Project Elantra: On ABS

Last time on Project Elantra, we were in search for a better handbrake for slalom duty. We got distracted by buying a greasy and possibly carcinogenic car part from the surplus parts area of Evangelista, Makati, but got a stiff brake pedal that will help us stop better. But still, a stiff pedal does not make our car’s buttocks swing harder than JLo in a music video. We are continuing the installment on brakes by discussing why we removed the car’s Anti-lock Braking System (ABS), further bastardizing the braking system en route to getting the handbrake we want.

Well, we got off track again! But stay with me. You might just learn something about the physics of braking. Read on after the jump for more hydraulic shenanigans.

Don’t try this at home

We didn’t tell you this at the previous instalment, but, hell, better late than never. Please be remind that the most dangerous part of the car to tamper with is the brakes. Short of pumping nitromethane in your moped, of course. Generally, better assume that the boffins that designed your car’s braking system know a hell of a lot more about mechanical engineering than you do, even if you studied the course as your undergraduate. (I studied Business Economics myself.)

Once again, unless you absolutely know what you are doing, or at least paid for a truly comprehensive insurance policy, don’t consider attempting to replicate the preceding or succeeding braking modifications done to Project Elantra. Caveat lector. And don’t sue me.

Laying Down a Patch

In the process of figuring out the handbrake, we ended up ditching the car’s Anti-lock Braking System (ABS). To understand why that’s such a dumb idea, allow me to discuss the importance of ABS. By getting off-topic again.

The first thing that you should know is that the most important part of every motor vehicle is its tires. Acceleration, braking, steering, and support of vehicle, driver, passenger and payload weight is all acted upon the tires. Needless to say, when buying tires, follow the same adage on buying helmets. (“Buy a helmet that is worth the value of your head. How much is your head worth?”)

What allows the tire to grip the road are the following: (a) the tire is intermeshing with the road surface at a microscopic level (think jigsaw puzzle), and (b) the tire is literally sticking like glue to the ground due to molecular attraction between the tire rubber and the road surface. Also take note that the size of the area of the tire touching the ground (in short, contact patch) at any time is no bigger than even a letter-sized bond paper.

Fig. 1 Contact Patch. Image credit: enginebasics.com

There’s Friction among us

There are two types of friction: static and kinetic. Static friction is when two bodies of matter contact each other without “sliding” against one another (i.e. the legs of your furniture immobile on your living room floor). Kinetic friction is when the two bodies “rub” or slide against each other. The interesting thing about the two types of friction is that it takes a certain amount of force to overcome static friction, and yet once it is overcome, it takes less force to maintain a skid. Thus, static friction is stronger than kinetic friction.

Fig. 2 Diagram for Static friction. Applied force is unable to overcome the static force of friction, thus no motion. (Click image for source.)
Fig 3. Diagram for Kinetic Friction. Applied force is strong enough to overcome the static force of friction, thus, rightward motion of object happens. Applied force is then strong enough to overcome kinetic friction attempting to retard motion, thus motion continues. (Click image for source.)

(An obvious aside: the reason why drifters can maintain control of their cars despite looking quite out of control is because even though kinetic friction is weaker, a friction force still exists. Meaning, drift cars still grip the ground and their pilots can still effect changes to maneuver their cars around the course.)

When you accelerate, the engine provides rotary motion via the drivetrain to the driven wheels. The tires grip the road, translating the engine revolutions into the vehicle’s forward movement. Adding enough power to the tires that overcomes static friction results in spinning tires. When done spiritedly and continuously, you call that a burnout.

May the Forces be with you

Now, when you brake, the brake pedal generates hydraulic pressure, transmitted by the fluid inside the brake lines, to the caliper pistons, which in turn push the  brake pads towards the rotors. (If you have drum brakes, my apologies, but it applies to you too.) The kinetic friction in action between the pad and the rotor retards forward momentum, thus slowing you and the car down. This assumes that there is ample traction on the contact patch, as said traction provides the opposing forces to the pressure exerted by the pad to the rotor.

Don’t get it? Imagine yourself pushing against a rock, like in Fig. 2. As you exert a force against the rock, the rock also exerts a force against your hand. The opposite forces cancel out each other, therefore no net effect happens. You don’t get the rock moving, and the rock doesn’t crush your arms. (Read up on Newtonian physics for a refresher.) Going back to brakes, the rock is the rotor, with its foundations “rooted” on the contact patch and available traction. Your arms are the pads. But instead of nothing happening, or the rotors getting crushed, the motion of the vehicle is dissipated due to heat generated by the friction of the two surfaces. The net result is a zero-sum net effect, and the car stopping.

