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Old 22nd November 2009, 13:12   #16
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shan2nu,

Thats a great video, quite a learning.
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Old 23rd November 2009, 12:14   #17
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Originally Posted by DownTheLine View Post
Hi Friends,

My car jerks forward slightly shortly whenever I downshift the car, mostly at high speed, just like a bad downshift without rev matching. Not violent but you can definitely feel it.
I am wondering what could be the reason? Is it my bad driving habit or any other problem? Kindly help me out it is just 2 months old car..
You got front discs and you still downshift? Downshifting was used for preventing brake drum fade. Not a problem anymore with discs.

How to Avoid Down Shifting on a Manual Transmission | eHow.com

You also seem to be losing adhesion on the driving wheels. All the more reason to avoid downshifting.

Last edited by proton : 23rd November 2009 at 12:33. Reason: replaced 'traction' with 'adhesion'
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Old 23rd November 2009, 13:02   #18
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You got front discs and you still downshift? Downshifting was used for preventing brake drum fade. Not a problem anymore with discs.
People dont always downshift to help them slow down. If you're cruising in 5th gear and need to reduce your speed to around 30kmph, you obviously need to downshift in order to get a quick and smooth acc from 30kmph.

Moreover, even disc brakes can fade if you don't use engine braking (especially on mountain roads).

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Old 23rd November 2009, 13:43   #19
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Originally Posted by Shan2nu View Post
People dont always downshift to help them slow down. If you're cruising in 5th gear and need to reduce your speed to around 30kmph, you obviously need to downshift in order to get a quick and smooth acc from 30kmph.

Moreover, even disc brakes can fade if you don't use engine braking (especially on mountain roads).

Shan2nu
I'll bite

If you want to slow down in 5th, apply the brakes. Easy peasy. Modern discs do not fade to the point of being problematic. Drums expand>bad braking. Discs expand>better braking. Agree about the heat problem affecting pad effectiveness though.

If you want quick acceleration on change from braking and slowing down, shift to 3rd from 5th. Your synchros will take care of the speed differential if you HAVE braked and slowed down.

Safe driving means simple driving, which Heel and Toe is not, though I luv to do it!

Cheers!
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Old 23rd November 2009, 16:07   #20
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If you want quick acceleration on change from braking and slowing down, shift to 3rd from 5th. Your synchros will take care of the speed differential if you HAVE braked and slowed down.
You haven't understood the concept of downshifting.

Synchros cannot match the revs between the engine and the trans, they only help match the revs within the gearbox.

The engine rpm in a lower gear is always greater than that of a higher gear no matter what speed you downshift at. So shifting from 5th to 3rd even at 30kmph requires the revs to be matched.

Quote:
Agree about the heat problem affecting pad effectiveness though.
Thats what i meant. Our Innova is well known for showing brake fade pretty early. A tad of engine braking solves the whole problem.

Quote:
Safe driving means simple driving, which Heel and Toe is not, though I luv to do it!
Safe driving is safe driving. Simple and Complex depends on how an individual perceives these things.

For a person driving a car for the first time, even something as simple as shifting gears can feel like a highly complex maneuver.

Perceptions change as you learn new things.

All i did was provide a solution to the downshift/jerking problem (Which even i used to face before i started rev matching). People who find the technique useful will use it.

Shan2nu

Last edited by Shan2nu : 23rd November 2009 at 16:27.
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Old 23rd November 2009, 17:09   #21
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So heel and toeing is not safe!!! and when you are doing that you are not a safe driver!! Hmm!! that makes me one of the most unsafe driver's on the road!! Not to mention people like Tsuchiya!!

It makes me wonder!! where do people get such information from!!

Cheers
Shrey

Quote:

Safe driving means simple driving, which Heel and Toe is not.

Last edited by ssjr0498 : 23rd November 2009 at 17:11.
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Old 23rd November 2009, 17:53   #22
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Shan2nu wrote:
You haven't understood the concept of downshifting.

Synchros cannot match the revs between the engine and the trans, they only help match the revs within the gearbox.


