Carbon Belt vs. Metal Chain Last Drive
7 min read
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In 1980 Gates Industrial Corp. and Harley-Davidson added a 3rd selection of bike last drive—the Gates toothed belt and sprockets on the FXB Sturgis mannequin. The brand new Gates drive was basically silent, required no lubrication and little upkeep, and shortly established itself as being a minimum of as sturdy because the metal curler chains it changed. Gates’ literature describes it as “the one belt drive system designed particularly for bikes.” Many thousands and thousands extra belt-equipped H-D bikes have adopted.
Such toothed belt drives have lengthy been extensively utilized in business, and are acquainted to motorsports followers because the blower drives seen on Prime Gasoline dragsters.
Riders have eternally debated the final-drive drawback: chain or shaft? Shaft-drive advocates level to cleanliness, low noise, and lengthy life/low upkeep. All in favor of chain drive word comfort of ratio altering (necessary in racing), gentle weight, low price, and lack of bulk. After 1971 the choice of a curler chain with its lubricant sealed in place by tiny O-rings modified the dialogue considerably. Chain life and cleanliness improved considerably.
In 1980 the tensile energy of Gates Poly Chain toothed belts got here from the superstrong aramid fiber, DuPont Kevlar, and the physique of the belt was polyurethane. When the phrase “belt” is used, individuals usually suppose first of the previous fabric-reinforced rubber V-belts used to drive automotive equipment (invented by Gates in 1917). V-belts drive by friction alone, however toothed belts are a optimistic drive, like chains or gears.
Early on this century Gates started to develop a brand new belt whose energy relies upon superstrong carbon fiber cords, and it got here to market in 2006–07. Carbon fiber relies upon lengthy, largely crystalline components aligned with the fiber path. A well-publicized utility of carbon fiber is in Boeing’s 787 airliner, whose construction weight was lowered by a claimed 20 % by changing conventional aluminum construction with carbon-reinforced composite. Carbon fiber bolstered plastic (CFRP) is acquainted to motorcyclists because the light-weight materials from which the bodywork of high-end sports activities bikes are made.
Tensile Strengths of Metal and Carbon
How can a versatile belt be as sturdy as or stronger than a curler chain? Typical high-strength steels provide 120,000 psi tensile energy, however carbon fiber routinely achieves 500,000 psi or extra. And carbon is gentle. Metal has a density of seven.8 (which means {that a} cubic inch of metal weighs 7.8 instances greater than a cubic inch of water), whereas carbon fiber’s density is slightly below 2.0.
Way back supplies researchers understood that sensible metals by no means come near the energy they show as good crystals. That’s as a result of metals are polycrystalline: made up of a jumble of tiny, randomly oriented crystals bonded collectively.
At current each chains and belts are extremely engineered merchandise of nice reliability. Confidence in them is excessive as a result of each types of drive are backed by a long time of expertise.
Belt Integrity
Once I requested Gates engineer Jeff Schubring in regards to the bond of belt enamel to the carbon wire band, he mentioned, “The drive required to shear the enamel is healthier than the modulus of the belt.”
Put on Resistance
Curler chain inevitably wears at its greater than 100 joints, barely rising in size over time. This size improve requires periodic readjustment of chain slack, for extreme slack can result in the chain’s leaping on the sprockets. Connecticut rider Richard Schlachter was comfortably main the 1981 Daytona 200 when his chain started to “ratchet,” to skip on the sprockets. Through the use of much less throttle he was capable of salvage third place.
A toothed belt drive has no joints to put on, and the carbon fiber materials that gives its energy can’t stretch, so adjustment is rare.
Schubring mentioned, “We have now pointers for a way a lot (middle distance) variation might be tolerated.”
Regular Improve in Belt Functionality
Metals sometimes fail in fatigue (the buildup of inside materials injury throughout 1000’s of stress cycles results in crack formation). To extend their resistance to fatigue, the plates of premium curler chains are shot-peened. Carbon fiber shows exceptionally excessive inherent fatigue resistance. The late John Britten mentioned to me within the Nineteen Nineties, “When you get used to working with directional supplies like carbon fiber, you lose belief in metals—they start to look like tightly packed sand.”
