Bedding-in Brake Pads and Rotors. What is that??
The Final Lap - Jan. 2010 Newsletter ver. 1.0


To all enthusiasts,

With this being the first newsletter of 2010, I would like to wish you a Happy and Prosperous New Year. The year of 2009 just flew by, and it seems as if I say that every year. Ha ha ha ha, because it really does fly by. Sometimes, you feel that there isn't enough time in the day to accomplish what you need to do and not enough months in the year to accomplish yearly goals. With that in mind, we must strive harder this year. I've made some mistakes last year and this year, I will forge on and plan accordingly, all the while learning from my mistakes and pushing hard to reach my goals. I think everyone should do the same, so we can look back at the end of this year and see how much we've accomplished. In this months newsletter, I will talk about bedding-in your brake pads or better known as "burnishing" in the racing world. In order for you to accomplish your goal of 1st place on the podium, you must have excellent braking capabilities and those brakes will not work to their fullest potential, unless the pads have been bed-in properly before the race. I know you are probably thinking, that you've never heard of this technobabble before, but that's ok. Inline Four is here to educate, not only sell parts. So we begin...

Bedding-In Brake Pads and Rotors

When's the last time you bed-in your brakes? If you're an enthusiast who wants to get the most out of your car on the street and track, your answer to that question hopefully isn't, "what the heck is this guy talking about?" As aggressive street and track drivers, we're constantly upgrading our cars, and we've accepted that preparing our new parts for heavy use is not only the best way to get the most out of them, it's also common sense. When we get a new car, we seat our piston rings through a specified engine break-in procedure. When we get a new set of race tires, we heat cycle them so we can get the most wear and grip out of them over the long haul. When it comes to brake pads however, we tend to ignore them. Somewhere along the way, it becomes a fairly common practice to just slap on a new set of pads and go bombing around the racetrack on the warm-up lap.

There are a whole bunch of reasons why that's a bad idea, and they all add up to costing you a lot of time and money.

What is Bed-in?

The goal of bedding-in your brake pads and rotors is to mate them together properly and prepare them for heavy use. Let's begin by first taking a closer look at how exactly pads and rotors interact. When you look at the coupling between pads and rotors, you have two potential friction mechanisms, abrasive or adherent. The abrasive mechanism describes the situation when the pad in your caliper is directly rubbing against the rotor face. When you throw some new pads in the calipers and hit the brakes cold, that's what's happening. What you may not know, is that most pads today are actually designed to work optimally in a different manner. With an adherent pad, the pad material is transferred to the rotor face in a thin layer when heated, which fittingly, we call the transfer layer. Then the pad in your caliper actually rides on that thin layer of pad material that you've put down on the rotor, rather than rubbing directly on the iron rotor face.

Drag racers should be familiar with the concept. On a drag strip, you do your burnout in the box to get the tires spinning. As they spin, they heat up, and start laying rubber down on the track. When you see the pros run, they extend that burnout up to and past the starting line, laying rubber the whole way. When they launch from that rubber-coated surface, their tires dig in and have more grip than if they were trying to launch from the uncoated track. The like material, the rubber on the track and the rubber on the tires, bonds together more solidly than the differing materials of the tires and track. Well, it's the same situation with brake pads. With most pad materials today, some hot pad-on-pad action will give you more friction than a pad-on-rotor interface.

So what does all of that mean? It means that if you don't lay down a nice, even transfer layer of pad material on your rotors, you're leaving performance on the table! A good transfer layer is going to give you superior brake pedal feel, as your pads will bite more evenly on your rotors. In most cases, you'll also have less noise. When the pad in the caliper runs on a layer of pad material on the rotor, rather than directly on the iron rotor face, you tend to hear a lot less noise and squealing. You're also going to get less pad and rotor wear. More concerning however, is that if you don't intentionally establish a good transfer layer on your rotors, you may do it accidentally when you really heat the brakes up for the first time through aggressive driving. Then you run the risk of getting uneven pad deposits on your rotors, which means the dreaded thud-thud-thud vibrations when you step on the brakes. In the worst case scenario, your rotors may not even be recoverable, which means you'll need to buy new ones. That's always a fun scene at the dealership, when they tell you need new front and rear pads and rotors, and by the way, that will be $1,000 please.

