How Gear Ratios Define the “Character” of Your Car

Having a clear understanding of the term gear ratio and the impact of this parameter on speed, acceleration dynamics and fuel efficiency allows you to choose the optimal driving mode. This parameter is extremely important for any car, regardless of its price and year of production. Frequently, unexperienced auto enthusiasts pay little attention to gear ratios when buying a new or used car, but a competent analysis of technical car parameters (including gear ratios) turns out to be a key to the successful car choice. In this article, we will consider how gear ratios can affect performance potential of a car.

Highest gear

First of all, when looking for a car, it is recommended to pay attention to the gear ratio of the highest gear. This relevant parameter specifies the maximum RPM rate at cruising speed, which has a direct impact on the fuel economy and noise intensity. To put it shortly, a taller gear ratio ensures lower fuel consumption and less noisy operation, but at the same time, it will be necessary to downshift to achieve better acceleration dynamics (for example, when it is necessary to overtake other cars). The optimal RPM rate when driving at cruising speeds is approximately 1600-2000 for diesel-powered and 2000-2500 RPM for petrol-driven cars.

For instance, the transmission unit in the GT86 has 6 gears with quite close gear ratios, to accelerate up to 100 km/h (70 mph) the engine has to operate at 3000 RPM. This is the reason for the significant amount of harmful emissions equal to 181 g / km. This is too much for a car equipped with a two-liter engine producing 200 hp and good aerodynamics. Moreover, such a setup will lead to increased noise intensity during the operation (especially in case with significant mileage), and it will be a significant drawback if you decide to sell this car. This can hardly occur in cars that come with automatic transmissions, which have taller gear ratios, but many admirers of classic sports cars are extremely wary of automatic transmissions in performance cars.

It should be remembered that the more powerful engine is installed in your car, the lesser RPM rate is produced by the engine at cruise speed, and the less noise you hear when driving. For instance, the Golf Mk6 1.6 TDI equipped with a 5-speed manual transmission cruises at 2300 RPM, while for more powerful SEAT Ateca 2.0 TDI that comes with a 7-speed DCT transmission this parameter is approximately 1700 RPM. That is why in some modes of operation cars with more powerful 6-cylider engines consume a bit more fuel than cars with 4-cylinder engines.

Learn more about how car gearing works

“Short” gears, determining the need for frequent shifts, are considered to be the key to aggressive driving. This means that the more intense the speed-up, the lower the maximum speed that a car can pick up at one gear. “Short” gears improve acceleration characteristics and make the car more performance-oriented, but at the same time badly affect top speed and fuel economy (it can be solved by using a transmission with more gears).

However, there are some exceptions to this rule, as the most powerful cars do not need low gear ratios in several first gears – their traction is quite enough to ensure intensive acceleration and not to bother the driver with the necessity of frequent gear changes. For instance, the Dodge Challenger Hellcat can reach the speed of 101.3 km/h (63 mph) in 1-st gear without any additional shifting. But the most vivid instance of non-aggressive gearing is the Koenigsegg Regera, which reaches 402 km/h (250 mph) in 1-st gear. It is not about setting a speed record, but rather a reasonable engineering approach and bearing in mind the engine potential and adhesion to the road surface. In other words, if such performance car is equipped with a transmission with shorter gears, then there will not be any benefits in terms of dynamics, as the process of gear shifting will require more time; excessive traction and torque will simply lead to slipping of the wheels.

Koenigsegg Regera

It is also worth noting that with a large number of gears, engineers will have to do a lot of work to keep the engine operating with the RPM rate, allowing achieving maximum power and torque, when shifting gears. At the same time, it will significantly complicate the design. It has long been proven the acceleration up to 300 km/h in sports cars is fully ensured by the thrust of powerful engines –lower gear ratios are simply unnecessary.

When it comes to civil vehicles (road cars) intended for everyday use, first gears in transmissions for these cars are quite short (with low gear ratios), allowing the car equipped with less powerful engine to move confidently on loose surfaces and to accelerate under heavy loads. It is also important to consider such parameters as gross vehicle weight (GVW) and its running weight, as the difference between these values determines the actual vehicle capacity, or load capacity, and the higher the capacity, the shorter the first gears should be.

Close and Wide Gear Ratios

The gap between gear ratios also plays an important role in determining the “character” of any vehicle. Closer ratios ensure the maximum acceleration that can be achieved. In addition, if the fuel efficiency is considered to be a priority, close gear ratios allow keeping the RPM rate in an optimal zone, facilitating to enhancement of the engine service life. At the same time, close gear ratio has one significant drawback, as it makes the highest gear too short or makes the 1-st gear too long, and both variants are undesirable. There are two solutions for this problem: either increase the number of gears (at the same time raising the cost of design) or use wider ratio.

The choice of the solution is determined by the type of car being designed. For performance-oriented cars engineers usually resort to closer gear ratios implemented in the gearbox design. If the car comes with the engine having wider powerbands, then closer gear ratios are simply unnecessary. In such cases, engineers go with wider ratios.

At the same time, it should be noted that closer gear ratios do not always ensure better performance characteristics. For instance, if we get away from the automotive world and consider a sports bicycle, then will see that, as a rule, it has 8 gears with close gear ratios, thereby allowing the most rational use of the bicycle’s operating capacity. However, when using such design solution, it will be necessary to shift gears very intensively in the interval from 1-st to 5-th gear to ensure maximum acceleration. The same idea applies to cars. The necessity to shift gears very frequently, as a rule, makes the engine to operate in non-optimal mode, especially if an inexperienced driver is behind the wheel.

All these shortcomings are eliminated in so called stepless types of transmissions (better known as CVTs), which smoothly change gear ratios, depending on the selected driving mode. But CVTs also have some soft spots, therefore it can be said that so far automotive engineers haven’t managed to design an ideal mechanism capable of transmitting high amounts of torque and quickly adjusting to accelerating dynamics of sports models.

Final drive change

If you want to make the most of your car’s dynamics characteristics, the most efficient solution here is to change a final-drive. This procedure implies installing a new diff with an alternative internal gear ratio. A lower number presupposes longer gears and a higher number means shorter gears. It doesn’t mean that you’ll be able to determine how close or wide the gear ratios are, but it will allow you to change all your gears by the same amount that is best suited for you.

But this method cannot be considered as a panacea for all woes, as it is possible to change the abovementioned parameter only in a very short range of values, otherwise it will do more harm than good. It should be remembered that if you decide to do this trick, it will be necessary to adjust the speedometer, otherwise its values won’t show a real car speed because of the new ratio.

Learn more about final drive and its role in your car

This type of tuning can be implemented without too much difficulty in FWD and RWD cars, but in some FWD and AWD cars this procedure is simply impossible. Many cars come with gearboxes, which have a built-in differential, thereby making it quite problematic for DIY- car owners to change the final drive. In addition, some cars (for instance, Audi R8) have different final drive ratios in front and rear drives.

But sadly, more and more manufacturers chose to use integrated units, therefore to improve performance capacity of your car without causing any damages you’ll have to visit a professional tuning shop and pay huge amounts of money.