RWD - Not Necessarily the Ultimate Driving Machine

Not Necessarily

The masses have been trained through careful advertising campaigns to believe that rear-wheel-drive is the end-all be-all of performance, but is it really?  What about front-wheel-drive and all-wheel-drive?  Surely there must be some benefit to these other wanna-be 'Ultimate Driving Machines', right?

Up a creek, or in a creek?

In 2010 BMW CEO Norbert Reithofer let it slip (link) that an internal study revealed "80% of BMW 1-Series owners thought their ultimate driving machine was front-wheel-drive."  Well, that's embarrassing.  It would seem that even BMW owners aren't aware of what makes their 'Ultimate Machines' so ultimate.  Do you?

A pendulum has never been so interesting

In Mechanical Engineering, complex problems are often related to any of several basic principles, one of which is the pendulum.  You are probably thinking right now "wow, a pendulum, so what?" Pay attention, your mind is about to be blown.  A pendulum is inherently stable because gravity pulls the mass downward and aligns the pendulum to a vertical position.  If the pendulum is pushed such that it rocks side-to-side, it will always return back to the stable, vertical position.

An inherently unstable inverted pendulum

The opposite of a pendulum?  You guessed it, an inverted pendulum.  This model is inherently unstable, but vertical, for now.  If the pendulum is pushed, sneezed at or even looked at wrong, gravity rapidly swings the mass 180 degrees around.  The clever ones in the group have likely caught onto the analogy by now, but the author will proceed for the rest of the class.

Why your rear-drive car is an inverted pendulum

 Getting back to cars, a rear-wheel-drive car is a classic inverted pendulum.  In a perfectly straight line, untouched by turns, that rear-wheel-drive car is going to stay straight, for now.  But what happens if you enter a turn while under heavy throttle?  The inverted pendulum, or car, swings around 180 degrees and your BMW 1-Series owner ends up in a creek without a paddle.  Probably wishing you had an inherently stable front-wheel-drive car right now, huh?

The Honda Civic, losing races since 1973

Now hold on a moment, before everyone rushes out to buy a Civic Si or Neon SRT-4, you may want to keep reading.  Front-wheel-drive has it's drawbacks too.  Imagine you are launching from a standstill in your Honda Civic, what happens?  The vehicle rotates about it's center of gravity due to the forward force, this rotation, or weight transfer, shifts weight off of the front wheels and onto the rear wheels.  This transfer of weight is bad for a front-wheel-drive vehicle as it reduces traction and results in a big smoky burnout without any forward motion.  A rear-wheel-drive vehicle benefits from weight transfer, but if launching on a street - traction is still a limiting factor.

Having one wheel spin like crazy isn't ideal, neither is a hole in your transmission.

To make matters worse, your front-wheel-drive econobox likely has an 'open differential' which acts as a power fuse.  Essentially, once a wheel loses traction, all power is transferred to that wheel which results in even more spinning.  Ever notice during a front-wheel-drive burnout that one wheel spins while the other simply rolls?  Open differential.  (Note, the Neon SRT-4 came stock with a limited-slip style differential which did not have this issue, thanks Getrag!)

Can your rear-wheel-drive vehicle do this?

By now you are likely asking, "Alright, so what vehicle drivetrain is not an inverted pendulum and is able to grip while rapidly accelerating from a standstill?"  All-wheel-drive is the answer.  Again, before you run out and buy a brand new Subaru Impreza WRX STI, keep reading as there are more tradeoffs.  The addition of both front and rear differentials with axles and supporting driveshaft, an all-wheel-drive setup is heavier than both front and rear-wheel drive setups.  Beyond additional mass, all-wheel-drive vehicles such as the Mitsubishi 3000GT VR-4 experience significantly more power loss through the drivetrain than their front-wheel and rear-wheel drive contemporaries.  Given 300 horsepower at the crankshaft, a stock '93 VR-4 (link) sees roughly 240 horsepower at the wheels - a whopping 20% drivetrain loss! Ouch!  Subarus see similar results (link).

