Saturday, January 24, 2009

(58) I'd like you to meet my old friend, G

I haven't done a tech article in a while.

So guess what? That's right. People easily bored should run like mad from this one.

Today I want to talk about grip. Stickyness. Plantedness. Responsiveness. Face-bending, eyeball-popping, spleen-tearing, eardrum smashing good-ole G-forces.

So how do G-forces effect what the driver does? At the very basics of it, G-forces effect the overall traction of a car. As a sum of the traction force of the tires, the car can only generate a certain amount of G in a single direction. Say your car can do 1G of sideways acceleration. Meet the force vector:



The force vector, aka the Bible of lateral and longitudinal G.


As we can see from the above graph, G-force is divided into 4 basic sections: braking, acceleration, and left and right cornering.

Now, the only problem with the accepted norm of the above is that a force vector for a car, as in a sum of 4 tires, is not actually a circle. It's more like an egg. A car can generate more force back to front in braking than it can on acceleration and side-to-side cornering. Why is this? Well, for one, a car has only so much power available to it to accelerate. This is the weakest link. The second weakest link is side-to-side cornering. A tire's contact patch is not perfectly round. It is always "taller" than it is wide, even on super-fat tires like Formula 1 tires. This means the tire has more traction forwards and back than it does side to side. So as a result a Formula 1 car, even with it's near-circle-shaped contact patch, can generate nearly 5.5 G under braking, but only manages about 4.8 G under cornering.

This means that no matter how hard we turn the wheel, we will never use 100% of the car's overall capability. So how do we do that? With our left and right feet. Since a car always has front and back traction available, it would be quite a waste not to use it, no? This is why you'll never see a quick driver without his feet doing something, be it braking, accelerating or shifting.

If you're smart, you may have picked up there that while a tire can only generate a certain amount of G in any one of the 4 directions, it can also combine two bits of each direction to boost it's total G capacity over the accepted limit. If we're cornering at 1G, and accelerating or braking at 0.3G, then it boosts the tire's overall G capacity or rating to 1.3G since we're using the additional reserve of grip from the front or back acceleration zones of the tire. You may have also picked up that magazine's accepted "generate G on the skidpad" tests are flat out inaccurate since they only test sideways acceleration.

The other side to the force vector is what the G-forces of the car as a whole do to the individual tires. I covered this slightly last year when I went to Skip Barber.

When people talk about "feeling" the car under you, they are talking about the tires' relative contact patches. When a car is sitting still, each tire's contact patch on a general road car is about the size of the palm of your hand. Now imagine how all the weight of the car, all of the bumps it communicates to you, and everything you feel of the road is done through those four little hand-size patches. That's really an engineering marvel right there. So obviously, proper use of these contact patches is critical for getting the most out of the car. Lets run through a regular old corner and see what these things look like as we do so.




Braking.


This is where it begins. Under the brakes, the weight of the car goes forward as a result of the G we get from the frontal traction of the tires, which equates to the face-pulling G. As the car's weight shifts forward, it puts more pressure on the front tires, increasing the available grip. This is partly why road cars have front brake bias. Slam on the brakes and you get more grip from the front to evade something. In a racing car, with downforce, this effect is much reduced. Fast drivers tap the brake if they require a quick direction change. This gets the car to bite in the front and turn in quicker, eliminating any understeer.




Corner entry and trail-braking.


Corner entry is a transition phase. This is where the entire corner can be won or lost. The weight of the car is going forward and a little to the outside. It is absolutely critical to have a smooth transfer of load here and to keep it moving. If the load becomes stagnant and constant, it gets that much harder to get the car to do what you want and you will have a bad exit unless you can control the car like Ayrton Senna, in which case you would've had a perfect entry anyway.

