jueves, diciembre 19, 2013

Sram fallos en frenos de disco hidràulicos para bicis de carretera

Mikel Kolino: Q36.5 Longsleeve Hybrid Que. Esencialmente la mejor
Más información en http.//wwwmikelkolino.com
Como debe de quedar un maillot bien hecho en el ciclismo.


A Racer’s Dream // The full length movie


SRAM Road Hydraulic Brake Recall – STOP USE IMMEDIATELY

On November 4th SRAM identified and announced a technical issue with respect to a narrow production range of its RED 22 and S-700 Hydraulic Road Brakes. At that time, it was described as a performance and safety concern with no reported failures in the field.

It has recently come to our attention that during last weekend’s Cyclocross racing in the US, in sub freezing temperatures, several failures were reported. In these conditions the master cylinder seals failed to hold pressure resulting in abrupt loss of brake power, and an inability to stop the bike. These failures are related to product that is outside the originally stated date code range and unrelated to the original failure mode. No injuries have been reported to date.

As a result of this new finding, SRAM requests that anyone who has a bike equipped with SRAM Hydraulic Disc or Hydraulic Rim Brakes stop using the bike immediately. All products shipped to date, and currently in the market or in inventory will be recalled.

Further, we are asking our Bike Brand customers, OE factories, Distributors and Dealers to cease all sales and shipments of SRAM RED 22 and S-700 Hydraulic Road Brakes. A total of approximately 19,000 brake systems have been shipped to date into the global market.

Quarantine efforts currently underway with Factories, Bike Brands, and Distributors will be broadened to include all Dealers with inventory on bikes, or as Aftermarket product. Additional information related to timing and replacement of product will be forthcoming.

As originally announced we have reported this issue to the US CPSC and will be cooperating with the agency to announce a Safety Recall. We will also be contacting and working closely with appropriate like agencies in Europe and globally.

SRAM engineering and manufacturing is committed to the highest Quality standards. On behalf of all employees at SRAM we apologize for the business disruption to our customers business and to the individuals who have placed their trust in our products.





RAM unveils True 22 11-speed drivetrains, hydraulic brakes
By Caley FretzPublished Apr. 15, 2013Updated Apr. 15, 2013 at 5:39 PM EST

The Red HRD brakes are designed specifically for road use, with a larger front piston (19mm) and more pad retraction to keep them quiet. Photo: Caley Fretz | VeloNews.com

SRAM had these disc-capable Specialized Roubaix frames on hand for the new HRD brake system and 11-speed Red 22. Photo: Caley Fretz | VeloNews.com

Bulbous levers house the master cylinders in the new SRAM Red 22 and Force 22 groupsets. Photo: Caley Fretz | VeloNews.com

The Hydo Road Rim (HRR) brakes feature a quick release and pad contact adjustment, just like a regular mechanical rim brake. Photo: Caley Fretz | VeloNews.com
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WESTLAKE VILLAGE, California (VN) — SRAM has lifted the veil on its new 11-speed, hydraulic road drivetrains. As reported by VeloNews earlier this month, the Chicago-based manufacturer will offer new Red and Force groupsets that feature options for disc and rim brakes and will be cross-compatible with some pre-existing SRAM components.

The latest launch details three important developments, and a mass of small updates. First, and most obviously, SRAM has moved to 11-speed with two brand new road groups, called Red 22 and Force 22. Second, the company has unveiled its long-awaited hydraulic brake systems, both disc and caliper. Third, Force 22 gets some of the whiz-bang tech updates we first saw with Red 2012, including Yaw front shifting.

Both new groups fall under the guise of SRAM’s True 22 moniker, setting them apart as the first 11-speed drivetrain systems designed to be used in all 22 gears, from big chainring and biggest cog to small chainring and smallest cog.

Of course, this is already possible on most groupsets; it’s just not recommended. Both Shimano’s and Campagnolo’s user manuals specifically advise against riding in the big/big and small/small combinations. That doesn’t stop people from doing it all the time, of course, and the electronic systems in particular have little issue with it thanks to their auto-trim front derailleurs.

Nonetheless, it is admirable that SRAM has finally endorsed this sort of cross-chaining. It can do so thanks to careful tuning of chainring and cog teeth, front derailleur shape, and the chain itself, which is now designed to work at the extreme angles caused by cross-chaining.

Small mechanical changes for Red 22
The only real change to the shifting system of the new Red group is the addition of an 11th gear, and the collection of small tweaks associated with that change. It’s still mechanical, still ZeroLoss, and still feels the same.

Weights are just about identical, ergonomics are identical, and the same technologies carry over. This was done on purpose; even the graphics remain only modestly altered, allowing riders to mix the new 11-speed parts into their 10-speed groups without wrecking the look.

