Trail Turn Assist, the Rivian "Tank Turn," and other environmentally destructive tricks.

During my test of the new Ford Bronco—a vehicle I liked a lot—I tried out its Trail Turn Assist feature, as you can see demonstrated in the video above. TTA drastically shortens the turning circle of the vehicle by applying the brake to an inside wheel, essentially dragging it through the turn.

Of course, in a normal scenario you wouldn’t be initiating a 360-degree turn such as in my demonstration above, conducted in a heavily used wash and cleaned up afterwards. Its utility would be negotiating a tight maneuver when, say, a boulder threatens the outside corner of the vehicle, or a drop-off threatens the entire vehicle. However, there’s nothing to prevent an owner engaging it simply to show off how tightly he can reverse course. And no matter how briefly one engages it, it will impact the trail.

My approach to driving, or to teaching someone to drive—as with all instructors I know—is, at all times, to try to minimize or eliminate wheel spin, which causes both a loss of traction and control and results in degradation of the surface, particularly in places where multiple vehicles are likely to lose traction. And wheel spin while the vehicle is stationary does more or less precisely the same thing as a locked wheel while the vehicle is moving: It wears away at the substrate, increasing erosion.

I’m not going to claim I would never use TTA if I owned a Bronco, but I would be extremely reluctant to do so.

As potentially damaging as TTA is, it pales before the much-hyped “Tank Turn” the much-hyped Rivian electric pickup can accomplish. By powering both wheels on one side forward and both wheels on the opposite side backward, The Rivian can essentially spin in place. The resulting destruction of the trail is easy to see in the videos produced by the company itself. You can see the entire sequence here.

The Tank Turn “feature” has actually been delayed for an unknown period after the Rivian engineers recognized several issues—including the fact that when the turn is enabled, traction is completely lost. Thus if an owner were to initiate it on a slope, the vehicle would immediately begin sliding downhill.

Rivian will undoubtedly warn that the feature is only to be used on a “closed course,” just as they say for their “Drift Mode,” designed for “advanced drivers wanting to drift their R1T on a closed course.”

Wink, wink.

Sadly such hypocrisy is by no means limited to the Rivian company (see here). Every truck maker loudly proclaims adherence to Tread Lightly practices, while producing advertising material expressly promoting the exact opposite. There are certainly those consumers who are responsible enough to eschew aping the ads, but there are tens—hundreds—of thousands who are not. I see the results every single time I head out on a trail, and it has been getting exponentially worse. Blame it on what you will, but there has been an unmistakable increase in self-centered behavior on public land in the last half decade or so. More litter, more driving completely off trail, more hooning on the trail. These are not the type of people who will respond to a friendly lecture. Yet they are the ones who will scream when severely damaged trails are shut down by overworked and underfunded public lands managers.

Short of funding a sniper division in the BLM, I really don’t have a solution.

Why you need the new edition of Tom Sheppard's Four-by-four Driving

If you want to be a better driver— and who doesn’t no matter what level we might consider ourselves to be at the moment?—and you don’t have this book, you need it. Trust me on this.

Full disclosure: I receive a bit of commission on every copy sold in the U.S., and I contributed the sections on winching and Hi-Lift/ARB jacks. But that’s not why I want you to buy it.

The reason you need it is because there is no other instructional book on four-wheel-drive technique that does what Tom Sheppard does in this one.

Four-by-four Driving doesn’t simply tell you how to drive in different situations. As the blurb on the back cover states, “I.T.D.S.—It’s the Driveline, Stupid.”

Knowing how to drive is great. Knowing why the vehicle does what it does, knowing how different drivetrains operate and how each reacts to differing terrain, knowing the strengths and weaknesses of each type of four-wheel-drive system, and learning how to exploit those strengths and accommodate those weaknesses, will turn you from a competent driver into a master of the machine and the terrain. I still learn or am reminded of those lessons every time I open my copy.

You can, if you like, just read the section in Four-by-four Driving that covers your own vehicle, but you’ll gain much more if you read through the descriptions of drivetrains and operating systems of vehicles around the world. Not only can you master your Tacoma, you’ll be able to hop in a friend’s Discovery or Wrangler or G-Wagen and master it too. In fact if you dedicate yourself to the first part of this book you could probably be air-dropped anywhere on the planet and stand a good chance of knowing how the dominant local transport works. Suzuki Jimny? Sure. Skoda Karoq Scout? Yep. On the off chance you find yourself in a Rolls Royce Cullinan, you’ll be right at home. And this edition includes, among other updates, full technical details of the new Land Rover Defender. (If you already own the fifth edition, note that the Defender coverage comprises the majority of changes to the sixth.)

