Changing gears - When – Part4 of how to drive a stick shift

Posted: Thu Feb 08, 2007 1:17 am

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. Never 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.