Wikipedia:Reference desk/Archives/Miscellaneous/2013 July 10

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July 10

Is it bad for a car to use a high gear at RPMs that are too low?

Suppose I am driving a car with a traditional manual transmission. I get my car going on first gear and then short shift to second gear. Is it bad for the car to be shifting too early such that you can feel that the car is significantly underpowered at the new gear? It's hard to describe, but the car kinda makes a lower-pitched wobble-wobble sound until the RPMs get higher.

As well, suppose I want to drive in such a fashion as to preserve the longetivity of my clutch. While shifting between gears, is it better to slowly re-engage the clutch such that the shift is smooth, or is it better to instantly pop the clutch back in, such as that the gear shift is hard and jerky? (This only applies to shifting while the car is already in motion. I know that revving the engine and suddenly engaging the clutch while at a standstill is bad for the clutch). Thanks! Acceptable (talk) 01:19, 10 July 2013 (UTC)

I've been driving stickshift for 21 years, so I hope you'll excuse the OR. For question 1) does no harm, but is annoying. You should learn to shift at the proper point, not too early or too late. That is, you neither want to redline the engine (shifting too late, so you're getting too many RPMS) or too early (where you lose ALL the power, which makes it hard to accelerate properly, annoys the passengers, and runs the danger of stalling the engine). Look for a happy medium. For question #2: always shift smoothly, again for many of the same reasons. I don't know that "slamming" the car into gear is harmful to the car per se, but it's certainly an annoying way to drive. You should release the clutch evenly and smoothly. Again, you don't want to "ride" the clutch by releasing it super slow, but neither do you want to just take the foot off and let it "snap" into gear: it makes for a jerky ride. Instead, release it smoothly; practice so that you barely notice the gear change. A properly driven stickshift should feel no differently than a properly tuned automatic. --Jayron32 02:26, 10 July 2013 (UTC)

That "lower-pitched wobble-wobble sound" is called lugging, and while it won't ruin your engine instantly, I don't think it's particularly good for it, either. Our lug page says it can "potentially damage the engine" (but then again, that's just a disambiguation page, and it doesn't cite a reference). —Steve Summit (talk) 02:35, 10 July 2013 (UTC)

I just did a database search for various permutations of "engine lugging," and got a lot of hits in newspapers and magazines that say it's bad for the engine and/or transmission, but don't say how bad or why. I do remember when I bought my first VW Beetle, the previous owner gave me a copy of John Muir's How to Keep Your Volkswagen Alive; A Manual of Step-By-Step Procedures for the Compleat Idiot, which stated early on that lugging the engine was just about the worst thing a person could do to an air-cooled VW, and was to be avoided at all costs. I've since heard that the Compleat Idiot book is useful for makeshift repair or sloppy mechanics purposes, but shouldn't be considered gospel, and anyway, it applies only to a specific vehicle which doesn't have a lot of engine power and runs normally at low RPM and oil pressure compared to other vehicles. Having also been driving manual transmissions exclusively for 20-odd years, I would agree with Jayron's statements above. Probably also worth considering is the age of the vehicle; newer cars likely (yes, I know I'm speculating) have some mitigating technologies that older cars wouldn't, and older cars are more likely to already have engine/transmission/clutch wear that lugging or jerking the clutch are going to possibly exacerbate, and certainly not improve. --some jerk on the Internet (talk) 13:41, 10 July 2013 (UTC)

Using too few RPM's is called "lugging" and it's a bad thing - sure it won't trash the engine the very first time you do it...or the tenth time...or probably even the hundredth time...but if you do it habitually, you'll certainly cause some serious damage and shorten the life of your engine dramatically.

Generally, you want to be running your engine at 1500 RPM or more. It depends on the vehicle - and some odd-ball cars with things like Wankel engines are different...I wouldn't want to run an air-cooled VW bug at under 2000 RPM for long - but for your regular modern "family car" - that's a good number. When the car is just idling (with no work to do other than running the airconditioner and keeping the battery charged), low RPM's are OK. When you're pulling away from zero mph, obviously there is a transition between the idle RPM and the running RPM that you can't avoid. But once the car is moving, keep the RPM over about 1500 regardless of speed.

Remember:

   Torque = Horsepower / RPM

The amount of horsepower you're demanding from the engine depends on the speed you're trying to go - and whether you're going uphill or not and whether you're accelerating. It doesn't matter what gear you're in - for some particular speed, slope and acceleration rate, the horsepower required is always the same.

So if you need lots of horsepower to move the car - but the RPM is low, the torque has to be really high. High torque puts the biggest forces on the engine. People find this surprising - "The engine is turning really slowly...surely that's better for it?" ... well, no - because you're putting a lot of force on all of the moving parts.