Only after explaining drivetrains, traction-control systems, suspensions, and operating systems does the book start in on driving techniques, beginning with what I consider to be the basic skill that must underpin all others: mechanical sympathy.

Then, yes: You’ll learn how to drive on sand, mud, ice, and rocks. You’ll learn how to handle ruts, side slopes, water crossings, hill ascents and descents. Following this comes a chapter on recovery, both solo and assisted (and that brilliant section on winching . . . ).

Finished? Not even close. Now comes a section on advanced driving. If you ever find yourself plopped in the driver’s seat of a 60-year-old Bedford truck with a non-synchro gearbox, you’ll learn how to handle it. Or, want to show off by shifting the transfer case in an FJ40 or Series Land Rover from low to high range, while moving? That’s in there too.

Following all this are sections on expedition basics, tires and tire pressures, loading and lashing, oil types and grades, fuel, water . . .

But it’s in Four-by-four Driving’s former-RAF-test-pilot level of detail explaining how four-wheel-drive vehicles do what they do that the real gold of the book lies. Which explains why, unlike those 30 different watches you can buy that all claim to be “Used by Special Forces,” Four-by-four Driving actually is used as a training manual by special forces in both the U.K. and the U.S. It’s worth every penny.

Available right here.

Shackles: Are yours doing their job?

Proper shackle angle on an Old Man Emu suspension

I wonder if Obadiah Elliot had any clue, when in 1804 he patented a system of stacked steel plates designed to smooth the ride of a carriage, that his invention would still be in use two centuries later.

To be sure, the leaf spring has been eclipsed in sophistication by coil, torsion, and air springs, yet its simplicity, ruggedness, and low cost keep it standard equipment on the rear axles of millions of pickups and four-wheel-drive vehicles, as well as on the axles of larger freight-hauling trucks.

It’s not so much the cost of the spring itself that makes leaf-spring suspension systems cheaper to manufacture—it has to do more with the fact that a leaf spring also comprises its own locating mechanism. A coil or air-sprung beam axle requires a leading or trailing arm (or multiples) to secure it fore and aft, and a transverse arm such as a Panhard rod to locate it side to side. The leaf spring does both all on its own. Additionally, the stress a leaf spring applies to the chassis is divided between its front and rear mounting points, while the perch of a coil spring has to take all the load, requiring sufficient reinforcement.

Perhaps the biggest disadvantage of the leaf spring—that is, in the common configuration with multiple leaves—is inter-leaf friction, which not only hinders springing action but can vary or increase as, for example, the leaves become rusty. Some manufacturers such as Old Man Emu address this with a nylon pad at the end of each leaf, which can be lubricated.

There’s one situation, incidentally, when that interleaf friction can be an advantage—if you blow a shock absorber (as we recently did on our Land Cruiser Troopy), inter-leaf friction attenuates the endless cycling (bouncing) that would otherwise occur. If you’ve ever driven a coil-sprung vehicle with bad (or no) shocks, you’ll know what I mean. 

Those of you with leaf springs at one or both ends of your vehicle likely have never given much thought to the shackles—those brackets that connect the free end of the spring to the chassis. But they perform a critical function, and their orientation can affect several aspects of suspension performance.

A leaf spring in its static position has a specified eye-to-eye length. When it flexes as the vehicle travels over a bump or through a hole, the spring “lengthens” or “shortens”—obviously it actually does neither; as it flexes the arch in the spring simply decreases or increases, changing the eye-to-eye distance. A leaf spring attached rigidly to the chassis at both ends could not flex at all, so the shackle travels through an arc to allow this. Clearly, then, you want the shackle oriented so it does this job as effectively as possible. 

Take a look at this diagram.

Ignore for a moment everything but the angle at which the shackle meets the spring at the eye. This shows that angle as 90 degrees to the datum line—a line drawn straight between the eyes of the spring. For most practical purposes we can think of this as essentially right angles to the spring itself—an easy orientation to ascertain visually. 

The most obvious and important result of this angle is that it lets the spring flex to its maximum extent both when compressed and extended. You can see that if the shackle were angled as in “A,” the spring could flex a lot downward (as the shackle pivots forward), but when compressed, the shackle would quickly bind against the chassis. Exactly the opposite is the case with the shackle at “B.” The spring has plenty of travel when compressed, but very little when extended. Another danger of a shackle angled as at “B” is that if the spring flexes too much the shackle can invert and lock itself against the chassis, completely immobilizing the spring.

You might also read or hear that the angle of the shackle can affect the ride quality of the spring—and this is where things get vague. 

