2-1/2 tachometer

• 2022-04-28

Our company sell the size of 52mm(2") tachometer, also have 85mm(3-3/8") and 60mm tachometer. The tachometer is related to the speed of engine of RPM.

The engine speed is one revolution of the crankshaft. The engine speed is 1 revolution, that is, 1 rpm. The speed of the vehicle is calculated in minutes, that is, the speed of the general gasoline vehicle is 5000-6000rpm / min, and that of the diesel vehicle is 3000-4000rpm / min. To accurately calculate the relationship between engine speed and vehicle speed, we first need to know the tire specification, and then we need to know the transmission ratio of each gear of the transmission (including the final transmission ratio) Tire specification: tire width / aspect ratio R hub diameter. For example, for a 195 / 55r15 tire, its width is 195mm, the aspect ratio is 0.55, and the hub diameter is 15 inches (inches). Vehicle speed (km / h) = [tire width (mm) × (aspect ratio / 100) × 2 + hub diameter (inch) × 25.4] × three point one four one five nine × 60 / 1000000 / final transmission ratio / transmission ratio of corresponding gear × Engine speed (RPM). Of which:" × "60" refers to converting the engine speed per minute (RPM) to the speed per hour (RPH), "/ 1000000" refers to converting the tire circumference in millimeters (mm) to kilometers (km). In the above formula, for a specific vehicle, the tire specification and final transmission ratio are fixed parameters, and for a certain gear, the transmission ratio is also fixed. Therefore, as long as the gear and engine speed are known, the corresponding vehicle speed can be obtained.

Some are electronic. The engine speed is transmitted to the computer through the crankshaft position sensor, and the signal is sent to the instrument through the detection of the computer.

The relationship between engine speed and vehicle speed is directly related to the transmission gear (transmission ratio), differential (differential ratio) and tire radius. If the engine speed is 3000 rpm. The transaxle speed ratio is 0.694 for 4th gear. The final drive ratio is 3.789. The tire is 215 / 55r17. The calculated tire speed is 3000 ÷ 0.694 ÷ 3.789 ≈ 1140 rpm. The circumference of the tire (215x0.55) x2 + 17x25 4 ≈ 2098mm. The vehicle speed is 2391.7m/min, which is also equal to 2391.7x60m/h = 143.5km/h. Considering the wind resistance. Road surface and other factors, the actual speedometer display will be lower than the above results.