Re: Slipper Clutch Vs Engine Braking

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Re: Slipper Clutch Vs Engine Braking

From my experience on the Ninja 300, the slipper clutch comes into play only when downshifting, so in essence the engine braking is induced in any case. What the slipper clutch does is to match the revs of engine braking to the rear wheel which is controlled by the ECU and thus prevents the rear from sliding under you. As far as reducing engine braking is concerned, it depends a lot on where you are in the rev band. Since the rev band on a N300 is fairly wide a few downshifts in a low gear below 8000 rpm is not going to have any dramatic results in engine braking but will get different when one is higher up the rev band.

Re: Slipper Clutch Vs Engine Braking

Shorter version:

Yes, slipper clutch reduces (or kills) engine braking at high revs. Useful on the track, not for daily commuting.

Longer version:

Engine Braking Occurs when a gasoline engine is used to slow the bike down rather than the use of the normal hydraulic braking system with calipers, pads, and disks. It occurs when a partial vacuum is created in the engine as the throttle is released. The change in pressure in the intake system by the closing of the throttle bodies creates a braking force internal to the engine which is transmitted through the drive-train that slows the bike down. This is most noticeable going from wide open throttle (WOT, throttle bodies are open as much as possible) to fully closed throttle.

NOTE: Even with fully closed throttles, air is still able to enter the engine via the idle adjuster valve . The idle valve allows a small amount of air to enter the cylinders so that the engine is able to idle properly with no load. As the throttle bodies open, the required amount of air will enter through them instead.

This drastic change in pressure inside the intake path (near the throttle bodies) causes the work created by the piston in the Ignition Phase to be mostly transmitted to the piston in the Suction Phase to draw new air into the cylinder rather than to rotate the gears. Think of trying to fill your lungs with air, sucking through a paper towel roll and then trying to fill them again but this time sucking through a little mixed drink straw. Your lungs will have to work harder with the smaller straw. As the throttle closes the area that the air can travel through gets constricted just as the little straw has a smaller area (more constricted) than the paper towel roll. Well, the engine has to work harder to draw air in at the same rpm with a close(ing) throttle than it did with an open throttle.

Now, this engine braking as stated before gets transmitted through the transmission (drive-train) to the rear wheel. Since we were accelerating down the road and decided not to use the brakes for this turn coming up but chose to engine brake instead, we need to realize that the wheel has been rotating accordingly to push the bike forward. Well as we engine brake - the wheel is still trying to rotate at that speed we let off the throttle at; but now the engine is slowing is down. Without changing gears, you’ll feel this as the bike trying to throw you forward. As the bike accelerates, it seats down due to the interaction of the geometry of the swing arm with the sprockets and chain and therefore, as the bike decelerates, the bike leans forward. This becomes noticeable as engine braking is done at higher speeds (engine speeds and ground speeds).

Shifting can also cause engine braking. In the same process that you change gears when you reach a high engine speed (rpm), the reverse will happen when you down shift from a high gear to a low gear. Shifting from 4th to 3rd will require that the input and output shafts in the transmission match speeds. This is done by engaging the clutch (removing pressure), opening the throttle briefly, shift gears, slowly release clutch. Now you’ll be riding at the same speed in a lower gear but with higher rpms. If done correctly, it shouldn’t slow you down. If the engine speed is not increased enough, the speed of the rear wheel, that’s dictated by the output shaft, will be faster than the transmission’s input shaft. When the clutch is released, the inertia of the wheel and the output shaft will cause the engine to speed up while the throttle is held constant. Guess what - that’s engine braking for you! The engine will be trying to get more air through the throttle bodies but is having to work harder because of the constricted path.

When setting up for a corner, say at a track day, this can really mess you up. Under normal commuting speeds or canyon carving speeds, it’s less noticeable.

So this is where the Slipper Clutch comes in to play.
We know that the clutch assy is made up of plates and dogs that when pressure is applied, engage the transmission clutch gear (which transmits the rotating power from the crankshaft to the transmission from the primary engine sprocket) with the transmission input shaft that has the forward gear pinions. When pressure is released, the transmission clutch gear rotates while the transmission input shaft does not, and when pressure is applied, the transmission clutch gear and input shaft rotate together.
Since we’re not releasing pressure on the clutch as we shift to setup for that corner coming up, the speed difference between the gears causes the engine and wheel to change speeds as well. So let’s say we were in 6th and are shifting down to 3rd for the corner with engine braking. The engine is running at a mid range rpm, now we engine brake and shift down to 5th. The engine that was trying to slow down now has to jump in rpms to mesh the transmission speed with the ground speed. Now the shift down from 5th to 4th causes a similar jump in rpms and again from 4th to 3rd. Each time the engine has to work harder to get the new air into the cylinders at a higher rpm.

What makes a slipper clutch different is the interaction of the clutch plates with the transmission clutch gear through the use of two sections instead of one for the transmission clutch gear. The two sections have ramps and ball bearings that allow the part of the gear that is engaged with the engine pinion to keep rotating at the engine speed while the other section to rotate at the speed of the rear wheel and transmission output shaft. The ramps act in the same ways as one way screws. They allow rotation in one direction but not the other. So as the rear wheel tries to maintain ground speed and drive the front sprocket and transmission at a higher speed than the engine, the ramps slip up and the clutch disengages (pressure removed). Once the speeds begin to match again, the ramps allow the sections to mate up and continue to transmit power from the engine through the clutch through the transmission to the wheel. This ability to disengage the clutch allows the rest of the bike to remain smooth and stable negating the harsh engine braking that might happen when setting up for a corner. The benefits are usually seen at the higher range of engine and ground speeds.