Note that this diagram claims that a shackle oriented at “A” will stiffen the ride while a shackle at “B” will soften it. I could find no explanation as to the physics of this supposed effect. On the other hand, I found a source claiming exactly the opposite. This one noted that with the shackle at “B,” when the spring compresses the shackle has to travel slightly downward in its arc before rising to the rear, and this jacks the chassis slightly upward, exacerbating the effect of a bump. Makes sense.

Not finished, however. Yet another fellow, with experience setting up racing vehicles, argues adamantly that the shackle has no effect either way on ride quality unless it actually binds. He points out that no matter what, the force from the spring is virtually straight up and down at the axle; the slight fore and aft movement imparted from the pivoting shackle is indiscernable. (He uses this fact also to argue against shackle-reversal kits as a waste of money.)

While the ride question remains unresolved, there’s no doubt that proper a 90-degree shackle angle allows the spring to do its job through the maximum possible travel in both compression and extension.

Look at the opening photo, which shows the rear of my FJ40 and its Old Man Emu suspension. The shackle angle is, as one would expect from the company, spot on (the front is as well).

In contrast, look at the shackle angle on the front springs of our Troopy:

Much closer to “B” in the diagram, no? These springs were installed at a shop in Perth, Australia, after we took it in to have them diagnose a worrying clicking noise I could both hear and feel through the steering wheel, and which neither Graham Jackson nor I were able to diagnose in the field except to be pretty sure it was in the steering. But the shop diagnosed worn springs, so we let them replace both sides.

We picked up the vehicle the day before we were scheduled to containerize both our and Graham and Connie’s Troopy for shipping to Africa—and as I drove away from the shop the clicking was there as loud as ever. Some testy and hasty negotiating resulted in a refund of all our labor charges, but the springs stayed on. (After getting the vehicle home I disassembled the steering and found indeed that was where the noise was coming from—just loose bolts in the tilt mechanism.)

Examining the springs in Durban I realized they had too much arch, resulting in this poor shackle angle. Whatever you believe regarding shackle angle and ride quality, these springs also definitely ride more harshly then the previous set, so I’m on a mission to fix both issues.

The first and most obvious approach is to remove a leaf in the springs. This isn’t necessarily as simple as it sounds, because removing the wrong leaf could create stress risers in the remaining leaves and lead to breakage. (So-called “add-a-leaf” kits can do this as well.) However, it looked to me that removing the bottom leaf on these springs wouldn’t compromise the rest of the pack, and the bottom leaf was the only one not captured with a clamp (or rebound clip to give it its proper name). So I jacked up the front end, loosened the U-bolts, and pulled the bottom leaves.

Notice the near-total lack of a wear pattern on the tips of the leaves.

After tightening everything again, I took the Troopy for a drive to settle everything then examined the results. Note the shackle angle in the first Troopy photo, and compare it to the “after” photo below. 

If you’re thinking, “I don’t see the slightest difference,” congratulations. I don’t see one either. Clearly those bottom leaves are doing nothing at all—at least when the vehicle is static. They probably don’t provide any resistance until the spring is significantly compressed.

Since this is in no way an existential threat, I’m re-evaluating. I might still try removing another leaf, or I might just live with it for now—I certainly don’t intend to spring for new springs just yet . . .

Once more, with feeling: Drum brakes are not "better off road."

It never fails to surprise me how persistent myths can be, even when there is an abundance of authoritative evidence to counter them.

A recent, otherwise informative and enjoyable article in a magazine I receive highlighted a classic four-wheel-drive vehicle from the 1960s. In describing the mechanicals, the writer noted that the brakes were drums on all four corners—still perfectly common in those years (my 1973 FJ40 came with all-drum brakes). While acknowledging this as outdated technology, the writer nevertheless went on to say (I’m paraphrasing), that drum brakes are less susceptible to loading up with debris off road, and that they stay cooler than disc brakes.

These claims are, respectively, badly misleading and utterly wrong.

The claim that drum brakes are less likely to load up with debris—for example mud during an excursion through a mucky hole—might seem logical on the surface, since a disc brake’s rotor is completely exposed to the elements and is immediately doused with whatever comes its way. It is more difficult for gunk to work its way past a drum-brake’s backing plate and get into the mechanism. (No less an entity than Toyota Motor Corporation co-opted this line to excuse its parsimonious decision to retain rear drum brakes in the current Tacoma.) 

The problem is that, once that gunk does get into a drum brake’s internals—and it will—it stays there until you disassemble it and clean it out, a time-consuming chore. Ask me how I know. A disc brake might squeal initially as slush impacts against the pad and disc, but it will quickly wipe itself clean, and if there is anything left a quick powerwash will take care of it. Drum brake shoes ride farther away from their contact surface on the drum, allowing debris to be caught between them.

