When you think of a sequential gearbox, many people think of the expensive, high-end products used in professional racing. Sequential gearboxes are not complicated and are no more expensive in terms of cost than manual gearboxes for ordinary family cars, for example the most common motorbike gearboxes are sequential. So what exactly is a sequential gearbox? Why is there such a big difference in price? Let’s talk about this today.
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Let’s start with manual transmissions in family cars
A manual gearbox in a family car is characterised by the fact that the driver can select any gear in neutral and can also go straight from any gear to neutral. Just as when we drive with the gear lever in neutral, we push forward directly into 3rd gear, without first going from 1st and 2nd gear one at a time.
Because manual gearboxes shift gears by forks pushing the gears, the internal gearbox of a family car relies on fork shafts to drive the forks, and there are three fork shafts in total, each controlling two gears. The gearshift lever in a family car can be moved freely backwards and forwards, left and right to select the fork shaft, an action called gear selection. Moving backwards and forwards is to drive the fork shaft to complete the gear change, this is called shift operation. As the gear lever can select the fork shaft for shifting at will, the manual gearbox of a family car is particularly flexible and the driver can control the gears flexibly according to the road conditions in daily driving.
In addition, the gear shifting gears in family cars have very dense teeth, which makes shifting less shocking and more comfortable. However, the denser the teeth, the more difficult it is to engage the gears, so family cars need to be fitted with a set of synchronisers to help the gears engage.
The overall structure of a sequential gearbox is not very different from that of a manual gearbox in a family car, the difference being that the fork in a sequential gearbox is controlled by a shift drum with slots designed for the different gears, in which the fork is embedded. When shifting, the shift drum is driven by the gear lever and the slots move the forks for the different gears.
So with a sequential gearbox you have to shift gears one at a time, for example if you want to shift from 1st to 3rd, a manual gearbox can take off neutral from 1st and go straight to 3rd. A sequential gearbox, on the other hand, can only shift from 1st to 2nd and then from 2nd to 3rd. The same applies to downshifts, which must be done sequentially, hence the name “sequential gearbox”.
Why do motorbikes and racing cars use sequential gearboxes, but not family cars?
Sequential gearboxes are used in motorbikes because they are small and the shifting action is simple and can be controlled by the foot. Because motorbike gearboxes are small, whereas the gearboxes of family cars are relatively complex and require more space. And motorcyclists no longer have the extra hands to shift gears, they have to shift them with their feet. If you then get a gear structure of a family car, not many people’s feet are likely to be able to control it. Sequential gearboxes are much simpler to shift, you just have to step back and forth, so they are the only way to go on a motorbike.
The main reason for using a sequential gearbox in racing is speed. Because motorsport is so intense, sometimes it’s a matter of seconds before victory or defeat. So it is very important that the rider can shift gears quickly. For example, if you want to change from 3rd to 2nd gear, you need to take off 3rd gear and then put it in 2nd gear. A sequential gearbox, on the other hand, only requires a push forward on the gear lever to immediately shift from 3 to 2. This is because pushing the lever forward drives the shift drum, and as the drum rotates the slides separate the 3rd gear fork and combine the 2nd gear fork, both of which are done at the same time, making the shift very quick.
The gearshift teeth of the sequential gearbox are large and sparse, which increases the shock of shifting but contributes significantly to the speed of shifting. The gears engage very easily when shifting because of the thin teeth, so the sequential gearbox can easily be shifted without pressing the clutch, which inevitably increases shift speed. In addition, the larger the teeth, the stronger the gears, so that the driver can still shift without clutching during intense driving without fear of damaging the gearbox.
I guess you can see why sequential gearboxes are not used in family cars, because they are simply not suited to the pace of family cars. Due to the sparse gear teeth, it is easy to stutter when shifting. Most importantly, it can only be shifted up and down in sequence, which is a very unpleasant experience for a family car. For example, if you’re driving in 5th gear and you come to a red light at a junction, we would normally put it in neutral and coast to the junction to wait for the light. With a sequential gearbox you have to downshift one gear at a time, which is very annoying.
Are sequential gearboxes expensive?
When it comes to sequential gearboxes many people think they are very expensive, but in fact structurally a sequential gearbox is simpler than a normal manual gearbox and does not cost any more than a manual gearbox in a family car. The main reason why many people think that sequential gearboxes are expensive is that they are used in professional racing cars. This is because the serial gearboxes in racing cars often need to be customised and the machining costs are definitely higher than those for mass produced cars. In addition, racing cars have a lot of horsepower and the gearboxes have to be lightweight, so more expensive materials and more advanced and complex machining processes may be used in some special areas. Some of the sequential gearboxes in racing cars are also electronically shifted, and an electronic control system costs a lot of money. Therefore, a sequential gearbox for a racing car is more expensive. On motorbikes, however, a normal sequential gearbox is used, so the cost is naturally very low.