Stainless Steel HP Caliper Pistons

• Brake Later
• Brake Harder
• Less Fade
• Mitigate Fluid Boil
• Less Heat

Fits Elise, Most Exige, All 2-Eleven

Price is for a full set of 4 pistons.

Background

As we increase the horsepower and grip in the Lotus, we will eventually find the limit of the stock brake components. Fortunately, the 2-Eleven, Elise, and many of the Exiges are equipped with Lotus branded race quality 2 piston AP calipers. While there's nothing wrong with the calipers themselves, the pistons within the calipers are made from machined aluminum billet. Aluminum has an extremely high thermal conductivity when compared to materials used to manufacture traditional high performance or racing caliper pistons such as titanium and stainless steel. The aluminum pistons are a problem because high friction racing and track-day brake pads get extremely hot. The heat generated in the pad transfers to the steel backing plate of the pad and then to the aluminum pistons in the calipers. The brake fluid is in direct contact with the caliper pistons and the high thermally conductive aluminum does a great job at transferring much of the pad heat to the brake fluid. Eventually, even the best brake fluids can get hot enough to boil and the brakes will fail.

Part of the solution is to replace the aluminum pistons with pistons comprised of a material that has lower thermal conductivity. In addition to lower thermal conductivity, vents and bridges can be designed into the piston. Vents and bridges help to decrease thermal transfer and allow air into the piston dish to aid in cooling.

Approximate Thermal Conductivity of common caliper piston materials (BTU/hr-ft-F):

*Aluminum: 136
*Stainless Steel: 8
*Titanium: 13

As you can see, stainless steel has only about 5% of the thermal conductivity of aluminum. It's typical to see stainless steel or titanium “vented" pistons in racing calipers.

Our vented stainless steel pistons may be the key to eliminating fluid boiling or increasing your brake system's performance in even the most demanding situations. Another benefit to these pistons is that they come with no weight penalty like a big-brake-kit. In many cases, it has been reported that less expensive ATE brake fluids can be used after installing these pistons.

A comparison of our Vented HP SS piston compared to the stock aluminum piston