Dear MOby,

Seems like almost every new motorcycle produced lately has a “slip-assist” clutch. Is that the same thing as a slipper clutch, and if not, what’s the difference? What gives?

Duke Snyder

Dial-up Modem


Another good question, and once again it’s Brian Gillen, MV Agusta Research and Development Director, to the rescue: While slipper and slip-assist might seem like the same thing, in reality they are different. The slipper clutch only reduces negative engine torque in trailing throttle situations (high-rpm downshifts), while the slip-assist does two things: It increases the clamping force under acceleration (allowing lighter clutch springs thereby reducing lever pull), and reduces negative engine torque under deceleration just like a typical slipper clutch.

A pioneer of the slip-assist clutch was the Italian clutch manufacturer Adler (Adige), with their APTC system. The first motorcycle to use it in production was Gas Gas, and it is now widely used by others including Ducati and Harley-Davidson.

What? I thought “slip-assist” was just marketing-speak for a slipper clutch, which we addressed a few weeks ago in Ask MO here?

BG: Close, but not quite: If you put lighter springs in a traditional slipper clutch it will slip under acceleration. The slip-assist APTC has a helix on the internal hub that basically screws the clutch together under power (augmenting the spring force) and unscrews under deceleration, effectively opening the clutch and allowing it to slip.

The Star… excuse me, Yamaha video below provides a good visual of how its slip-assist clutch works, sort of, though I’m not seeing anything about the helix on the internal hub Mr. Gillen speaks of? Anyway, Yamaha may have been the first to glom onto the marketing possibilities of the slip-assist clutch for cruiser riders: 20% lighter pull at the clutch lever, less effort!, who doesn’t like that?

Not sure how long Harley has offered this one, the Screamin’ Eagle Twin Cam Performance Assist and Slip clutch kit, but it’s the same deal, designed for `14 and later CVO 110-inch engines. Harley says it provides significantly more torque-handling capacity, is “designed for improved engagement grip, and provides minor slippage during downshifting to reduce shock to the power train,” while reducing hand lever pull effort by over one pound. All with only three clutch springs.

Weird how long it took the ramp, discovered more than 8 million years ago by the ancient Protuberans (I made that up), to find its way into your clutch. Slipper or slip-assist, both provide great benefits for all riders at very little cost (unless your bike doesn’t come with one).


When Will My Motorcycle Battery Die?

What’s Up With The Ducati Sixty2?

Oil’s Well: How Many Miles Before I Have To Change The Oil In My Motorcycle?

Why Do OEMs Use Ball Bearings In Steering Heads?


Send your questions to Askmoanything@motorcycle.com; send your complaints to We’reoutoftheoffice@cycleworld.com. If we choose to answer your question and get it wrong, consider it a valuable life lesson that’s absolutely free of charge.

 

  • Born to Ride

    First time I rode a APTC equipped bike (M796), I thought the clutch was broken when I went to start the bike. It felt like there was a massive air bubble in the hydraulic lines. I waved over the demo ride guy and he assured me it was completely fine. I thought it felt way too weird the whole ride having almost no resistance on the clutch pull. Then again, I was coming off of an S2R1000 with a dry clutch that requires all four fingers on the lever in stop and go traffic to modulate the friction zone. More time with it and I’d have likely ended up spoiled.

    • Bananapants Ficklefart

      Sounds addictive. I’m constantly shifting into neutral at stops to give my left a break, despite my MSF instructor’s voice in my head saying “DON’T DO THAT!”

      Next Harley WILL have a slip-assist. And ABS. To Hell with “Old School.” I’m ok with safety nannies now.

  • JMDGT

    Slip assist and slipper clutches are two of the greatest inventions in motorcycling.

    • Sayyed Bashir

      Only if you are racing.

      • JMDGT

        I don’t race and find the slipper clutch of great value.

        • Sayyed Bashir

          I have never needed a slipper clutch because I do not downshift aggressively or use engine braking. I use the brakes to slow down. I guess I am too gentle with the engine so it will last longer. My KTM 1190 R does have a slipper clutch (I had to check the specs) but I have never used it.

          • Kevin Duke

            C’mon, Sayyed, work that thing! You won’t break it! 🙂

          • Sayyed Bashir

            I didn’t even know I had it. I also never rev the engine higher than 6,500, even though peak torque is at 7,500 and the rev limit is 10,500. Probably due to my 30 years of Harley riding where peak torque is 2,750. By the way, while researching the peak torque of my 2007 Softail Custom, I came across your review of this bike in Moto USA in 2006 and a picture of you riding it (my bike is cream and burgundy). They also mentioned a wheelie but I couldn’t find a picture of it.

            https://uploads.disquscdn.com/images/e71bc6b9d31e017876059fd1e5fe22dff0bdc8954e23cd6c4254f35940de071a.jpg

  • ADB

    Now if Moto Guzzi would design one for my Norge….

  • DickRuble

    Slip assist is for sissies. Learn to use the clutch.

    • Sayyed Bashir

      I have a Harley with none of the above, and a KTM with all of the above, and I enjoy both bikes, except when it rains, and then I take the KTM because I value my life,

      • Andre Capitao Melo

        Yes, everyone knows that you have a KTM and a Harley…

    • spiff

      If you would be so kind as to let me have one it would be the slipper. If someone has a wild hair up their ass the slipper is the one that will keep them from skinning their knee.

    • webheadwilks

      The macho judge says so…..

  • kenneth_moore

    Does a slipper clutch negate the value of blipping your throttle to match revs when downshifting? I’m not sure I’d like that…blipping is fun and it sounds cool.