This tasty and delicious Useful Notes experience will be a primer for the uninitiated who wish to learn to... well... drive stick. Don't be alarmed by the length of this article; you can stop reading anytime you like. This article includes some background information that assists the understanding of the system, hence its length. Your time will not be wasted.
In a nutshell
- The gear lever is used to select 4-6 forward gears and a reverse gear. If no gear is selected, the car is in neutral.
- When pushed down, the clutch pedal (on the left) disengages the engine from the drive shaft. You use it for two things:
- In any situation when a gear is selected, the engine is turning and the car is stopping/stopped, otherwise the engine will stall.
- Whenever you are changing between gears.
- To get the car moving, you press in the clutch, get the car in gear, release the brakes (if necessary) and then slowly release the clutch. Unless you only want to move slowly, you give the car gas as you release the clutch. Releasing the clutch too quickly stalls the car.
- Lower gears give you more control over the speed of the car. Normally, you use first gear to get the car moving from stationary.
- Higher gears allow for smoother and more economical driving at higher speeds.
Now we can beginBefore we get to the How in question, we should touch on the Why. Why do we have to shift at all? Most road vehicles are powered by internal combustion engines (be it gas, diesel, biodiesel, ethanol, gas and ethanol, or liquid natural gas). These engines create rotating power by squeezing a mixture of fuel and air, then exploding it. The mechanical assembly of the engine uses the energy released in this explosion to create a rotating motion. To make a vehicle go down the road, we power the wheels with this rotating motion.
However, there are a couple limitations that these engines have. They have a minimum operating speed; that is to say, if you slow down the rotation of an engine below a certain speed, it can't sustainably create the circumstances for creating explosions, so it peters out and stalls. Also, the engine has to be made of materials, and designed and manufactured with an eye to making a profit by the manufacturer. Engines are generally extremely robust if you use them for their intended purpose, but if you rev them up too fast, there will be a failure. As engine speed increases, the loads on internal engine parts increase dramatically, so there's a restriction on engine speed on the tachometer denoted by a red line. The driver is supposed to keep the engine speed below this speed to prevent failure. The restriction is sometimes built in to the fuel or ignition systems of the car too; if you try to over-rev, the car may not let you.
So! We can't have an engine spinning really slowly, and we can't have an engine spin too fast. What we're left with is an operating range, usually between 1500 rpm (rotations per minute) or so up to 5500+ rpm on the high end of things. Diesels and high displacement gas engines tend to rev lower, small displacement and racing engines rev higher. Most engines idle at lower speed than where they can produce usable power. We can use this rev range to accelerate or decelerate our vehicle. If we connect an engine straight to the drive wheel, the wheel note can spin anywhere from 102-376 mph. This is absurd, so we put a gear ratio note to slow everything down proportionally. Now, we can move between 7 and 25 mph.
However, we still need to get from a stop to 7mph, and to slow down to a stop once we get to our destination. Below 7mph, the engine will stall. When we try to brake, the brakes will be slowing down the wheels while the engine will be accelerating them. If the brakes win, we'll come to a juddering halt when we cross below 7mph. When we try to start the engine, we'll have to push the car to 7mph before the engine can take over, which is pretty tiring and potentially messy if we slip and fall. What we need is a way to separate the engine from the wheels while we do these things, but then reconnect them later.
Clutches do the same thing your brakes do, but in a different way. The brakes are stationary (don't move with respect to the car), and squeeze against the brake rotor (flat frisbee attached to the spinning wheel) until the rotor matches the speed of the brake (stopped). The clutch spins at the speed of the wheels, and squeezes against the flywheel (a disc on the end of the engine, spinning at engine speed) until the engine and the wheels are turning at the same speed. Matching up the speeds is done with friction between the (brake and rotor)/(clutch and flywheel), which causes wear on replaceable material (brake pads/clutch material). Since the clutch allows us to make slightly different speeds work, we can use clutch friction to accelerate the car from a stop to our example 7 mph.
To accelerate without the engine fully engaged, we turn the engine on with the clutch pushed in, then gradually release the clutch, while helping the engine with a little gas. That's in bold because we'll come back to it later. Here's an exercise that can illustrate how this works:
Fundamental Experiments (basis for understanding):
So, if we're too fast on the clutch with no gas to help the engine, it bogs down and stalls. If we're gradual on the clutch, the engine can keep up with the load, and eventually we can get into gear even without help from the gas pedal. If there's too much help from the accelerator and the clutch is fast, you can burn out. If we combine all these ideas, the best way to start the car from zero is to gradually move the clutch pedal while giving a little help with the accelerator. The quicker you transition, the more gas you'll need. Once you're in gear, don't touch the clutch pedal unless you want to change gear or stop. Remember the shot of Marty McFly stomping on the brake and clutch in Back to the Future? That's how you brake if you're not going to stay in gear. Another note is that whenever you're feathering the clutch, you're causing wear on the materials, which adds up over time. Clutches are made to be worn, but if you develop bad habits, you'll need to do so more often.
