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Misha
Site Owner



Joined: Aug 02, 2006
Posts: 704
Location: McLean, VA, USA

PostPosted: Thu Feb 08, 2007 1:17 am Reply with quote Back to top

When you are driving an automatic car, your transmission is deciding when to switch gears. When you are driving a car with manual transmission this is your job. While it is definitely not a rocket science, it still requires some thought and skill.

There are quite a few myths circulating around on what is good and what is bad and how you should and how you should not switch gears. I can't just cover them all, so you ask if you have any concern, OK? You can hear for example that you should never let your engine rev higher than, say, 2000 rpm. Others will tell you - you should rev it all the way up to redline before switching to the next gear.

While both these approaches can have their place in experienced driver arsenal, he does not limit himself to one single approach. Why? Because there is no such thing as one-fits-all switching gears algorithm.

The general idea is to match your shifting points to your current driving style. Not your general driving style, but how you drive at the moment. If you are just sightseeing, you can cruise at say 40 mph in the fifth gear, no problem. Your engine speed will be around something like 1500 rpm then. If you are accelerating as fast as you can, the same 40 mph you will pass while in the second gear on most cars.

There is a couple of limitations to consider. First is the highest possible engine speed or redline. It depends on a particular model and normally is in the range of 4000-7000 rpm. Usually smaller engines have higher limit, and bigger ones - lower. When you shift gears up, you don't really have to worry about accidentally hitting it on any modern car - all of them have rev limiters that electronically cut the fuel if you approach safe rev limit.

But you have to worry about this when you shift down. If you shift to too low gear for the car speed, you force engine to rev higher than the limit, and this can cause serious damage to the engine immediately. When you get more experience, you will get a feel for that, but for now a couple of rules of thumb will be useful:

1. Unless you know what you are doing, don't shift two or more gears down.
2. Never shift down if your engine revs in the upper third of its speed range. (You need a tachometer to employ this rule)

If you don't have a tachometer, look at your speedometer - usually manual car speedometer has marks that show maximum speed for every gear. If your car does not have these marks, poke into your owner's manual - chances are it has maximum speeds listed for each gear. This can guide you to what gear you can safely shift down at a given speed, as well as to at what speed you have to switch to the higher gear.

Second limitation is the lowest possible engine speed. Well, the lowest is zero, but zero does not cut it, because engine can't move your car when its speed is zero. What I mean is the lowest engine speed it still can move your car. It is higher than idle, and depends on your intentions. If you are just cruising, this speed will be pretty close to idle, but if you want to actively accelerate, it is something in the middle of your rpm range. Remember that engine speed will drop significantly when you switch to higher gear.

If you listen to your engine, it is really easy to tell what lowest speed is - as soon as you try to accelerate, your engine sounds extremely tired, and does not produce any worthwhile acceleration. There is no immediate danger in this, but if you constantly force your engine to work that hard on that low speed, you get higher engine wear and worse fuel mileage.

To summarize - the more actively you drive, the higher you shifting rpms will be within those two limits.


Last edited by Misha on Mon May 28, 2012 12:00 pm; edited 4 times in total
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FRE
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Joined: Oct 05, 2008
Posts: 79
Location: Albuquerque NM

PostPosted: Sun Oct 05, 2008 5:40 pm Reply with quote Back to top

In the fuel mileage thread, I have posted a message on how to shift for maximum fuel efficiency; it differs from what the site owner recommends.

As to the advice never to shift down more than one gear, I strongly disagree!! For example, if I am driving at 50 mph in 5th gear (with my car), and need considerably more power to pass, it is perfectly reasonable to downshift from 5th gear to 3rd gear. For example, it would make little sense to waste time by shifting from 5th to 4th, then immediately shift from 4th to 3rd. Of course, one must know what one is doing and not shift to such a low gear that the maximum engine speed would be exceeded. If one is concerned that shifting down 2 or more gears would cause excessive wear on the synchonizers in the transmission, one can double clutch. However, I am not going to explain that here.

When maximum performance is required, it is, with MOST cars, obtained by shifting at the red line on the tachometer, although with some cars better performance would be obtained by shifting at a slightly lower speed. With my motorcycles, maximum performance would be obtained by shifting below the red line (which is 11,000 on one of my motorcycles, and 11,800 on the other one, but do not try running a car engine that fast!!).
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Misha
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Joined: Aug 02, 2006
Posts: 704
Location: McLean, VA, USA

PostPosted: Mon Oct 06, 2008 12:27 am Reply with quote Back to top

I think you forgot for whom this post was written - for the people who learn how to drive stick, and don't have any experience with this.

Two gears down were given as a rule of thumb, which definitely is not precise and does not cover all the bases. It does however prevent an inexperienced driver from blowing the engine on downshift, and therefore does its job Smile

If you have better rule of thumb, I will happily include it here.

And yeah, I do agree on shifting up at the redline when you want maximum performance, no question about that. Smile


Last edited by Misha on Mon Oct 06, 2008 10:49 pm; edited 1 time in total
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FRE
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Joined: Oct 05, 2008
Posts: 79
Location: Albuquerque NM

PostPosted: Mon Oct 06, 2008 1:35 pm Reply with quote Back to top

I'm not saying that a person just learning to drive should often downshift multiple gears. However, there are often circumstances when it is the best technique.

