# Double clutching **URL:** \ **Category:** Factual Questions\ **Created:** [November 22, 2002, 5:35am UTC](https://boards.straightdope.com/t/double-clutching/138106 "2002-11-22T05:35:05Z")\ **Posts on this page:** 15\ **Page:** 2
**Author:** ![alex\_arg](https://avatars.discourse-cdn.com/v4/letter/a/ebca7d/32.png) [@alex\_arg](https://boards.straightdope.com/u/alex_arg)\ **Post date:** [November 22, 2002, 9:26pm UTC](https://boards.straightdope.com/t/double-clutching/138106/21 "2002-11-22T21:26:36Z")
Thanks to all. I’ve tried this , what was that phrase? Oh yeah, easier said than done. Whoops. Forgot that Fast and Furious makes a lot of gaffs when it comes to cars. You’d think they’d have some sort of consultant for that. Anyway, I’ll keep trying, this would have been definitely helpful with my past car, which had problems when i downshifted into 2nd and the revs went up too much ( I can’t explain what happened in english, but what basically happened was the gears wouldn’t work). Still good to know to impress the girlies though. ---
**Author:** ![honkytonkwillie](https://avatars.discourse-cdn.com/v4/letter/h/3da27b/32.png) [@honkytonkwillie](https://boards.straightdope.com/u/honkytonkwillie)\ **Post date:** [November 26, 2002, 11:03am UTC](https://boards.straightdope.com/t/double-clutching/138106/22 "2002-11-26T11:03:25Z")
> [@](#): > > \*Originally posted by Gary T \* > \*\*This was answered above, but here’s the brief version: > > _Why do you have to put it into neutral and let out the clutch first?_ > > Because it not just a matter of raising the engine speed, the whole point is to **raise the speed of a rotating shaft in the transmission**. Gotta be in neutral and have the clutch pedal up to make that happen. \*\* So how does the speed of the **rotating shaft** in the transmission increase when everything behind the flywheel is disengaged whilst in neutral, with or without the clutch pedal pressed in? ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [November 26, 2002, 11:20am UTC](https://boards.straightdope.com/t/double-clutching/138106/23 "2002-11-26T11:20:10Z")
Being in neutral with the clutch up is NOT the same as having the clutch in. If you are in neutral with the clutch pedal up, the rotating shaft in the transmission spins, as Gary T said. If the clutch pedal is in, there is no link between the shaft and the engine, hence you’re only raising the engine speed without spinning the shaft. Or something like that. ---
**Author:** ![TheLoadedDog](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheLoadedDog](https://boards.straightdope.com/u/TheLoadedDog)\ **Post date:** [November 26, 2002, 11:21am UTC](https://boards.straightdope.com/t/double-clutching/138106/24 "2002-11-26T11:21:31Z")
Neutral is a state of the gearbox itself. With the clutch engaged (closed), and the gearbox in neutral, the rotating shaft mentioned becomes an extension of the engine. This means that the driven gearing on the “engine side” on the gearbox exactly matches engine speed. ---
**Author:** ![Tristan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tristan/32/18058_2.png) [@Tristan](https://boards.straightdope.com/u/Tristan)\ **Post date:** [November 26, 2002, 11:50am UTC](https://boards.straightdope.com/t/double-clutching/138106/25 "2002-11-26T11:50:15Z")
They had a consultant. His name is RJ DeVera. The problem is, he is known for putting together nice show cars. Not actual track driven cars. Hence, a slew of errors on the engines and performance of many of the cars. But the looks they carry were, at the time, the sort of looks that were winning car shows. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [November 26, 2002, 2:12pm UTC](https://boards.straightdope.com/t/double-clutching/138106/26 "2002-11-26T14:12:59Z")
_So how does the speed of the rotating shaft in the transmission increase when everything behind the flywheel is disengaged whilst in neutral, with or without the clutch pedal pressed in?_ You misunderstand neutral. Not everything behind the flywheel is disengaged in neutral. Those things are disengaged when declutched. The transmission’s input shaft and countershaft are constantly connected to the clutch disc, and constantly spinning whenever the clutch is engaged (pedal up). In neutral, there is no connection of motion to the output shaft, which is constantly connected to the drive wheels. When a gear other than neutral is selected, the input shaft motion is connected to the output shaft through the chosen gear. Then, of course, the car can move itself. The most obvious _ **effect** _ of being in neutral is the same as the obvious _ **effect** _ of disengaging the clutch (pedal down)–the car won’t propel itself. But there are two different mechanisms involved–being in neutral is not the same _ **condition** _ as being declutched. ---
