testes guiadores de carbono

CENTER OF CONTROLYou can see the glimmer in many bikers’ eyes at the sight of carbon-fiber bikes. But with carbon-fiber bars, some people’s foreheads are drenched in sweat. Our lab test attempts to uncover whether it is wise to trust the black luxury material even with the most delicate parts.

CARBON-BARS

A bar's life in time-lapse: the testing machine “VR-3” squeezes ten years into nine hours.

After passing the test many bars still look great but already have ten years of hard riding under their belt.

Text Stephan Ottmar Pictures Daniel Simon ---- And again the cell phone of BIKE tes-ter Martin Peukert rings. At the other end the testing machine “VR-3” is beeping loudly. A tested bar broke – that much is clear. Now there is no time to waste. The breakage has to be evaluated, a new bar has to be put onto the machine and the machine needs to be started anew. Martin starts off running. Time is of the essence since all in all 60 precious handlebars are being put through the test cycle on the testing machine. Every single one will be bent, compressed and pulled for eight hours.Fifteen models from eleven different ma-nufacturers are being put to the test. We test four samples of every bar. That's a world premiere. Never before has anyo-ne taken such a comprehensive sample. The balance is excellent. Nine models re-ceive all points possible. If you compare this result with past tests, you will see that carbon fiber is first choice as a material for handlebars.

Normally these kinds of tests are limited to a maximum of three samples. With such an important part we wanted to be on the safe side. There's a good reason for it:

Carbon-fiber problem: spread

The main problem of composites is cen-tered in manufacturing methods. Current-ly, there is no cost-effective way to me-chanize manufacturing of the black fiber. That‘s why the bars are being laminated by hand. By doing so, small irregularities can lead to capital weaknesses. And what

worker puts out constant results day after day? Proof can be found in the weights of the products. A spread of five percent is not unusual.

Horror scenario: bar failure

The big danger for users: slightly dama-ged carbon fiber will fail suddenly – similar to aluminum. A weakened bar can break apart with a sudden crack during a des-cent. The results are open for your ima-gination.Neither a cracked frame nor brake failure is as scary as bar failure. Handlebars are safety-relevant parts of outmost priority. That is why we leave no stone unturned during testing. The weakest of the four samples is the deciding factor for the test result. Only if all four samples are yielding good results will the grade be positive.FSA, Easton and Truvative all had one weakling on their team. Even big-name manufacturers, who invest lots of time and know-how in their development, ap-parently have problems in manufacturing. After less than one-tenth of testing time, a Truvative “Team Carbon” said good-bye. One Easton and one FSA followed suit relatively soon after. This is why buying a bar can be like playing the lottery.Much worse are Control Tech and Ritch-ey. Of the models “WCS Carbon Riser”, “WCS Carbon Flat” and “Crossbow”, none of the tested samples reached significant runtime. Just one “WCS Flatbar” finished the test. We strongly discourage buying those products.

Significant is the thin midfield. The bars either break early or never. Therefore the list of “Best of Class” is fairly long. Weight-conscious racers use Race Face and Syn-

tace. These two manufacturers cover the bases from light to strong very well.

The Test

The testing machine demands eve-rything of the bars. In less than nine hours a full life of a handle bar is simula-ted. For this, a complex of loads is used. Through real-life riding the loads acting on a bar have been measured. The tes-ting machine transfers those loads from real-life into the lab. Since simulating a test track is not yet possible, the most important loads are being picked. That is how the complex of loads has been created (page 38).

Six different loads are created. Natu-rally, different events happen with dif-ferent frequency. What biker rides only standing or drops every few yards over high steps? In addition, light crashes are simulated. Everyone falls off of the bike occasionally. After a big crash, though, there is only one thing to do: replace the bar and stem. Neither aluminum nor car-bon fiber offers enough margin for safe-ty. Whether a bar has already been da-maged is not always evident, so always take the safe route and replace it.