The other claim, that drum brakes stay cooler than disc brakes, blithely ignores basic physics. Stopping a moving vehicle requires converting its kinetic energy into thermal energy. Period. All brake systems, whether drums or discs, have to absorb and then dissipate the exact same amount of heat when stopping an equivalent vehicle from an equivalent speed. Period. And while drum brakes absorb heat just fine—my FJ40, which now has four-wheel-disc brakes, stops no shorter than when it had all drums the first time you do so—they are are significantly worse at dissipating the heat they have absorbed. On a long, winding downhill road towing the 21-foot sloop I owned at the time the 40 still had stock brakes, the pedal would get progressively softer and less effective as brake fluid boiled into gas at the system’s wheel cylinders, where the drum brakes were retaining huge amounts of heat. Converting to disc brakes solved the issue as their rotors, exposed to the air, more rapidly dumped that heat.

So, once more, with feeling: Drum brakes are not “better off road.”

For more on this, please read here and here.   

Tom Sheppard's Four-by-Four Driving, 5th Edition

Can you learn to be a better 4x4 driver from a book?

The answer is yes. And no.

Don’t stop reading, because that’s not an evasion. 

The “no” part of the answer is easy to explain. Simply put, nothing can substitute for having an experienced human instructor in the seat next to you, or outside your open window, to give you second-by-second advice on your control inputs and choice of lines. Not long ago I watched Tim Hüber stand next the the driver’s window of a Range Rover while he had the owner repeatedly back up and slowly inch over a soccer-ball-sized boulder. Back and forth, back and forth. The aim was to hone the driver’s ability to gently ease over an obstacle or down a ledge, rather than bouncing and compressing the suspension, which reduces ground clearance and increases the chances of contacting bodywork. The fellow finally nailed it, and negotiated the following driving course with consummate grace. I can think of dozens of other instances I’ve watched (or, indeed, have experienced as a student), with such skilled and patient instructors as Sarah Batten, Graham Jackson, or any of the ex-Camel Trophy team members who’ve taught at the Overland Expo for a decade now. 

Having a live instructor is especially vital when learning to drive in conditions new to you, or more extreme than you’ve experienced before. This applies to such procedures as driving on side slopes, negotiating steep hill descents or difficult climbs, and similar situations where inexperience might either make you overconfident (unlikely), or too timid to fully exploit the capabilities of your vehicle.

However. You can significantly enhance your level of preparedness for that personal instruction by reading the right book. And I know of none better than Tom Sheppard’s Four-by-Four Driving. I’ll offer full disclosure right now: I wrote the chapter on winches and winching, and the section on the Hi-Lift jack, for this and the previous edition. But that’s a fraction of what this book is about.

(And in case you think you’re beyond such a primer, note that Four-by-Four Driving is the mandatory textbook for several trainers I know who contract with two governments to teach Special Forces operators advanced driving and recovery techniques.) 

Why is it so good? I think the answer lies largely in the fact that Sheppard was a test pilot in the RAF before he took to solo exploration of the Sahara. And when you’re flying an experimental jet aircraft, poor preparation and bad driving won’t just get you stuck—it will get you killed. Thus Tom insists that a thorough knowledge of the vehicle itself, and especially its driveline and four-wheel-drive system, is the key to being an effective driver. Think of it in terms of a maxim:

If you don’t know how the vehicle operates, you won’t be able to operate the vehicle. The more you know about how it operates, the more effective an operator you will be.

For this reason, a full 20 percent of Four-by-Four Driving is devoted to an exhaustive look into the drivetrains and systems of vehicles from the Suzuki Jimny up to and including the Bentley Bentayga. While you might be tempted to find your own model in here and only read about that, don’t. Learning about other approaches will help you understand both the strengths and weaknesses of your own ride. Besides, if you ever have the opportunity—or need—to drive something foreign to you, you’ll look like a hero if you hop in and immediately turn that LR4’s Terrain Response dial to the proper setting—or, for that matter, are aware that you’ll need to get out and lock the hubs on that Troopy before pulling back on the transfer-case lever.

Just a partial table of contents

The driving section then begins with another vital subject: mechanical sympathy; that is, how to drive with awareness of the vehicle and the right touch to avoid stressing or breaking it. Further discussions cover suspension articulation, low range and when to use or not use it, throttle and brake control, followed by extensive sections on types of terrain and the techniques used in each: sand, mud, tracks, deep ruts, rocks, water. What is the correct way to ascend or descend or traverse a steep slope? To cross a deep ditch or sharp ridge? Negotiate snow or ice? It’s all in here.