**Author:** ![racekarl](https://avatars.discourse-cdn.com/v4/letter/r/6bbea6/32.png) [@racekarl](https://boards.straightdope.com/u/racekarl)\ **Post date:** [November 26, 2002, 2:39pm UTC](https://boards.straightdope.com/t/double-clutching/138106/27 "2002-11-26T14:39:56Z")
Man there is a lot of misinformation floating around, along with a smattering of good data. As has been mentioned double clutching is the practice of putting the car in neutral and blipping (quickly revving) the engine to bring the engine up to the speed it will be running at in the next lower gear. That’s about where the accuracy ends in most of these posts… First off, all gears in a manual transmission are always properly meshed and always spinning. Changing gears without rev matching (whether accomplished via synchronizers or double clutching) will NOT cause any gears to grind together or knock their teeth off. Gears are changed in a transmission by coupling a new set of gears to the driveshaft. This is accomplished via a collar around the output shaft that slides back and forth engaging different gear sets. When you rev match you are matching the rotational speed of this collar with the next gear it has to engage, not matching the speeds of different gears with each other. Here are some smaller quibbles I have: > [@](#): > > For acceleration, you don’t need to use the clutch. You must have a syncromesh trans. You Not true at all; You can upshift without the clutch (commonly called “powershifting”) regardless of whether or not you have syncros. Because the engine will naturally be running at a lower RPM in the higher gear, the drop in RPMs during the time you are off the throttle during the shift is generally enough to make the speed of the collar’s dog teeth line up with the next gear, regardless of syncros. That being said, don’t try this at home… > [@](#): > > Being able to accomplish “heel and toe” driving, where the heel of the right foot applied the brakes while leaving the toes of that foot just above the gas pedal was widely admired. The theory was that less time was required to get off the brakes and back on the gas. I don’t know if this is still in practice. That is not the theory. The reason you want to heel and toe is directly related to double clutching. You want to be able to blip the throttle to double clutch downshift while still braking, hence you need the left foot for the clutch and the right foot must do double duty on the brake and throttle. This technique is still very much in use today, as most race cars do not have syncronized transmissions. > [@](#): > > Before then, only the gearset you were using was spinning inside the transmission Not true, see above ---
**Author:** ![zwede](https://avatars.discourse-cdn.com/v4/letter/z/ac91a4/32.png) [@zwede](https://boards.straightdope.com/u/zwede)\ **Post date:** [November 26, 2002, 2:57pm UTC](https://boards.straightdope.com/t/double-clutching/138106/28 "2002-11-26T14:57:30Z")
> [@](#): > > \*Originally posted by racekarl \* > \*\*Man there is a lot of misinformation floating around, along with a smattering of good data. > First off, all gears in a manual transmission are always properly meshed and always spinning. \*\* Well, if you want to nitpick… In most manual trannies REVERSE is not meshed except when in reverse gear. Some of the newer high-end transmission, such as the Tremec T-56 used in Vettes & vipers have reverse fully synchronized and meshed, but many still have reverse un-synchronized and not in constant mesh. Just felt like nit-picking… 🙂 /Markus ---
**Author:** ![racekarl](https://avatars.discourse-cdn.com/v4/letter/r/6bbea6/32.png) [@racekarl](https://boards.straightdope.com/u/racekarl)\ **Post date:** [November 26, 2002, 3:13pm UTC](https://boards.straightdope.com/t/double-clutching/138106/29 "2002-11-26T15:13:13Z")
Yes that is true about reverse, although I’d hate to see someone try to double clutch their way from first to reverse :eek: ---
