If you are looking for CVT help for your UTV, you can most likely find it here. We outline good points and what does what. Clutching is a subject that a book can be written on (and there have been several) but we are giving you the shorter version that applies to most CVT clutches. We have a great knowledge of CVT clutching and try to help our customers as much as possible with setting up their machine. A properly tuned clutch makes a massive difference in how your machine performs. You can have all the horsepower in the world but if you can’t transfer that to the ground then it’s not doing you much good.
Engagement RPM: This is the RPM where the primary clutch engages and starts to move the vehicle.
Peak RPM: This is your RPM near full shift of the clutch and tells us how your clutching is acting overall. To check this, we suggest a 10-20 MPH roll on then go wide open throttle and take note of your RPM around 55-60 MPH. If your machine is geared extremely low or is of smaller engine size you can do this check at a lower speed. A good rule of thumb is to check roughly 30% below max speed of your vehicle.
- More overall primary clutch weight = Less peak RPM and a slower RPM sweep up to peak RPM
- Less overall primary clutch weight = More peak RPM and a faster RPM sweep up to peak RPM
- Tip weight on the clutch arm (hole #3 on most AA weights, #4 on select models, furthest from the pin) = More pressure at higher speeds when the clutch is fully shifted. For example: If your RPM is correct at 0-55 MPH but ramps up too quickly at higher speeds, tip weight would be the best bet to solve your issue. Keep in mind more tip weight has more force behind it, so it will affect your overall RPM more than heel or middle weight would. More tip weight can also slightly increase your clutch engagement RPM.
- Mid weight on the clutch arm (hole #2 on AA weights) = Your 25-55 MPH range weight and belt pinch. This is a pretty safe place from which to remove or add weight as its effects are not as drastic as tip or heel weight but is felt all throughout the RPM range.
- Heel weight on the clutch arm (hole #1 on AA weights, closest to the pin) = More clamping pressure at lower speeds. This increases clamping force at lower speeds to grab the belt hard under acceleration in the 0-25 MPH range. If you have too much tip weight it often times will not put enough pressure on the belt and it will slip down low. You would then want to transfer some weight to the heel for better belt pinch. Mud and slower speed riders typically benefit from all heel weight. More weight towards the heel will normally result in a slightly lower RPM clutch engagement than mid or tip weight.
- Keep in mind with weighting clutch arms that springs, helixes, clutch arm design and much more have to do with where the weight should be placed. Our kits do a great job of letting you know where to place the mass of the weight with what kit, tire size… ect. Try sticking close to our recommendations when/if adjusting and only change far away from that if you have to.
- Primary spring: The spring in your primary clutch (normally the front clutch, attached to the motor). The first number (starting rate) represents when the spring will collapse and start to engage the clutch. A higher starting rate will have a higher RPM stall while a lower starting rate will have a lower RPM stall. The second number in the spring rate represents the spring pressure near full shift. The ending rate controls peak RPM. The higher the ending rate, the higher the RPM. The lower the ending rate, the lower the RPM. This spring has a huge effect on how quickly the primary clutch back shifts and up shifts as well. Higher rates will back shift faster, but up shift slower.
- Secondary spring: This is the spring in your secondary clutch (larger, normally near the back). The is the first number in the spring rate and controls how fast the secondary starts to shift. The is the second number in the spring rate controls peak RPM. This spring has a huge effect on how quickly the secondary clutch back shifts and up shifts as well. Higher rates will back shift faster, but up shift slower.
- Helix Angle: The helix is in your secondary clutch and controls the rate of shift. This is the most tunable part of your secondary… kind of like the weights in the primary. The only catch is you can’t adjust it, so you should rely on your clutch tuner to get you the best option for your setup, then fine tune with the weights. The helix has angles on it which ride on sliders or rollers. The steeper the angle, the faster the secondary clutch will shift, and the slower the back shift will happen. The shallower the angle, the slower the secondary will shift, and the quicker it will back shift. We have different angles as well such as straight angles, progressive cut angles, and custom length blend angles.
- Horsepower vs clutching: More horsepower should make your peak RPM rise. Clutching may need to be adjusted when adding horsepower by adding weight. Sometimes when adding tunes and increasing rev limits, we go lighter on weight to further increase RPM to make more power and wheel speed. This varies by machine and modifications, luckily our clutch kit setups outline all of this and tell you your max RPM for the modifications we offer.
- Tires vs Clutching: The larger and/or heavier the tire, the more it will load the clutching and decrease peak RPM. Lighter weights are suggested with larger tires to bring your RPM back up to peak power for your modifications. Smaller and/or lighter tires are the opposite and would require more weight as they have less load.
- Gearing vs Clutching: Gearing has everything to do with clutching. Lower gearing will raise peak RPM and will require more weight in the clutch. Higher gearing will lower peak RPM and require less weight in the clutch. Because of the gear reductions, those with portals and tracks often times to have to add weight to a setup, even with the heavy load of larger tires or tracks.
- Altitude vs Clutching: Higher altitudes will result in a power loss from your machine. Turbo models will have less loss, but still some. Naturally aspirated models will have much more loss at higher altitude. The higher you go up, the more weight you need to remove. A good rule of thumb is 1-2 gram for every 3000 ft on turbo models, and 2-3 grams for every 3000 ft on NA models.
-Mike @ Aftermarket Assassins