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I've got a 2014 Renault Clio diesel, so it's pretty easy to roll off from a flat standstill with just the clutch. When I do that, it does so smoothly, that is as I raise the clutch the car just moves accordingly.

On hills, however, it behaves a bit differently. I get to the biting point and let off the brakes and it doesn't roll backwards. Now: (1) if I keep raising the clutch, after the biting point, I don't get the car to move right off. Instead, I have to keep "inching up" till there's a sudden pull. It's definitely not as smooth as on flat roads. Or, (2) if at the biting point I press the throttle, it immediately goes forward.

Why is it behaving that way? I hope the explanation was clear enough.

From Comment: I'm fearing it may be due to wear and perhaps will need repair soon. Is that OT here? I'm asking because other cars I drove never had this behavior: after the biting point letting out further the clutch just made the car move on the hill. Just like on flat roads.

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    I don't think this is on topic here, but the simple answer is gravity. It takes a lot of energy to raise objects against gravity. – Rory Alsop Jun 25 at 21:00
  • @RoryAlsop: I'm fearing it may be due to wear and perhaps will need repair soon. Is that OT here? I'm asking because other cars I drove never had this behavior: after the biting point letting out further the clutch just made the car move on the hill. Just like on flat roads. – newuser Jun 25 at 21:09
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    The behaviour sounds perfectly normal. Some cars need more revs than others – Rory Alsop Jun 25 at 21:40
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    Does the car have an electronic handbrake? It may be automatically applying it for hill starts, and not being smooth about releasing it. – Andrew Morton Jun 27 at 14:46
  • My car doesn't have an electronic handbrake, but it uses the main brakes for hill hold. It's 2016 Toyota RAV4 hybrid. I'm pretty sure there are other main brake hill hold systems too. – juhist Jul 16 at 8:30
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TL;DR: As Rory said in the comments, it doesn't sound too out of the ordinary.

In addition to that, I will say that spinning your clutch this gradiently will wear it out faster because of the amount of time the plates are rubbing against each other. It's ideal to traverse from bite point to full engagement as quickly as you can while maintaining smooth motion.

Long-winded explaination: There are many variables between cars and environments that can dramatically change how they behave. The 3 biggest I can think of offhand are:

  1. Gearing
  2. Torque arch through rpm
  3. Condition of clutch assembly

1 and 2 will affect the performance like you're talking about, but I don't think 3 would considerably.

From what I can tell, your car is a turbo diesel model, and that turbo dramatically affects the torque arch. At low rpm the turbo will not really spool (spin into a functioning range) and will not provide any increased power. Additionally, I read one thing saying that the 2014 Clio had longer gearing, which again reduces torque to the wheel. Applying the throttle and bringing the rpm will spool the turbo and cause a pretty significant spike in torque and power allowing the car to roll into motion more fluidly.

As Rory is saying, gravity is the enemy in the case of hills. If you're in a 45° slope, then ~1/2 the weight of your car (I'll round it to 800kg) is being pressed against the trans. At the bite point, your engine may provide just enough force to hold the car in place (800kg up the hill), but not enough to move forward because of the loss in friction to the plates. For a little bit, adding more force will continue to pre-load the clutch springs. Once you provide enough energy to move forward, you broken the equilibrium and inertia. Now the energy stored in the springs can also discharge and, depending on the turbo and torque arch, the car can spring into motion rather than easing into it. This can vary somewhat depending on the condition of the springs and friction plates which can bite more easily since they're all moving in the same direction now.

This doesn't happen on the flats because you're only fighting inertia, which is much weaker than gravity.

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It sounds strange that you say on a hill with the clutch depressed that the car doesn't roll backwards. Perhaps the brakes are binding, OR the clutch itself is either worn, badly adjusted (if cable operated) or there is a slave cylinder issue/leak allowing the clutch to drag.

If the clutch has been in the vehicle for many many miles, you can often get a build up of clutch dust (which is basically its friction material) trapped between the fingers of the clutch cover, this restricts the clutch cover from operating smoothly, especially when the clutch gets hotter. So you then get the situation occuring where.. when you're releasing the clutch pedal.. the clutch releases in jerky steps, and this will definitely cause the car to suddenly pull away rather then gradually move away. If this is the case the clutch requires replacement.

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