Transmissions in the World of Auto Racing

Auto racing is a motorsport involving the racing of automobiles for competition. A reliable and efficient transmission is an indispensible part of each racing car and a key success factor. A top-quality race transmission should provide rapid gear shifting, withstand severe overloads, be immune to driver’s errors during gear shifting, ensure optimal selection of gear ratios. Carefully adjusted and balanced transmissions allow racers to get a split second advantage over other competitors during acceleration or turning of corners that may be decisive at the finish.

The car racing plays an important role in development and testing of innovative technologies during the structure planning for new cars and their separate components, including transmissions. Leading world manufacturers of cars and automobile components have their own racing teams or financially support independent teams. In addition to advantages associated with testing of new technologies, participation in well-known auto races is a great opportunity for advertising and brand building. Nowadays, there are many different categories of auto racing competitions, which have different rules and requirements for cars and their components. In this article we will review recent trends related to transmissions used in the most popular and entertaining auto racing competitions: Formula 1 and Drag Racing.

General Info

Common street driven cars with manual transmissions have a synchronizing mechanism (“synchromesh” gearboxes) for enhanced operability, robustness, and smooth operation. The driver can select any transmission gear at any time. The switching of gears in this type of manual gearboxes is performed with depression of the clutch pedal.

But, driving a race car is quite a different story. Manufacturers of sports vehicles cannot use standard “synchromesh” gearboxes, because synchronizers (when interacting with more powerful engines) are incapable of enduring increased power that leads to malfunctions during changing of speeds. The synchronizer is a vital component of vehicle gearboxes, which is intended for faultless mesh of the sliding coupling with the fixed (usually through the needle bearing) gear wheel. The synchronizer structure includes a conical clutch and baulk ring. In addition to smooth gear shifting, the synchronizer reduces the wear of mechanical joints and, as a result, prolongs the service life of the gearbox. However, for engineers of racing cars this useful mechanism turned out to be unnecessary. But why?

Synchronizers, undoubtedly, simplify the process of transmission gear shifting, but on a scale of auto racing synchronizers operate very slowly. Therefore, dogbox transmissions, which are mainly used in racing cars, do not have synchronizers. In addition, synchronizers have many small teeth, thus they would not last long under heavy loads which occur in auto sports.

Learn more about synchromesh unit

The main attraction of dogbox transmissions is very quick clutchless shifting. Instead of a large number of small teeth, which are engaged when the transmission gear is shifted in standard manual gearboxes, a dogbox gearset uses large "dogs" – square-shaped blocks on the end surface of the gear wheel and clutch (usually 5-7 dogs per wheel).

These dogs are much bigger and more durable than synchronizer teeth, allowing the dogbox to handle a higher horsepower engine. And to ensure the rapid gear shifting performance, dogs move into mesh with the width clearance. That's why you may hear clattering of metal elements in the Rally car during gear shifting— dogs of the gear wheel and clutch collide with each other.

Dogbox transmission explained in more detail

The “searching” (H-pattern) mechanism operates as a gear changing solutions applied in common manual gearboxes, only more seamlessly and without the clutch pedal depression: the driver only has to release a gas pedal a little and shift a gear. The clutch is only needed when starting from a standstill in first gear. This gear shifting mechanism is often called as an H-pattern, because of the path that the shift lever takes as it selects different gears. As switching of gears in transmissions with the H-pattern mechanism requires additional attention and dexterity, engineers of racing cars came up with more easy-to-use sequential gear shifting mechanism as an efficient alternative to the H-pattern.

H-pattern shifter

The sequential mechanism allows drivers to shift gears sequentially upshift or downshift (in other words the driver cannot omit the 3-rd gear and shift from the 2-nd to the 4-th gear). During racing competitions the sequential transmission is more convenient and much faster, but technically this solution is much more complicated. Since sequential transmissions gained popularity and recognition in the world of auto racing, we will review this technology in more detail.

Sequential shifting mechanism

Sequential transmissions

The main peculiarity of the sequential gearbox is strict order of gear shifting operations. Usually the shift lever is pulled back to upshift and pushed forwards to downshift. The need for such transmission occurred because H-pattern shifting mechanism turned out to be too complicated and time-consuming for racers at high speeds.

