A Bit About Brake Discs

Thinking about upgrading your brakes? 

That’s a good idea. We’ve touched on the import of brakes in the past. Upgrading braking capability sometimes falls by the wayside with the Harley-Davidson crowd, and it’s a shame—a well-balanced bike is fun to ride, and improved braking makes riders faster. The later you can brake, the less time you’ll spend off the throttle. And on the podium, if that’s your thing.

Up until the past decade or so, factory brakes were usually a little lackluster. (They still can be improved, they’re just not as glaring a problem as they once may have been.) The poor braking is made more noticeable by the sheer mass of the bikes—most Harley-Davidson motorcycles aren’t class-leading in terms of weight, and the resultant mediocre stopping distance is probably why you’re reading this piece. 

How far do you wanna take it?

As mentioned in that previous article, there’s a bit of an order to doing things, and it makes sense to do a bit of an analysis. Things to consider include your riding style (are you an aggressive rider, a mild rider, a commuter, a “mostly-street-but-I-want-the-aggressive-look” type?), your budget, and your mechanic’s input if you’re not doing the work yourself. A full suite of oversized Brembo calipers with race-only pads and a numerically low master-to-caliper bore ratio sure does look great, but the bill can be hefty and boy, most street riders wouldn't appreciate the low-speed manners and noise that come along with a racy setup like that.

For most riders, a change of brake fluid is table stakes. If your bike didn’t ship with braided lines, swapping those hoses is another upgrade that should be at the top of the list for improved feel and feedback. This upgrade is important enough the factory does it for you on most late-model machines. Take a look; you might already have braided lines installed. Assuming you’ve got those two items checked off the list, the next upgrades most riders consider are new pads and rotors.

Friction 101

Your stock bike has pads and discs that are designed to exhibit good manners at street speeds and fairly low temperatures. An OEM brake system usually is very linear-feeling. The pads are quiet and don’t dust the wheels very much, and because the metallic content of the pads is low, they’re very gentle on the factory discs. 

But when the going gets tough and the parts begin heat-soaking with heavy use, the fading begins—loss of brake efficacy becomes more and more apparent. The cumulative effects stack up, too—overheated pads change permanently at a molecular level, and “glaze” can be more than just a layer that scrubs off on the next application of the brakes. The delta between “hot” and “cold” gets larger, and riders who really cook off material will notice a regressive (not progressive!) lever or pedal, and warping becomes a real possibility, usually manifested by brake pulsation that is often permanent.

So the “middle ground” of brake performance usually leaves the major factory components—master and caliper(s)—in place. Focus is on maximizing the hydraulic items linking them (fluid and lines) and installing rotors that can handle a set of more-aggressive brake pads.

TC Bros. Discs

Many OE Harley-Davidson brake rotors are solid, one-piece stamped units — built for OEM volume production, not performance. They work. If you’re swapping solid-mount rotors for floating rotors, you’re in for a treat. But even if you are substituting TC Bros. floating units onto a vehicle already equipped with floaters, you’re still going to notice the upgrade.

Our discs are laser-cut to reduce the risk of warping—they’re truly flat. They’re a full-floating design—the carrier and friction surface are two separate pieces, connected by buttons that let the rotor truly float for unmatched braking feel and feedback. You’ll also get lower heat transfer into the carrier due to this construction technique.

Here are a few tricks we employ to make our discs truly performance items:

• Stainless steel bushings—Stainless hangs tough for longer than aluminum and conducts less heat between friction surface into the carrier.
• CNC-machined billet aluminum carriers—Black anodizing assists in corrosion protection and provides a clean look.
• Riveted pins—Riveting provides a simpler method of joining the carrier and friction surface; it’s a safer, more reliable assembly since there’s no retention clips to work free
• Stainless disc spring washers—Spring washers provide a small amount of constant tension that permit rotor movement while eliminating rattle

Our standard floating rotors offer a neat, OEM-type appearance—with full-floating performance underneath. The Profile™ series has increased surface area along the outer diameter. It’s more aggressive visually, reduces weight, and increases surface area, helping with heat dissipation. Both styles are available for mag-wheel models without carriers. And in many cases, they can be used on spoked wheels, too.

Another technique to achieve better braking without altering the hydraulic system is increasing the rotor diameter. It’s one of the simplest and most effective ways to increase braking leverage. TC Bros. adapter brackets permit use of up to a 12.6" rotor on many models—meaningfully larger than stock 11.5" or 11.8" brakes.

Oversized rotors are available for stock calipers, aftermarket axial-mount, and aftermarket radial-mount calipers. Our radial-mount conversion brackets orient the caliper bolts in the same plane as the rotor, increasing rigidity. They’re standard on the fastest production and race bikes built today.

So a TC Bros. disc can offer better braking feel than a solid OE unit without changing anything else. And if you elect to scoop a larger disc and caliper relo bracket, you’re definitely going to notice the difference. But we don’t recommend it. Here’s why: our discs are made of a metal alloy with a different Rockwell hardness than an original disc. You can simply swap your rotors, but it’s not best practice. Our discs will actually burnish a set of OE pads. Leave them on long enough and brake like you’re doing a quiet ride to the grocery store and you’ll think your setup was made of wood.

Our discs are made to stand up to a pad that bullies ‘em, like a sintered pad (or an aggressive semi-sintered.) Sintering is the process of using heat and pressure to cure the brake friction material. Your factory pads are semi-sintered, but as mentioned, the metal content is low to give that nice performance when you (or the original owner if you ride a used bike) test ride your bike at the dealership. Aftermarket performance-focused semi-sintered pads contain way more metal in the mix than an OE pad, and a fully sintered pad is almost completely made of metal (save some binders and fillers.)

We carry both types, and pads aren’t just an upsell item—you need to upgrade both at once. Unlike some of the other “performance” discs out there that are just regular ol’ rotors with a design stamped into them, ours truly require a more aggressive pad to function correctly. They also require you ride aggressively to get them good and hot so they bite in when you need ‘em to. Most riders are best served by semi-sintered pads—they’ll hold up for everything but heavy trackdays and stunt use, and while they may be occasionally noisier than a stock pad, they won’t be disruptive when riding at sane street speeds.

A quick item of note—not all bikes have single or dual discs, and some pads are used on front applications on some motorcycles and rears on others. Because we don’t know what you’ve got, we normally sell discs, fasteners, and pads by the brake, not by the whole wheel. (So pads are sold as sets of two and discs singly. For a bike with dual front discs, a complete bike brake job would involve the purchase of three separate discs, and three brake pad sets for a total of half a dozen individual pads.) This is notably different from car and truck pads, which are typically sold in a complete set for an axle, not a single caliper.

Conclusion

We encourage you to make pads and discs (and possibly a caliper relocation kit) your next stop after brake fluid and lines. Even if you are still in search of better feel or more braking power, pads and rotors will be required to support more exotic hydraulic solutions like aftermarket calipers with more or differently-sized pistons, upgraded master cylinders, and braided lines. We’ve got that stuff, too, but start here—you might be surprised, and better braking might cost a bit less than you’ve been led to believe.