Rev rises in neutral during hard braking.

[x97Melbourne]

Originally Posted by scorcherjf

I do the same... I'm pretty sure it's fine, been doing that on all my manual cars for years. If anything you'd be wearing out your clutch more by downshifting 5 gears coming to every red light.

I tend to leave mine in gear too. In the event you need to GO, I'd rather be in gear..even a high gear. And, taking it out of gear saves NO GAS, there is no fuel being delievered to the fuel pump unless you are accelerating...to my knowledge.
But, I have no answer directly relating to your question.

[scorcherjf]

Originally Posted by Lester

OK, what if some idiot swerves, cuts you off in traffic, runs a red light etc. - now you are not in control of your car if it is in neutral. If the car is in neutral, you have to take that extra second and 1/2 to put it back into gear, then make your evasive manuever. Too late, game over....hopefully nobody gets hurt.

In an emergency situation, you will need to have both hands on the wheel, you can't afford to be shifting back into gear and trying to emergency steer at the same time. No vehicle should ever be in left neutral while it is moving. There is no wiggle room here. It is plain and simple bad driving practice. In fact - it is a ticketable offense, although rarely written up.

Yeah I understand what you're saying. I was told this many times when I was learning to drive manual, so I do keep it in gear most of the time. But if I'm coming to a stop and I'm leaving it in gear, I'm pretty low in the rev's as I'm about to disengage before I come to a complete stop. If something happens where I need to turn in an emergency, I'm still moving from momentum, so I can still turn... in gear or not. Now if I had to actually speed up, I'd be too low in the rev's to get much acceleration anyway, so I'd have to downshift regardless. The only way I see one avoiding this situation is to always be in the 3000+ rev's while slowing down so you can speed out of there in an emergency... which is something I wouldn't do unless I was on a race track.

[Lester]

The nice thing about the 135 is you get plenty of torque at 2000 rpm, so if you are already in second and moving slowly you are ok to go.

[pondo]

Originally Posted by Tom K.

You initially said "hard", not emergency braking. I agree I'd probably react in an emergency by disengaging the clutch along with full braking - but theoretically, wouldn't you be eliminating some braking force by "freewheeling" the engine? And in an emergency, stalling the engine once stopped would probably be a secondary concern.


Tom

The contact patch of your tires provide a limited amount of friction to be used for stopping. Whether you are engine braking during a hard emergency stop or just using the brakes alone, your total net stopping power is still limited by how much friction your tires can take before sliding. Also take into consideration angular forces (such a emergency braking WHILE turning).

Emergency situation, hit the clutch and slam your foot on the brake.

[AlienDNA]

Originally Posted by pondo

Emergency situation, hit the clutch and slam your foot on the brake.

Or punch the gas and drive through it. Did you learn nothing from "Days of Thunder"?

[AlienDNA]

Originally Posted by Tom K.

Jeremy is correct. If you don't believe it, set the OBC to display instantaneous MPG and observe that coasting in gear gives the max 99.9 reading but in neutral, it will show about 50 mpg.

Tom

Probably, but the in-car isn't going to tell you really. I played with it today in traffic. Change your fuel economy metre over to Canadian (l/100km) first. Run it up in 2nd and let the car coast. You'll see 0 l/km for a looong time, then it will climb rapidly when your speed drops past a certain point. I don't even wanna think about the math on that (bad cold, lack of ambition).

For kicks, later stuck in surface street traffic, it would idle in first gear at 18 to 21 l/100km. Which is really, really bad. Sooooo, overall, your car lies to you.

But, yes Jermey and Tom are right: shifting to neutral is a really silly way to improve your mileage. Plus, you don't get the cool downshifting noise when you get that heel/toe just right.

[raisemyrent]

I believe the manual suggests to coast to a halt in whatever highest gear you got to, then clutch/brake at the very end...

speaking of gas mileage, perhaps there's a mechanism I don't account for, but how is coasting down in gear at say, more than 2k, more fuel-efficient than coasting in neutral at about 1k??

and yes "coasting" is ruled against

[AlienDNA]

Originally Posted by raisemyrent

speaking of gas mileage, perhaps there's a mechanism I don't account for, but how is coasting down in gear at say, more than 2k, more fuel-efficient than coasting in neutral at about 1k??

In any material sense - such as your petrol bill at the end of the year - there is no difference.

But if you care about mileage, what the heck did you buy a 135 for?

[jeremyc74]

Originally Posted by Markoni

The thing is you WON'T stall it if you're worth a damn as a driver. The vehicle gives you more than enough indication when it's time to clutch in. Clutching in immediately only negates all engine braking and unbalances the vehicle, both of which is bad.

You're not doing any good whatsoever leaving the car in gear during a true emergency braking situation. Traction is the limiting factor, not braking capacity. The calipers on a 135i (or most modern vehicles) are capable of locking the tires up without any engine braking at all. There's no "unbalancing" effect involved when you're at the limits of the tires anyway.

In an emergency (one where you don't even have time to think) you will find both feet planted hard on the floor.

[scorcherjf]

Originally Posted by jeremyc74

You're not doing any good whatsoever leaving the car in gear during a true emergency braking situation. Traction is the limiting factor, not braking capacity. The calipers on a 135i (or most modern vehicles) are capable of locking the tires up without any engine braking at all. There's no "unbalancing" effect involved when you're at the limits of the tires anyway.

In an emergency (one where you don't even have time to think) you will find both feet planted hard on the floor.

+1

If I need to stop in an emergency to avoid hitting a car/person/animal, the last thing I'm thinking about is using engine braking or when the best time to depress the clutch is. Both feet will be planted as fast as humanly possible.

[ExMX5]

Originally Posted by jotapeh

In an automatic, shifting to neutral slightly raises revs by about 100rpm. Noticed this while parked at a red light that was taking ages.

