Gearbox technologies

Gearboxes are complex mechanical devices which allow cars to operate at different road speeds while remaining within the rev range of the engine

Many performance cars are now fitted with ‘paddle shift’ style switches behind the steering wheel which are often marketed as sequential gearboxes, however these are often not true sequential mechanisms, but simple electronic manual controls to fairly standard automatic transmissions.

Below is an introduction to some of the different transmissions which can be fitted in performance cars:

Automatic transmissions with manual control (e.g. Tiptronic)

Technical summary

• Standard automatic transmission with manual controls
• Torque converter rather than clutch

These ‘Tiptronic’ style systems allow the driver to have greater control of gear selection in a car with automatic transmission by offering a ‘manual mode’. This mode can be controlled using paddle switches behind the steering wheel or by selecting a dedicated slot on the transmission control. The more advanced versions of this system are linked to the engine management controls, automatically raising the engine speed in response to a downshift and achieving the same quick, smooth gear change as heel and toe shifting allows. Even when in manual mode, certain failsafe controls are built into the system which will prevent. for example, the engine stalling from the revs dropping below a set limit. Good Tiptronic systems can reduce the shift time compared to a manual transmission, but many will not.

Advantages

• Paddles allow the driver to keep both hands on the wheel while changing gear
• Can allow the driver to lock the system into a particular gear, allowing the engine speed to run all the way to the rev limiter and extract full power from the engine
• Permits down changes in anticipation of a corner which will prevent unnecessary changes mid bend, which could potentially unsettle the car

Disadvantages

• Not as quick as DSG or true sequential gear changes
• Possible slight loss of power through the torque converter

What to look for:

Paddles which rotate as you turn the steering allow easy changes when steering lock has been applied

Example trademarks for this system:

Tiptronic (Porsche)
Steptronic (BMW)
TouchShift (Mercedes)
SportShift (Subaru)

Direct Shift Gearboxes (DSG)

Technical summary

• Manual gearbox with automatic or semi-automatic control
• Dual clutch, twin shaft
• Predictive pre-selection of gears

DSG gearboxes are a recent addition to the suite of technology now becoming readily available in production cars. The idea behind DSG is to provide fast gear changes with the longevity of a conventional automatic gearbox.

DSG is essentially a computer controlled manual gearbox complete with two clutches which each engage a different selection of gears. The first clutch engages the gears 1, 3, and 5 with the even gears engaged by clutch two. The beauty of the system is that the computer can predict which gear you’re likely to select and pre-select this (as long as it’s either one up or one down). When shifting to the pre-selected gear, all the system needs to do is release one clutch and engage the other. This can be done incredibly quickly and results in lightning changes.

The computer takes into account a variety of driver inputs when deciding which gear to select including throttle position, engine speed and road speeds.

Drawbacks of the system include the relatively heavy weight when compared to conventional manual or sequential gearboxes, and the fact that the really fast changes will only occur when the computer has pre-selected the correct gear.

Advantages

• Can provide extremely rapid gear changes to expected gears

Disadvantages

• Can be heavy due to added cogs and shafts required
• Relies on a computer to predict the gear that is likely to be chosen, unexpected changes can increase change time
• Expensive

True sequential gear boxes

Technical summary

• True manual gearbox
• Ability to shift without the use of a clutch
• Fastest consistent shift speeds

You’ll usually only find true sequential gearboxes in fairly serious racing cars as they’re expensive and require regular maintenance. However if you’re trying to shave precious seconds off lap times there’s no substitute. There are two main advantages of a sequential box which include the ability to rapidly change gear without a clutch, and the reduction in error which can result from a standard “H” gate gearbox.

How to use a sequential gearbox

True sequential gearboxes are usually set up to change down by pushing the lever forwards, and to change up by pulling back. The reason for this is that when braking hard, the resulting weight transfer will throw your body forwards and as this is when you’re most likely to change down, pushing the lever will be easiest. When accelerating hard your body will be thrown backwards, and pulling the lever will be the most natural motion

It’s important to push and pull the lever in a very deliberate rapid motion to ensure correct engagement of the desired gear.

Advantages

• Extremely quick changes regardless of which gear is selected
• Impossible to block change into the wrong gear

Disadvantages

• Expensive to buy and repair

Due the high levels of wear and stress involved with a mechanical sequential gearbox, you may find you need to rebuild it every now and then to ensure continued efficiency, this pretty much rules it out of most road cars.