About a year ago, I realized we were going to need to invest in a new family vehicle. The car that we had was dying fast, and I was worried about my wife getting to and from all of the places that she needed to travel. We started looking around for different places to shop, and I found an auto dealer that was absolutely incredible. I worked with them to negotiate a fair price for the car, and I learned a few tricks along the way. This blog is all about negotiating effectively with an automotive dealer, so that you don't end up with buyer's remorse.
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It does not matter if you are buying your first used truck, or an additional truck for your fleet, you can spend a lot of time choosing the truck you want. Although you may go on the lot looking for a specific name brand, there are several other things you need to consider prior to signing on the dotted line. One of these is your axle, or differential gear ratio.
What Is Axle Ratio/Differential Gear Ratio?
Your differential gear ratio is the number of times that your drive shaft, will turn in comparison to each one time your wheels turn. Unlike your light-duty pickup truck, where you may have only been offered the standard axle ratio, or one or two additional options, a semi-truck will often offer you a dozen or so options to choose from.
Your axle ratio directly impacts your truck's performance. It will affect the following:
To first be able to choose the correct ratio, you must understand the numbers you are considering.
For example: If you see a truck listed with a 3.55:1, this means your drive shaft is turning 3.55 times every time your wheels make one complete rotation.
This number is determined by dividing two numbers. The formula is:
The number of teeth found on the ring gear/ by the number of teeth on the pinion gear = gear ratio
One of the main things that you want to remember when you are looking at this number is the higher numbers represent the lower ratios. A 4.10 will be at a lower ratio than a 3:55. The higher numbers mean your drive shaft and your engine turns more every time your wheels turn giving you more power and torque on your wheels. You also need to remember that the size of the tire and wheel equipment will also affect your ratio, as well as your fuel economy.
Because your engine is working harder, this will have a direct impact on your top-end speed and your fuel economy. The additional power and torque you will gain from these lower ratios will come in handy when you are pulling heavy loads, operating in hilly areas, or working off-road.
The opposite is also true. You may want to consider a lower number, or a higher ratio if the majority of your driving will be freeway driving at lower RPM's. This means that your engine will not have to work as hard to get your truck to where it has to be. This will result in faster speeds and better fuel economy.
How Do You Choose The Right Ratio?
To choose the right ratio, you must first consider how, where, and what type of performance you are expecting when using your truck. To begin to do this, consider the following:
Speed/RPM - This is not just the maximum speed you want your truck to be able to run, but your RPM (revolutions per minute) your truck will be at your top speed. You will be happier in the long run if your truck is able to predominately be able to operate in its optimal operating range.
You can calculate your approximate RPMs based on your tire size, gear ratios, transmission type and MPH. By playing around with these calculators, you will get a feel for the right combinations that will deliver the performance you are looking for. It is recommended that for a diesel engine, you keep your RPMs between 1600 - 2800 while you are running at highway speeds.
Load - Will your loads be constant, increasing, or diminishing? If your loads will be constant, you may not want to be as concerned with your maximum road speed availability and focus on the gear ratio that is going to provide you with the best torque and fuel economy under these conditions.
If your load is diminishing, you will not necessarily need the maximum torque and pull throughout the day. You may want to choose a ratio that will allow for slightly faster gearing. This will give you access to better speeds as the day goes on.
If your load is increasing, you will want to choose a ratio that will give you the ability to have the most torque and pull capabilities throughout the day. This will allow your truck to continue to perform in optimal range even as the load it is carrying gets heavier.
These are just a few of the things that may determine the axle ratio that you choose. There are many others that may be important to your specific business such as towing capabilities, anticipated terrain, aerodynamics, and more. Choosing the right differential axle ratio will make a difference when you are choosing your next truck from a place like Arrow Truck Sales. It could determine how pleased you are with your selection.
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