- Those Poor Rotors
- Let's
look ot some common rotor "modification" and "performance"
upgrades that you may have been exposed to. We'll try to separate
the marketing from the engineering: Bigger rotors will make your
friends think you are cool, bigger rotors look sexy, but bigger
rotors do not stop the car. What a bigger rotor will do is lower
the overall operating temperature of the brakes--which is a GREAT
idea IF your temperatures are causing problems with other ports
of the braking system.
Take, for exomple,
a Formula 500 racer, a small 800-pound, single-seat formula car.
While the brakes are certainly much smaller than those found
on a 3000-pound GT1 Camaro, that does not necessarily mean that
they need to be made larger. In fact, installing o GT1 brake
package onto our formula car would probably do more harm than
good. That's a lot of steel hanging on the wheel that needs to
accelerate each time the gas pedal is pushed. So the motto of
this story is bigger is better until your temperatures are under
control. After that point, you are doing more harm than good,
unless you really like the look. (And hey, some of us do.)
-
- Crossdrilling
your rotors might look neat, but what is it really doing for
you? Well, unless your car is using brake pads from the '40s
and 50s, not a whole lot. Rotors were first drilled because early
brake pad materials gave off gasses when heated to racing temperatures,
a process known as "gassing out." These gasses then
formed a thin layer between the brake pad face and the rotor,
acting as a lubricant and effectively lowering the coefficient
of friction. The holes were implemented to give the gasses somewhere
to go. It was an effective solution, but today's friction materials
do not exhibit the some gassing out phenomenon as the early pads.
-
- For
this reason, the holes have carried over more as a design feature
than a performance feature. Contrary to popular belief, they
don't lower temperatures. (In fact, by removing weight from the
rotor, they can actually cause temperatures to increase a little.)
These holes create stress risers that allow the rotor to crack
sooner, and make a mess of brake pads--sort of like a cheese
grater rubbing against them at every stop. Want more evidence?
Look at NASCAR or F1. You would think that if drilling holes
in the rotor was the hot ticket, these teams would be doing it.
-
- The
one glaring exception here is in the rare situation where the
rotors are so oversized that they need to be drilled like Swiss
cheese. (Look at any performance motorcycle or lighter formula
car, for an example.) While the issues of stress risers and brake
pad wear are still present, drilling is used to reduce the mass
of the parts in spite of these concerns. Remember that nothing
comes for free. If these teams switched to non-drilled rotors,
they would see lower operating temperatures and longer brake
pad life, at the expense of higher weight. It's all about tradeoffs.
-
- Slotting
rotors, on the other hand, might be a consideration if your sanctioning
body allows for it. Cutting thin slots across the face of the
rotor can actually help to clean the face of the brake pads over
time, helping to reduce the glazing often found during high-speed
use which can lower the coefficient of friction. While there
may still be a small concern over creating stress risers in the
face of the rotor, if the slots are shallow and cut properly,
the trade-off appears to be worth the risk. (Have you looked
at a NASCAR rotor lately?)
|