It turns out that the answer to the question of "What drivetrain setup makes for the 'Ultimate' Driving Machine?" is quite complicated and subjective.  A quick recap of everything presented so far is in the table below.

Muddying the drivetrain selection waters

First, a front-wheel-drive platform is inherently stable with low drivetrain loss and weight, but does not have traction from a standstill - not to mention the understeer introduced by this setup when turning (a topic for another post).  Next, the rear-wheel-drive platform is inherently unstable with low drivetrain loss and weight, but can only obtain decent tracking when launching on a well prepped track surface.  Finally, all-wheel-drive has the bonus of stability depending on front/rear bias and can launch in the rain, but it has marks against it for being heavy with high drivetrain loss.

Which is best?  It depends on what you are looking for.  Do you want to go really fast in a straight line, and enjoy having the rear end kick out when turning under throttle?  Maybe go rear-wheel-drive.  Are you looking for a daily-driver that can only take on adversaries from a roll?  Perhaps front-wheel is your choice.

I'm sure the Supra can launch on a well prepped track (Video Link)

The author's heavily biased point of view is that AWD > RWD > FWD.

- Axle

Priceless Lamborghini Muira SV Burns

The Lamborghini Muira SV

Words to describe the emotions that arise when looking at the Muira SV arrive in a flood: sexy, stunning, fast.  But how do you relay the feeling of seeing this work of art on fire?


Details are sketchy, but from what the author can tell this is a 1971-1972 Lamborghini Muira SV.  Powered by a 4-carburetor 3.93L V-12 with 380 horsepower at 7700 RPM, the Muira SV only weighed 2,860 pounds.  This car was one of 150 built and valued as 'priceless'.

The Muira wails (link) at 50 seconds in.

- Axle

You Will Never Quote 0-60 Times Again

Zero to sixty times are a terrible way of comparing performance.  If you are already convinced that 0-60 mile-per-hour times, from herein referred to as 0-60, are not a good benchmark for automotive performance - thank you and move along.  If you are a stat-junky who lives and breathes 0-60 times, this article is for you.

False Advice? "It's not how you stand by your car, it's how you race your car"

So why are 0-60 times a nonsensical way to compare performance?  They simply do not tell you enough and can be misleading.  For the sake of argument, assume two cars have identical 5-second 0-60 times; one of these cars can still be further ahead by the time it reaches 60 miles-per-hour.  How is that possible, you ask?  Let's turn to Calculus for an answer.

 Calculus put men on the moon, pay attention.

Calculus tells us that the derivative of position is velocity, and the derivative of velocity (speed) is acceleration.  Okay, so what does this mean in practice?  If you have a graph of a car's speed versus time, the area under the curve (anti-derivative or integral) is the distance the car has traveled in that time.  So let's say that Paul Walker is the blue line (see graph below) with his all-wheel-drive Eclipse GSX and Vin Diesel is the green line in his rear-wheel-drive RX-7.  Walker and Diesel line it up and race to the next stop light, and in the process they both happen to hit 60 miles-per-hour in exactly 5 seconds, but Paul Walker is ahead.  How?

Speed vs. Time to 60mph: Blue is Walker, Green is Vin Diesel

This phenomenon occurs because Paul Walker's AWD Eclipse initially gripped and accelerated faster (see the blue line again) and covered a lot of ground, acceleration then fell short and the car's speed over time did not increase as rapidly as 'ol Vin Diesel's RX-7 (green line).  Vin's rear-wheel-drive RX-7 struggled for traction off the line, but once rolling it's superior power-to-weight ratio became the driving factor.  As a result, the Eclipse covered more ground than the RX-7 and made it to the next stop light first, even though both cars had identical 0-60 times.

Whether you win by an inch or a mile - Winning is winning.

Why be concerned with who covered more ground in the same amount of time?  Because that is how racing works.  No racer or sanctioning body (IHRA, NHRA) cares if your car made it to sixty first.  What matters is who made it to the next stop light first, or who made it to the finish line first.

