BMW i4 Big Brake Kit Upgrade / TTSPORT Classic 8657S
Big six-piston calipers do more than look good behind a wheel. Compared to a stock two-piston floating caliper, they clamp with more pad area and hydraulic pressure, which translates to shorter stopping distances and a more confident pedal when things get urgent. This case comes from one of our partner shops: a BMW i4 fitted with the TTSPORT Classic Series TT8657S front big brake kit.
The car rides on its factory 19-inch wheels, and the shop installed the TT8657S front calipers with 380mm high-carbon, heat-treated rotors — no wheel spacers needed on this setup.
Vehicle & Kit Specs
| Item | Specification |
|---|---|
| Vehicle | BMW i4, 19-inch wheels |
| Front caliper | TTSPORT TT8657S, six-piston forged |
| Front rotor | TTSPORT 380mm high-carbon, heat-treated rotor |
| Bracket | Custom vehicle-specific caliper bracket |
| Pads / lines | TTSPORT high-performance street pads, stainless steel brake lines |
| Hardware | Brake fluid, mounting bolts and fixing hardware |
Here's the official spec sheet for the TT8657S caliper used in this build:
| Brake Caliper | |
|---|---|
| Series | Classic Series |
| Model / Application | 8657S |
| Axle Position | Front |
| Piston Count | 6-piston |
| Piston Type | Two-piece heat-insulated pistons with dust boots |
| Piston Diameter | 30 mm × 2 / 34 mm × 2 / 38 mm × 2 |
| Caliper Dimensions | L 350 mm × W 165 mm × H 92.64 mm |
| Total Piston Area | 55.0 cm² per caliper, all pistons combined |
| Manufacturing Process | Two-piece forged aluminum body |
| Net Weight | 4.05 kg per caliper, without pads |
| Surface Finish | High-temperature gloss coating |
| Recommended Wheel Size | 18 in or larger |
| Recommended Rotor Size | Ø355–405 mm × 32–34 mm |
| Fitment & Installation | |
| Minimum Spoke Clearance (mm) | 107 |
| Caliper Mounting Type | Radial mount with vehicle-specific caliper brackets |
| Brake Line Fitting Type | Vehicle-specific fittings; caliper-side and chassis-side fittings vary by application |
The 8657S is the updated version of the original TT8657, revised at the piston, caliper window, and body dimensions. It's a two-piece forged aluminum caliper, which keeps unsprung weight down while giving the caliper body the rigidity a floating stock caliper doesn't have.
Why It Works
- Six fixed pistons (30mm/34mm/38mm pairs) spread clamping force more evenly across the pad than a sliding two-piston caliper, which cuts down on pad taper and improves pedal feel under repeated hard stops.
- The two-piece, vented pistons resist heat soak better than a solid piston, helping the caliper hold its bite instead of going soft as temperatures climb.
- A 380mm rotor puts more swept mass and surface area to work than the factory disc, which means more heat capacity and, in turn, better fade resistance on repeated stops.
- The vehicle-specific bracket sets the caliper at the correct offset for the factory 19-inch wheel, so the kit clears the spokes without spacers.
Installation Gallery
FAQ
What wheel size does the TT8657S kit fit on this BMW i4?
What rotor size was used on this BMW i4?
What's included in the TT8657S front kit besides the calipers and rotors?
Need fitment confirmation? Choose the closest TTSPORT series or send your vehicle, wheel size, and intended use before ordering.