The truly interesting bits of the Red 22 group don’t involve cables at all — the new HRD hydraulic disc brake system and HRR hydraulic rim brake systems are potential game changers, and are the genuine innovation in this round of Red.

Big overhaul for Force 22
Unlike Red 22, which remains unchanged save for the extra gear, Force 22 sees a massive overhaul. It gets exactly what we were hoping it would: all the tech introduced with Red 2012 last year, including the Yaw front derailleur, built-in chain catcher, decreased weight, hidden-bolt crankset, and more.

And it’s 11-speed, too, of course.

The new group does not get Red’s AeroLink brakeset, nor does it hit the same weight figures as the old Red group, but it does get closer. And the addition of Yaw front shifting should be absolutely celebrated, as it is such a massive improvement on SRAM’s old system.

Here’s the rundown:
Shift levers: Gain the same, much-improved shape as Red 2012; weight drops to 307 grams
Front derailleur: Yaw-compatible (modified for 11-speed); includes chain spotter; Red 22-compatible; 79g (claimed, 18g lighter than old version)
Rear derailleur: Gains AeroGlide pulleys, new graphics, WiFli (wide-range gearing) option available; weight remains unchanged from old Force
Crankset: Arm lengths down to 165mm; Yaw-compatible chainrings; hidden-bolt design; standard and compact rings as well as the new 52-36 chainring combinations available; 741g claimed with BB30
Brake calipers: Unchanged; new graphics, new pad compound
Cassette: Gets the same, semi-spidered design used on SRAM’s XO mountain bike cassettes; 16t cog present on all options except WiFli; 19g heavier than the 10-speed version due to the extra cog
Chain: New, narrower 11-speed profile; uses a silver powerlink (silver will be the 11-speed powerlink color); hollow pin design; 256g for 114 links

Red 22 and Force 22 compatibility
The move to 11-speed raises a heap of compatibility questions, particularly since SRAM debuted a brand new 10-speed group just a year ago. SRAM’s 11-speed retains normal, 130mm road spacing, and its 11-speed cassettes will be compatible with Shimano 11-speed, though neither brand really acknowledges it.

Like Shimano, SRAM’s 11-speed requires an 11-speed freehub. The cassettes are too long to fit on a 10-speed freehub.

Cog spacing is nearly identical to Shimano, as close as it was when both brands had 10 cogs. That means that, in theory, SRAM will now function with Campagnolo as well — though perhaps not perfectly. There might be a bit more noise, though we haven’t tested this.

As always, SRAM says the new kit is not compatible with the old. We’ll wait until we have the new groupset in-house to find that out for ourselves.

The rear derailleur cable pull is the same, so in theory, a 10-speed derailleur should function with the new shifters. However, the wider cassette will tax the rear derailleur more, reaching its outer limits. It may not work at all, depending on frame alignment.

The new front derailleur has been optimized for the 11-speed cassette spacing and slightly narrower chainring spacing, and given the Yaw design’s careful timing, it’s entirely possible that it won’t work with 10-speed systems. It’s also entirely possible that, since the cable pull has not changed, an old 10-speed front derailleur will work just fine with 11-speed kit. Our guess is that it will all work, but with a bit of chain rub on the front derailleur. However, don’t buy anything on that hunch; wait until we get a group in and test for ourselves.

Assuming you’re sticking with mechanical brakes, SRAM says would need the following to go from 10 to 11: new shifters, new front and rear derailleurs, new chainrings, new chain, new cassette. Keep your crankset and brakes.

Red 22 and Force 22 keep weight low
If we’re only talking mechanical braking systems, 11-speed Red and 10-speed Red are essentially identical in weight. The chain gets about 8g lighter while the cassette gets about 10g heavier. It’s a wash.

The hydraulic systems, though, are a different story. The HRR hydraulic rim brake system weighs 387g for lever, caliper, and 600mm of housing. We don’t have a HydroR shifter weight, but assuming it’s close to the mechanical shifter’s weight of 280g, that leaves 107g for brake and hydraulic line. A Red mechanical brake weighs about 130g, plus 20-50g for cable and housing, for a total of at least 430g. The hydro is lighter, then.

The HRD disc, which uses the same lever, comes in at 449g per wheel with lever, caliper, line, and 160mm rotor. That means it’s certainly within spitting distance of mechanical Red’s 430g. However, the equation must include about 100g of additional frame weight (according to Bianchi, who just debuted a new disc version of it Infinito frame), plus additional weight in the hub and a few extra spokes. The total difference is likely between 150 and 250g, then, depending on the other equipment used.

Why so soon?
SRAM debuted its 2012 Red just a year ago, and many riders are likely fuming right now, having just bought new kit only to have it replaced.

