Originally Posted by extrashaky
Luftwaffel defined it above, but to put it into easier terms:
This has to do with engine braking, using the compression of the engine to slow the car. If you downshift to use the engine to slow the car, the engine speed (RPM) has to come UP to meet the transmission speed. If you just downshift and drop the clutch, the car's momentum will yank the engine up to speed and shock the entire driveline behind it: transmission, u-joints, differential and axles. You can slip the clutch to bring up the engine speed less abruptly, but that puts more wear on the clutch disc over time.
However, imagine instead that you bring the engine RPM up with the throttle instead, so that it's spinning fast enough that there is no jerk, and you don't have to slip the clutch. That's rev matching. You just blip the throttle up so that the engine speed and transmission input shaft speed match. It puts less wear on the clutch and every component behind it.
Some cars actually rev match for you. The latest Corvette will do it. Apparently you can flash a tune on our cars that will do it also. The computer recognizes when you're downshifting and blips the throttle on your behalf to make your downshifts smoother.
I've been wondering what happens if you try to downshift and the car also tries to downshift.
Most people who use engine braking without rev matching simply slip their clutch to bring up the engine speed. Doing that puts more wear on the clutch surface and springs, but it won't necessarily hurt the car. Maybe it takes 5K or 10K miles off the clutch. Maybe not.
You're right that heel/toe isn't necessary in normal street driving. Rev matching is a good skill to have, though, because that's not really about what's necessary. It's about driving more smoothly and putting less wear on the car. Maybe it'll last a long time without any advanced techniques. Maybe it would last even longer with them.
Not wrong. It's just that the throwout bearing and pressure plate will get less wear if you get into the habit of taking the car out of gear and letting the clutch out when you're going to be sitting long enough for that to make sense. How much less wear? Who knows. Maybe it's not enough to even matter. But it doesn't really hurt anything to do it.
I usually watch the traffic lights or pedestrian signal on the cross street. When it turns yellow, I put the car back in gear to be ready to go.
The part that may not have been clear is that people are talking about engine braking, using engine compression to slow the car instead of/in addition to the wheel brakes. So as that applies to your question, I do in fact step down through the gears one at a time to slow the car. I normally use the engine to slow the car without even thinking about it.
It's a stylistic choice. If I weren't using engine braking, I would do it exactly like you're doing it.
The next obvious question is: Why do I use engine braking?
For one thing, it's smoother and feels more stable. When you use the brake pedal, the car wants to rock forward. Accelerate again and the car rocks back. Use engine braking, and it feels more like the stopping force is more centered.
Second, it keeps you in the correct gear. Suppose traffic in front of me slows down, and I use engine braking to slow down also. Then traffic takes off again. I'm already in the correct gear to accelerate. Suppose I'm in a slow-moving lane, and I get a chance to slip into a hole in a faster-moving lane. The car is already set up for that move before I even know I have the chance to make it.
See, I was taught to always be driving the car. A lot of people are only really driving the car when they're accelerating. If you take the car out of gear and coast to the stop light, coasting really isn't driving. I like to drive the car right up to a stop, ready to drive away from it.
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