Modulus is an important parameter of gear. When selecting automobile gear modulus, factors such as strength, noise, lightweight and processing technology should be considered. Table 1 shows the range of common modulus and diameter process parameters of gears for passenger cars and commercial vehicles.
| Gear type | Passenger car Shaft gear | Passenger car Discoid gear | Commercial vehicle Shaft gear | Passenger car Discoid gear |
| Modulus | 1.25-5 | 1.25-4 | 3-5 | 2.5-5.5 |
| Diameter / mm | 30-120 | 50-200 | 60-150 | 80-250 |
In the process of transmitting torque and changing speed, automobile gears are usually in the working environment of high speed, high load, alternating impact load and so on. Automotive gear materials not only need good machinability and heat treatment carburizing and quenching performance, but also must meet the reasonable cost demand. In order to ensure the stability of quenching depth of tooth surface and tooth top, carburized alloy steel with carbon mass fraction of about 0.2% and adding Ni, Cr, Mn, Mo and other alloy elements alone or in combination is usually selected.
| Types of materials | C | Si | Mn | P | S | Cu | Ni | Cr | Mo | Ti |
| 20CrMnTi (China) | 0.17-0.23 | 0.17-0.37 | 0.80-1.10 | ≤ 0.035 | ≤0.035 | ≤ 0.030 | ≤0.030 | 1.00–1.30 | – | 0.04–0.10 |
| 20MnCrS (Chinese imitation) | 0.17-0.22 | ≤0.25 | 1.10-1.50 | ≤ 0.025 | 0.02–0.04 | 0.01 | 0.03 | 1.00–1.30 | – | – |
| 20MnCrS (German) | 0.17-0.22 | ≤0.04 | 1.1-1.4 | ≤ 0.025 | 0.02–0.04 | 0.01 | 0.03 | 1.00–1.30 | – | – |
| 20CrMoH (Japan) | 0.20 | 0.25 | 0.73 | 0.030 | 0.030 | 0.01 | 0.03 | 1.05 | 0.20 | – |
| Steel A | 0.17 | 0.07 | 0.87 | 0.060 | 0.012 | 0.01 | 0.03 | 0.95 | 0.39 | – |
| Steel B | 0.19 | 0.50 | 0.31 | 0.006 | 0.018 | 0.01 | 0.03 | 2.11 | 0.41 | – |
| Steel C | 0.18 | 0.72 | 0.30 | 0.006 | 0.018 | 0.01 | 0.03 | 1.43 | 0.44 | – |
Japan and Germany have conducted long-term research and development in the field of automotive high-strength gear low-carbon alloy steel materials. Table 2 shows the composition of common automotive gear materials. At present, the automotive gear steels at home and abroad are mainly 20CrMnTi (domestic), 20mncrs (German system) and 20CrMoH (Japanese system), and the steels a, B and C in the table are high fatigue steels.