The sexiest cover of Motor Trend, ever - No arguments here.

So what is a better benchmark for Vin Diesel's RX-7, you ask?  Time to travel a distance and the associated final speed.  AKA: The 1/4 mile. If you have ever looked inside the cover of a popular car magazine, such as Motor Trend, you will find a dizzying array of comparisons based on 0-60 times affiliated with 1/4 Elapsed Time (ET) and 1/4 Trap Speed.  There is more information in these numbers than is on the surface.  Let's decode a sample from the mid 1990s, a heads-up comparison of two Japanese Titans, the Mitsubishi 3000GT VR4 and Toyota Supra Turbo.

Excerpt from the Motor Trend article

If you notice, the all-wheel-drive 3000GT makes it to 60 miles-per-hour faster than the similarly powered low-gear spin-happy Supra, but again - we have thrown that benchmark out the window.  Moving on, the 3000GT and Supra finish the 1/4 mile simultaneously in 13.6 seconds.  This means that if both cars leave the starting line together, they would both cross the finish line at exactly the same time.  Fantastic!  But there is more.  The 3000GT had accelerated to 101 miles-per-hour in the 1/4 mile, while the Supra is now traveling a staggering 106 miles-per-hour; this means that if the race were to continue for another inch, the Supra would walk past the 3000GT.

Based on this information, we know that the 3000GT must have a lot of "Low-End" in the form of traction to be able to complete the 1/4 mile simultaneously with the Supra.  We have also learned that the Supra must lack traction, which we knew, and have superior acceleration once rolling.

Not condoning street racing, but the video above was relevant.

In summary, to all my friends on 3SGTO (link), if you want to stand a chance racing against a Supra; race from a standing start.

-Axle

Why Your Car is Not a Sleeper

There you are, mid conversation with a friend who happens to own a 2006 Chevrolet Corvette Coupe base. As you continue about admiring the 400 horsepower LS2 V8 under the hood, your friend mentions how much of a 'sleeper' the car is; an argument breaks out.

Your 2006 Chevy Corvette is NOT a Sleeper

The argument begins but always resorts to the basic definition of a sleeper. A quick Wikipedia search yields the definition of "A sleeper (US English) or Q-car (British English) is a car that has high performance and an unassuming exterior. Sleeper cars are termed such because their exterior looks little or no different from a standard or economy-class car." Let's break that down a bit further, in order to be a "sleeper" a car must:

1. Have high performance.
2. Looks like a standard or economy-class car.
3. Have an unassuming exterior.

Beginning with 'high performance' - let's quantify this term as 'faster than the medium trim level of an entry-level sports car'.  Picking at random from the offerings of the Big 3 (Ford, GM, Chrysler), the 2013 Ford Mustang GT fits the bill.  So how fast is a '13 Mustang GT with a 5.0L putting out 420 horsepower and 390 lb-ft of torque?  MotorWeek puts this vehicle at 13.5 @ 108 mph in the 1/4 mile.  So this will be our benchmark for 'high performance'.

 The Low-Bar Benchmark for High Performance

Next, how does one define an 'economy-class car'?  For starters, it is what is generally known as a crap-box.  We are talking the standard entry-level crap-box such as a 4th gen (1993-1996) Mitsubishi Mirage.  This is a car that in no realm of reality that someone would consider fast with it's 1.5L 92 horsepower motor.

You Can't Get More Economy-Class Than a 4th Gen Mitsubishi Mirage

Finally, what exactly is an 'unassuming exterior'?  The consensus on this one is one of two things: stock or beat up.  If the car has a legendary small-block-chevy with blower hanging out the hood, it is not unassuming.

A car that exemplifies the aforementioned attributes of High Performance, Economy-Class with an Unassuming Exterior belongs to 3SGTO's (link) PostMan.  Apparently when PostMan has free time, his hobbies include performing an all-wheel-drive conversion with 4G63-T (Of DSM/Evo fame) with TD05 16G turbo swap into a 4th-Generation Mitsubishi Mirage.