Source(s) - experience + various articles.

Re: Slipper Clutch Vs Engine Braking

Re: Slipper Clutch Vs Engine Braking

Wow!That's one good read, thank you! Is Throttle Blipping sort of manual alternative for Slipper Clutch?

Re: Slipper Clutch Vs Engine Braking

Advantages of slipper clutch:

While riding a corner you require to downshift.
You have to give the bike slightly more throttle prior to downshifting, so that you are at a higher RPM to match your speed.
Example, if you are cruising in 6^th gear on the highway at low rpm, and you want to shift quickly straight to 4th.
You will have to raise the rpm a little high.
Now suppose if you are not matching the rpm/revs and just shift to 4^th gear from 6^th gear at the same rpm, the result is wheel locking up (as the wheels + engine are running faster in 6^th gear and you want to make it slow at 4^th gear, wheel minus engine)

A slipper clutch is designed such that you keep slipping if you downshift too quickly/aggressively without matching the right engine rpm.

Re: Slipper Clutch Vs Engine Braking


So the wheel locking can happen even in street as most of us are use to engine braking by downshifting. And having a slipper clutch for a street bike too will help reduce the wheel hop, correct? Ideally we should be rev matching during this process and most of didn't practice and got used to quick stop in a wrong way. By wrong way i mean engine and transmission damage on the log run (?)

Re: Slipper Clutch Vs Engine Braking

Motorcycle gears are not syncromesh type like in Automobiles, they are constant mesh type (all are in touch) where in all gears are engaged and the one which is being used is locked. Therefore chances are bright for damage if not used with correct practice.

Re: Slipper Clutch Vs Engine Braking

Thanks. Yes throttle blipping is the manual way of achieving the same effect.

See, unless you ride like a maniac 'on a frequent basis' and dump the clutch at very high RPMs in too low a gear will you damage the drive-train. Until now, even racers used to blip the throttle. And addition of slipper clutch hasn't increased the engine life even on a moto gp bike (no official sources to claim so).

Therefore, it is safe to say that a commuter doesn't need a slipper clutch. I engine brake all the time and I'm about to hit 1 lakh km on the ODO. My bike is stock.

Re: Slipper Clutch Vs Engine Braking

Whoa!!! A topic that was discussed to its death sometime back. Anyway, though my N300 is equipped with a slipper clutch I don't recall I have got into a situation where the slip function of clutch has ever activated in the 3 years of ownership. I was lucky enough to learn riding on 2 strokes where keeping the revs in the power band was crucial enough for performance that learning how to dip the engine was essential part of riding skills.

My personal take on this feature is that its a good riding aid. However, it cannot be a replacement to good riding skills. There is a limit to how much back torque the slipper system can neutralise. I have seen people slamming down through the gears in frantic bid to slow down and the bike doing a tap dance and getting all twisted and unbalanced while the slipper clutch tries to do its work. One of the essential things about riding well is how smooth you are in your downshifts. You need to be able to downshift without upsetting the balance of your bike if you really want to control it. Engine dipping is the art of downshifting by matching the engine speed to the rear wheel speed. This ensures that your transition from upper gear to lower gear is seamless and the balance of the bike is neutral during the transition. Engine dipping is an acquired skill which will require lots of practice and understanding of what the bike and engine does and how it reacts to inputs.

Given a choice between a slipper clutch equipped bike and one without it, I would select the slipper clutch one for its aiding capability. However, will it be a deal breaker for me if a bike is not equipped with a slipper clutch? No, absolutely not. I depend on my dipping skills and not on a slipper clutch.

Re: Slipper Clutch Vs Engine Braking

Thanks for sharing! It is informative.. do you mind sharing the thread from the earlier discussion if you have the link?

The frantic part is all I wanted to understand considering most of us learned riding during the Non-ABS era and downshift is considered to be a common and safe practice for stopping. Most replies here point to the fact that SC is not much helpful for everyday riding, even your comment that in 3 years you have not seen it activate point to the same

Re: Slipper Clutch Vs Engine Braking

I am going to stir a hornets nest by saying this as it will go against everything that you have learnt, and been told by people as common knowledge; the engine is not a brake!

The purpose of an engine is to drive a vehicle not slow it down. Use brakes to slow down, period! Assuming that even if a engine can be used as brake, its a really inefficient brake. There is no linearity to the slowing down of the vehicle when you use back torque to slow the vehicle down. Its more like a 'on/off' switch which suddenly pulls the rear wheel speed down to match the engine speed. Its just not right. The consequences of such abrupt and inefficient braking is that the bike tends to become unbalanced and you will be subconsciously giving inputs to try and rectify the situation which in most cases make a bad situation even worst as the inputs are subconscious and you actually have no idea what you are doing.

For the earlier discussions, please do a search forum database.

Re: Slipper Clutch Vs Engine Braking

^^^ Amen to that!

Re: Slipper Clutch Vs Engine Braking


damn. i thought you were saying it depended on earned riding skills. but i do say, engine itself is a brake coupled with skills of eyes and other organs.

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also please note by this, clutch and brake pad life has only increased. for example, my 390 pads were change at 35000 kms even though another 5k could be covered. a 150ps remap car had its brake pad change at 65000 kms and stock clutch going strong even after 120000 kms on odo.