Appropriately, all bars are clamped on the testing machine with a suitable stem. For technical reasons we had to use a substitute stem because the vibrations of the machine loosened bolts. After eight hours of run time the machine stops the test. Many bars survived the time wi-thout damage and withstood 150,000 load changes. About such samples, Jo Klieber, Syntace boss and developer of the testing machine “VR-3” says, “Expe-rience shows that

CARBON-BARS

Blind trust: At high speed you have to be able to trust your material.

Carbon fiber material: processing, strengths and risks

Production processEven today manufacturing of carbon-fiber pro-ducts requires lots of manual labor. Layers of material are added by hand. For bars, so-called prepregs made of unidirectional fibers are used. The individual fiber mats are already drenched in resin so the right combination of resin and fibers is ensured.A bar consists of a base, middle and top sheet. Each sheet is made of several layers of pre-pregs.Those layers are glued to a flexible rod. For grea-ter strength, more layers are used. An interesting note: Only the top sheet is end-to-end for optical reasons. Below the top layer the sheets are quite often criss-crossed.After the last sheet has been glued, the rod is pulled out and substituted by an inflatable blad-der. Now the bar will get its final shape: It is placed in a negative mold. In an oven the bladder is inflated and pressed to the mold. This autocla-ve method is very laborious, but its advantage is the production of highest quality parts. After mol-ding, the bars are cut to size and lacquered in several layers.

Material propertiesCarbon fiber is anisotropic, which means it can bear loads only in one direction. Perpendicularly to the strands it can bear only a fragment of the load. As a result we have the interwoven structure with its carbon-fiber typical looks. Fiber strands are run in all directions and make the material stronger in all directions.

Comparison of carbon fiber and aluminumEverywhere you read how much better the mate-rial properties of carbon fiber are in comparison to aluminum. If only tensile strength were of im-portance, a bar made of carbon fiber would only weigh one-tenth of an aluminum bar. But tensile strength is not the only important property. Alu-minum has advantages in many other areas that outdo carbon fiber. So in fact, the weights of bars made of one or the other material barely differ. As soon as manufacturers get a handle on the variants that occur in production, they can start making composite bars lighter. While aluminum has reached its limits, carbon fiber still has lots of potential.

bars reaching this number of load chan-ges do not break in the real world.”

Carbon fiber beats aluminumWhile frames made of the high-tech ma-terial are widely accepted, there is still a lot of skepticism about handlebars, but without reason. The carbon bars tested break all the records: 75 percent of all tested samples pass every hurdle easi-ly. During the bar test in BIKE 10/02, we tested almost exclusively aluminum bars and the number of bars that passed the test was below 30 percent.

A few rules have to be observed however. Always install the bar exactly as speci-fied in the manual. Use the stated torque values when installing, not only for clam-ping the bar to the stem but also for the fastening the controls. Only cut the bars as far as the manufacturer specifies. The manufacturer must also state that moun-ting bar ends is admissible. After small crashes and at the end of the season, you should inspect the bar and replace it if you see damage. After bigger crashes replace the bar and stem – safety first.

Bike tester Martin Peukert now can sa-vor his leisure time. The testing machine won’t be calling him at ten at night any-more. Now it is time for manufacturers to react to the results of his tests and take

action. A few can relax, though.

Dipl. Engineer Dirk Zedler, BIKE contributor and bicycle technical expert: www.zedler.de

Installation influences riding pleasure and breakage

The analysis of many broken bars yiel-ded a clear picture: the majority of bre-akages have been caused either by a bad combination of parts or poor instal-lation. So observe these tips: Always use bar and stem from the same ma-nufacturer and with the same quality. Stay within the recommended torque values by using a suitable torque wrench and check frequently. Contact the manufacturer of the stem to check whether the stated values are good for

carbon-fiber bars. The torque values stated for controls are usually too high for carbon. Use carbon-fiber mounting paste for controls and bar ends. The paste increases friction and a lot less torque is needed for the same result. If you want to cut the bar, contact the manufacturer to check on where the re-inforcements for the bar ends and con-trols are located. If you install controls outside the reinforced areas, breakage is imminent.

