Whether it's in the woods or on the motocross track, one of the critical components that have a significant effect on rideability and traction is your engine’s clutch. The clutch is responsible for transmitting power from the crankshaft to the final drive of your machine. Traditionally, powersports machines are offered with manual transmissions and use wet, dry, or slipper clutches.
At Rekluse, we specialize in high-performance clutch solutions that are easily installable into engines traditionally utilizing wet clutches. Auto clutches have inherent advantages over the other clutch types mentioned. Before considering an auto clutch, it’s important to understand all the essential details of what an auto clutch is, how it works, and the numerous benefits that street and dirt riders can expect. Different auto clutch options are available depending on the type of riding and budget, so it’s important to understand which one is right for you.
Auto clutches have inherent advantages, but it's important to understand all the critical details to know what's right for you. (RadiusCX cable actuated model configuration shown)
What is an auto clutch?
An auto clutch is a type of clutch that automatically engages and disengages the based on engine RPM, and ultimately, the power being transmitted to the final drive. The ability to engage and disengage the clutch via rider input through actuation of the clutch lever is retained; however, rider modulation of the clutch isn't necessary in many situations.
An auto clutch allows easy starting and stopping without using the clutch lever, and virtually eliminates engine stalling. Unless you have mastered clutchless shifting, the clutch lever is still used when shifting gears.
Star Racing Yamaha has utilized Rekluse auto (RadiusCX) and manual (Core Manual TorqDrive) clutches throughout the 2019 and 2020 MX season.
Justin Barcia and the Monster Energy / Yamaha Factory Racing Team utilized the RadiusCX auto clutch for select rounds of the 2020 Lucas Oil Pro Motocross Championship.
Rekluse auto clutches automatically engage and disengage the clutch based on engine RPM. The option for rider modulation of the clutch via the lever is retained, but unnecessary, except for during shifting.
An auto clutch should not be confused with an automatic transmission. Shifting gears is still an essential aspect of riding an auto clutch-equipped machine. An auto clutch is also different than a slipper clutch. When aboard a slipper clutch equipped machine and the throttle is chopped, the clutch disengages. When riding an auto clutch-equipped machine and the throttle is chopped, power transmission to the final drive is maintained, effectively maintaining engine braking.
A unique characteristic of Rekluse auto clutches is their ability to retain engine braking when the throttle is chopped.
How does an auto clutch work and what is an EXP disk?
Centrifugal force is the governing force that allows an auto clutch to work. Centrifugal force is the resulting force that acts on an object rotating around a centerline. The heavier the rotating object or, the faster the object is spinning, the more inertia it will have, and the more force it will exert.
An auto clutch features a special clutch disk that is designed to utilize the principle of centrifugal force. The Rekluse clutch disk that gives an auto clutch it’s automatic properties is called an EXP disk. The EXP disk essentially acts as a friction disk that responds to engine speed.
The Rekluse EXP disk is the key ingredient to Rekluse's auto clutch formula. It's a friction disk built to respond to the centrifugal force of the spinning engine.
The EXP disk is comprised of wedges that are positioned circumferentially around the clutch disk. The wedges are tuned and designed to respond to increases and decreases in engine speed. As engine speed increases, centrifugal force increases, and the wedges in the EXP disk exert an outward force on the two halves of the EXP disk, causing them to expand and the clutch to engage. As engine speed decreases, centrifugal force decreases, and the force exerted by the wedges decreases in the EXP disk, resulting in contraction of the two halves, which causes the clutch to disengage.
To ensure the clutch is disengaged at idle, the clutch is set up so that a small gap of about 0.030” exists between the clutch pack and pressure plate. Off idle, as the throttle is applied and engine RPM increases, the EXP disk expands outwards, overcomes the installed gap, and engages the clutch. Since the auto clutch automatically engages at engine speeds higher than idle, the functionality of the clutch lever and traditional clutch deactivation/actuation methods can be retained without any modification. Finally, because an auto clutch works exactly like a standard clutch above idle, features associated with traditional clutch operation such as engine braking are also retained.
Depending on your application and the auto clutch package you have, Rekluse has proprietary designs for adjusting installed gap, which is a critical step in optimum auto clutch performance.
Advantages of an auto clutch
If you’re considering switching to an auto clutch, here’s a few of the advantages and how they’re possible:
No Stalling - Since the auto clutch engages and disengages as a function of engine speed and at idle the clutch is set up to be disengaged, stalling is not possible.
Tunable - Rekluse EXP disks are tunable. The EXP disk can be tuned to engage at various engine speeds, and how quickly or “hard” the clutch engages can also be manipulated.
Dead-on power delivery - An auto clutch simulates perfect clutch modulation which results in better traction.