Sequential gear shifting in action

Sequential manual transmissions are true manual transmissions, and should not be confused with automatic transmissions that provide some degree of user shifting input (Tiptronic transmission). Lack of the clutch pedal in sequential gearboxes is compensated by installation of the electric control unit (ECU), which is responsible for the gear shifting process. Thanks to the hydraulic mechanism, gears are shifted as fast as possible and the process itself does not require 100% accuracy as in standard manual transmissions. In the process of driving the car with such gearbox the driver just has to estimate the road conditions and loads, which are imposed on the engine.

Principle of operation of a sequential gearbox

The ECU sends a signal to the gearbox, where special sensors are installed. These sensors receive the signal and transmit a new command (signal) to the progressive system (unit), which includes the information on the car speed. The progressive system (unit) is a special transmission component, which is responsible for adjustment of data on the engine operation. This unit receives signals (degree of the gas pedal depression, information from switched-on air conditioner etc.) from different sensors and on the basis of received information the progressive unit calculates and adjusts the speed rate.

The design of sequential transmission is based on application of straight-tooth gears. The usage of such gears is considered to be more rational when comparing with spiral (skew) gears applied in manual gearboxes. Straight-tooth gears have high efficiency rates, because they practically do not create friction during operation. However, these efficient gears have one drawback, namely, they transmit a smaller torque, so to compensate for this drawback, engineers apply gears of larger diameter. Another peculiarity of the sequential gearbox is the usage of a servo-hydraulic actuator.

Sequential gearbox in section

Engineers used gear ratios with low spread and a longer first gear to make the acceleration in sequential transmissions more efficient. In standard transmissions, on the contrary, the first gear is “short” taking into account possible driving under severe road conditions, and not for dynamic acceleration. The shift lever is designed as long as possible to bring it closer to the steering wheel – that allows the driver to additionally reduce the gear shifting time. The lever is equipped with the mechanical lock, which prevents accidental engagement of the N-gear or Reverse. Steering wheel shifting paddles help to save even more time. In Rally Racing due to rough driving, it is more convenient for pilots to pull and push the lever, then select gears as in standard manual transmissions. In addition, such kinematics of the lever allows saving several milliseconds at each shifting.

Sequential gearboxes are also used in nearly all modern motorcycles as it is too cumbersome to have a conventional H-pattern shifter and would take up too much space in the confines of a motorcycle frame. Having control over the gear shifter, typically with the rider's left foot, frees their hands to operate both the clutch and brake without letting go of the handlebars.

Informative video about sequential transmissions in motorcycles

Sequential transmissions are rarely applied in civil vehicles. The rapidity of transmission gears engagement in sequential gearboxes save some time, but at the same time produces high shock loads on transmission gears leading to their premature wear. For example, gear shifting on civil vehicles takes 0,6 of a second, while with sequential gearboxes shifting takes 0,2 of a second. To shift 5 gears sequential transmissions will beat a standard transmission by 2 seconds, and even more, because the engine’s RPM stays within the range of maximum power. For example, in drag racing 2 seconds is a huge advantage, because usually results in this type of racing depends on fractions of a second. But driving the car equipped with the sequential gearbox on urban roads may turn out to be a nightmare. For example, when drivers get stuck in the traffic jam or make a 90-degree turn, then we have to downshift from the 5-th to the 2-nd gear. In case with sequential transmissions we cannot act the same way: the driver has to downshift sequentially, by means of throttling, to the 4-th, 3-rd and then — to the second gear.

