It has been said that to a camera or the common observer, tires are a bunch of round black things. That is doubly true of CVT drive belts. Talk about unsung heroes; the belt driving a machine with a CVT is hidden in a vented cover, and they don’t even have different tread patterns. But even if they look the same, all belts are not equal. Belt technology has had to increase as power output of CVT-equipped machines has gone up. It is no coincidence that the advent of “extreme-duty” belts appeared at about the same time high-horsepower UTVs did. Sure, ATVs do need replacement belts, but not at the rate that UTVs do when pushed hard.
A CVT belt is a type of V-belt. As such, it is the side of the belt that is doing the work. For that reason, the angle of the side of the belt must be compatible with the faces of the CVT. The width of the belt must be precise as well. A belt has to be strong along its length. Engineer Eric Murray from Carlisle put this requirement very well: “Picture accelerating 1600-plus pounds as hard as the fastest side-by-side can by pulling it with a rope. That is what is happening inside your transmission.” And, unlike pulling a UTV with a rope, the belt has to do that work constantly. The heart of your ATV or UTV could be said to be the engine, and the body is the chassis and drivetrain. The only connection between the two is the belt. Break the belt and a ton of power and a yard of suspension won’t stop you from walking.
WHY AND HOW
In addition to being strong along the length, the belt must be rigid and highly resistant to bowing from side to side, but bend easily along the length of the belt. Again, Murray elaborated: “The clutch/belt system has to do a few things simultaneously. First, it has to transmit all the power the engine can put out. If you have a big side-by-side that’s putting out 90-plus horsepower, all that power goes through the belt. The clutch squeezes the sides of the belt hard enough to accelerate the machine and whatever it’s loaded with. This means there can be over 1000 pounds of squeeze force trying to crush the belt from the sidewalls. At the same time, it’s rotating fast enough to spin the secondary clutch, in some cases, over 9000 rpm. Simultaneously, it’s shifting up and down in both clutches to deal with changing loads, both from the engine and back through the drivetrain from the wheels. It does all this while running at temperatures ranging from minus 30 to over 200 degrees. It’s a hard life.”
The belt is made from rubber (usually fiber-reinforced) that is rigid across but flexible along the length. The “cog” design on the inside helps the belt be strong sideways, but bend easily. The cog on top also aids bending around the pulleys, but adds side-traction, making the cross section strong and generating cooling air in the CVT case. Between the top cog and the inner cog is the cord. The cord gives the belt the strength lengthwise. The cords are bound into the fiber-reinforced rubber of the cogs with adhesive. The face of the cogs has a fabric cover.
With all of the loads facing modern CVT belts, the search for materials that will perform better is constant. Better compounding, adhesives and the tensile cords are all continuously scrutinized.
HEAT IS THE ENEMY
The consensus in the industry is that belt temperatures over 200 degrees are bad and that 400 degrees is critical, but SxS competitors in WORCS have reported belt temps of 1000 degrees and claim that the belt is so hot it is gooey at that temperature. High-end SxS racing, high-horsepower machines with paddle tires, and mud-boggers with tall, aggressive tires are the hardest machines on CVT belts. Snowmobiles use a similar clutch, make incredible power and have a track that puts a heavy load on the belt. But, a snowmobile belt is used in the cold and without a confining belt case aside from the body of the machine.
It is interesting that mud-bog runners are considered tough on belts. One of the points that Dayco makes is that snorkels on machines hamper the cooling. Adding length or bends to the CVT-case breathers harms cooling. Naturally, a bogger would point out that the case doesn’t like mud or water, either, so snorkels are the lesser evil.
Engine mods, big tires and a heavier machine all add to the heat that the belt must endure. If you start to make changes like these, then EPI feels you need to make changes to the clutching to keep the heat down.
THINGS THAT MAKE IT GO BOOM
The CVT case has inlet and outlet vents and, in some cases, filters on the inlet vents. These vents are critical to belt life. Running with them restricted (by dirty filters, mud or whatever, including rodents) will make the belt run hotter. The belt will not necessarily fail immediately, but the rate of breakdown of the rubber compounds is greatly accelerated when the environment is hot. Some brands of UTV actually have air pumped into the CVT case, and some racers are fan-forcing air into the CVT case to keep belt temps down.
You can damage a belt going slow too. Running at low speed in high range can burn up the belt, and so can riding or driving with the brake on. The same thing is true when the wheels are stuck. The drive clutch spins, but the belt doesn’t—that burns the belt in one spot. It may not fail right then, but belt life is shortened.