Quote
Unsynchronized transmission

The earliest form of a manual transmission is thought to have been invented by Louis-René Panhard and Emile Levassor in the late 19th century. This type of transmission offered multiple gear ratios and, in most cases, reverse. The gears were typically engaged by sliding them on their shafts—hence the term "shifting gears," which required a lot of careful timing and throttle manipulation when shifting, so that the gears would be spinning at roughly the same speed when engaged; otherwise, the teeth would refuse to mesh. These transmissions are called "sliding mesh" transmissions and sometimes called a crash box. Most newer transmissions instead have all gears mesh at all times but allow some gears to rotate freely on their shafts; gears are engaged using sliding-collar dog clutches; these are referred to as "constant-mesh" transmissions.

In both types, a particular gear combination can only be engaged when the two parts to engage (either gears or dog clutches) are at the same speed. To shift to a higher gear, the transmission is put in neutral and the engine allowed to slow down until the transmission parts for the next gear are at a proper speed to engage. The vehicle also slows while in neutral and that slows other transmission parts, so the time in neutral depends on the grade, wind, and other such factors. To shift to a lower gear, the transmission is put in neutral and the throttle is used to speed up the engine and thus the relevant transmission parts, to match speeds for engaging the next lower gear. For both upshifts and downshifts, the clutch is released (engaged) while in neutral. Some drivers use the clutch only for starting from a stop, and shifts are done without the clutch. Other drivers will depress (disengage) the clutch, shift to neutral, then engage the clutch momentarily to force transmission parts to match the engine speed, then depress the clutch again to shift to the next gear, a process called double clutching. Double clutching is easier to get smooth, as speeds that are close but not quite matched need to speed up or slow down only transmission parts, whereas with the clutch engaged to the engine, mismatched speeds are fighting the rotational inertia and power of the engine.

Manual transmission - Wikipedia, the free encyclopedia

Would you agree the only time the engine speed and the speed of the connected gear box part is not the same is when the clutch is depressed?

Shan2nu wrote:
The engine rpm in a lower gear is always greater than that of a higher gear no matter what speed you downshift at. So shifting from 5th to 3rd even at 30kmph requires the revs to be matched.

That’s where the synchro kicks in.

Shan2nu wrote:
Quote:Agree about the heat problem affecting pad effectiveness though.

Thats what i meant. Our Innova is well known for showing brake fade pretty early. A tad of engine braking solves the whole problem.


But the Innova's brake performance is an exception. Would you agree that a well designed braking system delivers adequate braking without fade?

Shan2nu wrote:
Quote:Safe driving means simple driving, which Heel and Toe is not, though I luv to do it!

Safe driving is safe driving. Simple and Complex depends on how an individual perceives these things.

For a person driving a car for the first time, even something as simple as shifting gears can feel like a highly complex maneuver.

Perceptions change as you learn new things.

Always design for monkey business, I was told. Safe driving is driving designed for the novice driver. The strange thing is that safe vehicles are the ones with the most technology built in. Heel and toe and double declutch are vestiges of the dinosaur boxes.

The more things you have to do, the less time you have for the road. Synchros save you from H&T, ABS saves you from pumping and EPS saves you from steering into the slide.

Heel and toe today is for the performance driver, and performance and safety are a bit antithetical, wouldn’t you say?

Shan2nu wrote:
All i did was provide a solution to the downshift/jerking problem (Which even i used to face before i started rev matching). People who find the technique useful will use it
.

And all I did was try to promote safe driving!

Consider, isn’t it funny how the problem of jerking crops up with downshifting for braking?

Simple solution: use brakes for braking!

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Old 23rd November 2009, 23:45   #23
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Quote:
Would you agree the only time the engine speed and the speed of the connected gear box part is not the same is when the clutch is depressed?
Which is why you need to rev up the engine while downshifting dude!! Engine revs drop the moment the clutch is pressed, so how can you possibly be maintaining a higher engine speed if you downshift without rev matching?

Quote:
Heel and toe and double declutch are vestiges of the dinosaur boxes. Synchros save you from H&T,
At 50kmph my car does 1700rpm in 5th and 2400rpm in 3rd. If i downshift from 5th to 3rd at this speed, i need to make sure the engine revs are at 2400rpm when i leave the clutch in 3rd. If i dont do this, the flywheel and the clutch come into contact at diff speeds, which causes the car to jerk/bog down.

Synchros are not designed to match the speeds between the flywheel and the clutch. They only match the speeds of the gears/cogs inside the transmission, saving you the task of only double declutch.

