2025 International LT Transmission & Axle Gear Ratios

The 2025 International LT is a flagship Class 8 aerodynamic tractor designed primarily for long-haul and regional-haul operations. Selecting the correct powertrain configuration—specifically the transmission and axle gear ratios—is critical to optimizing a fleet's total cost of ownership. Whether you are aiming for maximum fuel efficiency through engine downspeeding or need the startability to pull heavy loads over mountainous terrain, the International S13 Integrated Powertrain, alongside Cummins/Eaton combinations, offers a variety of gearing setups.

Below is a comprehensive guide to the transmission and axle ratios available for the 2025 International LT.

Transmission gear ratios

The 2025 International LT is heavily marketed with the new International T14 14-speed automated manual transmission (part of the S13 Integrated Powertrain), as well as the Eaton Cummins Endurant HD 12-speed for Cummins-powered chassis.

International T14 14-Speed AMT

The T14 is a 14-speed automated manual transmission designed to pair directly with the S13 engine. It features two crawler gears for excellent low-speed maneuverability and startability.

Eaton Cummins Endurant HD 12-Speed AMT

Commonly paired with the Cummins X15 engine, the Endurant HD is an industry-standard 12-speed automated transmission optimized for on-highway efficiency.

Available axle ratios

The International LT utilizes Meritor or Dana Spicer tandem rear axles. For 2025, fleets are heavily adopting numerically lower ratios to support engine downspeeding (running the engine at lower RPMs at highway speeds).

How to identify your axle ratio

Identifying the exact axle ratio on a Class 8 truck like the 2025 International LT is slightly different than identifying a passenger vehicle:

• The Line Setting Ticket (LST): International trucks feature a Line Setting Ticket, usually found printed on the inside of the glove box door or standard passenger door jamb. This document lists every component built into the truck at the factory, including the specific rear axle code and ratio.
• Axle Tag: Crawl under the rear of the tractor and locate the metal identification tags bolted to the differential carrier housings of the tandem axles (Dana or Meritor). Wipe away the grease and grime to read the stamped ratio (e.g., "RATIO 2.64").
• VIN Decoder / Dealer Build Sheet: Any International dealership can pull the truck's build sheet using the last 8 digits of the VIN to verify the factory-equipped gear ratio.

Towing vs MPG impact

In the commercial trucking industry, rear axle ratios dictate the balance between pulling power and fuel consumption:

• Numerically Lower Ratios (2.15 - 2.64): These are considered "fast" or "tall" gears. They are best for fuel economy. By utilizing engine downspeeding, the truck can cruise at 65 mph while the engine turns at a highly efficient 1,000 to 1,150 RPM. However, startability under a heavy load on a steep grade will suffer.
• Numerically Higher Ratios (3.55 - 4.10): These are "short" or "low" gears. They offer maximum mechanical advantage, transferring more torque to the tires. These ratios are essential for heavy-haul configurations (80,000+ lbs), off-highway operations, and routes through mountainous terrain, though they will negatively impact highway fuel economy.

Common issues

While the 2025 International LT features robust, modern driveline components, heavy usage can lead to several recognized axle and driveline issues:

• Power Divider (Inter-Axle Differential) Wear: Drivers forgetting to disengage the power divider lock on dry pavement can cause severe binding, leading to excessive wear or catastrophic failure of the inter-axle differential gears.
• Pinion Seal Leaks: High mileage and extreme cold/hot duty cycles often lead to worn pinion seals, resulting in gear oil leaking onto the driveshaft and chassis.
• Ring & Pinion Whine: Improper backlash adjustment from the factory or subsequent repairs, along with low fluid levels, can cause the ring and pinion gears to overheat, creating a noticeable metallic whine on deceleration.
• Transmission Air System Leaks: Automated manual transmissions rely heavily on compressed air for shifting mechanisms. Worn pneumatic lines or faulty shift actuators can leave the transmission stuck in gear.

Find a driveline shop on Repairius. Ensure your Class 8 truck is running at peak efficiency by having a certified diesel technician maintain your transmission and tandem axles.