My Linea jerks while downshifting the car

Shan2nu · 24th November 2009, 18:23

Quote:

Sorry to split hairs, but I feel it's important to ascertain if he was unhappy about forward movement or not. The quote shows that he does. One would conclude that he expected engine retardation, but got a surprise, no engine retardation.

So in the interests of safety, would you say heel and toe is recommended as a remedy for this problem?

There is no way the car can lurch forward if you downshift. He prob felt that way since the jerk causes the driver to move forward.

If you believe the car actually lurches forward when downshifting, please explain how this is technically possible?

Shan2nu

proton · 24th November 2009, 18:36

Quote:

Originally Posted by Shan2nu

There is no way the car can lurch forward if you downshift. He prob felt that way since the jerk causes the driver to move forward.

If you believe the car actually lurches forward when downshifting, please explain how this is technically possible?

Shan2nu

I did here:
http://www.team-bhp.com/forum/1596238-post17.html

Also described as "break away"!

DownTheLine · 24th November 2009, 19:09

Let me pitch in I am the one who was facing this problem. Probably I had not put my problem correctly and that's why the whole confusion surfaced. By downshifting I mean not only changing the gear directly from 5th to 4th or so on.. , but also apply the brake to slow down the vehicle.

Thanks a lot all of you (Shan2U, Jaisha, Proton), this thread is really very informative for all new driver like me, and guess what happened after this discussion .. my problem has been resolved. Now I am extra careful while shifting the gears from high to low by using proper braking.

I would love to use the heal/Toe method but I think it will take some time to me to learn that

Shan2nu · 24th November 2009, 19:40

Quote:

I did here:
http://www.team-bhp.com/forum/1596238-post17.html (My Linea jerks while downshifting the car)

Also described as "break away"!

Which part of it?

Losing adhesion on the driving wheels wont accelerate the car. Locked wheels can only reduce the rate of deceleration, but you will still have retardation with locked wheels.

Anyway, i think we're pretty much clear about rev matching, heel n toe, synchro etc etc....now.

Quote:

Thanks a lot all of you (Shan2U, Jaisha, Proton), this thread is really very informative for all new driver like me, and guess what happened after this discussion .. my problem has been resolved. Now I am extra careful while shifting the gears from high to low by using proper braking.

No prob. Glad we could help.

Quote:

I would love to use the heal/Toe method but I think it will take some time to me to learn that

Ofcourse it will. I wasn't expecting you to learn it in a day. Hehe

Shan2nu

proton · 24th November 2009, 20:25

HaHa!

I'm not totally sure about how we helped, but I sure got a nice brushing up from all this, so thanks all for a very enjoyable discussion.

Must add that there are very real benefits from rev matching as Shant2nu points out, the most important to me being, it saves your clutch. So blip the engine a bit when you de-clutch: it's safe and will reduce the jerking.

G'night all!

DownTheLine · 24th November 2009, 21:21

Rev matching and gear shifting

Introduction

Each gear has an effective operating range of speeds which depend on the rev range of the engine. The faster the engine rotates, the quicker you can go – up to the point when you need to change up a gear. Within the operational rotational speeds of the engine, there is a range of optimum efficiency known as the 'power band', and this is where the fastest acceleration can be obtained (see Diagram 1).
Diagram 1: The power band of an engine in any particular gear

Most gearboxes are designed so that when you change up a gear when accelerating, the next gear will be at the start of the engine's power band (see Diagram 2). This design provides maximum acceleration all the way up to the top speed of the car.
Diagram 2: Comparing the power bands in two gears

At most speeds, a selection of gears can be used (see Diagram 3).
Diagram 3: Gear choice at different speeds

In the illustration above the driver could choose second, third or forth gear. In second gear the engine speed would be at the top of the power band, not leaving room for much useful acceleration until the rev limiter is activated. In forth the revs would be too low, leading to sluggish performance (but perhaps decent fuel economy). In third gear the engine would be at start of the power band providing maximum acceleration – this would be the choice of the performance driver.

