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Old 09-04-2013, 07:51 AM   #1
Ds650rida
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To double-clutch | Or to not double-clutch

"Granny shifting, not double clutching like you're supposed to" - Dominick Toretto

I've heard a lot of debate over the years from "smart" people saying that double clutching is only used on old cars and 18 wheelers. And they always love to bring up that famous line from the fast & the furious. The most common reasoning behind this is because our newer cars have synchros which alow the speed of the gears to be matched. While this is true in regards to upshifting, I use it 98% of the time when downshifting. And I'd like to use this time to explain why; mainly because I'm bored at work.

Theory:


This is a blocker ring. Used in all modern manual gearboxes. Its typically made of bronze, but I believe that old T5 trannies used a steel ring with a paper type of friction material inside. Its sole purpose is to slow down the next gear so that the synchronizer collar can easily slide over the dog gear and engage the next gear.

Now bronze is pretty soft stuff (forget about the t5 paper) and its using friction, regardless of the oil in the transmission, to slow down the next gear. So my theory is that when downshifting, instead of trying to slow down the next gear you want to select, it is now trying to speed up the gear. And we should all be able to figure that this will create more wear and therefore shortening the service life of your transmission. This is the same reason why you wouldnt (shouldnt) downshift without rev-matching the engine.

So when double clutching, you are simply rev-matching the engine AND transmission. And therefore the blocker ring can go back to doing its job (slowing down).

Technique:
I've personally been using this technique for years and on various types of cars. Anytime I need to select a lower gear, I just give the throttle a blip while in neutral with my foot off the clutch.

When coasting towards an intersection in neutral, I'll give the gas pedal a flick before pressing the clutch and selecting a gear.

While it was hard to mentally train myself to remember to do this everytime, and even harder to perfect, the results speak to me loud and clear when I get it right.

Every time I get a smooth engagement into a lower gear, no pushing or forcing. The shifter just falls right into place.

Just to name the cars that I've driven and used this technique on: NA Miata, E36, Scion TC, S14, Integra, SW20 MR2, Evo 8, STI. Thats a pretty wide array of age and layouts, so I think its safe to say that this can be universally used.

I suggest anyone who reads this to try it and impress your passengers with your seamless downshifts. Yes, its confusing as hell at first. However if you think about how much you drive your car and how many opportunities you have to practice, you should be able to get it right within a week or 2.

Btw, the 2% that I dont use this technique is when I simply forget and when I'm using heal-toe coming into a corner (although I've tried).

Edit: please check out this video, this guy sort of reinforces my theory http://www.youtube.com/watch?v=Z9HVk...ature=youtu.be

I will go back later and proof read this on the computer so please forgive any errors.

Here is a video displaying a heal-toe double clutch downshift http://www.youtube.com/watch?v=0j-3xIZK-Bk


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Last edited by Ds650rida; 09-07-2013 at 07:06 PM.
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Old 09-04-2013, 05:38 PM   #2
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Is there an advantage while downshifting to hit the gas with it in neutral?

I hit the gas with the clutch pressed to match the revs.
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Old 09-04-2013, 07:14 PM   #3
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Technically, you don't want to "cruise to a stop in neutral" because you braking power is vacuum generated by an engine under load....
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Old 09-05-2013, 07:30 AM   #4
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Yes there is an advantage, you should be able to feel a significant difference in how easily you can select a lower gear.


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Old 09-05-2013, 07:35 AM   #5
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Isnt most vacuum generated at idle? Coasting to a stop is just my driving habits. The only reason I can think of to keep the car in gear is to be able to potentially avoid an accident that required throttle to maneuver around. Or if you need to in order to keep your engine running (light flywheel or bov on maf setup)


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Old 09-05-2013, 02:51 PM   #6
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Quote:
Originally Posted by Ds650rida View Post
Isnt most vacuum generated at idle? Coasting to a stop is just my driving habits. The only reason I can think of to keep the car in gear is to be able to potentially avoid an accident that required throttle to maneuver around. Or if you need to in order to keep your engine running (light flywheel or bov on maf setup)


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No, proper deceleration is parts both engine braking and pedal input, as can be seen by driving any Auto car: IE automatic transmissions do not switch into neutral, but instead engine brake as soon as deceleration begins, and you'll find your owner's manual likely alludes to this, too. Engine braking creates a buttload more vacuum which is amplified by the brake booster for the braking system over idle.

Also take into consideration that if you're not in gear, you're not going to be able to move. Not a whole lot of people have the ability to act in a panic situation like that and make a good outcome of it, and even when they do posses those instincts, other elements usually
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Old 09-05-2013, 08:15 PM   #7
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The engine also uses more fuel when in neutral and coasting to a stop vs engine breaking. Someone went into the whole logistics of it in another thread somewhere on the forum about gas mileage.
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Old 09-06-2013, 11:20 AM   #8
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I see your point. However, I wrote this topic based on the technique used to get back into gear. Coasting to a stop is what I often times find myself doing and I'm sure a lot of other people do the same. I'm not saying its right or wrong.


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