Modular Disc Brake | Seven Cycles

Disc Brake Mount Design Details

Do you know why Seven uses a modular disc brake mount?

Seven's disc brake mount system is pretty unique. Most metal frames have a welded brake mount, and many of those are welded to the chainstay tube. Most carbon frames use an integrated mount that's molded into the frame. Conversely, Seven's solution employs our exclusive modular bolt-on CNCed aluminum mount that connects directly to the dropout plate. What is the purpose — and maybe even some benefits — of our design?

It's proven: In the more than 5,000 bikes we've built since low-mount disc bikes came to dominate the market, we have not had a single call about misalignment, squealing, or chatter regarding our bolt-on brake mount. We have never had one of our mounts and disc-specific dropout interfaces fail, crack, break, or get damaged.

Right-sized: We offer two versions of our mount: The SL and the XX.

The SL is our super stout design weighing in at 38 grams, including hardware. This mount comes on all of our S and SL models. It's optimized for stiffness and no maintenance.
The XX is our lightweight offering weighing in at 26 grams with hardware. This mount comes on all of our XX models. We shaved every gram we could without sacrificing perfect performance for many years. Cost no object.

seven-disc-brake-mount-assembly — *Seven's simple low-mount disc brake system. On the left is the SL design. On the right is our XX design. One machined aluminum part and two bolts. Simple, stout, serviceable.*

Super stout: Torsional stiffness is paramount for a disc mount. Thin wall tubing (where many metal frames have disc mounts installed) acts as a shell, whereas Seven's mount is bolted directly to our solid dropout plate. The plate is significantly stiffer as a mounting surface than the thin-wall tube.

Our SL mount excels with bikepacking, clydesdales, mountain biking, 180 mm rotors, and riders that are tough on equipment. CNCed from a solid chunk of 6061 T6 aluminum, there is no stiffer brake mount available.

Combine Seven's custom dropout plate with our exclusive aluminum mount, and you have the stiffest system possible.

seven-disc-mount-on-frame — *Seven's XX brake mount. Clean, elegant, and lightweight.*

Aligned: Nothing on a bike is more sensitive to misalignment than a disc brake system. Difficulty getting the rotor to not rub, chatter, squealing, and poor service life are possible signs of misalignment. All welded structures (and all baked carbon frames) have some distortion. And, as the weld bead quantity increases relative to total mass, distortion likelihood increases almost linearly. On most metal frames, a welded mount has the highest heat-to-mass ratio of any frame subassembly. Of course, a welded mount can/should be machined after welding to eliminate inherent misalignment, but with Seven's heat-frees mount, there's no need for post-weld fixes.

Lightweight: While possibly not the lightest mount system, our XX design is 26 grams with hardware. We estimate that the most popular titanium welded assembly is about 35 grams.¹ Regardless, even if you're a gram counter, the brake mount is not a place to shave weight. Brake performance keywords are stout, straight, and secure. Lightweight is maybe eighth on the list of brake mount desires.

seven-disc-mount-dura-ace — *Seven's XX disc mount with brake installed. Nearly invisible. Never failed.*

Futureproof possibilities: Because our brake mount is replaceable, your Seven may work with future brake designs. While the pace of brake system evolution has slowed, we know that more “improvements” are always on the way. Because our mount bolts on, it may be possible in the future to install an updated mount that, by definition, would be more likely forward-compatible than a welded mount.

Localized rigidity: Many welded brake mount assemblies are two separate pieces, one for each caliper bolt. It doesn't matter how stiff each individual mount is if the tube or bridge between the mounts is bending or twisting — as is the case with many systems we've evaluated. Both of Seven's mount designs are CNCed from a single block of aluminum, ensuring torsional stiffness from end to end.

There is more to our brake mount design, but that's enough for today.

The next time you look at a Seven, even its simplest element, you can be assured that we've overthought every millimeter of the frame's design intent.

Footnotes and math proofs

We arrive at 35 grams by the following math: Two titanium slugs 24 mm long, about 14 mm diameter, and bored to a 5 mm I.D. are about 33 grams, plus weld bead equals about 35 grams. We do not include 3D-printed titanium dropouts/mounts as a weight comparison due to durability concerns.