When asked why the brand went with such a quick turnaround, road product manager Charles Becker stated simply that the market wasn’t ready for 11-speed at the time, mostly because all the auxiliary products (freehubs, wheels, etc.) were not yet ready.

“The market at the time wasn’t ready for us to go 11,” Becker said. “Now it’s ready. Back then I didn’t know it was going to be 11 months. It’s not just a group; you need to have all the necessary auxiliary products. Now that Shimano and us are following the same path, we have the same requirements in spacing and alignment, it made sense for us to have an industry standard that has compatibility.

“One reason why we didn’t do a complete graphics redesign is because the 10-speed is still valid, and while many things change, the major technologies are the same. … I’ll continue to ride my 10-speed bike for a while. When you are at the bleeding edge of technology, you have to expect new things. We’re not going to prematurely make the product [10-speed] obsolete.”

To that end, SRAM made it clear that it would continue to offer 10-speed Red and Force for the foreseeable future.

How long will it be until we see 11-speed Rival and Apex? That’s still up for debate. It’s mostly a matter of keeping the groups at price-point, Becker said. If it means a $1000 bike has to become a $1500 bike, or that it has to sacrifice quality in other components to maintain its price point, that’s undesirable.

“We’re ready to unleash it,” Becker said. “But it’s a dialogue and an agreement with the rest of the industry. I would hate to see a bike get an extra gear and everything else on the bike has to become cheaper and worse to afford it. That would be a bad tradeoff.”

He has a point, and we won’t hold our breath for 11-speed Rival. Perhaps 2015?

Introducing road hydraulics
Now, to the interesting bits, the technology we’re truly excited about.

Why hydraulic? Well, the fact that just about every other wheeled sport on the planet, including the dirty side of our own chosen activity, has already made the move to hydraulic brakes should provide a bit of a hint.

Braking is not about power; it’s not about locking up wheels, either. A stick in the spokes can lock up your wheel, but that’s not very effective braking. The “I can lock up my wheels just fine” argument only paints its purveyor as woefully uninformed. Even worse is the “I don’t want to accidentally lock up my wheels” argument; you are far more likely to do so with an unpredictable, cable-actuated brake than with a good, purpose-built hydro. The focus is not the point of lock-up, as that is determined by tire traction, but what is happening in the lead-up to that point.

Braking is about controlling power, dolling it out in perfect increments to sit right on the edge of wheel lockup without going over it. Locking up is bad, inefficient braking, with less steering control and none of the stabilizing effects of the spinning wheel. It is to be avoided, but a good brake should allow you to get very close with ease.

Hydraulics, and hydraulic discs in particular, decrease the amount of hand force required for the same brake power. They do not suffer from housing contamination, so braking remains predictably light through the system’s entire lifespan — or until it needs to be bled again. They can be finely tuned for modulation and power, adjusted for the platform in which they are mounted and the braking that they will be asked to perform. In theory, anyway.

Let’s take a look at how SRAM tried to do just that.

Both of the new hydraulic brake options, the HRD disc and HRR rim, will be actuated with the same levers: either the new Red 22 HydroR lever, or the 10-speed compatible S-700 lever. That means that you could, if you really wanted to, pick up a disc fork for your current frame and run a hydraulic rim brake on the rear with a hydraulic disc on the front, both actuated with the same set of levers.

HyrdoR Disc
SRAM didn’t simply plop one of its mountain systems onto a road bike; those brakes are far too powerful, and would easily overcome the traction of small road tires. The HydroR system was designed from the ground up for road and cross use, utilizing a road-specific master cylinder and finely tuned piston sizes to decrease outright power and increase modulation.

That purpose-built master cylinder is placed into the top of its road shifter, resulting in a distinctively bulbous knob. The rest of the shifter shape remains largely the same, including the smooth transition from bars to tops that we love from SRAM. The knob is slightly squared off, and though visually obtrusive, has no detrimental effect on the ergonomics of the shifter itself. In fact, the tall knob adds a position we rather appreciated when on the rivet. It’s almost like having a pair of “ups” to match the drops.

Both shift and brake paddles can be independently adjusted for reach, just like mechanical Red, and both standard and moto (left brake lever actuates rear brake) versions will be available.

SRAM’s HRD disc calipers are front- and rear-specific, utilizing a 19mm piston up front and a 18mm in the rear to better match the traction (and thus modulation) requirements of each wheel. The caliper and piston ratios are road-specific, as well, resulting in a softer modulation curve and less power.

The brakes’ ultimate power is not all that different from the company’s BB7 brake set, but modulation is drastically improved. “We could have made the brakes more powerful,” Avid product manager Paul Kantor said. “But the focus was on everything that happens before you lock up the wheel.”