An Unholy Union: A Mitsubishi Mirage with AWD and a 4G63-T

But does this car meet all of the criteria?

1. High performance?  How about 0-100mph in 10 seconds?
2. Economy-Class Car?  I challenge you to find something more economy than the Mirage.
3. Unassuming Exterior?  The paint speaks for itself.

PostMan's All-Wheel-Drive Test

PostMan's Mitsubishi Mirage From Hell - 0-100mph Test

Kudos to you PostMan, you truly are hauling the mail.


- Axle

Rod Knock on a 3000GT VR4

Video courtesy of ForestGump on 3SGTO.
Link to thread on www.3sgto.org

We feel your pain.
-Axle

Suspension Alignment Terminology

A Mitsubishi 3000GT Receiving an Alignment

Camber, caster toe.  The mysterious terms used by those 'in-the-know' and alignment shops.  Let's delve into the terminology and demystify it. 

 First things first, why does alignment matter?  If a vehicle's suspension is aligned properly, it should travel perfectly straight down a flat road without input from the driver (assuming you aren't experiencing violent torque steer - a topic we'll save for another post).  Besides rolling straight and true, an aligned suspension allows for even tire contact with the ground and reduced tire wear.  So what aspects of suspension alignment provide for this excellence in vehicle ride and handling?

Universal Coordinate System for a Vehicle

Vehicle Toe - Birds Eye View

Vehicle Camber

Toe. Suspension toe is known as the angular rotation of the wheel relative to the z-axis (see figure to left).  When the driver turns the steering wheel, the front wheels rotate relative to the z-axis and the vehicle turns.  But what if the vehicle wanders lanes without driver input to the steering wheel?  Toe alignment is the likely culprit. 

As shown in the figure below, if a single wheel has toe-in or toe-out, the vehicle can steer in that direction without driver input.  This scenario will require the driver to provide steering input in the opposite direction to keep the vehicle traveling straight. 

If the alignment shop says that 'toe' was adjusted, this is what they are talking about.  Every production car that the author can think of has adjustments for toe through the use of tie-rod ends.

Camber.  A properly aligned street car should rest without camber.  Camber is rotation of the wheel relative to the x-axis (see figure above).  A sign of out-of-adjustment camber is tire wear along the tread edges.  Uneven tire wear happens because the weight of the vehicle is resting along either the inside (negative camber) or the outside (positive camber) of the tire.  If you could imagine, not utilizing the entire surface patch of the tire can also show itself with decreased traction - especially in wet conditions.

Most production vehicles have camber adjustment for the front wheels, but this is increasingly going away as a result of cost savings by the OEMs.  Few, if any, vehicles allow for camber adjustment of the rear wheels - although 'camber plates' can be purchased in the aftermarket.  Two reasons for out of whack camber are:

1. The vehicle has been lowered resulting in negative camber.



Vehicle Caster

2. The vehicle has been in an accident (crash, pothole or otherwise) resulting in negative camber.

Caster.  This is the least well known of the suspension angles and there is a reason for that. There are no production vehicles which allow for caster adjustment from the factory.  Caster is angular position of the strut/wheel relative to the y-axis.  If caster is out of specification, the vehicle has likely been in an accident.

Due to vehicle kinematics, which is a topic for another time,  positive caster results in a vehicle which is more stable and less likely to wander on the road.  The detriment of increased positive caster is increased steering weight, which is offset with power steering. 

When inspecting a used vehicle for purchase the author prefers, along with other checks, putting the vehicle on an alignment rig (see first figure).  If the vehicle is at stock height and camber is beyond adjustment and out of specification, it has likely been in an accident.  If the caster is out of specification, remember this cannot be adjusted and is another sign the vehicle may have been in an accident.

-Axle

3 Pieces of Advice for 20-Something College Grads

Exuberant and Woefully Naive

Congratulations, you have earned a college degree and landed that first job.  Now what?  For starters, don't screw it up.

