One of the jobs we tackled this week was changing the gearing ratio in an off-road jeep. I figured now would be a good time to write up a blog on the subject.
First of all, why would anyone want to change the gear ratio in their vehicle? Depending on what your goal is, whether it be faster acceleration, a higher top speed or a creeper gear for off-roading, a simple gear change can give you the edge your looking for.
In our application the customer was looking for a higher numerical gear ratio in order to provide his vehicle with a slower 1st gear. He had already done the research himself and figured instead of the stock 4.10 gears he wanted 4.88s. This changes the speed in which he can travel in 1st gear within a given RPM range. For example if he were to travel at 1500 RPMs he may be cruising @ 5 MPH. Now with the gear change in place @ the same RPM he would be looking @ more like 3 MPH.
Another application where this type of gear change would be desired would be drag racing. Although slow speeds are not the point of this type of racing the gearing is. Getting from point A to B as fast as possible is greatly attributed to the gearing. When you increase the numerical gear ratio it allows the car to accelerate at a faster pace without adding any horsepower by putting the motor in a more desirable RPM range. but will not allow a high top speed. I'll explain this more in a future blog.
If you'r looking to run high MPH with these types of gears you may end up running out of gear at 95 MPH which will not suffice, depending on the motor's capabilities. This is when going to a lower numerical gear would better suit the situation. Racing at Bonneville to see who can get the higher top speed would need gear ratios more like 2.18 or 2.50s or for some of the streamlines like in the picture will use 1.90 or 1.50s. Choosing these types of gears will get you well above 200 MPH but your acceleration will suffer.
For what ever application you'r looking for just keep in mind what you'r trying to accomplish and choose your gears wisely.