Testing cycle: complete life of a bar in time-lapse

CARBON-BARS

2,5 Hz

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Offset70 msOffset

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© Jo Klieber / Germany

17. May 2006I:\TESTMASCHINE\TESTSTANDARDS DH + RC (Artworks & Texte)\DH Standard\VR3 DH 2002.4 v01.ai

Pull

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Stem & Handlebar Test Machine VR-3

Repeated until failure of specimen1 s

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500 load cycles

Test procedure (Load collective)

Climbing Hard Climbing Jump / Impact

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Each 4000 Lc

A: Loadpoint: 40 mm from bar end. B: Top distance between cylinders = Bar width -100 mm. C: Headtube angle: 72°. D: If no manufacturer restriction, standard test w/ MTB-stem block ID #256#.

E: Rod end w/ clamp: 500g +-125 g. F: Grip clamp width: 50mm. G: Temperature: 18°-28°C. H: Random specimen of 3+1 required. I: Tighten all screws w. 150% of recommended max. torque.

4 times 4 times

Lab test: 480 hours permanent operation

Lab testSince it does not make any sense to make a real-life test, we rented space at Syntace in Ta-cherting, Germany, where the VR-3 is located. The VR-3 is a bar testing machine developed by Syntace in conjunction with several testing insti-tutes and BIKE. The machine is connected to a huge compressor and is able to apply its force in well-controlled doses. It can exert either push or pull forces on both bar ends.The testing cycle is stored in the machine’s brain (page 38). Every bar goes through this cycle either until it breaks or 210,000 changes of loads have been reached. After that, the machine stops. The bar has done its due. The run time equals a life span of about ten years. But be aware: weather influences are not part of the simulation. This test focuses on mechanical forces.

The testing cycleThe offset impact at the beginning (0) and the drop/hit (5) are special events that don’t happen very often. The events simulate very hard riding or light drops. Steps 1 and 3 simulate riding while

standing. In those events the rider pushes down one side of the bar and pulls up on the other. Steps 2 and 4 simulate bumps and rough ground as they occur in real rides under varying condi-tions. Exact testing forces can be read in these “load situations.”All in all, the test runs through 1002 changes of loads with varying loads and force transmissions. After one cycle runs its course, the game starts anew. A good bar runs through the cycle 210 ti-mes for a period of about 9 hours.

The meaning of it allEvery type of bar is tested four times. This way we are able to uncover variance in the production process. If the numbers of successful cycles for one type and model are close to each other, it is possible to make a prognosis about life expectan-cy. If there are mavericks, it is a sign of variances during the production process. We bolted all bars with recommended torque values.

Installation and maintenance: torque values are decisive

Torque wrenchTo install an expensive and delicate carbon fiber bar you need a torque wrench. Normally, if bolts are tightened by feel only, the disparity between it and the correct value is too high. If the stem plate is tightened too much, there is too much stress in the clamping area. The fibers don’t have enough room to move and can break. The same holds true for all controls like brake levers, shifters, lights and screw-on grips.

Mounting pasteTorque values, instructions for installing bar ends and cutting the bar should be part of a good manu-al. Please read the manual before installation.Mounting paste disperses the pressure onto the material and improves clamping of the bar onto the stem. The paste is infused with plastic par-ticles. They roughen the surface of the clamping areas of bar and stem without damaging them. The effect: Even at low torque values the bar is tight and the strain on the material is lower.

Routine checksAfter a long period of use, the stem works its way into the material of the bar. Damage can also occur at shifters and brake levers. Winter tune-up is the perfect time to perform a comple-te check including dismantling the bar. Carefully inspect the clamping areas. In case of irregula-rities such as cracks, nicks, or chips, replace the bar.

Pictures of breakage

Breakage in the clamping areaThis is the classic of carbon fiber materials. Through permanent pressure on the underside of the bar, the structure becomes waved. If the radius of the wave gets too small, the bar breaks.

Forced breakageThis form of damage only occurs under extreme forces, like the appea-rance of a bar after a huge drop. The fibers are torn in the direction of force pull. (This damage did not occur on the testing machine, we created it on purpose.)

