Brake pads vary greatly in a few key ways. Initial bite, braking performance when cold or hot, rotor "friendliness" (how much they chew up brake rotors), dust, and noise are the main concerns for most of us that pay attention to such things. I've been running Porterfield's R4-S brake pads on my V8 Vantage for several months, including track days, and today I'm swapping them out for the more track-oriented R4 pad. Replacing brake pads is pretty easy on these cars.
Here's a quick overview of the two pads:
I'm expecting a few things that are generally assumed to be true when going from a street-biased pad to one that's track-biased:
Better initial bite when warm
Better high speed braking
Better heat tolerance on track
Worse initial bite when cold
Worse brake dust
These assumptions are pretty straight forward and, while I fully expect them each to be true, the point of this comparison is to see the extent of each. That is, the R4-S is a silent brake pad - is the R4 going to be unbearable? Or will its noise be entirely tolerable, if noticeable at all? The R4 pads should work far better than the R4-S pads when they're hot, but will they be able to easily stop the car when cold like the R4-S pads can?
We can see some obvious differences just looking at the pads. The chamfer (the beveled edge) of the pads, or lack thereof, is a key indicator of the different intended uses for each pad.
The brand new R4 is on the left, the used R4-S is on the right:
The chamfer (the beveled edge) on the R4-S gives that pad a couple key advantages in street performance. The chamfer helps prevent pad material from building up on its leading edge. That buildup can cause brake squeal, especially during low-speed braking - like in a parking lot. Brake chatter is also eliminated since the pad-rotor contact is smoothed out by the chamfer where the two meet. Since the R4 doesn't have a chamfer, it's far more likely to have brake squeal and chatter due to material buildup on its leading edge.
The extreme chamfer on the R4-S, however, comes with a big drawback where performance is concerned. Take a look at the difference in the contact patch where the pad meets the brake rotor:
The R4's contact patch is a hair over 5" long. The R4-S is only 3.5" long - only 70% as large as that of the R4! Although the contact patch of the R4-S will continue to grow as the pad material wears down, the R4's will still be larger - and it will be consistent, which should help with the driver's confidence in the brake pads.
After bedding in the new pads, I'll be testing them out on both street and track. Hopefully they'll be able to handle the job while cold without any noise (that'd be ideal). For some people, noise is an acceptable trade-off for a high-performance brake pad. But I'm not one of those people. I can handle brake dust, but I don't want the embarrassment that comes with a squealing brake pad!
So stay tuned for more as I put the R4 through its paces!