**Author:** ![zeb\_1568](https://avatars.discourse-cdn.com/v4/letter/z/ba8739/32.png) [@zeb\_1568](https://boards.straightdope.com/u/zeb_1568)\ **Post date:** [November 26, 2002, 5:45pm UTC](https://boards.straightdope.com/t/double-clutching/138106/30 "2002-11-26T17:45:24Z")
In the scene some of you were referring to in “The Fast and Furious” I believe Vin Diesel is wrong anyway but I may be the in wrong to…I’m not really sure Maybe someone can help me out. You see they’re racing down a straight road the whole time to see who gets to finish first(no need to deaccelerate right?) Anyway Vin says the racer “wasn’t double clutchin like he should have” but why would he need to? If they’re racing down a striaght road why would they need to double clutch unless he was referring to it as double clutching into a higher gear which makes no sense… Can anyone help me out here? ---
**Author:** ![Frank\_2](https://avatars.discourse-cdn.com/v4/letter/f/8c91f0/32.png) [@Frank\_2](https://boards.straightdope.com/u/Frank_2)\ **Post date:** [November 26, 2002, 6:44pm UTC](https://boards.straightdope.com/t/double-clutching/138106/31 "2002-11-26T18:44:14Z")
> [@](#): > > \*Originally posted by zeb 1568 \* > \*\* but why would he need to? If they’re racing down a striaght road why would they need to double clutch unless he was referring to it as double clutching into a higher gear which makes no sense… Can anyone help me out here? \*\* > [@](#): > > \*Originally posted by alex\_arg \* > **Fast and Furious makes a lot of gaffs when it comes to cars.** > [@](#): > > \*Originally posted by Tristan \* > **They had a consultant. His name is RJ DeVera. The problem is, he is known for putting together nice show cars. Hence, a slew of errors on the engines and performance of many of the cars.** Basically don’t believe anything in that movie. You cannot double-clutch to win a race, it’s never too soon to hit your nitrous, the floorboard will not fall out of your car, and you can’t shift a transmission through 8 gears (unless you have an 8 speed). ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [November 26, 2002, 7:18pm UTC](https://boards.straightdope.com/t/double-clutching/138106/32 "2002-11-26T19:18:26Z")
Maybe, double cluthching when shifting UP may make the shift smoother. Pushing the clutch in the first time takes some of the pressure off the drivetrain, and takes some of the “twist” out of the llinkage. The second clutch push, along with the shift itself, will get you into the next gear easier. The whole thing should take less then a second to do. ??? How does that sound??? When I went to solid motor mounts I didn`t miss shifts anymore because the linkage was more stable and the drivetrain doesn`t “twist” as much. Could this be what they are refering to?? ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [November 26, 2002, 7:24pm UTC](https://boards.straightdope.com/t/double-clutching/138106/33 "2002-11-26T19:24:10Z")
QUOTE—Basically don’t believe anything in that movie. You cannot double-clutch to win a race, it’s never too soon to hit your nitrous, the floorboard will not fall out of your car, and you can’t shift a transmission through 8 gears (unless you have an 8 speed). -----QUOTE Yes, you can hit the nitrous too soon. If your not hooked up and you hit it you`ll be buying now tires sooner. ---
**Author:** ![racekarl](https://avatars.discourse-cdn.com/v4/letter/r/6bbea6/32.png) [@racekarl](https://boards.straightdope.com/u/racekarl)\ **Post date:** [November 26, 2002, 7:40pm UTC](https://boards.straightdope.com/t/double-clutching/138106/34 "2002-11-26T19:40:43Z")
Well whuck, it’s an interesting theory, but why would you bother with two movements of the clutch when none would suffice during an upshift? In street racing they wouldn’t be going for smoothness anyway, they’d just want to slam it into the next gear as fast as possible so they could get back on the throttle. I think they just wanted some saucy dialog that would sound cool to moviegoers, the majority of which probably weren’t old enough to drive anyway, and so wouldn’t be bothered by such an obvious gaffe. ---
**Author:** ![Critical1](https://avatars.discourse-cdn.com/v4/letter/c/3e96dc/32.png) [@Critical1](https://boards.straightdope.com/u/Critical1)\ **Post date:** [November 26, 2002, 8:46pm UTC](https://boards.straightdope.com/t/double-clutching/138106/35 "2002-11-26T20:46:42Z")
yeah for an upshift when acceleration is all that counts Speed shifting would be Way better than double clutching. speed shifting, depressing the clutch only far enough to get out and into the next gear instead of to the floor. [Previous page](https://boards.straightdope.com/t/double-clutching/138106.md?page=1)