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KNOW BRAKES.

with Jeff Ritter

Episode 2: Swapping Between Street and Track Brake Pads

In the last episode of Know Brakes, we examined the pad and rotor bed-in, or burnishing, procedure.  I showed you how to take a new set of pads and rotors and prepare them for heavy use on the road and track.  Hopefully you've had a chance to try that procedure and have realized the host of benefits it provides.

If your car is a dual-purpose street and track car, you likely swap between street and race pads on a regular basis.  In fact, the mere thought of jacking up your car and changing pads for the millionth time probably makes you cringe.  In this episode of Know Brakes, we're going to focus on how to cleanly make that swap between street and track brake setups while avoiding the vibration, judder, and uneven pad deposits that often accompany that switch.  You'll go to the track each weekend confident that you're getting the most out of your brakes.

One of the first keys to understanding the procedures in this video is recognizing that street and track/race pads are different.  Most pads specifically designed for one of these venues don't work well in the other.  Street pads have low noise and dust, but don't hold up to the heat generated on the track. On the other hand, Semi-metallic race pads are formed from more abrasive materials that can handle high temps.  They perform well on the track, but make noise, dust, and eat your rotors when driven cold on the street (for a more in depth discussion of this topic, see my article on how to choose the best street and track pads.)

The other key piece to understanding why the procedure outlined in this article/video works is recognizing that brake pads operate in either an abrasive or adherent manner.  When pads are cold, they are abrasive.  They scrape your discs to generate friction and slow your car.  However, after you heat them up through a series of stops, they become adherent and stick on the rotor face, creating a pad transfer layer.  Street pads will make that switch from an abrasive to adherent mechanism at a much lower temperature than a race pad will.  That's why it's much easier to bed-in a street pad (you don't need as much speed or as many stops).  That's also why it's much quicker and easier to remove a transfer layer from your rotors with a race pad.  If you just drive around with your street pads for a long time, the transfer layer will eventually wear off.   It will just take much, much longer than if you use an abrasive race pad.

Once you have dedicated street pads and dedicated track pads for your dual-purpose street and track car, you'll be faced with the dilemma of how often to swap your pads.  This is a purely personal choice that I won't go into here.  However, managing that swap properly will mean the difference between getting the most out of your brakes in both venues vs. giving yourself a string of costly headaches.

The first rule to remember when switching brake pads is to always start with a clean slate.  By a clean slate, I mean a clean disc face.  Prior to bedding in any set of pads, you need to first make sure you remove as much of the existing pad transfer layer from the rotors as possible.  It doesn't matter if you're swapping from street to race pads, race to street pads, or one street compound to another street compound.

Let's take a look at a couple of common examples.  Let's say I run Hawk HPS as my daily driver street pad.  I do a bed-in on those pads, and I get a nice even transfer layer around my rotors.  The brakes are working great on the street.  When I get to my weekend track event, I drop in some Ferodo DS1.11's.  I go out in my first session and get the Ferodo's hot enough transfer onto my rotors.   What I've done is stacked one transfer layer on top of the other.  Some of the Hawk material was surely scraped off, but it's likely that I now have a good deal of both materials on the disc face.

Another common scenario would be if my car was a track-only weekend toy.  I was running my Ferodo DS1.11's, but I wore them out at my last event.  On the night before my next event I switch to a Mintex F2R pad.  I got out on the track.  During the first few stops while my new F2R's are cold, they're scraping the old material off of the rotors.  However, once the new pads heat up, they start to lay down a layer of material on top of the remaining DS1.11 material.

So what's the issue?  The problem is that in most cases when stacking pad materials, I'm going to get some nasty vibrations.  The composition of pad materials from various manufacturers is quite different.  They have a wide array of base metals, fillers, and lubricants.  Different pad compounds from the same manufacturer will also vary in their constituent materials and the ratio of those materials.  When you try to lay these materials down over each other, that doesn't typically happen in an orderly fashion.  The underlying material may smear on the rotor face or aggregate in one area.  The new pad material starts to collect on these high spots, and then you're looking at some ugly uneven pad deposits.  These pad deposits translate to vibration and judder.  Eventually, they can harden and become extremely difficult or impossible to remove, necessitating a costly set of new rotors.  When you mix pad materials in this manner, you're also contaminating your new pads. The old pad material is embedding itself in the new pads. It's extremely difficult to predict what impact this will have on the new pads, the consistency of their performance, their longevity, etc.