The following extensive section is all about recovery, both assisted and solo, and includes an utterly brilliant chapter on winching. :-) A short but fascinating chapter on advanced driving covers such arcane skills as changing from low to high range on the move, or driving a non-synchro transmission—just in case you ever get the chance to take a Bedford RL on safari. There are also useful sections on trailer towing for those of you with adventure-type trailers.

That would be a complete book, but Tom continues with a section on expedition basics—sort of a flash introduction to the last word on the subject, his Vehicle-dependent Expedition Guide—as well as sections on loading and lashing, equipment, fuels, oils, tyre repair, and vehicle selection for expeditions.

That front section, however, is why you should buy this book. For the fifth edition Tom immersed himself in the latest models and technology and updated anything that remotely hinted at being past its sell-by date. There’s even a brief flash of a disguised Rolls-Royce Cullinan careening along the face of a sand dune, with a typical Sheppard wise-cracking caption: “No, your Ladyship, the brake is on the LEFT! And Rolls is the marque, not the aim.”

Read this book. Then go get some professional instruction. I’ll bet you at some point your instructor will look over at you and say, “You’ve done this before, haven’t you?”

Factory vs. aftermarket

Aftermarket starter on the left; Toyota starter on the right

If you’ve ever turned over an engine by hand you know it’s no easy thing to do. You’re working against a lot of internal friction, plus the compression as each piston rises on the firing stroke. Your starter has to do the same job, except a lot faster. So it clearly needs to be built well.

Take a look at these two starters for a Land Cruiser F or 2F engine—an aftermarket unit on the left and a factory Toyota unit on the right. If you’re not familiar with how a starter works, notice the small gear visible at the top of each unit. When you turn the ignition key to start the engine, that gear slides forward and engages the flywheel behind the engine, and spins it rapidly to enable the ignition to catch and start the engine. Once it starts and you release the key, the gear slides back out of engagement.

It should be obvious that that gear is subjected to a great deal of stress—which is why the factory starter has a nose cone that supports the end of the shaft on which the gear slides, hugely increasing its stiffness (and also possibly helping keep random dirt and debris away from the shaft and gear).

Now look at the aftermarket starter. No nose cone, no support for the gear. Cheaper to make, for sure.

Which would you expect to last longer?

The truth about aftermarket "high-performance" brakes.

Few people reading this would argue that the single most important component of your vehicle is the braking system. Everything else—engine power, handling, comfort, fuel economy, off-pavement capability, number of USB outlets—is secondary to the critical need to be able to stop that vehicle safely and quickly, time after time.

Yet despite that single-purpose, critical function, there are a lot of myths circulating about brakes, how they work, and how they can be improved—and a lot of those myths originate from, or are promulgated by, companies trying to sell you something.

In terms of physics, brakes do exactly one thing: They convert the kinetic energy of the moving vehicle into thermal energy, i.e. heat. All brakes function this way, whether disc, drum, or Fred Flintstone’s feet. In fact, even the parachute on a top-fuel dragster converts the kinetic energy of the vehicle into heat, through friction with the atmosphere; it is simply dissipated more diffusely in the dragster’s slipstream.

The energy those brakes must convert does not increase linearly with speed; instead it increases with the square of speed (kinetic energy equals mass times velocity squared). Thus a vehicle moving at 50 mph requires four times as much energy conversion to stop as one moving at 25 mph, and one moving at 100 mph requires sixteen times as much. Given the same speed and the same vehicle weight, the heat produced by stopping is also the same, whether it is done via cast-iron drum brakes on a Series 2 Land Rover or the carbon-ceramic discs on a Porsche GT3.

The basic operation of a brake goes like this: When the driver presses the brake pedal, the pedal pushes a plunger into a hydraulic cylinder filled with brake fluid—a viscous substance resistant to heat. The cylinder, called the master cylinder, is connected to a brake caliper in each wheel via tubes. The caliper wraps around the perimeter of the brake disc, and incorporates a piston on each side (sometimes several), which bear against brake pads made of friction-resistant material. The master cylinder forces the brake fluid, which is essentially incompressible (more about that later) through the tube and against the pistons in the caliper, which in turn push the brake pads against the disc, squeezing the disc (also called the rotor) with tremendous force, creating friction and slowing the vehicle.