The author has three pieces of advice to help you 'not screw it up'.

1. Get a room mate
2. Don't take on new debt
3. Stop buying things you cannot afford

"Get a room mate? Why on Earth would I do that!?" you say.  Money.  A simple fact of life is that feeding and providing shelter for one person is quite expensive, but doing these things for a second person under the same roof does not add as much cost as the first person.  If a one bedroom apartment costs $700, and a two bedroom apartment with twice the square footage costs $1100 - then living with someone else and splitting the rent saves you $150 a month.  Remember that two bedroom apartments typically have larger common areas such as bathrooms, kitchens and living rooms.  But who should you move in with is a topic the author wouldn't touch with a 10-foot pole, you need to figure that out for yourself be it a: coworker, girlfriend, wife or friend.

Lenders See You as Prey

Don't take on new debt, that sounds easy - it isn't.  Upon graduation you are now considered prey by lenders, sales men and credit card companies.  Salesmen see you as a recurring stream of payments into their company, nothing else.  There is a seemingly endless flow of 'free money', but it isn't free.  Buying a new car turns into a $400/month payment until you're thirty years old.

Money isn't given away for free, everything that is purchased on credit is saddling you with a new monthly payment that isn't going away.  Key point: don't take on new debt and put your money into paying off student loans.

The third piece of advice is to stop buying things you cannot afford.  What does this mean in practice, you ask?  It is simple, if you cannot afford to buy it in cash, today, don't buy it.  Purchasing things on credit is selling your future to be happy today.  Cut up those credit cards as they are not needed to purchase things that you can afford.  If you are down to your last $300 but want to purchase a new 70" 3D television - you cannot afford it.  If eating out to the tune of $20/night ($140/week - $560month) is going to make it hard to pay the rent, stop eating out.

The Average American has $15,216 in Credit Card Debt

Back to the big picture, how will these 3 pieces of advice help you out?  Imagine this, it is your 30th birthday and you are debt free; Student loans are paid off and you have a big savings account ready to purchase the home of your dreams.  Now, think of the flip side: You have a six-year-old car with $400/month payments, $50,000 in debt with student loans and credit card bills and struggling to pay the rent.  Which sounds better?  You decide.

-Axle

Why Your Daily Driven Project Car is a Bad Idea

 So it is 8AM on a Monday, you walk out to start your car and go to work.  As the key turns in the ignition, your daily driven 1999 Mitsubishi Eclipse GSX stumbles to a start then quickly dies - It is time to call a cab.  But how did it come to this?
 

Your 1999 Eclipse GSX Project Car

 Daily driving a project car is a common pitfall of young car guys.  There is an old adage that there are three things that a car can be, of which you can only pick two:
1. Fast
2. Reliable
3. Cheap
 
So you have modified your daily driver to have 450 all-wheel-horsepower (AWHP), and you can run 11s in the 1/4 mile.  That's great - but now you can't drive to work because your $20,000 investment doesn't start every time you turn the key.  This is a problem, and car guys have either been there, or have a friend who has been.

So what is the solution, what is the great wisdom that only experience and age can teach you?  When it comes to cars: Spend your top dollar on a slow reliable daily driver, and spend your bottom dollar on a project car.  As a reader, you may be asking yourself,  "what does this mean in practice?"  It is simple, really, buy a late model Honda Civic for $10,000-$15,000 as your daily driver and DO NOT MODIFY IT.  Next, pick up a non-running 1992 Nissan 300ZX TT for $500 and park it in the garage.

Your Slow and Reliable Daily Driver

There are two benefits to this strategy, the stock and slow Honda Civic (or whichever boring entry-level car you prefer) will start every time you turn the key.  This daily driver will be numbers two and three from the list above, slow and cheap.  Meanwhile, the twin-turbo Nissan in your garage will meet numbers one and three, fast and cheap - but not reliable.

In summary, if you can't afford to buy a second project car: stop modifying your daily driver.

-Axle