We’ve already analyzed the main peculiarities of sequential gearboxes, but let’s sum up all the advantages of using this type of transmission in auto racing:

• High speed of gear shifting operations is the main advantage of the gearbox based on the sequential mechanism. The process of shifting a gear in sequential transmissions takes only 150 milliseconds. The main reason for such high speed of operation lies in abovementioned design features: straight-toothed gear wheels and the servo drive based on hydraulics;
• Lack of any speed losses during the transmission gear shifting – gears are not only switched very rapidly, but this process does not affect the car dynamics;
• Quick gain of maximum number of RPM – sequential gearboxes better interact with the car engine due to the fact that the gear shifting process occurs in the optimal range of the engine RPM for the acceleration rate;
• The driver’s hand experiences no kicks or vibrations thanks to adjusted mechanisms of the sequential gearbox;
• Reduced fuel consumption, which is possible thanks to design peculiarities of the sequential gearbox.

Disadvantages of sequential transmissions are the following:

• High susceptibility to wear-out of transmission components due to frequent accelerations and aggressive driving style;
• These transmissions are very sensitive to operating conditions;
• High prices for sequential transmissions and their maintenance service;
• Sequential transmission spare parts and repair procedures for this type of transmissions will come at a high price.

Transmissions in Formula 1

Formula 1 (F1) racing cars have semi-automatic sequential transmissions, with FIA rules noting that eight forward gears (from 2014 season onwards) and one reverse gear must be applied, with rear-wheel drive. The gearbox is made of carbon titanium, as heat elimination is a crucial issue, and is mounted on the back of the engine. Fully automatic transmissions, and mechanisms such as launching control and anti-slipping devices, are prohibited, to keep pilot skill relevant in driving the car.

F1 transmission system

The F1 pilot starts shifting gears with the help of paddle-shifters located on the back of the steering wheel and the electro-hydraulic mechanism executes the actual shifting as well as throttle control. Clutch operating control is also carried out electro-hydraulically, except to and from a standstill, when the pilot operates the clutch with the help of a lever installed on the back-side of the steering wheel. Transmissions in modern F1 racing cars are capable of withstanding very high loads. For example, during the race in Monaco gears are shifted about 4000 times at a temperature of 140 degrees, and any transmission malfunctions may lead the car off the track, therefore engineers pay special attention to reliability of the transmission and hydraulic control system.

Learn about peculiarities of Mercedes F1 gearbox

Due to changes in requirements for F1 racing cars introduced in 2014, now engineers have to adjust car components, and transmissions in particular, to strict rules:

- New rules limit the minimum width and weight of gear wheels and determine the space at which their centers are located relative to each other;

- New rules clearly define basic dimensions of the transmission;

- Gear ratios are fixed for the whole season. Previously, F1 teams could select from 30 options of gear ratios, but now teams have only 8 gear ratios. However, engineers may replace gears or dog rings during the race in case of the damage. Gears must be made of steel;

- Each pilot may use only one transmission for 6 consecutive races. However, teams may use a new transmission earlier if the old one got out of order in the previous race;

- F1 teams cannot use automatic gearboxes or CVTs.

When shifting gears with the help of paddle-shifters, the F1 pilot closes a contact of the ECU (electronic control unit), then the electronics sends a signal to the hydraulic system with the response reaction, which prevents any power losses, and simultaneously switches off one gear and engages the next one.

The bottom two paddles control the clutch, the top two paddles are to shift gears up and down

Sequential transmissions in F1 races not only shift gears, transmit torque from the engine to wheels, but they also form the structure of the car rear elements. Performing the supporting frame function, F1 transmission must withstand the load received from the rear suspension and endure the pressure produced by the rear suspension and pressure from the downforce caused by the rear wing of the car. The F1 sequential transmission is an important part of the safety structure, because it acts as an “anchor” for the rear wheel safety cables. In addition, F1 transmission processes the energy received from the emergency attenuator.

But all the same, the main purpose of the sequential transmission in F1 races is changing the ratio of speeds between the powertrain and wheels. The hybrid propulsion systems currently applied in F1 are distinguished by their flexibility in transmission of the torque when comparing with engines of past generations (such as V10 and V8).

At first glance, new regulation rules, introduced in 2014, requiring the teams to use 8-speed sequential transmissions and fixed gear ratios may seem ridiculous, because F1 cars became less demanding on the number of gears. However, this measure turns out to be correct considering that gear ratios are selected once for the entire season. The 8-speed sequential transmission is equally good for slow and high-speed tracks and technical specialists of F1 teams don’t have to adjust the transmission specifically for each track. In addition, such transmission allows teams to significantly save fuel.