Reduces physical and mental fatigue - Since the utilization of an auto clutch yields fewer situations where the rider needs to engage the clutch, physical fatigue is reduced. Mental fatigue is also reduced since riders no longer need to focus as much on clutch operation.
Clutch lever is still operational - If circumstances arise where manual clutch operation is advantageous, this can easily be accomplished.
Engine braking is unchanged - Because an auto clutch operates just like a standard clutch above idle speed engine braking is not affected or altered.
(RadiusCX DDS for KTM / Husqvarna hydraulic actuated model configuration shown)
Who benefits from using an auto clutch?
Rekluse auto clutches are designed for numerous applications and offer riders inherent advantages in each of them. There are application-specific advantages that riders can benefit from as well:
Motocross
- Automatic modulation of the clutch allows riders to ride a taller gear through corners.
- The rear brake can be applied fully without fear of stalling.
- Ease of operation allows the rider to focus more on their line.
Woods
- Automatic modulation of the clutch allows for better traction in slippery conditions.
- Navigation of technical terrain is easier.
- Ease of operation allows the rider to focus on their line.
"In the slicker, rockier, rooty-er stuff, I trust RadiusCX [auto clutch] more than my finger." -Ryan Sipes (Photo: Future7Media)
Trail
- Navigation of technical terrain is easier.
- Automatic modulation of the clutch allows for better traction in slippery conditions.
- Steep and technical hills can be navigated without worrying about feathering the clutch to keep the RPMs up and the bike running.
Zach Bell and the Precision Concepts team races WORCS and other West Coast GPs aboard their RadiusCX equipped KX450s.
Rekluse RadiusCX Auto Clutch for the Kawasaki KX450
Adventure Bikes
The RadiusX auto clutch covers a wide range of Adventure Bike applications:
Photo: Gnarly Routes
Yamaha YXZ1000
The Rekluse EXP 3.0 auto clutch for the Yamaha YXZ1000 allows you to operate the manual transmission with ease, with smoother clutch engagement which comes in handy when maneuvering at low speeds in technical terrain.
Photo Credit: UTV Action, Cain Smead
Auto clutch durability
Similar to OEM applications, auto clutch durability depends on the end user and how aggressively they operate their machine. That said, Rekluse auto clutches are designed to last at least as long as OEM clutch applications. Since the clutch is mechanically engaged at the same RPM every time, clutch wear is consistent which helps prolong clutch life. Auto clutch durability also depends on ensuring the clutch is within spec and adjusted correctly. Auto clutch riders need to perform a simple and quick check called “free play gain,” which is a comparative measurement taken at the clutch lever periodically.
Why are auto clutches innovative?
Rekluse auto clutches are innovative because there are no other clutch solutions on the market that offer significant rider advantages while at the same time retain conventional clutch functionality and ease of use. Innovation doesn’t stop at functionality, the number of installation options and the ease at which an auto clutch can be installed are also worthy attributes, not to mention the fact that no modifications are required to install any of Rekluse’s auto clutches.
All Rekluse auto clutch systems are drop-in, no additional modifications are required.
Auto clutch options
To help you understand how each clutch option differs, the highlights of each clutch are identified below, and a comparison table is presented that also shows key differences. Whether you’re a top-level racer, avid adventure rider, or dedicated trail enthusiast, there is an auto clutch option for you.
RadiusCX: $1,049 - $1,179 (Dirt Bike and ATV)
- Premier, top of the line auto clutch.
- Features all the latest technology offered: EXP, Core, and TorqDrive
- Increased friction disk count transfers more power to the rear wheel while eliminating clutch fade.
- Provides optimal lever feel.
- Yields highest level of durability.
- Increased oil circulation through the clutch.
(RadiusCX cable actuated model configuration shown)
RadiusX: $649 - $749 (Dirt Bike, ATV, ADV, Street)
- Excellent mix of performance and cost – uses OEM hub and pressure plate.
- Includes TorqDrive and EXP technologies
Core EXP 3.0: $949 - $1,079 (Dirt Bike, ATV, YXZ1000)
- Core EXP 3.0 uses OEM friction disks, meaning power transfer will be equivalent to stock engine performance.
- Includes EXP and Core technologies.
- Increased oil circulation through the clutch.
Understanding how Rekluse auto clutches work is proof they are an advantageous option over various applications. View Rekluse clutch options for your machine here on the website, or use the dealer locater to find your closest Rekluse dealer. If you have any questions at all regarding which clutch is right for you, installation, or adjustment, Rekluse experts are happy to help and can be contacted at 208-426-0659 or by email at customerservice@rekluse.com.
What the pros are saying:
Rekluse and Star Racing Yamaha – Clutch Technology for Champions
Dylan Ferrandis on Rekluse RadiusCX Auto Clutch
Precision Concepts Kawasaki Team Manager Robby Bell on Rekluse
Still not sure which clutch is right for you? Check out our complete guide here to help you decide!
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