To help us do this, we employ trail-braking. Bleeding off the brake as we exit a turn and modulating it as we go through it. This gives a snappier turn in and grip where it counts (the front). Too much trail brake lifts the rear of the car and you will spin from near-total loss of the rear contact patch. The idea is to get the front-outside tire as big as possible without destroying your rear grip altogether. This means sacrificing inside-rear contact area. It's just a fact of life and just another reason why racing cars have huge wings on the back. Again, you want the transfer of load to be smooth and progressive throughout the turn. This means never letting the brake pedal sit. Always smoothly let it out as you approach the apex. The apex should be your reference for how soon or late to come off the brake completely. It should, however, be throttle-only after the apex. If you're carrying brake past the apex then you should adjust your apex point or your speed into the corner.




Mid-corner or Apex.


This is the shortest phase of the corner. The apex or mid-corner coasting section should only last long enough to get your foot from the middle pedal to the right one; about 0.2 to 0.4 of a second depending on your skill. Obviously this is not a problem in Formula cars with left-foot brakes and no foot clutch. That does not mean, however, that this section should be any less smooth. All you're seeing here are snapshots of the corner phases, they do not illustrate the gradual transfer of load and G. If you are riding with a good driver, you will not be able to differentiate the phases of the corner, it will all seem a single, continuous glide from full straight-line braking to full acceleration. The human body is the best accelerometer. Learn to use it.

Again, this section should only last long enough for you to move your feet. Your foot should always be pressing the throttle or brake at all times. The only exceptions are a fraction of a lift before a high-speed corner and shifting up. Just make sure it's always smooth.





Corner exit.



The corner exit phase is the most important. What people never explain is that this is the phase where you have the least control. This is the culmination of the braking (speed), entry (control) and apex (line). A corner is cause and effect. This is effect. Corner exit is where you look to fix things that happen earlier. Almost never will you look at corner exit to fix corner exit. There is one thing and one thing only you can do wrong here, and that is apply too much power. Let me explain.

If you set up the corner properly, with the right speed, the right control, and the right line, the exit will pretty much happen by itself. The car is set here. You have tons of rear grip since you're accelerating and making the car squat down. This means that generally the car will understeer (unless it's badly set up). The only way you can make understeer go away is either using the brake (indicating a bad apex point or too much speed), or getting wheelspin (indicating a lack of sensitivity on your part). Some people say some wheelspin is a good thing. It really isn't. Wheelspin is like locking the brakes. You are beyond the limit of the tire. Don't do it, and it's really easy not to.

And again, this whole throttle-on business should be absolutely smooth. This is the easiest part of the corner. If you're unsmooth here and botch a perfect entry, then I don't know how you managed the perfect entry. The perfect exit is a pretty unthinking business. You should pretty much automatically reach the track out point.




Straight line acceleration.



What can I say? Go baby go.




Slip angle.




The one thing I haven't mentioned here is HOW tires get to their maximum traction. The tire, obviously, is a bubble of air. This air is very pliable. Not only do tire treads move up and down and compress (Z movement) but they also move and distort sideways (Y movement). Meaning, the side wall of the tire will bend. How much the side wall bends determines slip angle.

Slip angle is a combination of force on the tire and how the tire's rubber distorts in proportion to that force. Since the side wall of the tire requires a certain amount of force to distort to the maximum traction capability of the compound, you need to generate that force by going just a little bit sideways. The stronger the side wall, the more force you need to use to get it to bend. In layman's terms, tire point one way, car go another.

Slip angle can be anywhere from 2 to 8 degrees of "drift" depending on the tire, the pressure and the grip available on any given day, weather condition or car setup.

Karts are very, very, very good at teaching slip angle. Not only do they have no suspension (meaning, the tires ARE the suspension), but they have a solid rear axle. A solid rear axle requires a certain amount of drift to get the rear tires spinning at the same rate. This angle of slide is very similar to the angle required for proper slip angle.

