Home The Long Haul Blog Truck Spec'ing: Decisions To Make When Purchasing A New Truck

Truck Spec'ing: Decisions to Make When Purchasing a New Truck

March 28, 2024 Truck Sales Author: Rush Truck Centers Read Time: 8.5 Min

Determining configurations and specs when purchasing a new truck can be a challenge. Each choice can have an impact on another, and spec’ing the right or wrong types of equipment can have a significant impact on the operation of the vehicle.

While the thousands of possible truck configurations and choices can seem overwhelming, a trusted truck dealer can help you navigate your options and tailor a vehicle solution for your specific job or business needs. We identified the top things to consider before buying a new vehicle as well as some of the top decisions you will need to make when choosing its components.

Things to Consider Before Spec’ing Your Truck

Before you start down the path of spec’ing a new truck, you should first make sure you’re armed with key answers about what you ultimately need the truck to do and how it should perform.

  • Application: The biggest deciding factor that should guide many of your component selections is the application the truck is intended for. You should design a truck to accommodate your operational requirements, not modify your business operations to the truck you purchase.
  • Driver and Technician Needs: Speak with the drivers or technicians who will drive and work on the truck on a day-to-day basis. This can help you discover what is truly needed to satisfy your operational requirements and give you insight into any configuration issues present on the current trucks you own.
  • Payload: The payload the truck will be expected to carry will determine the engine, transmission, tire size and many other components you’ll need to spec. It’s crucial to ensure the gross vehicle weight rating (GVWR) and gross combined weight rating (GCWR) of your truck can satisfy your payload requirements and any trailers you may tow. Also, determine if the truck will operate fully loaded or with a diminishing load throughout the day.
  • Operating Conditions: Where will the truck be driven? Will you mostly drive it on flat, dry terrain? Or is the terrain hilly and mountainous? Take the weather into consideration and whether the truck will be required to drive in rainy, icy or extreme conditions.
  • Performance Requirements: How do you need your truck to perform? Be prepared to answer questions about your fuel efficiency goals, desired cruising speed, startability, high gear gradeability and more.

Selecting the Truck Engine

Prior to spec’ing the engine for your truck, you should first answer four questions: What do you plan to do with the truck? How much weight are you planning to pull? What are your fuel economy goals? And how fast do you need to go? Once you have the answers to these questions, a truck dealer can help you match your requirements to the right engine spec.

Anticipated life cycle, annual mileage, vehicle weight and the typical terrain of your routes should all be factored in when spec’ing your powertrain. Torque, horsepower and how much power is needed for your specific application should be prime considerations, but the engine size also plays a key role. Engines today are typically available with 11L, 12L, 13L, 15L and 16L displacements, and there are many trade-offs between efficiency and performance. In general, the bigger the engine displacement volume, the more air that can be pushed into the cylinders and the more power that can be generated. However, as displacement increases, fuel efficiency is likely to drop.

If you’re interested in alternative fuel options, there are natural gas, propane and electric options to consider. Many natural gas engines can provide equivalent performance to their diesel-powered counterparts while offering significant reductions in greenhouse gas emissions.   

At the end of the day, your engine needs to be able to do the job you need it to do with relative ease. If not, higher fuel consumption, higher potential engine wear and other negative impacts can occur.

Transmission Options

Spec’ing the correct transmission for your vehicle and its application can equate to fuel savings, reduced maintenance needs and less driver fatigue.

When selecting a transmission, you will have a choice between a manual, automated manual or automatic transmission. Manual transmissions have historically been preferred for their low acquisition cost, simplicity and the control they provide in technically challenging applications, but they require drivers who are skilled in manual shifting. Automated manual and automatic transmissions come with a higher price tag but can provide cost savings in the long run with their fuel economy, consistent performance, and reliability across duty cycles and driver skill levels. Fully integrated automated manual transmissions, like the International T14 automated transmission, are quickly becoming more commonplace in the marketplace thanks to their fuel efficiency and ability to reduce maintenance costs by limiting overspeeding, wheel spinout, manual shifting errors, over-torque and clutch damage.

Selecting a direct drive transmission vs. an overdrive transmission can also have an impact on fuel efficiency, but the choice will ultimately come down to your application as well as typical payload, routes and vehicle speed. Generally speaking, a direct drive transmission will provide the greatest efficiencies in on-highway applications on relatively flat surfaces. Overdrive transmissions are often the better fit for higher speeds, varied terrain, off-road requirements and heavier axles.

Identify the Correct Axle Ratio

The axle ratio defines the number of revolutions your engine’s drive shaft or output shaft must make to rotate the axle one time. Higher ratios allow more torque to reach the wheels and allow maximum towing and payloads on hilly terrain. However, since the engine needs to work more quickly to move the wheels, higher ratios tend to equate to lower top speeds and lower fuel economy. Inversely, lower axle ratios provide the ability to drive at higher speeds consistently while saving fuel but are best for flat terrain and lighter loads. Mid-range axle ratios can provide the best of both worlds and are ideal for fleets and trucks that require flexibility for operating on varied terrain with moderate towing and payloads.

