Axle ratios for a 1999 Ford F-250 *heavy-duty* varied depending on the engine, transmission, and options selected. Common axle ratios included:
* 3.55: A relatively common ratio offering a balance between towing and fuel economy.
* 3.73: A more common ratio geared for better towing and hauling capabilities.
* 4.10: Geared for heavier towing and hauling, at the expense of fuel economy.
* 4.56: Used in heavier-duty applications requiring maximum towing capacity.
To know the exact axle ratio for a specific 1999 F-250, you'd need to check the vehicle's build sticker (often located on the driver's side doorjamb) or the owner's manual. You can also look at the differential tag on the differential itself.
