars put around 140lb/ft to the wheels stock. 230/4 = ~58lb/ft per wheel, 140/2 = 70lb/ft per wheel, no kidding it breaks traction easier with 20% more torque going to each drive wheel.

if the earth's movement through space was instantenously stopped (like a car hitting a conrete wall), would half the people fly off while the other half squished into nothingness?

Oversteer scares passengers, understeer scares drivers.

Suberman needs to either improve his driving skills, grow a pair, or start sitting in the passenger seat where he can focus on less challenging tasks like finding the right radio station or getting my sunglasses out of the glove compartment when I need them.

Waiting for our great Oracle's reply to this.

I'm sure THIS time the light will go on and he'll recognize that if he closed his mouth and opened his ears he might actually learn something.

Titties.

Actually, I'm fairly certain, his majesty will declare Maloney's paper to be crap, that his degree should be rescinded, and that he fears for us all because in his opinion Maloney is absolutely wrong (for some reason or another).

:popcorn:

I'll take that bet. ;)

Just get rid of your car already so we can all go back to talking about how much we love ours....thanks!

For a guy on so many people's ignore list this is perversely gratifying. It's hard to know where to begin.

None of the posters actually understood what I wrote. I'm not sure if anyone understood what they thought I wrote. I have implemented a policy of never responding to wparsons as he is clearly an idiot, or so good at imitating an idiot no one can tell he's not really an idiot.

Most hilarious was the comment on Stig's lap in the 458. About the only places the Stig does allow a bit of oversteer is at the apex of hammerhead (logical, it's a tight bend and a transition bend, hence the name) and on the exit to hammerhead. All the remaining corners clearly show the 458 with the front wheels turned somewhat into the corner, as you would expect from an expert driver. I believe that's Ben Collins. I don't think many drivers in the world could beat Collins on that track although Rubens Barrichello did....

The engineer must know that mu is a constant by definition. He failed to note my qualifier when my little play on words caught him out. That's ok. His post at least confirms much of what I've been saying and with nifty charts. Thanks for the info, your text is not so useful and although your thesis is somewhat interesting and one can glean relevant information it isn't very helpful to the topics at hand. Engineers still avoid taking English at university except the mandatory course. Thanks anyway.

As for mu not being constant even though it is a constant this article goes some way to explaining my "oversimplification":

http://bsesrv214.bse.vt.edu/Hop/Pape...oefficient.pdf

I haven't read it but I have a pretty good idea what it does say.

I did like the perceptive if technically inaccurate suggestion that tire friction is non-Newtonian. It is true that tires don't behave strictly speaking as we might expect. Automotive engineers have not been troubled by the need to fudge the numbers a tad to match real world measurements though. It is perfectly correct that tire rubber meets the road surface in complex ways and also that considering mu to be constant as well as a constant means the actual performance of any given tire may be a bit different than the maths might predict but it is still obedient to Newtonian physics.

Use of the gravitational constant g isn't useful in analyzing oversteer relative to understeer because it is assumed to act through the imaginary CG. Use of g and fractions of g (which is actually absurd if one considers things properly) began with the aeronautics industry who do need to measure vertical g so it makes sense to use g for all accelerations in the pilot's 3D world. However, even there g is used for the entire vehicle and the entire pilot, not one end or the other. I'm pretty sure yaw, pitch or roll is neither measured nor displayed to the pilot in g, but I'm not a pilot.

Just as an amusing aside, a pilot or driver must fly by the sensations in his inner ear as compared to what he is seeing with his eyes. Neither pilots nor drivers can really "drive by the seat of their pants" that's all illusory. Without vision to coordinate with the acceleration your inner ear is experiencing you can neither drive nor fly. This is due to your inner monkey ....

I was particularly amused by the poster who suggested I get rid of understeer by pumping up my front tires and letting some air out of the rear tires...no, I won't be doing that.

I do note that Whiteline offers a 24 mm front bar (substantially stiffer than the stock 18 mm) which is really odd if much of what others have said about this car is correct. Please note that whiteline suggests this is your best bang for your buck:

http://www.whiteline.com.au/search_2011_4.php

I suspect they are right.

For my purposes I would consider fitting rear springs from the GT86 instead, if indeed the rest of the world gets a more softly sprung car than we do in North America. The gt86 apparently has softer rear springs than either the BRZ or the FRS but, squidgier front springs than the BRZ. In the wet softer rear springs should help but apparently not the gt86 as all testers report the gt86 is a real handful in the wet, as we have all discovered it is in the dry. No doubt that whiteline bar would be even more effective on a gt86.

