SRAM has developed an all-new braking system that handily addresses the minor deficiencies of its Avid XO and XX1-level trail brakes. The brake platform is called “Guide” and it will be a SRAM-branded product that is intended specifically to serve elite-level all-mountain and trail riders. The new brake is the end product of an intensive, three-year development program that began with a series of test sessions where SRAM’s engineers and selected riders evaluated top performing models from major component makers. Based upon information gathered from the trail sessions, SRAM then outlined the performance goals it wanted to hit with its new braking platform: quicker action, more precise engagement control, and independent adjustments for lever-reach, pad contact and engagement – and then developed three different prototypes to explore the best mechanical option to achieve those goals. The result was a distinctly different lever design, a new rotor configuration, and a familiar, four-piston caliper. We were invited to ride-test the SRAM’s Guide Trail Brake in Moab, Utah, on some of the same terrain where those first product evaluations took place – and it seems that the Guide team has met or exceeded their expectations.
• Purpose: AM/Trail
• Contact point adjust
• Tool-free reach adjust
• MatchMaker X compatible
• Lever pivots on ball bearings
• 4-piston Guide caliper
• New Centerline rotor
• Colors: polished silver anodize or black anodize
• Weight: 375 grams (front system, 160mm rotor)
• MSRP: $199 / €177 per side
Inside SRAM's Guide RSC Trail BrakeGuide Lever
From the outside, the Guide brake lever’s in-line master cylinder and reservoir looks much different than its predecessors, with a larger reservoir, a shorter, forged-aluminum lever blade and a forward-pointing reach-adjustment dial. From tip to tip, the Guide lever is the same overall length as the present trail brakes, but with additional clearance made for GripShift levers at the outboard end and a larger volume for fluid in a piggyback reservoir. The lever-reach dial has been moved from below the lever blade, where it interfered with twist-shifters and some lock-on grips, and placed facing inward up top. SRAM uncoupled the Guide’s lever-reach and free-stroke (engagement point)
adjustments so Guide owners can quickly fine tune their brakes. Like all SRAM brakes, Guide levers are Matchmaker compatible and ambidextrous, so users can switch sides without bleeding hoses. SRAM did not give us the individual weight of the lever assembly, but the total system weight for a charged brake: lever, caliper, and 160mm rotor is 375 grams, with a $199 USD MSRP. Colors are polished or gloss black
.New Master Cylinder
In the search for an extremely precise and repeatable engagement feel, SRAM abandoned the simpler TaperBore master cylinder
of its Avid Elixir brakes in favor of the sliding cup-seal and port system that most hydraulic types employ. Because the cup-type piston must travel a measured distance before it closes off the bleed port and begins to actuate the caliper, a “dead band” is created that causes unwanted play in the brake lever’s travel. SRAM’s designers solved this with a cam-driven swing link which moves the master cylinder piston quickly past the reservoir’s bleed port so the brakes will begin to actuate at the moment the lever is squeezed. The swing link is designed to quickly drive the brake pads to the rotor, after which, the lever-mounted cam is profiled to ensure that when the rider squeezes the lever, the clamping force at the caliper becomes linear and easy to modulate. Inside the Reservoir
SRAM officials stated that there are always one or two bubbles left inside a well bled braking system that normally do not affect braking performance because they migrate into the brake lever’s reservoir. Often, especially when the bicycle is inverted, a bubble can find its way through the open port inside the reservoir and migrate into the brake hose, causing the lever to feel spongy. Multiple applications of the brake lever will force small air bubbles back into the reservoir – most of the time - but SRAM wanted to eliminate the problem altogether.
More fluid volume was added to the reservoir to ensure that there would be ample reserves to compensate for 100-percent pad wear, and SRAM engineers also designed a short tower around the bleed ports in the master cylinder reservoir to guide any trapped air away from their openings, should the bike be flipped up-side down. Clever enough, but to ensure less bubble formation and more consistent braking feel, the brains there designed a more flexible butyl separator-membrane in the reservoir cap. The pull of the stiffer plastic membrane, say the scientists at SRAM, can draw molecules of air through the membrane over time and also affect how crisply the lever returns. New Rotor
Guide Brakes also feature a new rotor design called “Centerline” which refers to a series of elongated vents in the center of the braking track, as well as a new 12-spoke configuration (up from six spokes)
that is intended to allow for more precise expansion and contraction of the disc as it is heated. The revisions are reported to control warping and lateral distortion of the rotors and to assist cooling. Centerline rotors will be available in 140, 160, 180 and 200-millimeter diameters and the standard, six-bolt hub interface.Familiar Caliper
Guide calipers are essentially the same four-piston items, paired in 14 and 16-millimeter diameters, that are presently used for Avid’s XXI and X01-level Trail Brakes. Sintered metallic pads as standard equipment, and a new optional organic pad has been developed for those who want a more quiet running system. Like Avid brakes, the new Guide platform is charged with DOT 5.1 fluid – a more advanced formulation of the standard DOT-4 automotive brake fluid. Guide brakes are bled and serviced with the same system that SRAM uses for Avid brakes – and the pads are interchangeable with AVID four-piston trail brakes as well.
SRAM will offer Guide Brakes in three price points: the top-drawer RSC (Reach adjust, Swing link, Contact-point adjust) with a claimed weight of 375 grams for a complete front brake at $199 a side; the RS, with reach adjust and swing link features at 380 grams and $149; and the $129-per-side Guide R model, which is limited to lever reach adjustments only and said to weigh 375 grams.
Compatibility and Delivery
Guide brakes are projected to arrive in bike shops around July, 2014. SRAM says that the levers will fit Shimano shifters as well as its own triggers and GripShift options, and as mentioned earlier, the clamps and lever design allow the right and left side levers to be easily reversed. Matchmaker compatibility ensures that SRAM’s shift levers, and RockShox’s dropper-post and fork lockout controls can be mounted directly to the handlebar clamps.
Pinkbike’s First Impressions:
| SRAM treated us to three days of riding in Moab, where the terrain gave us ample opportunity to test the Guide RSC Trail brakes to the limits of their performance - not long enough to hand you a definitive verdict, as we will when we do a longer-term test at home, but we rode them hard enough to say that SRAM now has a brake that can proudly stand alongside XX1 in looks, performance and power. We rode the sintered metallic pads on both cross-country and all-mountain bikes and in all cases, we never were wanting for more stopping power, while the pressure required to mete out a maximum braking effort was comfortably low. To put the new Guide brakes in perspective, we never needed more than one finger and Guide brakes require slightly more squeeze force than Shimano XTR Trail brakes do for the same stopping power. Where SRAM's new stoppers stand above the crowd, however, is in the modulation department. Guide brakes feel seamless on trail - to the point where we forgot about braking completely, even in the most technical situations. It took a while, but it seems SRAM finally got the brake thing right. - RC |