The drum brake, which has virtually disappeared except on the rear axles of the cheapest economy cars and Toyota Tacomas (see here), is different. Instead of a flat disc there is a cast-iron drum shaped like a flat pan with vertical sides, turned vertically so it rotates with the wheel. The master cylinder pushes against a slave cylinder (a quaint term, no?) which in turn pushes a friction-resistant brake “shoe” against the drum. Drum brakes have (mostly) gone the way of flathead V8s and carburetors because they retain more heat (more on that soon) and don’t work well when wet.

There have been many advances to the basic hydraulic braking system. Originally (and still in a few applications) each caliper employed only one piston and the caliper could slide slightly back and forth. The piston pushed one brake pad against the disk while simultaneously pulling the opposite pad against the other side. This was much less efficient than the later multi-piston calipers. Modern brake calipers on high-performance sports cars can employ six or even eight opposed pistons.

Virtually all brakes today are power-assisted via a vacuum-operated device incorporated into the master cylinder. This reduces braking effort, sometimes hugely in the case of a heavy truck. Also, all brake systems are now (by law) dual-circuit: The master cylinder is essentially two master cylinders combined in line, each of which operates on both front brakes and one rear brake. This redundancy insures that if one circuit fails, the vehicle will still retain reasonable stopping power.

A big advance in the efficiency of brakes arrived with anti-lock braking systems (ABS), which use a simple sensor at each wheel to monitor revolutions of the wheel. If a sensor detects a wheel locking up (i.e. turning slower than the others or stopping altogether), the ABS computer pulses power to that brake so that it unlocks. This system reduces braking distances and increases the driver’s control over the vehicle. (To see why a turning tire stops shorter than a skidding tire, look here.)

As vehicles have become heavier—and wheel diameters larger—manufacturers have been installing larger and larger-diameter discs in their brake systems. Most disc brakes are now ventilated—the disc comprises two discs joined by a vaned center section to dissipate heat more effectively. Thanks to such advances—as well as better tire compounds—average braking distances have been steadily shrinking.

Mostly.

Obviously it’s easier to stop a light vehicle than a heavy one. By extension we can state categorically that it is easier to stop, say, a stock FJ60 Land Cruiser than one that has been modified with an ARB winch bumper and a Warn 9,000-pound winch, a rear spare/jerry can rack, a roof rack, a 60-liter fridge, a drawer system, an auxiliary fuel tank, and . . . you get the picture. With surprising suddenness your 5,000-pound Land Cruiser x velocity squared can become a 7,000-pound Land Cruiser x velocity squared.

I discovered the results on our own FJ60 on a biological survey in Mexico’s Sierra Madre some years back. This 60 had a turbodiesel engine conversion plus most everything on the list above. And on a steep, winding descent of about 3,000 feet, the brake pedal began to feel mushier and mushier, even as I downshifted to use engine braking. By the time we reached the plains the brakes had seriously deteriorated, and only regained effectiveness after ten minutes of cooling down.

I had experienced classic brake fade.

Brake fade can occur essentially two ways. First, a brake pad can overheat from extended application—such as a long descent—and form a slick glaze on its surface. When this happens the brake pedal will still feel firm, but increased pressure will have little or no effect. Second, the brake fluid itself can heat to its boiling point. When this happens, the fluid turns to a gas—and gas, unlike the fluid, is compressible. So your desperate standing on the pedal just compresses the gas in the calipers and does little to squeeze the brake pads. This is what we experienced. The condition can be aggravated if you don’t regularly flush your brake system. Brake fluid is hygroscopic, meaning it absorbs water, and since water has a much lower boiling point than pure brake fluid, old, contaminated fluid can cause premature boiling and fade.

Of course even stock vehicles with no weighty accessories bolted to them can be subject to brake fade, and even if no calamities ensue when it occurs it is a deeply unsettling experience. The logical first response is, “I need better brakes!” Indubitably true, but the path to obtaining them is fraught with hype and numerous ways to spend lots of money for very little if any gain.

Let’s start with that brake fluid. Brake fluid is graded on a DOT scale, based on its minimum  boiling point, both dry (uncontaminated with water), and wet (contaminated). Most braking systems come from the factory filled with DOT 3 fluid, which has a minimum boiling point of  401ºF dry and 284º wet (see now how much water can degrade your brakes?). Dot 4 fluid is rated at 446º and 311º minimum, respectively, and DOT 5.1 fluid carries a 518º and 374º rating. So simply spending 20 bucks or so upgrading your brake fluid can give you a full 100-degree margin over DOT 3 before gassing occurs. Note that these standards are minimums; many premium brake fluids will perform well above that and will say so on the label. And what happened to DOT 5 fluid? That’s a silicone-based fluid as opposed to the glycol base of DOT 3, 4, and 5.1. You can mix glycol-based fluids all you like, but cannot mix glycol and silicone fluids.