Principle of operation

The structure of the sequential F1 transmission includes two shafts, which are named as gear-shifting shafts. The first shaft operates with the even numbered gears (1,3,5,7), the second shaft interacts with remaining gears. The process of gear shifting is performed with the help of the transmission dogs. The first shaft engages one gear, while the 2-nd shaft prepares the next gear to be activated. A short moment, when two pairs of gear wheels are engaged simultaneously, occurs between phases of fuel combustion in cylinders by means changing gear wheels and locking rings. As soon as the next gear gets engaged, the previous gear gets free from the load; this helps to avoid the transmission damage. Any error or delay in this process may lead to the failure of the whole mechanism, and therefore the F1 teams have to ensure maximally accurate positioning of dogs on the shaft. The ECU also contributes to the gear shifting process: it “learns” by remembering the location of the gear wheel depending on the shaft rotation speed that also helps in accurate and rapid gear shifting.

Seamless gear shifting

Sequential shifting with high-precision control systems made it possible to shift gears very quickly. The seamless shifting allows changing gears without any interference in transmitting of the torque, which saves about 0.3 of a second after going round the lap in comparison with old types of transmissions. Shift time for F1 cars approximately equals to 0.05 seconds.

Materials and price

Among transmission manufacturers for F1 we should point out such well-known companies as Xtrac and Hewland Engineering. The transmission housing is made of carbon, but sometimes transmission parts are made of aluminum or titanium. The internal parts of the F1 sequential transmission are made of steel. These parts are of very high quality, because they are checked twice for any impurities. Bearings are made of ceramic materials, which should endure significant loads and high friction.

The F1 sequential transmission, which is exposed to a large number of races and high loads, are very expensive. The cost of development, assembly and maintenance may reach up to 4 million pounds per year. Spare F1 transmissions in the disassembled state cost about 150 thousand pounds per piece. Despite the fact that the price for the F1 sequential transmission seems quite expensive, today F1 teams spend less money for transmissions thanks to new regulations, which limit the number of gear ratios. Previously, 6-speed transmissions were assembled from 70 variants of gears before each race, which, in fact, cost money. This way of reducing costs was well accepted by F1 teams.

AN INSIGHT INTO F1 GEARBOX MANUFACTURER HEWLAND ENGINEERING

Drag Racing Transmissions

Drag racing, form of motor racing that emerged in the US and in which 2 competitors contend in speed from a standing position side-by-side on a drag strip—a flat, straight-line course. The standard distance of a race is 402 meters (or 1/4 mile). The National Hot Rod Association ( How a Top Fuel Dragster Works

NHRA) oversees the majority of drag racing events in North America. The next largest organization is the International Hot Rod Association (IHRA). Nearly all drag strips are associated with one sanctioning body or the other.

There are hundreds of classes in drag racing, each with different requirements and restrictions on things such as weight, engine size, body style, modifications, and many others. However, for professional drag racing engineers develop special cars, which are named as dragsters. There are 3 main classes of dragsters: Pro Stock, Funny Cars, and Top Fuel.

In drag racing, everything is subjected to one goal – achieving maximum acceleration at a distance of 402 meters. Therefore, in terms of design, drag racing cars have maximally light-weight structures with powerful engines. Control systems of dragsters, on the contrary, are often quite primitive, since competitions are held on an ideally straight track. In some categories the engine capacity of professional dragsters may reach up to 10-12.000 hp when the car weight amounts to less than 1 ton. Such cars cover the distance of 402 meters for 3,7-3,8 seconds and speeds up to 500-530 km/h, the acceleration up to 100 km/h takes 0,8 of a second.

