Talk:Clutch control

This technique is useful if the accelerator mechanism is broken. It can be temporarily fixed to half-power and use clutch control to go to the garage. - forcage

Hill starts
I have no reference for this, so I haven't put it in the article, but it is interesting to note the difference between British and Australian hill starts. In order to pass a British driving test you have to perform a contortion, and look over your shoulder, while revving the engine and slipping the clutch. I described this to an Australian friend and he was appalled at this ill-treatment of the clutch. "If you did this on an Australian driving test", he said, "you would definitely fail". Can anyone confirm this? Biscuittin (talk) 20:44, 23 July 2009 (UTC)

Deceleration
From the article:


 * "Typically with motorcycles and in motor sport, the clutch is often used to facilitate the use of resistance from the engine spinning at high speeds to decelerate the vehicle more quickly, often accompanied with normal braking. This is achieved by placing the vehicle in a gear that would ordinarily be too low for the current speed and momentum of the vehicle and by partly engaging the clutch. When this happens momentum energy from the inertia of the vehicle is taken away to spin the engine as close as possible to it's maximum capability. As the vehicle is decelerating the clutch can be further released to transfer more energy to keep the engine spinning as quickly as possible. Once the clutch is entirely released this cycle proceeds downwards through the gears to further assist deceleration. If the clutch is controlled improperly while this is being attempted damage or extra wear to the engine and gears is possible, as well as the risk of wheels locking up and a subsequent loss of proper vehicle control."

The assertion in the first sentence is absolute nonsense. Also, as far as I know, downshifting is performed in order to keep the vehicle in gear through turns and deceleration so that it will be in gear when/if more power is required.

Although downshifting can be used to decelerate the vehicle via engine braking, it can never cause the vehicle to decelerate more quickly. On any vehicle, the brakes are normally powerful enough to lock up the wheels (which is why we have antilock brakes)--that is, the brakes, by themselves, without assistance, have more stopping power than can ever be used. Using engine braking in addition to normal brakes will not allow a vehicle to stop faster than simply using normal brakes, unless some outside influence has reduced the effectiveness of the braking system. (The reason for this is simply that, if your wheels do not slip as you apply engine braking, you could have instead simply applied the service brake harder.)

Is there some strange exception to this that I'm not aware of? ...can we at least get some source for this paragraph? --and then change it so that it doesn't break any known laws of physics? J.M. Archer (talk) 21:41, 28 August 2009 (UTC)

Hi, I am responsible for writing the above section you are complaining about. You are complaining that you can't use engine braking (assisted by the clutch to get the most out of engine braking) to break faster than the normal brakes attached to a vehicle ("it can never cause the vehicle to decelerate more quickly") but you are wrong, which is why the first three words I used were "Typically with motorcycles". I ride a 125cc motorbike that has two terrible drum brakes. The fastest way to stop is to also use engine braking with the clutch. It is impossible to do an emergency stop without doing so for example. How do you recommend the paragraph is edited to reflect these circumstances? You could also take in to consideration that in racing vehicles, if the brakes aren't up to temperature yet (or have cooled down), then engine braking is also necessary to decelerate the vehicle in the fastest way.Alsweetex (talk) 13:47, 23 November 2009 (UTC)

No loss of torque?
The laws of physics surely show that the following paragraph must be wrong:


 * "As the clutch slips, engine speed is lost but torque is not lost except through the effect of the new engine speed on the engine torque itself ... So slipping the clutch actually gives more torque to the wheels even though the fraction of power wasted in the clutch increases much faster."

Slipping the clutch means reducing the force on the plates, and this itself will reduce the torque available (since frictional forces are roughly proportional to the force between the surfaces). In addition, the slipping clutch will provide less torque than the engaged clutch since the coefficient of dynamic friction is typically less than the coefficient of static friction.

Slipping the clutch may indeed provide more torque to the wheels in some circumstances, but only when engaging the clutch fully would slow the engine to a speed where its output would be less than the torque transmitted by the slipping clutch. Louiskennedy (talk) 08:34, 6 September 2010 (UTC)


 * I think you are partly correct. It is my understanding that an engine may, for example, produce it's maximum torque at 7000RPM. If the clutch is being slipped and therefore only partially engaged at that number of revolutions per minute, then the maximum torque of the engine is being applied and the only loss of energy ought to be the heat generated from the plates moving against each other? Whereas, if the clutch were to be fully engaged then the engine would produce less torque because the engine speed would be lower.


 * I guess the question is: is it true that if you rev a vehicle to it's "red line" and slip the clutch all the way to the point (the RPM) where the advantage of slipping the clutch is outweighed by the power lost from the friction and heat produced by the clutch, will you have accelerated in the fastest manner?


 * The key here I think is to remember that when a vehicle is stationary then the engine speed it would be maintaining to fully engage the clutch would be zero RPM, which as we all know, doesn't produce enough torque to let the vehicle pull away.--Alsweetex (talk) 05:56, 9 October 2010 (UTC)

There is a significant loss of torque. Just drive any vehicle with a worn out clutch. When it slips the vehicle doesn't want to accelerate properly, it feels sluggish. This is because engine torque is being wasted due to the clutch slipping. It makes sense, therefore, that forcing the clutch to slip via pedal input will similarly reduce the amount of torque actually making it to the wheels. 74.240.230.64 (talk) —Preceding undated comment added 10:57, 25 September 2012 (UTC)

"Dropping the clutch"
How about an explanation of "dropping the clutch"?
 * What's to be explained? — Preceding unsigned comment added by 68.191.42.175 (talk) 00:29, 16 July 2012 (UTC)
 * How to do it without shattering your input shaft maybe? Or why dumping the clutch is incredibly hard on the hardware and only adviseable on racing vehicles not intended to last all that long? 74.240.230.64 (talk) —Preceding undated comment added 10:55, 25 September 2012 (UTC)

Balancing the clutch is terrible!
"Drivers can frequently be observed slipping the clutch when they are trying to stay stationary on a hill without using neutral and the brake. They apply the clutch to climb a bit, then release to roll back, then apply again, etc. so that the car stays in about the same place. With enough practice, alternating is no longer needed. Applying the correct amount of clutch pressure and throttle causes just enough force from the engine to counter gravity and keep the vehicle stationary (See Balancing the clutch)."

I'm sorry, but I highly doubt drivers can 'frequently' be observed doing this, because if they did, transmission shops would have gilded waiting areas from all the money they'd make on clutch replacements. This sort of abuse will fry a clutch in as little as 10,000 miles, voids the warranty on new cars, and is generally absolutely terrible driving practice indicative of someone who needs to quite literally start from scratch as far as driver's education is concerned. 74.240.230.64 (talk) —Preceding undated comment added 10:54, 25 September 2012 (UTC)

Here in the UK it is a common practice to "balance the clutch" when you will only be stationary momentarily. It is in fact taught in driving lessons and me and my friends and relatives have driven many thousands of miles without adverse clutch wear, yes it will need to be replaced every 60-90,000 miles, but that is entirely because it is a wearable part (like cam-belts). So in fact it is not terrible at all!