Changing up / up shifting

Lower gears provide greater acceleration due to a combination of the gearing and higher engine speeds. Therefore, when accelerating hold on the lower gears for as long as you can, but be careful not to hit the rev limiter (as this slows you down). Only change up when the engine has passed through the upper limits of the power band, not before.
Changing down / down shifting

When approaching a corner, you need to select a gear which will provide maximum acceleration at the exit, and this gear needs to be engaged before entering the corner. This means braking to the speed where you can safely turn into the bend, then shifting before turning in. Gear choice is especially important here – ideally you need to select a gear which will cause the engine speed to increase to a sensible point within the power band so that plenty of power is available when accelerating out of the turn. However if you do select the correct gear and let out the clutch swiftly, three things will happen:

Significant levels of engine braking will occur
In extreme cases, the wheels can lock up
Forward weight transfer will occur

None of these are good when you're trying to maintain control of a car driving at the limits of grip. Rev matching is the solution
Introduction to rev matching

Rev matching is a technique which should be second nature if you want to be quick on the track.
When is it used? When changing down to create smooth, fast gear changes.
What rev matching does:

Reduces stress on the driveline
Prevents forward weight transfers when down shifting
Reduces engine braking and chances of wheel lock

Note: On the track, use the brakes to slow down and the engine to accelerate. Engine braking is not as efficient, and will not slow you down quickly enough for track use. If you have time to use engine braking, you're not going as quickly as you could.

How to rev match when changing down:

1. Rev matching is mostly used to change down in anticipation of a corner. Diagram 4 (below) shows a driver accelerating in third gear, approaching the top of the power band.
Diagram 4: Accelerating down a straight in third gear

Show me what this diagram means
2. As you approach a corner, brake until you have reached a safe speed to turn into the bend – engine speed will drop as road speed decreases. In Diagram 5 below the driver is in still in third gear, but is planning to select second. Engine speed has now dropped to the point where a change to second would be possible.
Diagram 5: Braking before a corner

3. While still on the straight, press the clutch in order to change down. This disengages the engine from the wheels and thus the engine speed starts to drop. The desired gear is second, but Diagram 6 shows that at the current road speed, the engine revs will need to increase in order to mesh smoothly when releasing the clutch.
Diagram 6: Pressing the clutch in preparation to change down

4. Select a gear which will provide decent acceleration at the exit of the corner, in Diagram 7 the driver has selected second gear. Simultaneously use the throttle to increase the engine speed in order to match the revs in second gear to the road speed.
Diagram 7: Pressing the clutch, and selecting a lower gear

5. Release the clutch smoothly and progressively, then start to accelerate out of the corner. If done well, there should be no jolt as the clutch is released.
Diagram 8: Second gear is selected, engine revs match road speed and the clutch is let out.

You don't need to be 100% accurate when raising the engine revs – you'll improve dramatically with practice

courtesy: Driving Techniques

Shan2nu · 24th November 2009, 22:03

LOL, somebody seems to have been bitten by the rev match bug. The more you read about it, more you'l want to try it.

Have fun!!!

Shan2nu

firstguri · 24th November 2009, 22:22

This is awesome man. Some driving lessons I tell you! My Linea is going to be rev-match'ed the first thing tomorrow for sure.

DownTheLine · 24th November 2009, 22:31

Quote:

Originally Posted by Shan2nu

LOL, somebody seems to have been bitten by the rev match bug. The more you read about it, more you'l want to try it.

Have fun!!!

Shan2nu

Yeah I got contaminated with this bug from you guys only and now it is just lingering on...

Mods: Kindly change the thread title to the appropriate one..

24th November 2009, 19:09	#33
DownTheLine Newbie Join Date: Aug 2009 Location: Bangalore Posts: 19 Thanked: 0 Times	Let me pitch in I am the one who was facing this problem. Probably I had not put my problem correctly and that's why the whole confusion surfaced. By downshifting I mean not only changing the gear directly from 5th to 4th or so on.. , but also apply the brake to slow down the vehicle. Thanks a lot all of you (Shan2U, Jaisha, Proton), this thread is really very informative for all new driver like me, and guess what happened after this discussion .. my problem has been resolved. Now I am extra careful while shifting the gears from high to low by using proper braking. I would love to use the heal/Toe method but I think it will take some time to me to learn that
	() Thanks

24th November 2009, 20:25	#35
proton BHPian Join Date: Jan 2008 Location: Bangalore Posts: 204 Thanked: 393 Times	HaHa! I'm not totally sure about how we helped, but I sure got a nice brushing up from all this, so thanks all for a very enjoyable discussion. Must add that there are very real benefits from rev matching as Shant2nu points out, the most important to me being, it saves your clutch. So blip the engine a bit when you de-clutch: it's safe and will reduce the jerking. G'night all!
	() Thanks