Again, this is odd tuning if oversteer is faster.

I really was hoping for more reasoned posts. Just have to try again I guess. I'm patient and persistent.

Maybe somebody will actually quote a specific refutation from an actual suspension engineer? What an idea? We now apparently have one, or at least a wannabe one, but he still has difficulty reading and writing, and with a Masters degree (don't ask a practicing engineer what he thinks of engineers with masters degrees, just btw, they may suggest only incompetent engineers stay in school longer than they need to ...just sayin'. That's the basis for all those Howard jokes on Big Bang: no PhD AND "just" a Master's degree. All the engineers with only a bachelors degree roll on the floor laughing at that continual running double joke.)

There's so much fail in this post I don't even know where to start. So I won't.

@mrceltic, I told you so. :D

Mu is a variable not a constant. g, the acceleration due to gravity on earth's surface, is also not a constant. It is another example of a variable. G, the universal gravitational constant, however, is a constant. Some examples of other constants would be;

e, euler's number
Pi, the ratio of a circle's circumference to its diameter
L, Avogadro's number

variables such as g and mu are often assumed to be constant values, because in many real world applications this assumption is perfectly valid. With respect to tires however, the effective coefficient of friction cannot be assumed to be a constant.

Perhaps I missed your play on words due to your misunderstanding that Mu is not a constant. That's ok

My post in no way confirms what you have been saying. I was specifically trying to help you understand that axle distribution is critically important because the coefficient of friction is not a constant with respect to tires.


First of all, the tire is both sliding and gripping simultaneously within the contact patch at all times. There is not some step where the tire goes from gripping to sliding. The relative quantity of gripping or slipping within the contact patch depends on the demands on the tire.

The dynamic coefficient of friction also has a large effect on the tires performance. In fact at very low normal loads, as seen in the provided data, the effective coefficent of dynamic friction can actually be larger than the static coefficient of friction.

The slip angle the tire is undergoing does not magically decrease when the tire begins to slide. If this were the case, the tire would self correct for excessive steer angles and always settle in a position that optimized grip.

This is entirely untrue. Over/Under steering behavior is related to the yaw angle of the vehicle relative to its heading. Given an equivalent deviation from the optimal path, whether it is one that tends to increase the cornering radius, as in understeering, or decrease the cornering radius, as in oversteering; the forward speed lost from scrubbing the tires is the same.

I have no idea why you feel the need to attack and belittle me, nor why you feel I lack literary ability. I have said nothing hostile towards you and have only tried to provide sound information. I am by no means a "wanna be" engineer. I chose to continue my education because I had both the talent to acquire scholarships and desire to better understand exactly this topic.

As a gainfully employed practicing engineer in the automotive industry, I have no concerns observing some of my fellow engineers with bachelors degrees spending their days detailing drawings. I can assure not all the engineers with bachelors feel as you have described. Typically those that convey that opinion do so in frustration over their own lack of ability to do so.

There is so much crap spread over the internet with regards to vehicle dynamics that I simply wanted to correct some of your misinformation. Your attacks are clearly in an attempt to incite some type of hostility, however, I in no way have any interest in attacking a persons character and for someone of your qualifications I cannot understand why you do.

Except of course when it's a new user on the boards who takes the time to share his knowledge and expertise with a stranger...

Hypocrisy, irrationality, and loneliness; all the requirements to be a troll. All you're missing is a bit of originality.

Double or nothing; Suberman apologizes to Maloney for his personal attack and admits he's a paralegal of average intelligence.

:bow:
I'm almost willing to bet my car. However, I've seen too much evidence that Suberman is willing to say anything to nettle us. In fact, this last week, his posts have been so over the top with ignorance and blatant misconstruing of facts, that I'm positive he's just trolling.

:popcorn:


I'm just so glad there is another engineer in here, saying the same thing as the rest of us, so I know I'm not losing my mind.

Are you really basing real life on a TV show?

BTW Suberman. I have nothing but respect for M. Eng. In my field, I feel like doing a masters isn't going to get you very far, because the vast majority of our work is more dependant on experience.

With that said, certain fields, like Electrical, Mechanical, Software, Chemical, the new guys with the most education are typically the most valued and trusted, and if a B. Eng or a practicing engineer is laughing behind their back, it's because they are jealous. I know it's been a long time since you've been to school Suberman, but very few are qualified to be taken on as Masters or Doctoral candidates. Too few spots for too many students.