We can roll! Now what?:
Most cars have a first gear that works between about 5 and about 15-20 mph. Different engines have different characteristics, and differences in transmissions exist too, so a different car model will be slightly different. Anyway, what do we do when we want to go faster than 20 mph? We can change our gear ratio, but that means our car won't be in gear until a higher speed, which means there will be a lot of wear on the clutch, which gets expensive. Why not have a box in between the clutch and the wheels that lets us choose between several different gear ratios? We can have a set for starting and operating 5-20 mph, then another for 15-35, and another for 30-55, and another for 50-90. Each ratio will allow us to use our engine, with all its limitations, to drive the vehicle in diverse circumstances. This gear ratio picking is what a transmission does. 5-20 is first, 15-35 is 2nd, and so on. There's overlap between gears so you have a buffer where you can choose to shift.
I'll post some pictures I took at the same car speed (recalling Back to the Future) so you can see the relationship between gears and engine speed.
How does shifting work? Since we're changing the relationship between the wheel speed and the engine speed, we should use the clutch to separate them. Then, move the shifter from the gear you're in through neutral and into your desired gear. Neutral is the horizontal slot in the shift pattern; put the shifter there, and your wheels are disconnected from the engine as surely as if you were clutching. This separation happens inside the transmission, so you can still clutch if you want to. Anyhow, with the clutch depressed, move the shifter into your desired gear. Release the clutch. If the engine was spinning at a different speed than it needs to be to match this gear and wheel speed, you may notice the car suddenly slowing down or speeding up while your car's wheels accelerate your engine using the clutch. This lurch is the hallmark of a new driver, and will go away when you get a sense for the engine speed you'll need when you release the clutch, and match the revs with the accelerator while you're shifting. note In this way, you can put it in neutral, change speed with the brakes, and still know roughly what RPM you'll want for a given gear. This comes with practice. You'll hit a point where you don't need the tachometer, you can tell what you need from listening to the engine, and it'll happen subconsciously.
Another note about neutral is that it's better for the car than holding down the clutch for long periods of time. If you're at a traffic light, put it in neutral and let go of the clutch. For starters, this means you can rest your foot and not have to worry about releasing the pedal by accident. But it also saves wear on a component called the throwout bearing, which is designed to survive as long as the clutch does, and should be replaced at the same time.
Where is first?:
If you shift at a low RPM, it's generally more economical, but less powerful, so you accelerate slowly. This can be frustrating for newer drivers who think their car should be powerful; if they're in a high gear and flooring the accelerator, they still pick up speed slowly because they're not in the engine's power band.
- clutch in, shift to neutral, clutch out.
- Now your transmission is at the right speed with the wheels, and the engine side of the transmission is at engine speed.
- Rev match
- so that the engine is at approximately the right speed for the new gear.
- Clutch in and shift into the new gear, clutch out.
- The clutch-side shaft and the wheel-side shaft in the transmission are spinning at approximately the same speed, so the new gear engages without grinding.
In cars with synchromesh, double-clutching isn't necessary, but it's still best practice, since it reinforces rev-matching and extends the life of your synchroes. Also, it's a great way to prepare yourself for heel-toe downshifting. Once you can double-clutch and revmatch pretty well, you're ready.
In the vast majority of vehicles with a transfer case, the driver will be able to use the transfer case lever to select 4 possible positions:
- 2H - 2-wheel drive, high range. This is the "standard" operating mode for the vehicle. Only two wheels (usually the rear) receive power from the transmission and drive the vehicle. This results in the greatest fuel economy and reduces wear and tear on the drivetrain, as the parts which power the front wheels are not in use.
- 4H - 4-wheel drive, high range. Selecting this position engages the transfer case via a chain, hydraulics, or gears, and allows it to send power to both the front and rear wheels. This results in greater traction in slippery driving conditions (light snow, loose gravel, or dirt roads), but increases fuel consumption and wear on the vehicle.
- N - This disengages the transmission entirely from the wheels, much like Neutral in a manual transmission. It's generally not used, except when shifting on to...
- 4L - 4-wheel drive, low range. This puts the transfer case in a lower gear, which allows the vehicle to operate at much slower speeds while still utilizing the available power of the engine. In the example above, first gear was not usable in the vehicle until it was traveling at 7 mph. A low range gear reduction in the transfer case would allow first gear to be used at a much lower speed—perhaps 2 or 3 mph. This reduction is across the board for all gears, so it accordingly drastically reduces the functional top speed of the vehicle. It is therefore only useful in situations where extremely low speeds are desired, such as offroading or driving in snow.