BMW i4 (eDrive40) Big Brake Kit Upgrade / TTSPORT Classic 8657S
BMW's sport sedans are built around sharp handling and strong straight-line pace, but the factory brake package on cars like the i4 eDrive40 isn't always sized for repeated hard stops or spirited driving. This installer case documents a straightforward fix: a TTSPORT Classic Series TT8657S six-piston front kit dropped in behind the car's stock 19-inch wheels.
The shop behind this build fitted the front axle with TTSPORT's TT8657S six-piston caliper and matching 380mm high-carbon heat-treated rotor - a straight bolt-in upgrade over the stock BMW front binders, using the car's factory wheels.
Vehicle & Kit Specs
| Item | Specification |
|---|---|
| Vehicle | BMW i4 eDrive40, 19-inch factory wheels |
| Front caliper | TTSPORT TT8657S forged six-piston, two-piece monobloc |
| 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 fittings |
The full official spec sheet for the TT8657S caliper used on this build is below.
| 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 kit ships as a complete axle set: calipers, rotors, vehicle-specific bracket, pads, stainless lines, and the fluid and hardware needed to finish the job without sourcing extra parts.
Why It Works
The TT8657S is the updated version of TTSPORT's earlier TT8657 caliper, with revisions to the pistons, caliper venting, and overall dimensions. A few fundamentals explain the improvement in pedal feel and stopping power:
- Two-piece forged construction keeps the caliper body stiff under load, which cuts the flex that produces a mushy pedal in a stock floating caliper.
- Two-piece, heat-insulated pistons resist deformation under sustained heat, so clamping force stays consistent lap after lap or stop after stop.
- The forged, lightweight caliper body reduces unsprung mass compared to a bulkier factory unit, which helps the suspension track the road.
- The 380mm rotor was chosen within TTSPORT's recommended 355-405mm range for this caliper, giving more thermal mass than the stock disc without requiring a wheel change.
Because the bracket is machined specifically for this platform, the caliper lines up on the factory hub without spacers or modified suspension geometry - the car keeps its stock steering and wheel offset.
Installation Gallery
FAQ
Does the TT8657S kit fit under the BMW i4's stock 19-inch wheels?
What's included in this TTSPORT big brake kit for the i4?
What rotor sizes work with the TT8657S caliper?
Need fitment confirmation? Choose the closest TTSPORT series or send your vehicle, wheel size, and intended use before ordering.