I requested Schubring how carbon fiber is bonded to the opposite components of the belt. He defined that the matrix of the belt is polyurethane rubber, and that “the magic is our chemists.”
They work in an ever-active space—that of creating chemical coupling brokers able to bonding strongly to each the fibers and to the matrix that surrounds them. There may be regular evolution on this subject, permitting periodic reductions within the width of belt required to transmit a given load.
Due to this regular progress, a Gates belt equal to a 530 curler chain is now equal in width to or barely narrower than that chain. The newest Gates Carbon Drive X9 belt, as in contrast with the product it replaces, permits use of both a 9 % narrower belt than earlier than, or of 10 % smaller sprockets.
Shock Loading of Drives
As a result of we’ve got for some years seen the first chains of traditional bikes changed by Gates belts (significantly in racing), many assume that belts should have shock-absorbing properties.
No, toothed belts will not be shock-absorbing or springy. In the event that they had been, their pitch would range, resulting in ratcheting on the sprockets (skipping enamel). Shock-absorbing components initially equipped with the motorbike—on crankshaft or clutch or rear wheel—are retained when a belt drive is adopted.
Schubring notes that for motorbike and scooter drives “shock hundreds within the system are sometimes a lot larger than peak motor torque—within the vary of two to a few instances. So the energy of the belt from the tooth to the wire and major physique of the belt wants to have the ability to deal with this with out breaking.
“With belts this comes right down to the width of the product,” Schubring says.
Energy transmission textbooks embody tables for estimating how a lot capability is required to permit for the “lumpiness” of assorted energy sources and hundreds—from smooth-running electrical motors to rock-crushers.
Gates manufactures the belts (technical growth and manufacturing of Gates carbon drive motorbike belts happen within the US) in giant widths that are slit to the specified width. “If in a given utility we encounter a problem, it takes solely a ten % width improve to double the product life,” Schubring says.
Chordal Rise and Fall of Chain Drives
We have now all heard the zhhh sound as a chain-driven motorbike coasts with its engine declutched and shut off. That sound is generated as a result of the “wrap” of a series round its sprockets just isn’t actually round: The chain’s wrap is a polygon with as many sides because it has pins.
As such a polygon rotates, its apices (plural of “apex,” proper?) have a barely larger diameter than do the facilities of its sides. The results of that is that particularly on sprockets with small numbers of enamel (reminiscent of 15) the chain’s rigidity aspect rises and falls barely because it runs onto the sprocket.
To visualise this, think about using in a automotive with 15-sided wheels. That is the so-called “chordal rise and fall” of a series drive. A part of this course of is an audible sequence of small impacts because the chain’s rollers hit the sprocket—the zhh you hear. Industrial drive catalogs advocate that sprockets with fewer than 20 enamel be averted if attainable.
Toothed belt drive doesn’t generate chordal rise and fall.
Overseas Object Injury
What occurs if a pebble is trapped between belt and sprocket? “We get belts returned with stones embedded in them,” Schubring says. “The shopper’s situation was the ticking of the stone hitting the sprockets—nothing to do with failure.
“Sprockets might be made in such a means that they shed stones, simply as is finished with chain sprockets for filth bikes.” Gates presents the Mudport sprocket design that permits international supplies to flee pulleys.
Belts Are Enticing Electrical Bikes and Bicycles
Mild weight and low friction are at all times of curiosity to bicycle makers and their prospects. “Belts are a game-changer for electrical bikes,” Schubring says.
As a result of electrical motors are basically silent, different noise sources stand out. The quiet operation of Gates toothed belts is suitable with electrical traction. Additionally, electrical drive is far smoother than the pulsed torque of IC engines, so a belt to transmit 100 electrical motor horsepower might be narrower for a given service life than one transmitting 100 ICE horsepower.
