Shimano's IceTech rotors have been proven to be highly effective in reducing heat at the disc rotor. It is no surprise that the XTR RT99 rotors are the best of the line-up, and it stands to reason that the technology will filter down over time. Managing heat at the rotor is crucial to disc brake performance, pad and rotor wear, and protecting the caliper as well. Of course, this is also the key to protecting you and your fellow riders. With the RT99's IceTech Freeza rotor Shimano has acheived a 30% reduction in heat at the rotor versus the previous RT98 IceTech rotor. That is an impressive result- one you will feel on the bike.

The construction, shaping, and structure all contribute to the improvement in heat reduction. The actual rotor ring consists of three layers. Stainless Steel is used on both sides, with an aluminum core, all bonded together to create the braking element. This creates strength and durability and reduces weight, while changing the heat absorption properties, as aluminum cannot hold heat the way steel does, so it wants to release that energy. The aluminum becomes a fin radiator structure, called Freeza, within each arm of the rotor, and those fins, along with the rotation of the disc and airflow, encourage rapid dissipation of the heat, keeping the whole rotor substantially cooler than a steel version.

The shaped and cut-out braking zone ring is designed for excellent pad purchase and contaminant release. The rotor provides great stopping power and control, even when conditions are wet or muddy. This ring is pin-mounted to the aluminum carrier at five points (four on the 140mm), and that star spider centers on the mounting area. This is a Center Lock interface, which is Shimano's highly efficient and simple rotor mounting system. A threaded lock ring for QR style Center Lock hubs is included to lock the rotor down. For those who require a 15/20 mm thru-axle lockring, please see the SM-HB20 Center Lock Hub Lockring.

Keen-eyed observers will notice that the 140mm rotor differs from the 160/180mm versions. On the 140, the star shaped spider carrier does not have the open cut-outs found on the larger rotors. The short distance of the 140mm spider doesn't give Shimano enough structure for full cut-outs. Instead you can see that the engineers simply sculpted the aluminum to reduce weight without sacrificing strength.

One other note. Shimano dropped the Freeza portion of the name from the initial version. The RT99 has been updated and simple called the XTR IceTech RT99 Disc Rotor. Stopping power and heat reduction are exceptional, and the cooler rotors favor more modulation and lever feel. That is why these rotors are recommended for use with Shimano's road hydraulic disc brakes, as well as the traditional XTR trail usage. For maximum effect, use with Shimano's IceTech, finned disc brake pads. Once you go with this set-up, you won't want to run anything else.