If the ability to drive a vehicle with a stick is becoming more and more uncommon with today cars and automatic gearboxes, the proper skill of being able to match revs on manual transmission downshifts is becoming the lost art.
So what is rev matching? Rev matching is a technique to prevent shock loads through the transmission when down shifting. The usefulness of rev matching in street, daily driving is limited for most of the time, aside from sounding cool and impressing your friends in a narrow streets or tunnels. But out on the curvy road or on a race track, its benefits are almost must to learn!
While in motion, the engine speed and wheel speed of a vehicle with a manual transmission are kept in sync when the clutch is engaged. However, when you change a gear, that mechanical link is severed briefly, and the sync between the motor and wheels is broken. When upshifting during acceleration, this isn’t much of an issue, because there’s not a huge difference between engine speed and wheel speed as a car accelerates.
But when slowing down and downshifting when you are let’s say approaching a corner at high speed, that gap of time cause by the disengagement of the clutch to the engine causes the revs to drop. Without somehow bringing up the revs, to help the engine speed match the wheel speed in the gear you’re about to shift, you’ll get a sudden bounce when re-engaging the clutch as physics brings everything back in sync. That bounce or the sudden jolt can be a big problem when you’re driving fast, causing instability or even a loss of traction, particularly in RWD cars.
So the point of rev matching is to blip the throttle simultaneously as you downshift gear in order to bring the engine speed closer to match with the speed of wheels, before you re-engage the clutch in that lower gear. So in turn, rev matching provides a much smoother downshifting, without any bounces or jolts.
When braking is thrown in, you can use a so called “hell-toe” technique of downshifting, which involves some extra skills to learn because you have to use basically all three pedals at the same time with just two feet. But let’s leave that for now, I’ll write about heel-toe technique some other day.
But there’s a catch. It sounds easier than done. Even if you’re aware of the elements of how the rev matching works, perfecting it to the point of making it useful is quite difficult. That’s why you need a time to practice. Just find an empty road and do the downshifting until you get hold of it. Trying that out on a race track at high speeds it’s not an ideal time, drawing your attention away can result in a crash. My advice is to master it before you try it out on a race track!
For even better understanding of what rev matching is, watch this video from one of my favorite YouTube channels, Engineering Explained.