Heel and toe is not something of the past. It is very much used on synchromesh manual transmissions even today.

Quote:
Heel and toe today is for the performance driver, and performance and safety are a bit antithetical, wouldn’t you say?
Performance driving is not rash/careless driving. You can be a performance driver and be safe at the same time.

Quote:
Consider, isn’t it funny how the problem of jerking crops up with downshifting for braking?
The prob of jerking crops up whenever you try to downshift. Try shifting from 5th to 3rd without the intention of braking. You will still feel the jerk.

Shan2nu
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Old 24th November 2009, 10:13   #24
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Originally Posted by Shan2nu View Post
The prob of jerking crops up whenever you try to downshift. Try shifting from 5th to 3rd without the intention of braking. You will still feel the jerk.
Boss, what scenario are you describing where downshifting from 5th to 3rd is without intention of braking?
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Old 24th November 2009, 10:36   #25
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Boss, what scenario are you describing where downshifting from 5th to 3rd is without intention of braking?
A scenario where im cruising at a sedate speed in 5th and need sudden acc from there on. I just rev match into 3rd and acc. Have done it so many times.

Downshifting is done for 2 reasons :
1. To assist the brakes in decelerating the car with the use of engine braking.
2. To reduce the load on the engine and give it better leverage by shifting into a gear with a higher ratio.

Dont tell me you've never downshifted without braking?

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Old 24th November 2009, 10:47   #26
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Quote:
Originally Posted by Shan2nu View Post
A scenario where im cruising at a sedate speed in 5th and need sudden acc from there on. I just rev match into 3rd and acc. Have done it so many times.

Downshifting is done for 2 reasons :
1. To assist the brakes in decelerating the car with the use of engine braking.
2. To reduce the load on the engine and give it better leverage by shifting into a gear with a higher ratio.

Dont tell me you've never downshifted without braking?

Shan2nu
Thanks.

Lets regroup.

Thread starter downshifts FOR braking. Instead of slowing down, the car jumps forward on releasing clutch. That's pretty scary, especially in downhill ghat sector.

Do you recommend Tsuchiya's technique for him?
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Old 24th November 2009, 11:04   #27
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Thread starter downshifts FOR braking. Instead of slowing down, the car jumps forward on releasing clutch. That's pretty scary, especially in downhill ghat sector.

Do you recommend Tsuchiya's technique for him?
Why should the car leap forward? You're only matching the revvs while braking, not accelerating.

Theres a diff between increasing engine speed and increasing vehicle speed. Downshift brake rev matching only increases engine speed while reducing vehicle speed.

Shan2nu

Last edited by Shan2nu : 24th November 2009 at 11:07.
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Old 24th November 2009, 11:20   #28
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Quote:
Originally Posted by Shan2nu View Post
Why should the car leap forward? You're only matching the revvs while braking, not accelerating.

Theres a diff between increasing engine speed and increasing vehicle speed. Downshift brake rev matching only increases engine speed while reducing vehicle speed.

Shan2nu
Did I get the original poster's problem wrong?

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Old 24th November 2009, 12:49   #29
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Quote:
Did I get the original poster's problem wrong?
The thread starter has not mentioned "braking" in his opening post. He was talking about the jerk while downshifting, in general (irrespective of whether he was braking or not).

Rev matching is a technical term by itself. It only means that the engine speed is being matched with the transmission speed wrt to the gear you're shifting into.

Heel n toe rev matching is used when you downshift while braking. Throttle rev match is used when you just want to shift to a lower gear without reducing vehicle speed (you dont touch the brake pedal in this case).

Whenever you shift into a lower gear with the vehicle in motion, irrespective of whether you do it for braking or otherwise, its important to rev match if you want a quick and jerk free downshift.

Shan2nu

Last edited by Shan2nu : 24th November 2009 at 12:50.
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Old 24th November 2009, 18:09   #30
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Thread starter wrote:
My car jerks forward slightly shortly whenever I downshift the car, mostly at high speed, just like a bad downshift without rev matching. Not violent but you can definitely feel it.

Shan2nu wrote:
The thread starter has not mentioned "braking" in his opening post. He was talking about the jerk while downshifting, in general (irrespective of whether he was braking or not).


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?
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