What Is a Gear Ratio?

Video Transcript

"What is a gear ratio? A gear ratio is a generic term that's used to describe the relationship between a drive gear and the gear that it is driving. In an automotive application this could be the gears in the differential, gears in the transmission, or any other gears that transfer energy from one component to another. When you talk about gear ratios, you are typically talking about the drive gear in a fraction over the driven gear so if the gear ratio is a three fifty gear ratio, that means that for every one revolution of the drive gear, the driven gear turns 3.5 times. The higher the number, the lower the gear ratio. So in other words a four eleven gear ratio for every one time that the gear turns, the driven gear turns 4.11 times, whereas a 2 gear ratio for every one time the drive gear turns, the driven gear turns two times. Now there are many gear ratios in a vehicle to consider. The transmission has several sets of gear ratio that allow you to go slowly or quickly depending on traffic and road conditions. There's also a final drive ratio which is the differential ratio. And changing any of these ratios will affect the performance of the vehicle and the fuel economy of the vehicle. Generally speaking, going with a higher numerical and hence lower gear ratio will allow for quicker acceleration, but will result in poorer fuel economy and a slower top speed, whereas a higher gear ratio, numerically lower, will generally impact your acceleration, causing the vehicle to accelerate slower, but will give you better fuel economy and a higher top speed."