Nearly every race car that has a manual transmission uses the sequential approach rather than the "H" pattern. There are four main reasons for this preference:
- The sequential shift is quicker. For example, to go from 2nd to 3rd gear on the "H" pattern, you have to push the lever up, over and up again. That takes time. On a sequential gearbox, you simply push the lever up for every gear change.
- The sequential shift is consistent. You do not have to think, "Let's see, I'm in second gear so I have to go up-over-up to get to third." You simply push the lever forward -- it's the same motion for every gear.
- The hand location is consistent. With the "H" pattern, the location of the shift lever changes, so you have to think about where to put your hand depending on which gear you are in. With a sequential gearbox, the shift lever is always in the same place for the next shift.
- The sequential shift has no surprises. If you mis-shift with the "H" pattern in a race (for example, down-shifting to 2nd when you meant to go to 4th), it is possible to blow up the engine. That can never happen with a sequential gearbox.
The other advantage is that the sequential shift lever takes up less space in the race car cockpit. You only need space for the forward/backward motion of the lever, not left/right.
Nearly all race transmissions use the sequential shift approach. The drum is rotated manually by a lever in the cockpit, or it is rotated by solenoids, pneumatics or hydraulics that are activated electronically. In the electronic case, the driver has a pair of paddle switches on the steering wheel to control the mechanism and never has to move his/her hands from the steering wheel.
Because of the advantages of the sequential approach, this type of transmission is starting to appear on cars in the high-end tuner market. A sequential manual transmission is not to be confused with a "tiptronic" sort of automatic transmission. The tiptronic system may duplicate the shift lever motion of a sequential gearbox. However, because a tiptronic transmission is an automatic transmission at its core, it still has the torque converter and usually does not shift as quickly.
For more information on sequential transmissions and related topics, check out the links below.