When sitting in traffic or at a long red light, is the Best Practice to have the car in 1st gear with your foot on the clutch, or in neutral with your foot off the clutch?
Some say that you should be in gear to be ready to move if necessary.
Some say that long-term clutch use can lead to premature wear of clutch components, such as the throwout bearing (and certainly many more if you don't get the clutch fully disengaged!).
My choice would depend on the duration of the stop. If you're rolling up to an intersection and see the light change to red knowing you will sit for a full cycle I'd opt for "in neutral foot off the clutch". Pulling up to an already red light I would go for "in gear clutch depressed" as you can figure you'll have a short wait. Having the clutch depressed adds wear to the throw out bearing, slave cylinder and clutch fingers. Having the clutch engaged with the transmission in neutral does not add wear to the clutch as it is mated to the flywheel and not slipping which is what causes the wear. This does add some wear to the transmission but it has been my experience that transmission bearings and gears are more robust than the clutch parts and seldom fail from wear. Some may argue that cycling the clutch adds wear but the use is momentary, not the constant load of holding the clutch disengaged.
As a somewhat paranoid motorcyclist, I'm a huge fan of remaining in first, with the clutch disengaged until at least one vehicle has fully stopped behind me, after that if the remaining stop time is long (frequently it isn't) I may switch to neutral.
Until that vehicle has completely stopped, you're at risk of being rear ended by someone failing to stop in time. Evasive action is much faster from first than neutral.
For cars, there's far less opportunity to take evasive action (A bike can slip between lanes, cars can't), so it may matter much less.
Guidance from the Institute of Advanced Motorists in the UK is to place the car into neutral and use the parking brake. The wear on the clutch from keeping the clutch pedal in isn't likely to be an issue(*), but in the event of the car behind bumping you your foot could slip off the clutch, propelling you into the car in front!
From an ecological perspective, a more and more accepted best practice is actually to come to a complete stop, change to neutral, put on the parking brake and turn off the engine. For anything over a 15 second stop (or thereabouts) this is less ecologically damaging, and is the reason many modern cars do this automatically.
(*If you don't push the clutch in fully, you can wear your clutch plates quite easily, so if you have a strong spring on your clutch pedal you should take care holding the clutch.)
Having driven a bus with a non-synchro gearbox and a wet clutch, I understand the meaning behind "stuck in neutral" - for if you didn't slide it into first before coming to a halt, there was no getting it into first without suffering the embarrassment of shutting down the engine. The habit dies hard; synchro or not, I still hold at a light in first gear, engine running, clutch fully depressed and some pressure on the service brakes.
When the clutch is depressed you are engaging the throwout bearing. This isn't an actively lubricated part (it relies only on sealed lubricant) and uses balls or rollers. Over time this bearing does wear out and replacement requires removal of the transmission. Unless you are in unpredictable traffic and might need to move at any moment, it's better to put the transmission into neutral.
In a properly maintained fully functional manual transmission equipped automobile, I prefer to be in neutral with my foot not on the clutch pedal. The reasoning is that if I happen to be rear ended or something, there is no way for me to accidentally take my foot off of the clutch and roll out further into cross traffic.
One important aspect not covered yet, is that the vehicle may be equipped with a start-stop system.
A start-stop system saves fuel by completely turning off the engine when stopped, to turn it on again when needed.
Specifically, the engine shuts off when the car has come to a full stop, the gear is in neutral, and the clutch engaged (different conditions apply for cars with an automatic transmission).
The engine starts again when the clutch pedal is pressed. So for this system to work, there's only one option.
When I had my first stick the guy who tought me kept saying, "save your brakes, downshift and let the engine slow you down". I found brakes are cheaper than clutches. With my present car (I love a 5 soeed stick) I try to not use the clutch as much as possible, including at a traffic lights. The only time I downshift is to maintain coltrol on really steep mountains!
One other wear part I don't see mentioned is the thrust bearing on the crankshaft. This (usually) plain bearing keeps fore and aft movement of the crankshaft in check. When you have the clutch depressed you are also pushing the flywheel and crankshaft forward. If you do this for extended periods of time you will scrape the oil off of this plain bearing and and cause wear. I've seen a few engines where the thrust face was nearly worn through.
I personally saw this on older longitudinal Datsun/Nissan straight 4 and 6 engines. YMMV.
Here's a picture of a thrust bearing near failure on a Porsche.
My style is foot off the pedal as much as possible. Foot on pedal = release bearing engaged which means wear on a low cost part that's just as difficult to replace as a full clutch job. If you know you're going to stop go for N and foot off the clutch pedal asap using your brakes to slop. Don't touch the clutch pedal until you're ready to go. Put your clutch money in the bank!