It will do little good to install better, high-temp brake fluid if your brake pads are sub-standard. Most vehicles come from the factory with organic-compound pads, or NAO (non-asbestos organic). These are sufficient for most use—they are quiet, don’t create much brake dust, and are easy on the discs—but if overheated can be subject to the glazing we discussed earlier. Semi-metallic pads, which are a mixture of iron, copper, steel, and graphite in an organic matrix, are significantly more resistant to glazing, at the expense of (sometimes) more noise, more dust, and faster disc wear—and of course slightly higher cost. A third type of brake pad, ceramic, attempts to solve the noise and dust issues of semi-metallic pads, and is resistant to fade, but less aggressive and generally not recommended for heavy-duty use, especially in cold climates—although the technology is still advancing..

So if your braking system is in good order, you’ve upgraded your brake fluid and switched to semi-metallic pads, and you’re still experiencing brake fade, what then? (I’ll refrain from suggesting, “Leave some of that crap at home.”) It might be time for a more drastic upgrade.

And that’s where marketing hype gets really tricky.

Many commercial kits (as well as a whole bunch of do-it-yourself threads on forums) “upgrade” the front brakes—where most braking occurs—simply by means of replacement calipers with more and/or larger pistons and larger pads than the originals. More pistons equals more squeeze and better braking, right?

Not so fast.

Remember all that kinetic energy we’re turning into thermal energy every time we stop? That energy (heat) has to be dissipated to enable repeated stops—or a safe descent down a mountain grade—without overheating the pads or brake fluid. And the way that heat is dissipated is through the brake disc. So if you install more powerful calipers on your existing discs, here’s what’s likely to happen: You’ll take the vehicle out for a trial run around town, and be impressed at the increase in stopping power. Those new four- or six-piston calipers grab that disc right now. Awesome. So you’ll then head confidently to that long downhill that resulted in a scary spongy brake pedal last month, and . . . oh. Whoa. Halfway down, the pedal feels like it’s got an entire bag of Sta-Puft marshmallows between it and the calipers. That’s because you’ve installed the means to inject more heat into the braking system without installing the means to get rid of it. As long as you’re just trundling around town you’ll get some benefit from the more powerful calipers, but under prolonged application all they’re likely to do is make your fade problem worse.

Okay . . . plan B then. Let’s install a set of those fancy (and awesome-looking) cross-drilled brake discs. You know, like Porsches and Ferraris have? Cross-drilled discs stay cooler, right, with all those holes?

Sorry . . . wrong again.

Cross-drilling of brake discs began in the early days of disc brakes, when existing pad materials and adhesives tended to outgas strongly when heated. Cross-drilling relieved the fractional layer of (compressible, remember) gas the pad would exude between it and the disc. But modern brake pads exhibit virtually none of this outgassing. More importantly, a cast-iron brake disc relies on its mass to absorb and dissipate heat. When you drill a bunch of holes in it, you are reducing that mass. (One company actually boasts that its drilled discs are 16 percent lighter than non-drilled discs.) Some arguments—especially from those who sell them—still maintain that the ventilation and added surface area of cross-drilled discs provide enough cooling to offset the loss of mass. But the further I investigated, the more testimonials I read from objective experts in the field who called nonsense. At best, many referred to any cooling effect as a wash, and several pointed out how often cross-drilled discs wind up plugged with brake dust—a giveaway that not much air flow is occurring through those holes (unlike the well-documented radial flow through the center vanes of a ventilated disc). Add to that the fact that, even when properly cast in and chamfered rather than simply drilled, cross-drilling can introduce stress risers into the disc that promote cracking, and you have a powerful argument against it, no matter how stylish it looks. (And if you look at the ads from companies who sell them you’ll be amused at how many mention the style factor as an actual reason to spend your money.)

The sole theoretical advantage to drilled discs mentioned by those same experts was a slightly enhanced initial “bite” in wet conditions, when the holes might provide an exit for surficial water on the disc. But brake pads quickly squeegee water off that surface anyway, so even this attribute is of questionable value in the face of the expense and loss in mass of a drilled disc.

Thus we can say pretty confidently that replacing your plain brake discs with cross-drilled discs of the same size will probably result in no reduction in fade, and could conceivably exacerbate it.

(Incidentally, the above does not apply to disc brakes on motorcycles, since a motorcycle disc is a solid rotor rather than a vented, double-sided unit. On a solid rotor, cross-drilling does at least theoretically create some turbulent cooling flow.)