For somebody who says they are wise enough to step outside when the monkeys are flinging shit, you are always there to throw the first volley...:slap:

No bet. I only have room for one car. On the other hand I would be taking the oversteering defective monster off your hands.....

Bullshit, you just can't find something to disprove what I'm saying. I've made direct references to posts made by guys from RCE and CSG that say exactly what I've been saying, yet you chose to ignore that so you don't have to admit that you're wrong.

Most hilarious is the irony in you commenting on MY comment about the 458 immediately after stating you have a policy of not commenting on my posts. Brilliant.

The bolded part needs to be kept right at the forefront of any argument you make though. I find it very amusing that you honestly believe a car can't be oversteering unless the front tires are turned into the slide. That right there is your single biggest failure in understanding any of this. If a car is oversteering by a few degrees, the front tires will still be pointed very much into the turn.

You must be equating any and all oversteer with a full out opposite lock drift, which is simply not even close to reality.

If you watch the video again, there is clearly mild oversteer happening at every turn, the only place there's any understeer is at the entry to the hammerhead, and it's VERY minor.

What relevance does anyone's writing abilities have in a discussion about vehicle handling dynamics? Why don't you stick to relevant facts instead of grasping at anything you can use as an argument against someone?

And here we have it, the actual reason for everything Suberman.

G is a measure of acceleration, lateral acceleration is a measure of grip. You can't measure under or oversteer in G, but that wasn't what I said. I said that if you try to get one end to sustain more G than the tires can provide that end is going to slide. You managed to skip right past the point and land on some completely irrelevant point, again. If it makes you happier, forget that I used G and instead look at any unit of measure that makes you happy. At the end of the day, if you ask the tires at one end of the car to provide more force against the pavement than they can that end is going to slide.

Reading comprehension isn't your strong suit, is it? That post was sarcastic, but the point was that since you like understeer so much you could create more by lowering rear tire pressure and increasing front tire pressure.

Link fail, that just takes you to a blank search result.

That won't change anything for you, I've provided direct quotes from crew members of F1 teams that stated the more oversteer a driver is comfortable with the faster the car can be setup.

I've said this before, but I'll repeat it again. A car biased towards understeer is easier for a novice driver to drive to the limits, but a neutral car that properly rotates off power (very mild oversteer) will ultimately be faster.

Before suggesting stiffer roll bars again you should remember that a stiffer roll bar changes the handling balance by actually reducing grip at that end, so a stiffer front bar is increasing understeer by reducing front grip. So now you're claiming that less grip up front makes a car faster, chew on that for a bit.

Props for the excellent selection of quotes tags.

Sent from my Nexus 5 using Tapatalk

this feels like a bar fight with a drunk homeless man with cognitive incensitivity to pain, he's too weak and disorientated to throw any real punches but god damn it he won't fall down.

I can't believe that you accuse other poster of having poor reading comprehension, and then you write this. Read again what I wrote, and then read again what you wrote.

I'm fairly certain that nobody is claiming that a power off oversteering car is faster, and the BRZ certainly does not suffer from this. A neutral car is fastest. Depending on the application and the drivers comfort, a car setup to slightly oversteer off the power may be better in an autoX, And a car that slightly understeers may be pushed harder by a skilled driver on a high speed track. The only reason for slight understeer is to allow a margin of error, after all, a car in the gravel is the slowest.

We're all just here to tell you that a car that is significantly understeering IS NOT the fastest car, as you suggest. By your own admission, tires without grip means that a car is already going slower that it could be. Subsequently, trying to steer an understeering car through a corner by power oversteering (4 wheel drift) is definitely not the fastest, that's just drifting; not a grip run.

Clear as day I remember a funny incident in grade 6 design and technology class. I was looking for a fretsaw to cut out a delicate design in a thin board and noticed that the only one our class had (cuz we low budget like that) was missing. I went around the room seeing who was using it and found the class hottie (Lindsey, ohh how I remember you) using the damn thing TO SAW OFF A PIECE OF TWO BY FOUR. She was going at it in a way a young boy could watch for hours… but I had to get my damn project done so I interrupted her and offered a trade. In my hand was a simple but reliable ripsaw. I explained to her that what she had in her hand was for delicate work, which I needed it for, and that the ripsaw was the perfect tool for her activity, all she had to do was keep the blade straight and put some power into it on the downstroke. She didn’t believe me, told me I was trying to trick her (wtf?) and to get away from her popular self (or something to that regard). My English wasn’t too good at the time and I was already nervous from having approached her so I just said fuck it and went on to do something else. She later snapped the blade and had the teacher yell at her for being an idiot (in much nicer terms though). She never did apologize to me however.