What happens (in detail) when the engine is lugging is that the forces on the internal components (con rods, pistons, crankshaft, bearings, clutch) are at the absolute maximum the engine will ever have to bear - yet the oil circulation (which is driven by the engine RPM) is running at the absolute slowest and at the lowest pressure. When the engine parts are being forced together by the larger-than-usual forces, and the pressure of the oil is too low - the oil can't force itself between the engine parts. This can result in "fluid separation" - where the oil that's supposed to form a thin film between the engine parts to keep them nice and slippery is squeezed out of the way by the high forces involved and you get metal-on-metal contact. Effectively, it's like running your engine without oil...and you know how bad that is - right?

This abuse of the lubrication system also produces a climb in oil temperature and can cause the spark plugs to get outrageously hot - and neither of those are very good for your engine either. Hot oil gets runnier and thins out and that makes fluid separation even more likely. And hot spark plugs can result in pre-ignition and back-firing - which are also in the category of: "A Very Bad Thing"...and even without that, the tips of the plugs will burn up more quickly than they should.

Another problem at very low RPM's and the tendency towards pre-ignition at high load is "knocking" (aka "pinging"). The pressure waves in the cylinder get out of sync with the piston motion and huge pressures and forces can develop that push the pistons out of alignment. This produces huge amounts of wear in piston rings and god-alone-only-knows how much additional wear. On older vehicles this produces a loud noise and results in spectacularly bad engine wear in extremely short amounts of time. Fortunately, modern vehicles have electronics hooked up to a microphone bolted to the engine block that detects the onset of knocking and attempts to deal with it by altering fuel and air flow and spark timing - so you won't get knocking anymore. However, before the electronics can detect it, there has to be some serious vibration, so it won't completely eliminate the wear. And when it does kick in, you'll get amazingly bad fuel economy and poor acceleration (which is actually a good thing if you are going to suddenly demand a lot more horsepower from an already suffering engine).

So don't do it. Keep an eye on your tachometer - keep the revs up there between 2,000 and 3,000 most of the time - downshift if the revs start to drop below that range.

CAVEAT: Large truck engines are designed to work at lower RPMs, so are some (but not all) diesel engines. You can still lug them if you get the RPM's very low - but it's not such a problem as with smaller car and pickup truck engines.

SteveBaker (talk) 13:24, 10 July 2013 (UTC)

Crankshaft (red), pistons (gray) in their cylinders (blue), and flywheel (black)

Failure of a connecting rod is one of the most common causes of catastrophic engine failure.

• It's actually pretty simple. When you're in the wrong gear, there is a lot of strain on the connecting rods that connect the cylinders to the crankshaft. This in turn puts a strong sideways force on the pistons that move up and down in the cylinders, causing them to scrape against the cylinder walls. If you do too much of it, eventually a piston will seize (get stuck in the cylinder), and its connecting rod will break, and your engine will be destroyed. Looie496 (talk) 14:54, 10 July 2013 (UTC)

@Steve: I have a 2012 Honda CR-Z with a manual transmission, and an idiot light that's supposed to tell you when you're in too high or too low a gear. When I'm driving on the flat, it seems to want me in sixth gear (the highest) at about 35 mph. I don't remember exactly what RPM that turns out to be but it's well under 1500, maybe around 1100 to 1200. I'm pretty sure it's optimizing first of all for fuel economy rather than engine life. I tend to keep it in a little lower gear than the light tells me to in a lot of situation — just feels too sluggish in sixth at 35 mph. Anyway, just a data point; curious to know if you have any insights. --Trovatore (talk) 03:43, 11 July 2013 (UTC)

Update: OK, I was a little off. On a flat stretch, in fifth gear, it gave me the "shift up" light if I drove at a constant 32 or 33 (the speedometer is very accurate BTW — I checked it against my GPS). At that speed, if I shifted into sixth, the tach stabilized at about 1350 or 1400, best as I could guess (it's an analog tach dial and I couldn't read it more precisely than that while paying proper attention to the road). So that's only a little below your 1500. But it's still quite a lot below your 2000 to 3000. --Trovatore (talk) 08:56, 11 July 2013 (UTC)

Eh? You should probably have mentioned that the Honda CR-Z is a hybrid...and a very strange one at that. If that's what you're driving then all bets are off! It uses a really weird (and kinda complicated) "parallel" transmission system where the electric motors assist the gasoline engine when needed - and especially at high torque demand. Recall that:

 torque = horsepower / rpm

...so low RPM and high horsepower demands usually means high torque - which is usually an engine-wrecking thing. However, almost uniquely of all cars, the CR-Z has the electric motor kick in and provide some extra torque. (Electric motors are extremely high torque devices - so they are just fine with that). This relieves the gasoline engine of most of the torque - and all of the problems associated with lugging should go away. So you can drive the CR-Z at low RPM's just fine - at least until the battery runs out - which it soon will because the gasoline engine won't be recharging it enough at such low revs.