What about the more recently popular slotted discs? Slots actually perform a different function than drilling. The edges of the slots perform a microscopic scraping function on the pad, keeping the pad surface fresh and possibly forestalling glazing. While they won’t in themselves enhance cooling or prevent heat-related fade, they might help forestall the fade resulting from overheated pads of inferior composition. Be advised, however, that slotted discs, as you might expect, will wear out pads more quickly than solid discs, and are likely to exacerbate any brake-dust issues.

Inevitably, aftermarket manufacturers are now offering discs that are both cross-drilled and slotted. At least the slots will provide some function, and where the slots are there is less room for the pointless holes . . . 

All this leads to a logical conclusion. Once you’ve optimized your brake fluid and brake pads—and assuming the rest of your braking system is operating as it should—the only sure way to add braking power and reduce the chance of fade is to install, surprise, larger brakes—specifically discs of larger diameter and/or width, with calipers to match. Sometimes this is possible within the constraints of your existing wheels and front end design, sometimes it is not. 

Automobile manufacturers are perfectly aware of this. To give you a random example—outside the realm of overland vehicles but one with which I’m familiar—when Porsche upgraded the 1983 911SC to the 1984 Carrera, including a 15-percent bump in power, they improved the braking by increasing the width of the front brake discs from 20 to 24 millimeters, while keeping the diameter the same at 289mm. For the significantly more powerful Turbo of the same era, they increased both the diameter and the width of the discs, to 300 and 32mm respectively. Those were the largest brakes that could fit within the factory 16-inch-diameter wheels. When Porsche added even more power, they switched to larger-diameter wheels as well to accommodate larger discs.

There is one minor exception to the only-bigger-is-better rule. If you look at different aftermarket discs, you’ll notice significant variations in the spacing of the center cooling vanes. Inexpensive discs will be made with more widely spaced slots, which means there is both less mass in the disc to radiate thermal energy, and less radial air flow as well. The one way an aftermarket disc of the same dimensions as the stock disc might outperform it is if the aftermarket disc has a higher density of vanes, and thus weighs more than the stock disc. StopTech, for example, makes a replacement disc for the Tacoma that is stock diameter, but weighs over a pound more, thanks to more closely spaced vanes. That translates to more thermal capacity.

A comparison of vane spacing on a vented brake disc.

Looking at our own class of vehicles, it is all too easy to find “high-performance” brake kits comprising nothing but inexpensive stock-sized replacement discs that have been cross-drilled and/or slotted. Some of the claims for these border on outrageous.

Note that line, “Improves stopping power up to 30 percent over stock brake rotors.” Seriously? Thirty percent meaning 30-percent shorter stopping distances? Or thirty percent less fade? I’d love to see an independent test of that claim. Also, there is simply no chance that their “custom slots” do any cooling, and they will more than likely increase dust due to the scraping function. Finally, check the “reducing heat” claim at the top, which we know from physics is impossible. The only component in this kit likely to modestly improve braking performance is the semi-metallic pads, if they are replacing stock pads—and those certainly won’t “reduce noise.” That’s a stunning amount of misinformation in a single ad.

Finding kits to actually upgrade brakes is much, much harder, in part because it so often requires installing larger-diameter wheels as well. TRD offers a front disc upgrade kit for Tacomas that increases the disc size from 319mm to 332 mm but still fits within the stock wheels. That’s a worthwhile enhancement.

Redline Land Cruisers offers a Big Brake kit for the front of FJ40s, 55s, and 60s that increases the disc diameter from 12 inches to a full 13.3 inches and includes calipers from a later 100-series Land Cruiser—a significant upgrade. But the kit requires a switch to 17-inch wheels for clearance (the company also wisely recommends rear discs, a larger master cylinder, and a proportioning valve to correctly balance front-to-rear braking force). They also mention a big brake kit for 16-inch wheels, but I’ve not received any more information on that one.

I’ve seen a few other legitimate kits for various vehicles, but there is far more in the way of chaff to wade through to find it. The good news is, I suspect for the majority of us a simple upgrade to better pads and fluid will solve anything but chronic brake fade. If that won’t do it, at least now I hope you’ll be better able to distinguish hype from fact. 

And if you really want to drill holes in something, maybe you could take up carpentry . . .

JL Wrangler frame issues

Photo: Brett Stevens

The folks over at Jalopnik have a good and extremely important article about the issues some owners are having with welds on JL Wranglers. The critical issue is the weld that holds the track bar to the frame, and the article includes photos and a video of the problem.

The track bar is what locates the front axle side to side, so if it goes so does directional control and steering—not a good thing.

If you own a JL Wrangler you will probably be receiving information about this, but in the meantime you might want to take action yourself. Reportedly FCA has issued a stop-sale order until the matter is addressed.