I like to pretend I know why this happens and I have some guesses, but to be honest they're probably completely wrong and I'd rather not put my stupidity into writing here on this board.

It happens because the engine is still loaded when in drive, even at a complete standstill. In this situation the transmission rotor is still pushing fluid against the stators so there is still force being applied.

Neutral disconnects the transmission and the engine meaning the rotor is no longer being turned.

It's kind of like a big fancy milkshake maker - when the jug's on it takes it down a notch, when it's off the motor spins freely. Your A/C will have the same effect - try it!

[Robert]

Originally Posted by Markoni

The thing is you WON'T stall it if you're worth a damn as a driver. The vehicle gives you more than enough indication when it's time to clutch in. Clutching in immediately only negates all engine braking and unbalances the vehicle, both of which is bad.

First of all, I admit I am not worth a damn of a driver. I have been driving auto for the last ten years and this is my first manual in the past year. However, I disagree with your statement and here's why.

1) If you are forced to come to a complete stop on the freeway and the car behind you is barreling down on you, the ideal situation is you have stopped in time and already engaged a lower gear. In fact, you would brake and heel-toe (brake+clutch+gas) to the lowest gear possible so the car can get the hell out of there fast. To wait until last possible moment to clutch in and then switch gear could lead to a) flat footed at 6th gear going 10mph or b) takes additional time to clutch in and switch gear, when you could have done it in one motion (clutch, brake, heel on gas and engage the gear) So, no, I would still hit brake and clutch at the same time and engage the next gear, rather than brake first then wait till car almost stalls to change gear.

2) Reality is the stop is unanticipated. This is not an approaching apex that the driver can anticipate. The stop is sudden and most likely while you are in the daze of commute. The timeline is waking up, noticing car in front of you is coming to a stop, slamming on the brake, checking rear mirror, changing gears, checking side mirror to cut out, and then checking blind spot; all in matter of 3-4 seconds. I don't buy that there is time to slow down first then switch gear at the last moment, then cut out. The best driver is one who kept his distance and who wouldn't need to slam on the brake in the first place, but those of us who commute hours everyday know it's impossible to do day-in and day-out.

3) I believe all F1 drivers are great drivers and they can shift in milli-seconds with their DSG, which is faster than any one of us can do and can never stall; yet they are still involved in accidents. With practice it become an instinct so you will probably never stall, but I rather have the clutch ready for next gear than wait an fraction of a second in gear.

[jeremyc74]

Originally Posted by Markoni

The point isn't to wait as long as humanly possibly to clutch in nor is it to clutch immediately. The proper way to stop in an emergency is exactly the same way you would stop normally, only a lot quicker.

I speak from experience so unless you guys have been in more emergency stops than I have, I'll pass on the BS rationalizations.

What you're talking about is a fast stop that you weren't expecting. What I'm talking about is a true emergency where you may very well hit what's in front of you no matter what.

You don't brake like you normally do. You slam your foot to the floor as fast as humanly possible and brace for impact. The clutch is the last thing on your mind, but I've been in that situation a couple of times, and I'd be willing to be that when all is said and done you'd find both feet firmly planted on the floor just like I did.

How long have you been driving that you think you've got soo much more experience than the rest of us?

[Robert]

Originally Posted by Markoni

The point isn't to wait as long as humanly possibly to clutch in nor is it to clutch immediately. The proper way to stop in an emergency is exactly the same way you would stop normally, only a lot quicker.

I speak from experience so unless you guys have been in more emergency stops than I have, I'll pass on the BS rationalizations.

Okay, look at it this way and forget the bs rationalizations. The assumption is the stop is sudden and a complete surprise and I will estimate it takes 3 seconds to come to a complete stop from 60mph. In this assumption, I wold clutch in at time = 0, clutch in immediately, and you would clutch in at time = 2, a second before coming to the full stop. Can you quantify the distance saved using engine brake by delayed clutching in for the 2 seconds. All facts here. If you can show me that we saved an extra foot or more I am convinced. Other assumption I didn't state above is we are slamming on the brakes as hard as we can and letting ABS kick in.

[raisemyrent]

Originally Posted by AlienDNA

In any material sense - such as your petrol bill at the end of the year - there is no difference.

But if you care about mileage, what the heck did you buy a 135 for?

haha I don't, I don't care about fluctuating gas prices or how so and so brand saves me 0.1 cents. Nor am I afraid of flooring it when the coast is clear. I was asking because I picked up on something that didn't make sense to me and wanted to expand my knowledge.

Originally Posted by mvaccaro

+1

+1

Originally Posted by ExMX5

It happens because the engine is still loaded when in drive, even at a complete standstill. In this situation the transmission rotor is still pushing fluid against the stators so there is still force being applied.

Neutral disconnects the transmission and the engine meaning the rotor is no longer being turned.

It's kind of like a big fancy milkshake maker - when the jug's on it takes it down a notch, when it's off the motor spins freely. Your A/C will have the same effect - try it!

This sounds like a very accurate explanation of the original issue to me, also, I knew this! A friend who's a mechanical engineer had explained it to me wayy back... does this mean I am getting old?

[Mad Dragon]

Originally Posted by wnta135

Could this be related to that fancy brake energy recovery system that's supposed to be on the 135i? A quick search did not find any details.

U.S. cars don't have that feature.

[esses]

In an absolute I'm-about-to-crash situation I brake, recall which lane/shoulder is open, shift eyes to that mirror to make sure its clear, and floor it.

I need to be in gear. I also need to be paying attention to the road and have properly set mirrors.

I thought they taught all this in driver's ed?

[Robert]

I was talking to a Mech engineer on cars and he said only certain cars benefit from gas saving while coasting in gear. Other car would still inject some fuel.