Brake modulation is the ability to precisely and accurately control the amount of clamping force on a disc with a given amount of pedal input. In other words, it means you can scrub off as much or as little speed as you want without tire lockup. Peak braking power comes just prior to lockup and it’s the ability to flirt with that limit that makes modulation so important.
A vehicles braking power is always limited by the amount of tire traction available. Most OE pads and all aftermarket brake pads can lock up a tire or two. However, a tire that isn’t rotating is also usually a tire that isn’t contributing any meaningful amount of control. Brake lockup is exactly what you do not want. No modulation is basically no braking vs. tire lockup. Having low modulation will mean it’s hard to feather the brakes and you can only really lock up the pads.
Proper modulation gives you access to the whole range of braking power desired and allows you to apply it evenly at will, giving you precise control over feathering the brakes, stopping firmly, or locking the tire(s). Many top level professional race car drivers will tell you that being able to modulate and trail brake into a corner is essential to producing the fastest possible lap times.
Whereas other manufacturers who choose to have an “on/off switch” type of compound will perform unpredictably between moderate braking force and lockup. This type of braking will skip that all-critical peak in deceleration. A properly engineered brake compound with excellent modulation will allow you to consistently hit that mark, and keep you there time after time.
Sometimes you’ll hear a person say “brake modulation is done with the foot”. That’s absolutely true in some sense but there are still characteristics that can be built into a brake system that can give it a substantial advantage over a competitor. One of the hallmarks of excellent brake modulation is predictability, but if you are using an “on/off switch” type of compound then you can never put 100% faith in your brakes’ abilities. Anyone who argues that their current brakes ‘can lock up a wheel with no problem at all’, is tacitly admitting that they do not work as well as they could.
A brake pad that has excellent modulation is one that you could take right to the edge of locking up and then control it there as you need it. Sometimes you just need to scrub off a little bit of speed without having it suddenly ramp up to full bite costing you time on the track. This is another advantage to running G-Loc compounds with our excellent modulation.