Generally, you initiate slip angle by trail braking just the right amount. At about-perfect slip angle, the steering goes somewhat light (on road cars this is less noticeable because of power steering). The main difference is that the car will feel at it's most planted, most "on-tails" state. This is what I was talking about when I said "corner exits are easy and happen pretty much by themselves". This is because the "self-aligning torque" of the rubber peaks and falls off a little bit just before proper slip angle happens. Self aligning torque is the rubber's want to come back to center. The less of this there is, the lighter the steering gets. You want some self aligning torque. This is what keeps you in slip angle and if it goes away, you will oversteer. It's all about feel. You want to be in the area just before the steering goes totally light. The actual degree band of slip angle is quite large; a few degrees at least. What happens inside this band, though, is quite pronounced. The difference between your banker and Nigel Mansell could be as little as 2 degree's difference in slip angle.

Slip angle is something you really have to get out there and do correctly more or less by fluke than learning about it on paper. Once you feel it, you'll know and you'll be able to do it. It's like a golf swing. The first time you get it, you have no idea what you did, but you did it and are now doing it more often.

And that, ultimately, is that. Every racecar driver (as opposed to people who drive race cars) thinks about all of that through every corner. Whoever said a driver's job is easy has never driven.

Thursday, January 22, 2009

(57) The new face of F1 and defining the definition

Lately there have been a few F1 car reveals. Apart from the rear wing, I really like them. I think the Ferrari (much to my dismay) is the best looking of the bunch with the Williams taking second. I think the ugliest is the Renault.

Also an update on the Cosworth standard engine story, the teams have all said "no way" to the idea so either Bernie's going to have to get his standardization fix from GP1 (which he's hinted at being a rival for F1), or he's going to make F1 an independent only operation since all the factory teams will have left if the standard engine comes out anyway.

I still think the best way to bring costs down is to just cap spending. But that's much too sensible for people like Mr. Ecclestone.

But that's not the point of this post. The point of this post is the fact that I'm stone dead bored and I need a dose of philisophicalness. The topic? What is a road car, and what is a track car? Get ready. This one's a long one.

This is a question that has seemed to be popping up in the last few days for me. And upon further investigation it would seem there are two main extreme camps here. You have people who think a road car is anything street legal (Al la an IndyCar with lights and indicators, some of which have been built), and as such a track car is anything NOT street legal. Some other people believe that a track car is anything designed to go fast in any way and a road car is like a Hyundai or something.

There are some cars out there, such as Radical racers, build-it-yourself kit cars and super-lightened versions of normal supercars that are utterly and completely tuned on the track. Most of these cars are just a metal plank with some wheels and an engine. The only real testing on the roads that these kinds of cars get is just a simple driveway roll to see if small pebbles will get stuck under the front splitter, or if they will explode if left idling in traffic too long. Not that any of these small, niggling and irrelevant "problems" would alter the end product in any way. Oh no.



A Radical SR-4 track car. Clubsport race version shown here (the road legal one isn't much different).


Some people would argue that these types of cars are road cars. As if you'd want to take one down the PCH at sunrise. Some would (and have) argued "but it has air conditioning!" Alright. I'll give you that. But it also has a spot to plug your helmet radio and a series of green, yellow and red lights showing you the optimum rev band and when to shift (at 12 THOUSAND RPM). Next!

So now the other side of the spectrum. It is equally insane. Some people claim that anything above a Miata is a track car, because "you can't use all of it's performance on the road". Well, you can, for one. You'd just be incredibly stupid. Not unlike those Gumball weirdos. We call this "purging the gene pool". It's just a real shame that sometimes innocent people get hurt or killed as a result.

Where was I? Oh, right. So sensibly you can't use most sports cars or any supercars to the limit on the road. That much I agree with. However, indifference to the government, the more grip and braking force you have, the faster you can go (theoretically) safely. Think about this. If an old Honda Civic can only corner at 0.65 G worth of grip, then if the car is required to make a snap maneuver at 70 MPH that requires 0.80 G worth of grip, then the old Civic will just understeer and/or not respond at all and you'll crash into what you were trying to avoid anyway. Now, if you had a Lamborghini with ESP, AWD and MASSES of grip from foot-wide tires, then a 0.80 G maneuver is a breeze. This is called active safety and is the best kind in my opinion.