The maximum braking force that can be applied is ultimately limited to tire grip, as again, it is the only part of the car that touches the ground. Static friction can be exceeded during braking when sheer braking power exceeds available tire grip, or when tire grip is reduced as the road surface becomes slippery due to water, ice, dirt, or oil. When the static friction becomes kinetic at the contact patch, the rotors lose the ability to push back hard enough on the brake pads, thus the friction from the brakes make the wheels immediately stop turning. That situation is called “locking up your brakes”

Fig. 4 Locked brakes. Image credit: Autoweek.com

Remember, kinetic friction is weaker than static friction. This means that the car will stop farther with locked brakes. And oddly, if you happen to be steering the car while locking up your front brakes, the car will not turn but instead plow off the road. That’s bad in slalom racing, deadly when that happens while driving a six-wheeler truck at the dead of night in a soaked and desolate stretch of Manny Villar’s C5 road. Don’t ask how I know.

Cadence Braking and ABS

So what can be done about locking brakes? Besides the obvious “don’t drive too fast when the road is wet” and “don’t drive too fast, period”, the practice before ABS was a technique called cadence braking. In cadence braking, the driver releases braking pressure at the onset of brake lock-up, then re-applies the brakes when locking ceases.  He repeats the process until the car’s speed reduces or the car stops. The problem with cadence braking is that it isn’t easy and that it goes contrary to a person’s natural response (stop braking when you want to stop!). Dedicated practice is needed to get someone to cadence brake as a natural response towards an emergency situation.

Nowadays, instead of car manufacturers expecting their customers to learn how to drive a car properly, they made ABS as part of their cars’ original equipment. What ABS basically does is to automatically cadence brake for you. The system is made up of wheel speed and vehicle speed sensors, a specialized pump mounted in-line with the brake lines, and a computer box. Upon detecting locked brakes via the individual wheel sensors, the computer sends signals to the ABS pump to relieve and apply brake pressure in multiple cycles per second. The system cross-references with vehicle speed to know exactly how much and how fast to pump the brakes.

Fig. 5 ABS Schematic. Image Credit: http://repairpal.com

ABS? What ABS?

We decided to deep-six the ABS. Even though this seems like a dumb move, we think there is a good reason for this.

Firstly, the thing is that when you upgrade, modify, or otherwise replace something the original manufacturer did, you have to reset or retune accordingly. For example, if you put as something as drastic as a turbocharger to your otherwise stock engine, the engine has to be adjusted somehow to account  for the additional airflow brought about by the turbo. Right?

In the olden days of carburation, it was a matter of adjusting some screws and calling it a day. (This is of course a gross oversimplification of installing and tuning a carburated turbo system. But adjusting any carb is done by fiddling some screws.) But in this modern day and age, if we are lucky, we can have our vehicle’s ECU reprogrammed. Or modify what the ECU sees and transmits by installing a middleman gadgets called piggybacks. Or replacing the stock ECU with a reprogrammable unit, like we did. (More on this in a future installment.)

The thing is, we did major changes to the braking system such as bigger calipers, brake master cylinder, and rear drum brakes. The change to rear drums alone is big enough to render the ABS computer box useless, as the rear wheel speed sensors are non-existent with the drums.

To remove the ABS, we had to replace all the brake lines. The stock brake lines are made of steel and should last the lifetime of the car. Replacing them with copper lines is a less-than-ideal solution. Copper is very malleable, so the tube is easy to cut, bend and flare, the latter with an appropriate flaring tool, of course. Its resistance against the elements is not comparable to steel, thus copper lines are not an OEM choice. We don’t mind, we’ll just have to inspect the brake lines once in a while.

We found some benefits to removing the ABS. It allowed us to lose an almost inconsequential amount weight from the car. Every little helps, right? Also, the space freed up from where the ABS pump was became a great place to relocate the oil filter. The liberated pump found use in the “B” Elantra as  a replacement for a unit we somehow managed to break.

I now have to learn how to threshold brake. Quite simply, threshold braking is applying just enough brake pressure to not lock the brakes. On practice, it’s not so easy. Braking is the hardest of all to master. So, I’d rather we didn’t remove the ABS. In the recent slalom race in SM Sucat, I was almost introduced to a concrete wall when I overshot the braking point and locked my brakes. Don’t remove the ABS.

Next time

We’ll probably not conclude the series on brakes just yet. As of this writing, we still have not figured out that perfect handbrake. We did pimp out our interior by stripping it and putting so much ricey gauges you’d think you’re in a Japanese plane cockpit. Let’s forget speed and racing for a moment and discuss that!

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