SRAM recommends the use of 160mm front and rear rotors for road and 140mm front and rear rotors for cyclocross, largely due to heat requirements.

Within the caliper itself, SRAM’s engineers increased pad retraction to help eliminate the annoying ting-ting-ting noises often associated with discs, caused most often by out-of-true rotors. A stronger pad spreader aids in the increased pad retraction.

Pad compounds and backing have been adjusted specifically for road use, too. The pads are now backed with steel rather than aluminum, and the holes usually found on the back of Avid’s mountain pads have been filled in. Both changes provide a better heat sink. The organic compound has been adjusted to fit the brakes’ desired modulation curve, too.

The HRD brake is missing one rather important component, though: pad contact adjustment. It’s a feature found on many mountain bike brakes, and one that is particularly suited to the road. A ting of a slight rotor rub is often drowned out by all the other noises produced by singletrack, but out on the road there’s nothing to distract.

The lack of a pad contact adjustment makes it impossible to fine-tune the feel of the levers to one’s liking, too. Lever throw will remain at its factory setting, as only the lever position can be adjusted. Those familiar with hydraulic discs know the trick of pushing the pistons in a bit with the wheel removed, but that’s not exactly an ideal method.

HydroR Rim
As for the HRR rim brakes, this one we don’t quite understand, to be honest. A rim brake, regardless of its method of actuation, still suffers from the same downfalls: it grabs an imperfect rim surface, its mount is one tiny bolt, its arms must be long enough to clear the tire, inducing flex — the list goes on. With the HRR, then, SRAM could create a more powerful brake, and a brake with better lever feel, and even improve modulation a bit, but it could not solve the larger, inherent problems with rim brakes.

Nonetheless, the HRR brake is intriguing if only as a baby step towards a disc setup, a way for the millions of road frames out there to go hydro. It features all the handy tech we’re used to on rim brakes, so the swap is relatively simple — it has a quick release as well as a tool-free pad contact adjustment that closely mirrors the micro-adjuster of a mechanical brake. Easy. There are few downsides, but the advantages in brake performance are also somewhat slim.

Tire clearance up to 28mm is excellent, though, as is the wide stance, compatible with today’s latest wide rims.

Solving the big problem of high heat
Heat. It is the downfall of any brake system, but the smaller braking surface of discs makes them particularly susceptible to problems; the smaller the rotor, the bigger the problem.

That issue is compounded on the road, where descents tend to involve much higher speeds and greater speed changes — from 45 mph to 10 mph for a switchback, repeated every half-minute, for example. That’s a lot of energy that needs to go somewhere.

Any disc can suffer from what is called “friction fade,” a result of excessive heat on the braking surface and pad surfaces. In fact, rim brakes can suffer from this too, and if you’ve ever noticed your carbon wheels braking more poorly after a few hard corners, that’s why. High heat simply decreases the friction at the brake contact points.

Hydraulics have an additional, and usually more dangerous, problem: boiling fluid. The brake system can get so hot that it boils the fluid inside the brake lines, vaporizing the non-compressible brake fluid, making it compressible. Compressible fluid inside a brake line allows the lever to continue its travel without actually squeezing the pads any harder. Eventually, the lever will reach its maximum travel. You can likely guess the result.

That’s a massive problem, but it’s also one that has been largely solved. High-temperature brake fluids and better cooling have kept brake fade out of the mountain bike world (mostly) for years now. SRAM still had to up the ante for its road discs, though, as the potential for excessive heat is greater.

With the aforementioned changes in pad compound and backing material, as well as its recommendation to stick with 160mm rotors on the road, SRAM says it is confident that users will not have any issues. It still retains a maximum weight limit of 250 pounds on its hydraulic discs, though. That weight falls in line with the max weight limit on many high-end carbon frames.

The company tested the brakes with even smaller 140mm rotors on roads like the Passo di Stelvio in Italy’s Dolomites. With its brake systems rigged up with heat and pressure sensors (pressure in the lines is indicative of any vaporization-caused fade), testers donned weight vests and full-face helmets and hit the descents as hard as possible. Short, hard braking and brake dragging were both extensively tested.

The results? No problems. Some friction fade was experienced when descending very aggressively (hard braking before corners), but the brakes never boiled, and adequate power was never lost.

The stresses caused by the steep, twisting descents were then replicated back in Avid’s lab.

That same lab had an interesting piece of data to share: on its dynamo tester, five minutes at 550 watts with a rim brake applied blew a tire off a carbon rim. Twelve minutes at 800 watts, with a disc brake applied, resulted in zero damage.

It seems SRAM has done its homework, then. We’ll find out soon, when a test group arrives.


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