Why Dual-Clutch Transmissions are not In-Demand in the World of Motorsports

In recent years, dual-clutch transmissions gained popularity among major automakers. These advanced units found application not only in powerful passenger cars, but also in numerous luxury cars. And that makes sense, as DCTs ensure smooth automatic running in normal driving, and extremely fast gear shifting while driving fast. But when it comes to racing competitions, DCTs are still mainly ignored by most of racing teams. But why?

Actually, DSG (direct-shift gearbox) is an electronically controlled dual-clutch multiple-shaft gearbox, so in the context of this article DSG and DCT are synonyms. To figure that out why they are not being used in racing, we turn to a great youtube video made by Nate Vincent, race driver of FCP EURO team, in which he provides a detailed comparison of his VW GTI TCR race car's old DSG transmission to a new sequential transmission, on which his team places high hopes for this year.

VW GTI TCR racing cars of FCP EURO

The thing is that last year FCP Euro bought two up-to-date Volkswagen GTI TCR racing models from Volkswagen Motorsports and equipped them with DSG transmissions. That choice was justified by reliability and robustness of the DCT solution at a given price. But throughout the course of the season, Nate and his team played the wrong card, as they simply could not compete head-to-head with the teams, using sequential gearboxes for their cars.

Now let us analyze all the facts that make a sequential gearbox so superior over the DSG solutions when it comes to racing competitions.

Nate Vincent explains the difference between the sequential gearbox and DSG

The first thing that catches your eye when comparing the abovementioned solutions is a significant difference in dimensions and weight: the sequential option is more compact and more lightweight than its dual-clutch counterpart (one hundred pounds lighter). The reason for such significant weight difference is that the DCT unit has 1 output shaft and 2 input shafts. Weight and space occupied under the hood play a huge role when engineers select internals for a racing car as they strive for maximum design optimization. The second distinctive feature of the DSG unit is significantly closer gear ratios. Another peculiarity of DSG noted by Nate is the fact that this unit is stuffed with bar-coded tags: they ensure that no one can change settings of this unit without VW Motorsports knowing.

One of the most important differences between the considered solutions lies in the gear engagement process. In contrast to a DCT, which runs with the help of helical (spiral) gears, a sequential uses straight tooth gears, thereby significantly reducing power losses. The main disadvantage here is that straight gear is extremely noisy. The sequential units also utilize dog teeth connectors instead of synchromesh g ears to shift gears. While synchromesh gears allow dual-clutch transmissions to shift smoothly, dogs operate quite forcefully, though very rapidly. The problem here is that dogs work very intensively and quickly wear out; therefore a sequential gearbox must be rebuilt every 5,000 kilometers. That is why passenger cars are rarely equipped with sequential gearboxes.

Sadev sequential gearbox

The sequential unit is equipped with a relatively light flywheel, ensuring less inertia required to spin this thing. The next thing to point out when we are talking about sizes of components in a sequential gearbox is a small clutch diameter ensuring reduced rotating diameter. Another important peculiarity of a sequential gearbox is its differential, as it has a mechanical pre-load on it instead of a computer-operated one used on DSGs.

That’s how gears are changed in the sequential gearbox

One of the most important problems of DSG units when it comes to racing competitions is the fact that its operation is fully controlled by the computer. While this system works pretty well for street cars, during racing competitions there may be some problems: for example, if the system thinks that you are speeding up it will automatically upshift, but the next moment you need to slow down the system won’t be able to downshift quickly enough.

Check out the whole video with Nate Vincent, it's worth it

All in all, the complexity of the DSG design, its solid weight and dimensions, numerous sensors make it a great solution for street cars, but not for auto racing.