Also think about this. With more grip comes more capacity for the unexpected. If you're going down a twisty road in a somewhat less grippy car like a sedan or something, and you're driving briskly but not overly fast, and an unexpected off-camber, downhill hairpin comes up on you blindly, then you're going to have to make an emergency apex with the tires screaming. You're at the limit and you're afraid that if you touch the brake you'll spin (you may or may not be a racing driver). So your only option here is to ride the car out. If there happens to be something in the path of your car, you will hit it. If you had a higher performance car with more grip, you would have made the surprise hairpin completely safely, although suddenly. But at least you would have been way under the limit and if there had been something in the way you could take appropriate action as a result.

It's always good to have a car which can get out of it's own way, both sideways and forwards and backwards.

Now, to my original point, is a sports car a track car? Short answer, no. Your average Miata is not tuned for the track (or if it is, it's in a very limited capacity). If it were tuned for the track it wouldn't roll as much as it does, it would be stiffer, it would come standard with a roll bar, and it would have a faster steering rack. Is it tuned to go fast? Yes, it is. Is it tuned to give great feel and pleasure from driving it, even at relatively low speed? Yes. Is it tuned to be comfortable? Yes. Does it have a 5 or 6-point harness? No. Does it have a fire extinguisher? No. Is it fireproof? No.

CAN you drive it racecar-fast on a track? No, but you can still have fun with it. CAN you drive it quickly (as in, to it's relatively low limit)? Yes, you could, but you also might die or kill someone else.



A Mazda Miata MX-5. Small, light, zippy, fun.


Now is a more expensive Nissan 370z a track car? It's stiffer than the Miata. But it's still tuned to go on roads. Is it comfortable? Depends on which suspension option you get, yes. Does it have a fast steering rack? No. Does it have a roll bar? No, but it does have a strength beam in the back. Is it fun to drive at low speeds? Yes. Does it roll excessively in corners? Not too bad, but could be a lot better. Does it have a racing harness? No. Does it have a fire extinguisher? No. Is it lined in fireproof materials? No.

CAN you drive it very fast on the track? Yes, just barely fast enough to "hang". CAN you drive it at the limit on the road? Yes, but again, you'd be crazy.



The new Nissan 370z. As good as the outside is, it's about 10 times better inside.


Porsche 911 GT2. Is it comfortable? No. Does it have a roll bar? Yes. Is it fun to drive slow/would you rent movies it in from Blockbuster? No. Was it tuned on the track? Yes. Will it burn? Some bits. Does it have a fire extinguisher? No. Is the badge just a sticker rather than enamel? Yes. Does it have a harness? No. Does it roll in corners? No, of course not. Eet iz German. Eet iz perfect.

CAN you drive it quickly on the track? You'd be crazy not to. CAN you drive it to the limit on the road, no matter how crazy you might be? No.

What? Did you just see what I saw? No? Why is that?

A racing car, being stiff and low and uncomfortable, cannot be driven quickly on the road. The road has potholes; you will crash from your stiff suspension bouncing off of potholes. The road has trees; one wayward oversteer with that 2-wheel drive system in a super light car (a Porsche, no less, which is impossible to save) and you will hit one and die. The car is uncomfortable; you will be battered and bruised even if you do survive not crashing. The car is low; it will cost you a fortune to replace the front splitter and the undercarriage.



The dreaded Porsche GT2.
Not really an animal to drive on the track, but pretty terrifying on the road for sure.


And so we've hit the point of no return for track cars. A track car CANNOT be driven quickly on the road, even if you were crazy. If you want to find out if a car is a road car, imagine yourself crazily tearing through various public roads. If you see yourself killed in your mind, or crashed, for whatever reason, then the car in question is a track car. If, however, you and the car in question survive your little daydream escapade, then it is a road car.

This is all very complicated. There's a lot to consider what makes a road car and a race car. It's not quite as simple as an if/then solution. Certainly it's a lot more complicated than the first two extreme viewpoints. I'm totally serious about the daydream thing. It covers all the bases, your personal preference and your perceived notion of a car. I should be a shrink.