So what about transmissions in drag racing? It is not so easy to find an appropriate transmission for drag racing, because control authorities (NHRA) apply different technical requirements for car components depending on the class in which the car competes. Let’s go through some points related to gearboxes in drag racing:

- All cars must be equipped with a reverse gear;

- A shield covering gearbox and reverser that corresponds to SFI Spec 4.1 is mandatory if engine burns nitromethane, methanol or is supercharged, or on any overdrive unit;

- Any non-OEM floor-mounted automatic gearbox shifter must have a spring loaded positive reverse lockout device to prevent the shifter from accidentally being put into reverse gear;

- Functional neutral safety switch is mandatory;

- All transmission lines must be metallic or high-pressure-type hose;

- It is allowed to use locking and self-locking differentials.

Inside Drag Racing transmission

It is interesting to point out that there is no common opinion on what is the best transmission solution for drag racing cars. Previously, drag racers gave preference to manual 2 or 4 speed gearboxes, because back then automatic gearboxes couldn’t handle the torque and horsepower of powerful engines. In addition, too much torque was lost in the torque converter.

Richmond 2-speed manual transmission for Drag Racing

Jerico 2-speed transmission

These days some racers remain faithful to manual gearboxes like Richmond or Jerico, but the development of new automatic transmission solutions gain more and more popularity, because new automatic gearboxes are compatible with powerful engines and provide additional gear ratios.

SuperGlide 4 transmission

TH400 Drag Racing transmission

Drag racers require reliable, lightweight, and efficient automatic gearboxes. The Powerglide and TH400 automatic transmissions, manufactured by ATI, have established themselves as perfect examples of endurance and reliability in competitive drag racing. Moreover, modern automatic transmissions for drag racing are equipped with lockup converters, which ensure that less of the engine’s torque at lower RPM is lost to converter slippage.

However, admirers of manual transmissions claim that automatic gearboxes, even with installed lockup converters, have multiple points where transmission slipping and torque losses can be introduced. Another argument against automatic transmissions is that these gearboxes have more failure probabilities. Furthermore, manufacturers of manual transmissions put a great deal of effort to upgrade the gear shifting mechanism. For example, B&M company solved this issue with the type of gear shifter that requires only to push or pull the lever to shift gears. Therefore, such manual solutions as G-101 or Jerico 5-speed racing transmissions continue to be relevant in the world of drag racing.

G-101 Drag Racing transmission

Jerico 5-Speed Drag transmission

Drag racing cars may be equipped with a transbrake. The transbrake is a mechanism that selectively places the transmission in 1-st and reverse gears at the same time, efficiently holding the car immovable as if the pedal brake was employed. This unit is used on automatic gearboxes equipped with a torque converter, where it is useful to accumulate hydraulic pressure before the car starts moving.

Drag racing cars may be equipped with a transbrake. The transbrake is a mechanism that selectively places the transmission in 1-st and reverse gears at the same time, efficiently holding the car immovable as if the pedal brake was employed. This unit is used on automatic gearboxes equipped with a torque converter, where it is useful to accumulate hydraulic pressure before the car starts moving.

More info on transbrake mechanism

The transmission selection for drag racing is determined by the engine power output. If the engine puts out less than 500 hp, then drag racing teams usually prefer to consider such companies as ATI, TCI, Mcleod, Richmond, B&M, which are famous in the world of drag racing for their high-quality products. But when the car has more powerful, engine drag racing teams prefer transmission solutions manufactured by Lenco, G-Force, Richmond Performance, or Jerico Racing Transmissions.

It is worth mentioning that in some popular drag racing classes such as “Top Fuel”, “Funny Car”, “Top Alcohol Dragster” cars do not have transmissions – the engine power is transmitted by means of clutches. In addition, drag racing teams, in contrast to Formula 1 and Rally, almost do not use sequential transmissions.

How a Top Fuel Dragster Works

All in all, it should be mentioned that the auto racing became an inseparable part of the auto industry. Major manufacturers of cars and car components invest significant financial resources in development of new technologies for racing cars and promotion of teams. Sequential gearboxes can be rightly called the result of a long evolution of sports transmissions, which combines advantages of manual and automatic gearboxes. This type of transmission reduces fuel consumption and ensures excellent acceleration performance. But we should not disregard the potential of manual and automatic transmissions in motor racing, which, for example, gets materialized in Drag Racing in the form of the most unusual transmission solutions.