In my opinion, one big reason to buy an E46 M3 with the SMG option is
that the semi-automatic gearbox allows full-time left foot braking. With no clutch
pedal to deal with, the driver's left foot is rendered redundant, so it makes sense
to put that foot to use doing something constructive.
After a little practice, left foot braking becomes completely natural,
and is just as easy as braking with the right foot. Left foot braking becomes a vital component
of the SMG driving experience, and brings the level of involvement, pleasure and potential performance up a notch.
Those who argue that using SMG decouples one from the car might feel
differently if they tried SMG in conjunction with left foot braking.
Prior to the release of SMG in the U.S., I had been quite curious to see how the
factory would approach a performance car without a traditional clutch pedal. How would the
brake pedal be designed? I was hoping for something new and unconventional to match the
nature of the SMG transmission.
However, I was sorely disapointed when
I first opened the driver's door of an SMG equipped M3. Because what I saw was that BMW had simply
"left out" the clutch pedal. The brake pedal was exactly the same unit as in the manual transmission car.
This state of affairs was not acceptable, and
it didn't take long to start developing something better...
It seemed that the proper solution for an SMG equipped M3 would be a wider brake pedal.
Since the driver's left foot usually resides on the foot rest, it made sense
to bring the brake pedal closer to this area. That way the left foot could comfortably move to
the brake pedal when used for left foot braking.
The challenge to adapt such a special pedal to the existing M3 architecture.
Luckily the factory took the path of least resistance when they removed the clutch pedal from the SMG M3.
BMW left the actual pedal cluster unchanged from the manual car, thus there was a perfect place to mount a
"second brake arm" to the pedal cluster. This second arm is absolutely necessary with a wider
brake pedal, as it is the only
way to transfer braking force from the left side of the pedal to the right side brake arm (which pushes
against the brake master cylinder). With a single brake arm and a wide pedal, pressing the left side
would simply twist the arm.
One thing that is critical to brake feel and performance is stiffness. Every part involved in the braking
process must be as stiff as possible. Any deflection leads to a loss of driver confidence and reduces the
operator's ability to modulate the brakes on the threshold of locking up the tires (which is where the ultimate
grip from the tires is produced). So the P7 brake pedal system had to be stiff -
compromise was not an option on this issue.
An additional challenge was that the P7 pedal had to be very lightweight. One might wonder
why this is important. After all, it's not a big difference to a 3000+ lb. car if the brake pedal weighs
2 lbs. or 4 lbs. right? Well, yes it is. The reason that a brake pedal has to be lightweight is that any added mass
can be felt as inertia when the driver steps on the brakes. The brakes work just fine in stopping the car, but the driver's
ability to quickly vary the braking force in order to "threshold brake" is hampered by the inertia of the pedal.
This inertia tends to resist being moved rapidly, even if it is only for very small distances. Mass located farthest
from the pedal pivot point leads to the greatest (rotational) inertia, hence the brake pedal itself required the greatest
scrutiny in the weight reduction effort.
This double requirement for the P7 pedal to be both very light and very stiff resulted in hundreds of
hours of development, as well as the construction of several prototype assemblies.
The solution is an end product manufactured entirely from CNC machined billet 6061 T6 aluminum alloy.