Finally, during a proper bed-in cycle, the rotors are introduced to heat stress through a progressive temperature increase. The rotors are brought up to temperature over time, rather than being instantly shocked at an extremely high temperature. Ramping up the heat in the rotors prepares them for heavy use as the metal gradually expands. Wild temperature swings from very cold to very hot are the greatest cause of cracked rotors, which is something we're obviously trying to avoid. If you think I'm exaggerating the importance of bed-in, take a guess at how many of the NASCAR teams are having their rotors prepared before they ever even see them. ALL of them! There are a select few high-end brake companies that perform pad and rotor bed-in for a long list of professional race teams.

A bed-in procedure will vary with the specific rotor and pad that you'll be trying to prepare. It's something that you'll need to figure out for your particular setup. Hopefully with a good understanding of the theory, along with a basic procedure to get you started, you'll be able to get the most out of your brake package.

Procedure Overview

Okay, so we have the basic theory out of the way, let's take a look at the actual procedure. First, make sure you have a safe location to perform a proper bed-in. You need a stretch of asphalt with long straights, good visibility, and no potential obstructions. Obstructions are other cars, walls, trees, your neighbor's cat, or any other living or inanimate object with which you probably shouldn't be colliding. With a street pad, you typically won't have to go over 60mph, but with race pads, you probably will. Make sure you are in a position to safely, legally, and repeatedly hit the necessary speeds. Inline Four in no way suggests or condones speeding or doing anything illegal in your car.

Now we're going to discuss a scenario of a bed-in procedure. In this scenario we'll be using an OEM-sized rotor and a common street pad. As described earlier, it will be much easier to generate the heat we need at lower speeds than if we were using a race pad and a larger rotor that flowed more air.

The first couple of stops will gradually bring the rotors and pads up to temperature. After a few stops the pads will start to smell...the resins holding the pad together will start to burn. By the fourth or fifth stops, we'll start to see smoke in most cases. This is where most people hit the panic button and quit the procedure. They think, "I'm hurting my car!" This is actually the critical point where you need to keep pushing through, since this is where pad transfer typically begins. After you've done the procedure enough times, you'll probably be able to feel the pad transferring to the rotor through your foot on the brake pedal. The next couple of stops are where the bulk of the pad material transfer will occur. Then we'll do a cool down, and take a look at what we have. Something critical to notice during the procedure...I never, ever come to a complete stop with my foot on the brake pedal! That's a big no-no, but happens all too easily when you're distracted or don't pay close attention. The reason why you don't want to come to a complete stop, is because the pad is so hot that if you happen to stop, it'll fuse itself to the rotor and will have an uneven pad transfer layer, with the outline of your pad in one spot!

Bedding-In Procedure

If you have brake ducts on your car, in conjunction with a big brake kit, you may want to block them off to allow the system to heat up more easily. First, accelerate up to roughly 60mph and then decelerate down to a slow roll...maybe 5 or 10 mph. Hit the brakes with a firm stop. Don't slam on the brakes, but press hard enough right before ABS intervention. Do not worry if the ABS comes on, but you should try to hold the brakes at a point just before ABS kicks in. That will ensure a smooth application of the pads against each rotor, rather than a series of brake "hits" from each caliper. Once down to 5 or 10mph, immediately accelerate back up to about 60, so the brakes don't have much time to cool off. With the cold pads and rotors, the pads won't have a ton of bite, and they may feel a little wooden. After a couple of stops though, they'll begin to "come in" a bit.

That was stop number 1. Repeat the procedure for stop number 2 and 3 after this stop, you may smell the resins and lubricants cooking a bit. You may even see some smoke coming off the front corners on the next couple of stops. Now after finising stop number 4, you should be seeing a good deal of smoke. This is where most people get freaked out, which is why they don't typically get a good bed-in completed. Your brakes aren't going to spontaneously combust, so no need to panic, particularly if your pedal still feels solid. There is a chance you'll experience pad fade at this point. You'll know that's happening if your brake pedal is firm when you press it, but the car still isn't slowing down. That means you need to be extremely cautious when performing your next couple of stops...you need to make sure you have plenty of room, because the car will require a greater distance to stop.

At this point you should feel the pads transferring to the rotor. To describe the feeling, the pedal feels a little bit different from the previous stops. The pads feel like they're compressing somewhat, and they also feel like they're sticking to the rotor a tiny bit when you release the brake pedal. You will see more smoke now as you pour more heat into the system. Now is when you really need to be careful not to come to a complete stop. If the police show up right now, just wave and yell out the window that you can't stop because you're performing a scientific experiment.

