Rev matching

Rev matching is the practice of raising engine RPM during downshifts to match the speed required by the new (lower) gear. Without rev matching, downshifting causes engine RPM to be below the speed of the rotating wheels, which causes a jerky engagement when the clutch engages. With proper rev matching, the engine and transmission speeds match, allowing seamless clutch engagement.

Rev matching is achieved through different methods. Manual rev matching by the driver (using the right foot on the throttle while the clutch is depressed and a downshift is being made). Heel-toe rev matching (combining braking and throttle blipping during a downshift, the most challenging form). Automatic rev matching by the car ECU (pioneered by Nissan SyncroRev Match in the 370Z, now common on many performance cars).

The benefit of rev matching is smoother and faster downshifts. The engine and transmission can engage without slip, the car balance is not upset, and the downshift completes in less time. Rev matching is particularly important for RWD cars under aggressive driving where mismatched RPM can cause the rear wheels to lock during the downshift transition. Most modern performance cars include automatic rev matching either as standard or selectable feature.