Water, mud or dirt in the CVT case, and especially on the sheaves (the drive faces of the clutches), all hurt belt performance and shorten the life of the belt. Having the belt too tight or loose will affect performance and belt life as well.
Dayco suggests, “Keeping your clutches clean will help improve your performance and save wear and tear on your clutches. Lightly sand your clutch sheaves [faces] with fine sandpaper or an emery cloth. The direction you must sand is from the center out to the edge. Work your way around both sheaves. Do not sand any grooves into the clutch sheaves. Sanding the sheaves will remove belt residue and give the belt a better surface to grip. Once you are done sanding, blow off any sanding dust from both clutches. Take contact or brake cleaner and clean the entire clutch except for the bushings. Do not use contact cleaner on any of the clutch bushings. Choose a contact cleaner that does not leave an oily film when it dries. Wipe the bushings off with a clean, dry cloth. Remember, the clutches are considered a dry part. No oil or grease is required. The inside hub of the helix is the only area where a small amount of grease may be applied. Clean your clutches every time you have them apart and/or several times a season.”CONCLUSIONS
Obviously there is a lot to consider here. Most of the problems noted occur frequently only in extreme use or, and in the case with riding too slow in high range, from improper riding technique. There is a reason that the CVT is so common: it works. If you are having recurring belt problems, certainly check that the clutches are working as they should mechanically. Consider an extreme-duty belt, and check into having the clutches fine-tuned for your riding conditions. Make sure that the belt deflection is inside the manufacturer’s specifications. Keep belt-cooling in mind, and make sure that the factory vents are not hampered in any way. Then have fun!THE BELTS
We asked leading manufacturers for prices on belts for two popular machines: The Polaris RZR XP 900 and the Yamaha Grizzly 700. Both have plenty of power, and they are commonly used in extreme riding. We asked for high-end, extreme-duty belts, but most of the aftermarket companies have a variety of belts for differing levels of use. After looking at prices, we felt that it made sense to go with the best models. Why do the job again? Some models like the RZR are very easy to change. Others are harder, and you will not want to be doing it again, so buy a heavy-duty belt. For comparison, we have included the price of the stock belt.
Carlisle makes a variety of belts and other rubber transportation products, and it looks like they make a handful for ATVs and UTVs. But when you actually look at the applications for a specific model, there are only one or two that apply. We concentrated on the Ultramax Hypermax belt, which is designed to deliver maximum performance and dependability. With specially formulated rubber compounds and extra-strong aramid cord, the Hypermax ATV/UTV belts have a two-year warranty that guarantees against defects in material and workmanship.
Dayco designs and manufactures high-end, quality CVT belts. Dayco makes the XTX belt for extreme torque applications, HPX for high performance and extreme use, and the HP it calls a “high-performance outdoor-activity” belt. Dayco makes belts for other brands as well.
EPI has developed CVT performance clutch kits for 20 years, and they consider the belt an important part of the kit. EPI introduced its first Severe Duty line of belts in 2007. They test to design a clutch kit and belt combination that will operate at an acceptable temperature while providing the most aggressive upshift and backshift possible. Quality control, close tolerances and the design make the Severe Duty belt ready for high horsepower, heavy loads and aggressive riding styles.
Gates is a big name in belts in general, and the company does a lot of testing as it designs the top-tier belts it makes. Gates makes a variety of belts, but for the RZR XP 900, it has the G-Force and G-Force C12. Both are solid belts with an aggressive top-cog design. The G-Force C12 claims to be “The first belt of its kind, with a carbon tensile cord for exceptional strength, flexibility, durability and performance in the most demanding off-road conditions.” The G-Force uses the same construction, but with aramid tensile cords.
For machines with engines 800cc or larger, High Lifter has the 3GX (3rd Generation Xtreme). This belt features high-temperature neoprene, made with the highest level of aramid fiber loading available. High Lifter does manufacture belts, but it has the 3GX made to its specs and sells Dayco belts for its Pro Series. The Pro Series is constructed with P-aramid cord reinforcement and engineered fiber-loaded, neoprene compounding. For the Grizzly 700, High Lifter specifies the Pro Series belt.
Moose has the ATV/UTV High Performance Plus belt for machines with engines 800cc and larger. It has specially formulated, high-temperature neoprene, with the highest level of aramid fiber loading available. The design features deeper cogs on top and rounded cogs on the bottom for flexibility and longer belt life. For machines like the Grizzly, Moose has the ATV/UTV High Performance drive belt, “Made with extra-strong P-aramid cord reinforcement and engineered, fiber-loaded, neoprene compounding designed to dominate any type of terrain.”