Suberman

You’re that blonde twat without a brain. Your intelligence is fake. You know things yet you do not understand. And you keep hacking away at life using the wrong tools. One day those tools will break and you’ll be in a very bad place. It’s probably too late for you now , though, to change your mindset, but maybe, just maybe tomorrow or the day after you’ll wake up with a eureka moment and stop pissing in your own coffee for once.

dbl post

It is not absurd in any way. 1"G" is 9.8m/s^2 (meters per second per second).
It IS a constant and is used in every physics class I have ever taken.
Of COURSE the "force of gravity" can vary based on altitude and even where on the Earth you are, but 1G is defined "1G = 9.8m/s^2" this holds even if you are standing on Mars.

And "Use of g and fractions of g (which is actually absurd if one considers things properly) began with the aeronautics industry " Umm... NO It started with these guys called Galileo and Newton just a bit before the "aeronautics industry". Their "1G" = 32.17 feet/s^2

If you dont like using 1G as a unit, then just convert to m/s.

And the reason 1G is used when talking about auto handling characteristics is that with 1G of downward acceleration, the most lateral acceleration a car can handle is 1G. This of course assumes no aerodynamic downforce and a max tire frictional coefficient of 1.0 (we all know that cars DO have downforce AND at least race tires can have a frictional coefficient of greater than 1.0 = "Sticky")
You could use m/sec^2 when discussing this, but it just shorthand to say "1G" instead of "nine point eight zero six meters per second per second"

Apparently you did not even read any of maloney2's paper (I read almost 40 pages of it) because his "English" is just fine. I did not find any errors. Do you care to point out any of his poor writing skills? (didnt think so). And as an Engineer myself, I take offense at your statement.
Maloney2 has presented evidence that he knows what he is talking about as his paper was reviewed by experts in the Automotive Engineering field.
How many peer reviewed papers have you written on tire handling characteristics? None? Oh, thought as much.

^^ Slight correction, you can have more than 1G of lateral grip without downforce and a coefficient less than 1. As weight transfers in a corner you end up with more normal force than just the force due to gravity.

:laughabove:

I think I peed a little.

The use of the unit g in lateral acceleration makes absolute sense. This is done so because the maximum lateral force that acts on the vehicle is a function of the mass. However, the acceleration of the vehicle itself is also a function of the mass so the mass term effectively drops out. The use of the unit g is really to give a sense of the overall effective coefficient of friction. When used to present results such as skidpad numbers it allows for easy comparison of a vehicles overall handling capabilities independent of its tires, mass, suspension etc.

A = F/M
F = FnMu
Fn = Mg

therefore,

A = MgMu/M --------> A = gMu or A/g = Mu

Where, A = the lateral acceleration of the vehicle, F = the lateral force acting through the vehicle's mass center, M = mass of the vehicle, Fn = normal load of the vehicle, Mu = the coefficient of friction, g = acceleration due to gravity on earth.

So really when someone reports the skidpad lateral g's of a vehicle, they're really reporting how effective the handling package of the vehicle as a whole is.

So when you made your point that g isn't useful for understanding handling balance your both correct and incorrect. It's true that you can not tell if a car is oversteering or understeering based on the lateral g's the car pulls on the skidpad, but if a car understeers very strongly or oversteers very strongly you can bet the car won't achieve very high skidpad numbers.

BTW I haven't been able to thank any posters due to my lack of posts but rest assured I appreciate many of your posts.

Sean

No you cannot.

The "normal force" IS the force due to gravity.
What you just said means "A car can weigh more than it weighs"



http://upload.wikimedia.org/math/0/c...413171d4bb.pngwhere

• http://upload.wikimedia.org/math/7/d...9fe4743bcc.png is the force of friction exerted by each surface on the other. It is parallel to the surface, in a direction opposite to the net applied force.
• http://upload.wikimedia.org/math/9/3...82a2d2cec1.png is the coefficient of friction, which is an empirical property of the contacting materials,
• http://upload.wikimedia.org/math/b/9...a42902b107.png is the Normal force exerted by each surface on the other, directed perpendicular (normal) to the surface.

If the "normal force" (Fn) is 9.8 m/s^2, and u (coefficient of friction) is 1.0, then the force of friction is 9.8 m/s^2 and cannot be any greater unless the coefficient of friction is greater than 1.0.