* Size of the body lift: A small body lift (1-2 inches) will likely have minimal impact on gearing. Larger body lifts (3+ inches) might necessitate consideration, but it's not automatic.
* Size of the tires: This is the bigger factor. Larger diameter tires effectively increase your overall gear ratio. A significant increase in tire diameter will substantially alter your vehicle's performance, potentially making it sluggish to accelerate and lacking in power, especially on hills. This is because your engine has to work harder to turn the larger tires.
* Current gearing: What is your current rear axle gear ratio? Trucks often came with different ratios (e.g., 3.73, 4.10, 4.56) depending on options and intended use. A truck already geared low (like a 4.56) might tolerate larger tires better than one with higher gearing (like a 3.73).
* Your driving style and terrain: If you frequently tow heavy loads or drive in hilly terrain, you'll feel the effects of the larger tires and potentially need re-gearing more than someone driving primarily on flat roads with light loads.
In short: A small body lift and small tire upgrade probably won't require re-gearing. However, a combination of a larger body lift *and* significantly larger tires almost certainly *will* require re-gearing to maintain acceptable performance and drivability.
To determine if re-gearing is necessary, calculate your tire diameter change. Then, use an online gear ratio calculator (many are available with a quick web search) to see how the new tire diameter affects your overall gear ratio. Compare this to your current ratio to assess the change. A substantial increase (more than 10-15%) usually warrants considering re-gearing. If you find yourself struggling with acceleration or hill climbing after the lift and tires, re-gearing is a strong indication you need it.
