Pad and Rotor
Bed-In Theory, Definitions and Procedures
by Matt Weiss of StopTech and James
Walker, Jr. of scR motorsports
#1: How can I tell if my brakes are
This is a question
without a single definitive answer; however, there are visual
indicators on the rotor itself which can help determine the state of
1. Rotor discoloration.
Typically, there will be a bluish tint to a used rotor which is from
heat. A more important color is a grayish tint or film on the face of
the rotor where the pads touch. This color is actually from the pad
material building up and is the best indication of how much pad
material is adhered to the rotor. In general, if the rotor face is
still shiny there is not enough pad material built up. Note that
different pads will generate different appearances, so take notice of
how the rotor appears before starting the bed-in process so you can
recognize any difference after.
2. Machining marks. On a
new rotor, you can often use machining marks on the rotor face to
assess the state of the bed-in. Typically, there will be either very
slight grooves from turning the rotor (like a vinyl record – ask your
parents) or more random marks from grinding the rotor surface during
manufacturing. Prior to starting the bed-in process take a mental
picture of the machining marks. If they are still very prominent
following bed-in, you may not be bedding-in aggressively enough. In
general it's alright if there are still slight traces of the machining
marks after a few bed-in cycles, but you should definitely see them
starting to go away.
What happens if I can't do the bed-in right away?
Often times, weather or
other conditions can prevent one from fully bedding-in the brakes
before having to drive the car. Fortunately, this is not a dire
situation. If you are running new street/performance pads and rotors,
remember that they are designed for the street and will slowly bed-in
by themselves over time. Typically just a few stops from moderate
speeds will start the bed-in process for normal driving.
In general, as long as
the brakes are not overheated, you can drive them at normal street
limits indefinitely without worrying about a formal bed-in. It's only
when you get them good and hot that a fully bedded-in system becomes so
important. This is why we recommend a slightly more aggressive bed-in
procedure than most…we know performance brake customers are not
“normal” and typically can't wait to try their new brakes at speed.
What do you mean I “un-bedded” the brakes?
If any brake pad is used
below its adherent operating temperature, it will create friction
through primarily abrasive mechanisms, slowly but surely removing the
transfer layer on the rotor. For this reason, most street/performance
pads like to be driven just a little bit aggressively every now and
again to maintain a proper transfer layer of pad material on the rotor
If the brakes are used
passively for an extended period of time, the transfer layer can be
completely removed, effectively un-bedding the brakes. The brake system
will still perform well under normal driving conditions, but before
heading to the autocross or your favorite canyon back road you will
want to perform a bed-in procedure. Failing to do so will only increase
the risk of TV generation.
#4: What precautions
must be taken when switching from street pads to track pads?
If you are changing pad
compounds, such switching from street pads to track pads, you need to
remove all of the material on the rotor and replace it with a fresh
transfer layer of material from the new pads. To be honest, rotors do
not like to have different compounds used on them, and virtually all
rotor and pad manufacturers recommend that you do not swap pad
compounds on the same rotors. The reality is, however, that most
customers don't have two complete sets of rotors, so here are our
recommendation for managing compounds between track and street use.
Note that diligent bedding-in is the key.
When switching from
street pads to track pads, one needs to make sure that as much of the
street compound is removed from the rotor as possible before aggressive
track use. The risk here is that any street pad material remaining on
the rotor will be subject to deterioration from overheating. This can
ultimately cause severe vibrations due to uneven pad deposits (a
smearing of the street pad material on the rotor face).
A common method for
removing street pad material is to install the track pad prior to
driving to the event. Because most track pads operate in an abrasive
mode during regular street operation, driving them to the track will
wear off any existing brake pad material en route. You will know when
the street pad material is gone by the squealing noises coming from
your brakes after a short while…
#5: What precautions
must be taken when switching from track pads to street pads?
Many people make the
mistake of thinking that because they have a used set of pads in the
past that the system does not need re-bedding when they are
re-installed. Remember, the same material must be adhered to the rotor
as the pad running against it for effective braking. Race pad material
must be removed prior to street use.
Since you're not as
likely to overheat the rotors on the street after a track event, over
time the street pads will remove and replace the track pad material on
the rotors naturally. However, the best solution where street pads are
being put back into service after a track day is to follow the original
bed-in procedure for the street pads after the swap.
#6: Do I need to bed-in
new pads if I do not change pad compounds?
Although you do not
typically need to establish a fresh transfer layer for a new set of
pads if they are of the same compound as the previous set of pads,
there is still a need to mechanically seat the pad face to the rotor
face. Because the pad and rotor wear together as a matched set, by the
end of a pad's useful life the rotor face is usually not completely
flat. Consequently, when installing new pads on a used rotor, there is
a small window of time in which the new pads will rapidly wear down
against the peaks and valleys of the existing rotor face. This process
of re-establishing the wear interface is often referred to as
At the same time, new
pads may need to be heated and cooled a few times before hard use in
order to burn off all of the residual manufacturing resins and excess
binding agents present in the pad compound. This process ensures that
the exaggerated fade present in new pads (the “green” fade) is not
experienced at speed when they are needed most. Unfortunately, this
process of heating and cooling the pads is commonly referred to as
bedding-in even though it has nothing to do with establishing a
transfer layer. Gassing-out is a more appropriate term for this process.
So, while establishing a
transfer layer is not necessary with new pads of the same compound,
performing a bed-in procedure will serve to establish the wear
interface as well as to expose the pads to their green fade in a
controlled environment. For this reason, we recommend performing a
formal bed-in any time rotors, pads, or both are changed, regardless of
pad compound or rotor manufacturer.
#7: Is bedding-in on
track different than bedding-in on the street?
When bedding-in a system
on the track, it is usually neither safe nor much appreciated if you
start braking to a near stop multiple times per lap, so a different
approach is necessary. A good rule of thumb is to start with 2 or 3
warm-up laps, slowly and evenly bringing the system up to temperature.
Follow immediately with 2 or 3 laps at speed. Note that more laps may
be appropriate for a light braking track, and fewer for a heavy braking
track. Ambient temperature should also be a consideration, as a cooler
day requires a few more stops at speed.
After several laps at
race pace using normal braking sequences, back off and let the system
cool for 2 or 3 laps while staying off the brakes. Out of courtesy,
maintain a reasonable speed and signal other drivers you are not
running at full song.
Following the cool down
laps it is usually best to come into the pits and let the system fully
cool. However, track time is typically limited so staying on course is
compelling. If the brakes are firm and vibration-free, take it back to
speed and you'll likely be OK.