Since stick-shift hybrids are almost unknown, and this parallel transmission gizmo is a Honda invention, your car may be the only model on the planet for which it's OK to drive at very low RPM in high torque situations! Honda will have been VERY careful not to have the shift indicator light be set up in such a manner as to cause unnecessary engine wear because they have to foot the bill for warranty repairs! So, don't sweat it - I'm sure it's all OK.

But for those of us who drive non-hybrids (and specifically not stick-shift, parallel transmission hybrids!) driving around at 1500 rpm is a very bad idea.

SteveBaker (talk) 13:15, 11 July 2013 (UTC)

Thanks, Steve! Good information as always.

But your hypothesis, although a reasonable one given the facts you've seen, doesn't really jibe with my observations. When I'm driving on the flat in the low thirties in sixth gear, at constant speed, the gauge that shows whether you're charging or discharging the hybrid battery tends to be right in the middle; no assist and no charging. So I don't think it's a matter of just using up stored energy from the battery.

Maybe it helps some that it's a small, light car, low air resistance and low rolling resistance, therefore less power required at a given speed? --Trovatore (talk) 21:36, 11 July 2013 (UTC)

Hmmm - weird. Then I can't explain it - but your car is so deeply weird, (cool and interesting!) that it's dangerous to draw any conclusions from the way it behaves for cars and light trucks in general. Suffice to say that if my car was driven like that, its' engine would probably be scrap metal within 10,000 miles - and that's probably true for 99% of cars on the road today. SteveBaker (talk) 01:42, 12 July 2013 (UTC)

It is a very cool car. I had two things in mind when I bought a new car: (1) I wanted a hybrid and (2) I wanted a stickshift. That made the decision pretty easy :-) --Trovatore (talk) 01:53, 12 July 2013 (UTC)

Breck Girl Whitehouse Station New Jersey

I am from Whitehouse Station and I was a Breck Girl and model who did covers and commercials. Including Redbook, Cover Girl, Sear, Spiegel, Head and Shoulders and so much more. — Preceding unsigned comment added by 71.2.35.153 (talk • contribs)

That's cool. Do you have a question you would like answered by the volunteers at this Reference Desk? Edison (talk) 15:39, 10 July 2013 (UTC)

If you're asking if that's enough for an article about you, the answer is most likely no, at least based on the information you have provided. Clarityfiend (talk) 23:27, 10 July 2013 (UTC)

Greek cities

I need a list of Greek cities with nine letters. How do I find that? I have already got a list of Greek cities but there are hundreds of them. Can I narrow the list down? Please explain how. Thank you 108.133.214.153 (talk) 16:16, 10 July 2013 (UTC) 108.133.214.153 (talk) 16:16, 10 July 2013 (UTC)

In the Romanization of Greek, the number of letters in a word can change. Do you need nine letters in the Greek spelling or in Romanized spelling?

—Wavelength (talk) 16:22, 10 July 2013 (UTC)

If you had your list of cities in a computer file, one per line, and you had a grep program, you could do grep '^.........$' list-of-cities. Although issues with character encoding might complicate things. 88.112.41.6 (talk) 21:31, 10 July 2013 (UTC)

If you had your list of cities in a computer file, one per line, and you imported it into a spreadsheet all you need to do is add a column with the a formula to determine the length of the text string. e.g.=LEN("text"), where "text" will be a cell ref to the city name. Simply sort the list on that column and scroll down.196.214.78.114 (talk) 13:00, 11 July 2013 (UTC)

I took the list here and pulled it into Excel. After some cleanup, I got this list: Cholargos, Vrilissia, Heraklion, Peristeri, Kallithea, Kalamaria, Ilioupoli, Keratsini, Chalandri, Giannitsa, Orestiada, Nafpaktos, Ierapetra, Ermoupoli. Hope that helps. Matt Deres (talk) 18:05, 12 July 2013 (UTC)

If you copy the list into notepad or some similar text file with an equal spaced font, you can scan down the list and find the ones of the same length by yourself, though it might take a while. I'd recommend resizing the window to ten letters wide, so you can easily see the right length as you run down it. 213.104.128.16 (talk) 16:26, 15 July 2013 (UTC)