Here is the first article that I was able to get published...17 years ago. Gear ratios...their effect on performance and fuel consumption By Sandman Kelley Have you ever been hanging out at your local parts store or wherever you might happen to be and heard people talking in a strange language? A language that sounds something like English but doesnt really make any sense. It might sound something like this Well I have a 4.11 rear with a 2.48 first gear. For lack of a better term this is known as the dialect of the gearhead. Gear ratios and their effect can be a tricky subject to say the least. However...a basic understanding of the way in which they function isnt as difficult as it may sound. The best place to start would be with the gear itself. A gear is a device that uses the laws of leverage to move an object that under normal circumstances could not be moved with the power source being used. As an example...let us say that we have a power source that can lift the weight of one thousand pounds the distance of one foot in one minute. As a hypothetical problem lets imagine that with the same power source we have to lift two thousand pounds the same distance. What do we do...the answer is simple...we use a gearset. To make things simple we will use an even ratio. If we equip our hypothetical power source with a gear reduction of 2.00:1 we are now employing the laws of leverage. We can now lift the heavier load the same distance without the need for additional power. However...now it will require two minutes instead of one. This is because of our gear reduction. You may have noticed this effect the last time that you saw a tractor trailer laboring up a long hill or mountain. The principal is still the same. This may seem hard to believe but given the proper gear reduction and enough time a lawn mower engine could pull a house from its foundation. The realm of possibilties are nearly endless. The gears inside an automobiles transmission and drive axle work in the same manner. When dealing with gear ratios there are three different types that you need to remember. The first of which...reduction...is the most common. When a gear set with a reduction ratio is being used the output shaft of the trasnsmission will spin at a slower speed than the engine. This provides power for acceleration...traveling up inclines and towing. The second type of gear ratio is known as direct drive. This is when the output shaft of the transmission and the engine are both rotating at the same speed. Direct drive was usually high gear in most older automobiles and a few new ones as well. This ratio provides no reduction and was most often used as a highway or cruising gear. The third type of gear ratio is known as an overdrive. This has become very popular in automobiles within the last fifteen years. It provides low engine speeds and increased fuel economy. An overdrive gearset allows the output shaft of the transmission to actually spin faster than the engine. Gear reduction and power transfer takes place in two stages along a vehicles drivetrain. The first of which is the transmission. This is known as primary reduction or primary gearing. Depending on whether or not the gearset being used has reduction properties to it or not. The second and final point of gear reduction takes place in the vehicles drive axle. This is known as the final drive. We have talked about primary gear reduction and final gear reduction. The last point that we need to cover is overall gear reduction. This is the reduction that is produced from the combined efforts of the transmission working in conjunction with the final drive gearing. If we have a primary first gear reduction of 2.50:1 and a final drive gear reduction of 3.50:1 then we have an overall gear reduction of 8.75:1. What that means is that for every time our drive wheels turn once...our engine has to turn eight and three quarter times. You can figure out what your overall gear reduction is by multiplying your primary gear ratio by your final drive gear ratio. If this were a direct drive transmission our overall gear reduction in high gear would be the same as our final drive ratio. That means that even in high gear our engine still has to turn three and a half times for every time our drive wheels turn once. This is why many automobiles have high gearing in their drive axle. Remember...the more times that an engine has to turn...the more fuel that it will consume. Even though that low gear reduction supplies power and acceleration in your lower primary gears it is still doing what it was designed for once youve reached your high gear and we end up paying for it in the form of poor gas mileage. However...there is a way to rob Peter without having to pay Paul. The answer is overdrive. Lets take another look at our hypothetical transmission and give it an extra gear...an overdrive~! A common overdrive gear ratio used today is 0.70:1. Once we shift into this gearset our engine no longer has to spin three and a half times for everytime our drive wheels turn once. It will now only have to turn less than two and a half times...(2.45:1). Thats a considerable difference. Through the use of an overdrive gear it is possible to retain a low finaldrive axle with its power and acceleration while still being able to enjoy all of the benefits of low engine speed on the highway. This can be very useful for multi-purpose vehicles such as pickup trucks and vans. This also allows for reduced engine emmissions. In closing...remember that your engine may be your power source but your gears make the work efficient.
Posted on: Sun, 23 Nov 2014 10:52:00 +0000