Here's a good example of uneven pad deposits:

uneven_pad_deposits_arrow_700

In contrast to the picture above, here's what a nice even transfer layer looks like:

img_0284_700

The purest solution is to have a matched pad and disc set for each pad compound.  You have a set of rotors that have been bedded with Ferodo DS1.11 for the track, and a set of rotors that has been bedded with Hawk HPS for the street.  You swap the rotors and pads, and you're instantly ready to go.  In that manner you never cross-contaminate, and you consistently have properly prepared brakes.  However, for many enthusiasts with a dual-purpose vehicle the cost of buying multiple sets of discs is prohibitive.  It's also more time consuming to swap rotors because you have to remove the caliper.

So how can we solve this issue?  We try to make sure we get as much of the old pad material off of the rotor before running a different pad material.  How do we do that?  We use the highly abrasive properties of our race pads to our advantage, by turning our car into a mobile brake lathe.

My Daily Driven Brake Lathe

If you read my piece on choosing brake pads, you know that most race or track pads are very abrasive when driven cold.  In other words, rather than transferring to the rotor face when cold, they primarily generate friction by scraping the rotor face.  We're going to use that trait to our advantage, and scrape the old pad material off of our disc faces.  We'll do so by performing a series of stops, without ever allowing the race pad to get hot enough to transfer to the rotor.  Some compounds are obviously more abrasive than others, but generally speaking, most race compounds with a high coefficient of friction will work for this procedure.  I've always used Hawk's Blue compound, which is a safe bet at a fairly affordable price, and comes in a wide range of applications.  When going to the track, I usually keep a set on hand in my toolbox in case I need to clean up my rotors.

If you think back to my bed-in procedure in Know Brakes Episode 1, you'll remember that the street pads I was using didn't start transferring to the rotors until they had a substantial amount of heat in them.  With race pads, that temperature point is even higher.  That makes it easier to quickly and safely get your rotors cleaned up and ready for a pad swap.  You can do some fairly aggressive braking without ever getting them to the point of material transfer.  So in this case, the procedure is actually the opposite of what you're trying to achieve with a bed-in.  In a bed-in, you're performing a series of stops and trying to get the pads hot enough to transfer to the rotor face.  During the pad-swap procedure, you're doing a series of stops while purposefully trying to keep your brakes as cool as possible.  That means, you don't block off your brake ducts, and you may need to let the brakes cool a bit between stops, rather than just hammering them relentlessly one stop after the next.

The easiest way to clean up your rotors with race pads is to simply drive them around as your daily driver for a few days.  Let's go back to our earlier street-to-track example.  You did your bed-in with your Hawk HPS street pads.  You have a track day coming up in a week.  You plan on using Ferodo DS1.11 for that event.  The easiest way to prep your rotors prior to bedding in your DS1.11's is to simply swap in the DS1.11's the weekend before the event and drive them around on the street.  In normal daily driving, you'll never get the race pads hot enough to begin transferring onto the rotors.  During that time they'll be operating in an abrasive manner, scraping the HPS material off of your discs.  By the time your event weekend rolls around, you should be back down to bare, shiny metal on your discs.  Sure they won't be quite as clean as if you were using brand new rotors, but you should be able to get just about all of the old pad material off of the rotors, providing the perfect canvas for laying down a layer of race compound through a proper bed-in.

Easy enough, right?  Well, there is a downside to this solution.  A common characteristic of semi-metallic race pads is that they often have a decided lack of cold bite.  That means when your wife takes your Viper to buy a gallon of milk and makes a panic stop, she may not get the results she was expecting!  Therefore, if you decide to go this route, please be extremely careful.  Leave yourself some extra stopping distance, particularly on the first few stops when the race pads are completely cold.  The other option would be to use sintered racing pads, which typically have great cold bite.