24th November 2009, 21:21	#36
DownTheLine Newbie Join Date: Aug 2009 Location: Bangalore Posts: 19 Thanked: 0 Times	Rev matching and gear shifting Introduction Each gear has an effective operating range of speeds which depend on the rev range of the engine. The faster the engine rotates, the quicker you can go – up to the point when you need to change up a gear. Within the operational rotational speeds of the engine, there is a range of optimum efficiency known as the 'power band', and this is where the fastest acceleration can be obtained (see Diagram 1). Diagram 1: The power band of an engine in any particular gear Most gearboxes are designed so that when you change up a gear when accelerating, the next gear will be at the start of the engine's power band (see Diagram 2). This design provides maximum acceleration all the way up to the top speed of the car. Diagram 2: Comparing the power bands in two gears At most speeds, a selection of gears can be used (see Diagram 3). Diagram 3: Gear choice at different speeds In the illustration above the driver could choose second, third or forth gear. In second gear the engine speed would be at the top of the power band, not leaving room for much useful acceleration until the rev limiter is activated. In forth the revs would be too low, leading to sluggish performance (but perhaps decent fuel economy). In third gear the engine would be at start of the power band providing maximum acceleration – this would be the choice of the performance driver. Changing up / up shifting Lower gears provide greater acceleration due to a combination of the gearing and higher engine speeds. Therefore, when accelerating hold on the lower gears for as long as you can, but be careful not to hit the rev limiter (as this slows you down). Only change up when the engine has passed through the upper limits of the power band, not before. Changing down / down shifting When approaching a corner, you need to select a gear which will provide maximum acceleration at the exit, and this gear needs to be engaged before entering the corner. This means braking to the speed where you can safely turn into the bend, then shifting before turning in. Gear choice is especially important here – ideally you need to select a gear which will cause the engine speed to increase to a sensible point within the power band so that plenty of power is available when accelerating out of the turn. However if you do select the correct gear and let out the clutch swiftly, three things will happen: Significant levels of engine braking will occur In extreme cases, the wheels can lock up Forward weight transfer will occur None of these are good when you're trying to maintain control of a car driving at the limits of grip. Rev matching is the solution Introduction to rev matching Rev matching is a technique which should be second nature if you want to be quick on the track. When is it used? When changing down to create smooth, fast gear changes. What rev matching does: Reduces stress on the driveline Prevents forward weight transfers when down shifting Reduces engine braking and chances of wheel lock Note: On the track, use the brakes to slow down and the engine to accelerate. Engine braking is not as efficient, and will not slow you down quickly enough for track use. If you have time to use engine braking, you're not going as quickly as you could. How to rev match when changing down: 1. Rev matching is mostly used to change down in anticipation of a corner. Diagram 4 (below) shows a driver accelerating in third gear, approaching the top of the power band. Diagram 4: Accelerating down a straight in third gear Show me what this diagram means 2. As you approach a corner, brake until you have reached a safe speed to turn into the bend – engine speed will drop as road speed decreases. In Diagram 5 below the driver is in still in third gear, but is planning to select second. Engine speed has now dropped to the point where a change to second would be possible. Diagram 5: Braking before a corner 3. While still on the straight, press the clutch in order to change down. This disengages the engine from the wheels and thus the engine speed starts to drop. The desired gear is second, but Diagram 6 shows that at the current road speed, the engine revs will need to increase in order to mesh smoothly when releasing the clutch. Diagram 6: Pressing the clutch in preparation to change down 4. Select a gear which will provide decent acceleration at the exit of the corner, in Diagram 7 the driver has selected second gear. Simultaneously use the throttle to increase the engine speed in order to match the revs in second gear to the road speed. Diagram 7: Pressing the clutch, and selecting a lower gear 5. Release the clutch smoothly and progressively, then start to accelerate out of the corner. If done well, there should be no jolt as the clutch is released. Diagram 8: Second gear is selected, engine revs match road speed and the clutch is let out. You don't need to be 100% accurate when raising the engine revs – you'll improve dramatically with practice courtesy: Driving Techniques
	() Thanks

24th November 2009, 22:03	#37
Shan2nu Senior - BHPian Join Date: Feb 2004 Location: Hubli - Karnata Posts: 5,533 Thanked: 125 Times View My Garage	LOL, somebody seems to have been bitten by the rev match bug. The more you read about it, more you'l want to try it. Have fun!!! Shan2nu
	() Thanks

24th November 2009, 22:22	#38
firstguri BHPian Join Date: Aug 2009 Location: Mohali Posts: 389 Thanked: 420 Times	This is awesome man. Some driving lessons I tell you! My Linea is going to be rev-match'ed the first thing tomorrow for sure.
	() Thanks