Breakage at a bendThe bend is a critical area for carbon fiber bars. High pressure on the fibers is responsible for failure at this location. Under pressure, fibers rip off.

Bad designAbrupt transitions are a bad design for any material, and this holds true for carbon fiber as well. The “Crossbow” has many abrupt transitions. A testing sample shows ruptures in five different places.

Overview of all 15 carbon fiber bars

Four of eight bars did a great job and are fully within the green area. Bars that constantly manage to withstand more than 80,000 changes of force are suited for mountain biking.

A flat bar has two bends fewer than other bars and is easier to manufacture. Five models can be recommended without limitation. They are fully race-ready.

Changes of force Changes of force

CARBON-BARS

Statement from the Control Tech regar-ding the test results of the “Crossbow”:“We inspected the Cross-bow extensively and tested it according to the Euro-norm and DINPlus. It passed those tests. The Crossbow is no downhill bar, therefore we think the requirements (...in this test...) were too high.”

Statement of Ritchey about the test results of the “WCS Carbon”:Within the two years of sel-ling the carbon fiber bars we never had any breakage in the clamping area. Never-theless, we will refine our internal testing procedure that is already beyond the CEN-Norm. Particularly, we will integrate more abrupt hits. We owe this to our cus-tomers.”

*The BIKE evaluation reflects the subjective impression of the test ride�**Because of bolts on the sta�

CARBON-BARS

Technical and other infoDistribution

WidthRise (height)BendWeightPrice

Test result: change of loads until breakageBar 1Bar 2Bar 3Bar 4

Conclusion: The distinctive design is the problem of the stem/bar unit. Too many transiti-ons make the part susceptible to breakage. The weight is too high for racers.

BIKE says* has weaknesses




Conclusion: Three out of four bars are great? Smells like variance. The design is OK, but there is a problem in manufacturing.

BIKE says * acceptable




Conclusion: FSA has the same problem as Easton, one maverick on an otherwise great team. The weight of the bar is the highest in this test. Too bad.

BIKE says * acceptable




Conclusion: Apparently FSA is better at making flat bars. Four bars survived the test without damage. That is a sign of quality. Interesting design.

BIKE says * super




Conclusion: Race Face shows how it’s done: light, sturdy and affordable. Three argu-ments for the “Next XC’. The oversize design saves another 10 grams according to BIKE measurements.

BIKE says * super




Conclusion: The narrow 25.4 mm diameter between bar and stem does its job as well as the oversized version. This product has only strengths. Nice surface.

BIKE says * super




Conclusion: The Trek brand Bontrager can take quite a bit of abuse. Sure, the “Race X Lite” is not especially light but a reliable partner for all riding situations.

BIKE says * super

*The BIKE eval�**Because of bolts on the sta�

Technical and other info


Conclusion: The definite loser of this test. Not a single bar made it through. The “WCS Carbon Riser” is full of safety risks. Not suited for a mountain bike.





Conclusion:Many racers already swear by the “Duraflite.” For good reason, it is the lightest bar in this test. Exemplary: The clearly stated torque values next to the clamping area.

BIKE says * super




Conclusion: The only bar to present four vastly different values. The first 2 are especially too low to use this bar on a mountain bike.

BIKE says * has weaknesses




Conclusion: If you shell out 159 Euros for a bar, you expect quality. It is what you get with the “Lowrider Carbon.” Light and sturdy are its attributes. The bar can be shortened as much as you like.

BIKE says * super




Conclusion: All four samples cruise through the test and achieve great results. Weakness: Because of its high weight it is not suitable for weight weenies.

BIKE says * super




Conclusion: The new Syncros “Factory Carbon” has a 31.8 mm diameter. It can be re-commended without limitations for competition.

BIKE says * super




Conclusion: After only half an hour one sample broke. This spread holds an inherent danger. Could be the bar holds up, could be it fails.





Conclusion: “Atom Flattie” from Use is a really hot item. The part has been designed with the help of modern technology and it pays off. Recommended without limitation.

BIKE says * super

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