Too often people think that once they get a license, there is no point to learning anything more. Too often, people think that if they can get from point A to point B, their ability to use the transmission is adequate. And, people who think like that and fail to strive to improve continually will never be good drivers. Being a good driver requires paying constant attention to what one is doing and looking for ways to improve. It also requires reading material on driving and learning from it, especially material on defensive driving to improve safety.

Many drivers have no idea what the maximum permissible speed is in each gear and have no idea that using the gearbox effectively will greatly improve the performance of the car. There is little point to having a high-powered car if they don't know how to use the gearbox effectively. The reason that many people think that an automatic transmission is faster is that they don't know how to shift gears effectively.

I had a neighbor who owned a Mazda RX 7, which was a very high powered car. When I commented on what a high powered car he had, he said that it wasn't especially quick. When I told him that he had to wind the engine up to get maximum power, he had no idea what I was talking about.

Rather than telling people not to downshift multiple gears, probably it would be better to tell them that downshifting multiple gears is an advanced technique and that it would be better not to do it until they have adequate experience because otherwise, they could damage the engine. That way they will be motivated to continue learning.

I know that I can safely exceed 90 mph in 3rd with my Mazda 3, so downshifting from 5th to 3rd makes sense when more power is required for passing. I double-clutch the downshifts to reduce wear on the synchronizers, a habit I acquired many years ago. I learned to drive on my mother's 1950 Chevrolet, on which low was not synchronized, so it was necessary to double-clutch to shift to low while moving. Also, at one time, I owned a Mazda RX 4, which was known to have weak synchronizers, so I always double clutched the downshifts, often doing a heal-toe double clutch. Later, when my sister owned the car, she refused to learn how to double clutch, and the synchronizers quickly failed.
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Misha
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Joined: Aug 02, 2006
Posts: 704
Location: McLean, VA, USA

PostPosted: Tue Oct 07, 2008 3:17 pm Reply with quote Back to top

OK, makes sense. I made some corrections, how do you like it now?
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FRE
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Posts: 79
Location: Albuquerque NM

PostPosted: Tue Oct 07, 2008 3:54 pm Reply with quote Back to top

Pretty good. Of course, as you imply, it's impossible to cover all situations in a short article.

I've wondered whether all late model cars have rev limiters. I know that many do, but I don't know whether all do. The manual for my Mazda 3 doesn't give a clue. So far as I know, all modern motorcycles have rev limiters.

I have never seen an American car on which the maximum speeds in the gears are marked on the speedometer. My 1964 Volkswagen had no such markings either. Unfortunately, the instructions for a car often also omit that information. Thus, it can be very difficult for a driver to learn how to use the gearbox to best advantage without risking damaging the engine. Tachometers normally indicate the maximum permissible engine speed, but that is sometimes above the optimum speed for maximum performace and many cars do not have a tachometer.

Unfortunately, it seems that there is no simple solution.
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Misha
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Joined: Aug 02, 2006
Posts: 704
Location: McLean, VA, USA

PostPosted: Wed Oct 08, 2008 2:08 pm Reply with quote Back to top

I think all fuel injected ones do. At least all that I happened to drive Smile

It is really very easy to implement since you already have the rev data and electronic injection control. It is just a question of writing a several lines of code Smile

And there is definitely no one-fits-all solution for the optimal shifting points, one just have to spend some time experimenting if he wants to get them precisely Smile
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arun
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Joined: Dec 25, 2009
Posts: 100

PostPosted: Fri Dec 25, 2009 8:44 am Reply with quote Back to top

The basic point while you accelerate up hill is as follows.. release the hand break then shift to 1st gear and slowly accelerate and quickly shift to 2nd gear and accelerate and never release the throttle.
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FRE
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Joined: Oct 05, 2008
Posts: 79
Location: Albuquerque NM

PostPosted: Fri Dec 25, 2009 4:12 pm Reply with quote Back to top

???

Never release the throttle? In other words, speed shift from 1st to 2nd without closing the throttle? Not really a good idea. Also, I can't imagine releasing the hand brake BEFORE shifting to 1st. Probably that's not what you really meant.

Usually, with my car, I don't use the hand brake when starting on hills, but on some cars it is difficult to do it without the hand brake. Also, if the surface is a bit slippery or if it is a steep hill, it certainly is better to use the hand brake, assuming that it is conveniently located. If taking a driving test, it would be good to check first to see if using the hand brake to start on hills is permitted. At one time, that was not permitted in Wisconsin and Minnesota, which was silly.

With my car, if I use the hand brake on a hill, I apply the hand brake BEFORE shifting to 1st. Then, I give it a bit of gas, partially engage the clutch, and quickly release the hand brake, all at the same time. It can take some practice to do it smoothly without racing the engine or rolling back. Before giving it some gas, it can help to engage the clutch just enough to cause the engine to slow down slightly, then step on the gas, engage the clutch a bit more, then release the hand brake.

It's easier with a Subaru or a Studebaker because they have automatic hill holders to prevent rolling back. It's a nice feature and I don't understand why other cars don't have it.

It's easier on my motorcycles because I can have my right foot on the brake, my right hand on the throttle, and my left hand on the clutch all at the same time. With little effort and after some practice, it is easy to start smoothly on hills without rolling back at all and with no engine racing.
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