was the only haul truck with a payload capacity of . Compared to the 797B, the 797F has a higher payload capacity and a more powerful, more efficient engine. These changes allowed Caterpillar to meet mine operator's needs to increase operational efficiency and reduce costs by increasing the amount of material hauled per trip. The 797F's increased payload capacity of is a increase over the 797B. Caterpillar replaced the gross [net ] Cat 3524B EUI 24-cylinder diesel engine used in the 797B with the gross [net ] Cat C175-20 ACERT 20-cylinder diesel engine, enabling the 797F to maintain the top speed of the 797B while transporting a heavier payload. Powertrain The Caterpillar 797 series trucks employ mechanical drive powertrains in contrast to the diesel-electric powertrains of similar haul trucks offered by competitors. During initial development in 1997, a diesel-electric powertrain was considered for the 797, but this powertrain configuration was not developed because Caterpillar considered a mechanical drive powertrain more appropriate for market conditions at that time. 797 engine A gross [net ] Cat 3524B HD EUI 24-cylinder, electronic unit injection, quad single-stage turbocharged, liquid aftercooled, four-stroke diesel engine powers the 797. The Cat 3524B HD engine is a tandem unit consisting of two 12-cylinder Cat 3512B HD engine blocks coupled to operate as a single engine with a combined displacement of 106 liters (6468 cubic inches). 797B engine A gross [net ], quad turbocharged Caterpillar 3524B engine powers the 797B. The power rating of the 3524B is valid up to an elevation of or with a high altitude arrangement. 797F engine A gross [net ] Cat C175-20 ACERT single block, 20-cylinder, electronic common rail injection, quad turbocharged, air-to-air aftercooled, four-stroke diesel engine powers the 797F. The power rating of the C175-20 is valid up to an elevation of or up to with a high altitude arrangement. Transmission The 797 series haul trucks are equipped with a rear-axle-mounted, computer-controlled, seven-speed planetary transmission with a separate lock-up torque converter. Both transmission and torque converter use a common powertrain oil. Wheels and tires Each 797 wheel is attached to the axle using 54 - nuts that are torqued to . A size 55/80R63 radial tire was developed by Michelin in conjunction with Caterpillar specifically for the first generation 797. The Caterpillar 797B and 797F run tall, Michelin 59/80R63 XDR. Most first generation 797s have been retrofitted to use the 59/80R63 tires as