To find the right axle ratio for your truck’s application, you should consider the following:

  • The target top-end speed
  • The typical terrain the truck will drive on
  • How the truck’s load will vary in weight throughout the day
  • The size and weight of any trailers being pulled and how often a trailer will be hooked up
  • How often the truck will operate off-road and on what kind of terrain

A knowledgeable dealer can help you spec the correct axle ratio to allow your truck to operate predominately in optimal operating conditions. Original equipment manufacturers (OEMs) also have software that can assist in calculating the ideal axle ratio for your application.

Drive Axle Configuration Options

A 6x4 drive axle configuration in which both rear tandem axles receive power has long been the standard. However, more and more fleets and truck drivers are making the switch to a 6x2 axle configuration in which only one of the rear axles receives power and the other is a “tag” axle designed to only bear weight. What’s the benefit of a 6x2 configuration over a 6x4? Up to a 2.5% reduction in fuel consumption and weight savings of up to 400 lbs., according to the North American Council for Freight Efficiency.

The tandem drive axles on a 6x4 configuration offer the torque, traction and handling that drivers need to accomplish even the toughest jobs. While spec’ing a 6x2 configuration results in less traction and torque, the lack of internal gearing on the tag axle offers weight savings that make it possible to pull heavier loads and means less maintenance is required, saving you time and money.

Trucks needing to go off-road or operate in icy, snowy, rainy or hilly environments will benefit from the extra traction and peace of mind provided by a 6x4 drive axle configuration. A 6x2 configuration may be more well-suited for over-the-road or long-haul applications in which the driver is mainly driving on flat, dry roads. There’s no right or wrong answer when it comes to your axle configuration, but spec’ing the right one will come down to your application, typical driving surfaces, weather conditions, fuel efficiency goals, payload and driver preference.

Selecting Drum Brakes or Air Disc Brakes

When selecting brakes for your vehicle, you’ll need to decide between drum brakes and air disc brakes. Drum brakes are durable and cheaper upfront and have been the standard in the commercial trucking industry for decades. But they are known to overheat in situations that require frequent breaking, leading to brake fade and higher replacement costs. Air disc brakes, on the other hand, have a higher upfront cost but are less likely to experience brake fade, offer shorter stopping distances and are easier to service.

The best brakes for your truck will ultimately depend on how you plan to use it. If you’re planning to use the truck for vocational applications that require higher mileage and frequent braking, or if your typical routes will force the truck to navigate steep declines or mountainous areas, air disc brakes are most likely the best option. Drum brakes are a good choice for lower mileage, less harsh environments and even long-haul trucking applications in which stops are less frequent. Driving habits, brake duty cycle, operating conditions, compliance and stopping distance are also variables that must be taken into consideration when deciding which brakes to spec for your truck.

Learn more about the differences between drum brakes and air disc brakes here.

Tire Choices

When investing in a set of tires, it’s recommended to do your research on the best tire model and tread design for your vehicle and its intended application. You should also consider tire load rating when choosing your specs to make sure the tires you select meet the axle weight rating of your vehicle. A tire’s load rating will directly impact the vehicle payload capacity and will vary depending on the size of the tire, construction, application and inflation pressure.

As you weigh your options, look into the estimated lifetime mileage, rolling resistance, weight requirements, warranty and retreadability of the tires you’re considering.

Electrical System Optimization

OEMs design the charging and starting systems on their vehicles for general use. This means that the batteries and alternators that come standard aren’t built to support things such as supplemental equipment with added power demands, extreme weather that results in above-average heating and cooling needs, and high stop-and-start duty cycles.

Under-spec’d batteries and alternators can cause starting problems, cause voltage spikes that damage electrical components or lead to premature battery failure. Increasing the number of batteries in your vehicle, increasing battery capacity, spec’ing larger, higher amperage alternators, purchasing solar panels, installing external chargers or adding DC converters are all possible solutions to help you account for added electrical demands.

Air System Capacity

Air dryers are installed between the air compressor and reservoir on commercial trucks and are designed to collect and filter out water, oil vapor and other contaminants before they reach the air brake system. As with electrical systems, OEMs typically design their standard air system for average usage. While the standard air dryer may work just fine for most applications when properly maintained, a mis-spec’d air system can allow contaminants to enter air components on the vehicle and jeopardize efficient operation.

Applications that involve frequent braking, liftable axles, air-ride suspensions, multiple trailers or high drop and hook activity may require higher-than-average air component usage. For these applications, spec’ing an air dryer with added capacity, extended purge capabilities or coalescing filters can provide benefits that have a significant impact on the life of brakes, transmission and other air components. A knowledgeable truck dealer can assist in selecting the right air dryer for your application.

Let Rush Truck Centers Help You Spec Your Next Truck

The knowledgeable truck sales experts at Rush Truck Centers are ready to help you spec the right truck for your business needs. We’re proud to represent industry-leading commercial truck brands such as Peterbilt, International, Ford, Hino, Isuzu and Dennis Eagle, and we have a large inventory of new trucks in a wide range of makes and models, specifications and applications.

Search our inventory or contact us today to inquire about spec’ing the perfect truck for your application.

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