Quick and Dirty Clean Discs

If you don't have the time or don't feel comfortable going this route, you can shorten this process down to an hour or less, which is what I did in this video.  I took my rotors with their nice layer of street pad transfer layer, and dropped in some race pads.  I went out on the road and did some fairly aggressive braking.  As soon as the pads started heating up, I let them cool down.  Again, the goal is to keep the race pads cool enough so they will keep operating in an abrasive manner.  If you get them too hot, they'll start to transfer to the disc, which is what we want to avoid during this cleaning phase.  It's just that simple. 

In the video you'll see the dark, blue/grey street pad material steadily stripped from the rotor face, revealing the silver bare metal beneath.  Also take note of how different my brakes sound in the beginning of the video when the discs had a layer of pad material on them, vs. the end of the video when they were back to bare metal.  As the pad material is worn off of the rotor face, you get more of a scraping and squealing sound.  That shows how far a good bed-in / transfer layer can go towards noise reduction.

In this manner you can get your rotors completely cleaned up and ready for a different compound in about an hour.  You don't have to drive illegally or break the speed limit.  You also don't have to worry about taking the discs off of the car, sanding them with garnet paper, or having someone else cut them for you.  The beauty of this procedure is that there aren't any hard and fast rules about how to get this accomplished.  You need to experiment, and it will also help you get a feel for the characteristics of the race compound you've chosen.  You'll have fun driving the car, instead of alternate solutions that require the removal of your rotors.  Once you have your disc face back down to bare metal, you can do a bed-in cycle with the new pads of your choice.

Taking it Home: From Track to Street

So you bed in your race pads on your freshly cleaned discs, and went to your track event.  Your brakes performed well, and you didn't run into any issues.  Now it's time to put the car back in street guise.  The easiest way to prep your brakes for the switch back to street pads is to just leave the race pads in the car and drive them home.  Just make sure you take note of how the rotors look before you leave the track, so you have a point of comparison.  Depending on how far you live from the track, there's a good chance your rotors could be fairly clean by the time you make it home.  If you're cruising on the highway, every once in a while you can lightly press your brake pedal for a few seconds to scrape off additional pad material.  As mentioned earlier though, be careful when braking with cold race pads.  Since they're bedded-in they'll likely perform better than if they weren't bedded, but they still won't operate as well as a purpose-built street pad when cold.

To reiterate, the fundamental rule is always go back to a clean rotor face before swapping to a different pad compound.  It doesn't matter if the pad you're switching to is new or used.  If the compound is different from what is currently in the car, and the pads you are removing were bed-in, do a disc cleanup with an aggressive race compound prior to dropping in the new pads, then follow with a proper bed-in.

I've used these methods for over a decade now, and I've almost never had any issues with vibrations or judder.  I've never had to take a set of rotors to a mechanic to have them cut, resurfaced, turned, or whatever you want to call it.  Most notably, on my last set of rotors I sampled somewhere in the range of 20-25 different pad compounds without ever having any judder or uneven pad deposits. 

Cold race pads are abrasive.  Use that characteristic to your advantage.  You'll have a lot less vibration and judder issues if you always start with a clean slate.  You'll also save yourself some money.  In my opinion, having a set of aggressive race pads in your toolbox that are only used for this purpose is not a bad idea.  Although there is an upfront cost, and it may require an additional pad change, you'll likely save money in the long run.  You won't trash rotors, your pads will be less contaminated, and your brake system will always be operating at its peak potential.


Disclaimer- This article and accompanying video are for entertainment purposes only, and Essex cannot be held responsible for any incidents arising from the imitation of this information/procedures.  Essex Parts Services Inc. in no way encourages you to use brake pads that are not DOT compliant, or to violate local traffic laws.  It is up to the vehicle operator to ensure that all components on their vehicle are street legal when operating their vehicle on public roads.