Now your pads will start to fade quite a bit on the final stops, the smoke will be heavy, and the brakes smell. After this point, you have to let the brakes cool down. For your cool down, you want to get air flowing across and through your rotors and pads. That means it's better to go cruise down the highway for five minutes than it is to putt around town at 30mph. You also don't want to be in a stop-and-go scenario where you have to come to a complete stop(remember cooking your pads against your rotors). For those that live in low populated areas, such as the countryside, it should be easy. For the city peeps, it can be a little tougher. Where I live, here in Garden Grove, CA., I do my bed-ins in the industrial business park around Inline Four, then I hop on the 22 freeway, which turns into the 405 freeway and i'll just cruise for ten to fifteen minutes.

Post Bed-In Inspection

When you get back home or to your buddies house or the shop, you can park and do your inspection. Even though the brakes aren't smokin hot, they will be somewhat hot, so I try not to pull the e-brake. Just put the car in gear and park on a flat surface, so the car doesn't move. When looking at the rotor, you should see a clean transfer layer of the brake pad material. It should be smooth, evenly distributed, and dark in color. You will see the transisition from the top of the rotor. The edges may be greyish in color, since they got cooked a bit. That's how they will look, and no you haven't hurt or ruined them. Best way to also tell, is how it feels after the cool down process. The pad will have a nice bite and the pedal will have a nice firm feel.

Race Pads and Big Brake Kits

If your rotors and pads don't look like this when you're done, then you just have to go back out and do another cycle. A cycle is the full series of stops. Chances are, you probably didn't get your setup hot enough, and it will take some practice to learn what it takes for the procedure to be effective on your specific car. This can become particularly challenging with race pads on a big brake setup. The rotors typically flow more air than the stockers, they are a larger heat sink, and race pads need a lot of heat before they start transferring material to the rotors. If after each stop you are immediately accelerating back up to speed, that means you have to perform your stops from a higher speed...80mph or 100mph are nice starting points. Keep in mind though, that the energy in those stops is much higher, so you may not need to do as many of them. Instead of 10 stops from 60, you may only need to do 6 from 100. Or, maybe it's 20 stops from 60, instead of 10. Again, it's just going to depend on your particular pad and rotor combo. Please keep your local posted speed limits in mind when working with race pads.

Rear Pads and Rotors

If you're driving a front-engine car and you take a look at your rear pads and rotors after the bed-in, the transfer layer will likely not be as extreme, and your rear pads probably won't look nearly as cooked. That's fine, and it's not a problem. That's because your car is using substantially less rear brake than a rear-engine or mid-engine car. If you're driving a Porsche GT3 like David's with his normally aspirated, high-compression engine dangling out back, you're using a lot more rear brake, and you'll likely see a more balanced bed-in on the front and rear.

An exception would be if you're driving a front engine car with severely undersized rear brakes. A good example would be a non-Track model 350Z. The rear pad on that car is the size of a postage stamp, and the rotors aren't particularly large either. That means it's not going to be terribly difficult to get some serious heat into the rear brake system on that car.

What Happens Over Time?

Okay, so you did your bed-in and your brakes have been flawless for a couple of weeks driving back and forth to work, and carting your girlfriend to the mall. You've had good bite, the pedal feels great, and you haven't heard any noise. Out of nowhere, they start to squeal a little bit one morning on the way to work. By the time you get home, they're making all sorts of noise. When you inspect them, the transfer layer is gone, the rotors are silver, and they look almost like they did when they came out of the box new.

That's completely normal. Just like the other parts of your car, your brakes and their transfer layer needs to be maintained for optimal performance. When you're operating your car in day-to-day driving, they're almost always cold. When they're cold, they slip into the abrasive friction mechanism we talked about at the beginning of this newsletter, under the "What is Bed-In?" section. That means that on your way to the store, they're constantly scraping away at the transfer layer you laid down on the rotor. The only time they might get hot enough to replenish that transfer layer would be on a canyon run or a trip to the track. Your only solution is to go back out and do another bed-in cycle to get them back in proper form.

Conclusion

Well, that about sums it up for bedding-in or burnishing brake pads and rotors. If you're conscious about properly preparing your pads and rotors for heavy use, it will pay big dividends in the long run. The harder you run the car, the more apparent those benefits will become. Your brake pedal will feel better, you'll have less brake noise, less pad and rotor wear, fewer judders and vibrations, and a much lower chance of trashing your rotors. You'll be getting the maximum performance out of whatever brake setup you're running at the time, you'll save money, and you'll enjoy your car a lot more. Don't forget to visit www.inlinefour.com for all your braking needs. Drive Safe!