But the question of whether or not something is a road or a track car is of little import in the grand scheme of things. What people really want to know is...

WILL IT BLEND?!

Friday, January 16, 2009

(56) I am now officially official!

That's right, I passed my driving test today! *dances*

I had 12 errors, mostly not looking at intersections, even though I know I looked both ways at most of them and knew what was coming. I guess he didn't see me looking. The only other things were wrong order of signal, mirror, look over shoulder and change lane (I did over shoulder THEN mirror), I didn't make the left turn lane-change as soon as he'd have liked, I didn't really yield to someone who could have made a u-turn into a gas station in front of me, and I made a u-turn a little too tight and got too close to another car for the examiner's liking (even though he was skewed pretty bad in his lane).

Well I'm glad that's over. Some studies have shown that the driving test is about as stressful as the SAT. I don't doubt that. My heart rate must have been at least 130 during the test.

One tick down, now I gotta get a job, my own car, and then I can go racing in earnest. That will be the easy part.

Yes!

Wednesday, January 14, 2009

(55) The saga of the Enduro

This story starts back in October.

At the end of our season, the instructors introduced us to the idea of an Enduro. Basically, it's a 4-hour Le Mans style race, with 4 drivers per team. The school would put on the race, and then it was up to the entrants to get their own ride. The school said they weren't going to run cars because the engines they use aren't the full on Rotax job.

Well, needless to say I went and put a few "ads" on some sites in the vain hope that someone would have a spot open. Needless to say, no one wanted a relatively inexperienced driver right out of speed's version of middle school (albeit a private, very prestigious middle school).

So with my hopes for an endurance race evaporated a fortnight ago (since it happens this weekend), I closed it out of my mind as something that was inaccessible to me at this moment in time.

Then I just got a call today from the school. They had apparently changed their mind and for a small fee was running 3 teams in the race with school cars which had been upgraded to the professional spec. Apparently I didn't get the memo a couple of weeks ago.

And I've just a few minutes ago decided not to do it. I really, really, really want to do it. But I've come to the conclusion that I'm not in shape. Karts are the most demanding vehicles to drive in "grassroots" level motorsport. Lots of professional GT and prototype drivers use karts to help stay in shape. So how on earth am I, who hasn't driven in months and hasn't been running or biking, going to drive one, in race conditions, for 30-odd minutes at a time? Even when I was racing regularly (and, admittedly, not working myself prior) I could feel myself falling off after 12 or so minutes.

And thusly, I have learned my lesson about "letting myself go". Don't do it. Am I being tough on myself? Probably. Are my standards too high? Not high enough, I say. If it's worth doing it's worth doing to the best of your ability, and if you cannot give that ability, why do it?

Next year, I will do it. But maybe next year I won't need to. Who knows.

Friday, January 9, 2009

(54) Hey man, got any speed?

I'm going through a lot of racing withdrawal right now. I'm trying to keep my attention occupied with racing and car chat boards, racing video games, re-runs on SPEED, you name it, but I can't scratch the itch. It's too much man! I gotta drive fast!

So to find some relief I went down with my dad to San Jose to see the auto show. Pretty standard stuff, the new 370z is amazing and the Aston Martins are cool etc etc. But the highlight was definitely the Bugatti Veyron. All 1.8 million dollars of it.

Up close it's absolutely amazing. The paint is so deep it sucks you in. All of the body panels match so perfectly you can't really see the seams. Everything on it is visibly built to the highest spec possible. The only disappointing part is if you look underneath the spoiler when it's raised up. There's all kinds of exposed underneath bits. Very high quality exposed underneath bits, but nevertheless, you aren't meant to see them.

The other surprise was the amount of racing cars they had in the entrance. They had a number of US Touring Car Championship cars, a couple of sports racers (those are like open wheel cars with bodies), and the pace car I always see up at Infineon.

Unfortunately this only seems to have made the cravings worse. March holds much relief for me with the start of various racing seasons, and then April for the start of the Jim Russell karting season.