Modify / Plan My Car Tools
Preview fitment and planning risks before spending money on changes.
Common jobs in this hub
Will this tire size change my speedometer?
This hub organizes tools, checklists, and result pages around this ownership decision.
Will new wheels sit farther out?
This hub organizes tools, checklists, and result pages around this ownership decision.
Can my setup handle this load?
This hub organizes tools, checklists, and result pages around this ownership decision.
Available tools
Start with these tools
Tire Size Comparison Calculator
Compare tire diameters, sidewall changes, and estimated speedometer error.
Wheel Offset Visualizer
Calculate inner clearance and outer poke changes when swapping to a new wheel width and offset.
Tire Size Compatibility & Speedo Error Calculator
Calculate if a different tire size will fit your car, how much it changes your ride height, and how much it throws off your speedometer.
Towing & Payload Calculator
Calculate your truck's real, safe towing capacity. The brochure number is a lie—find out what you can actually tow based on your GVWR and GCWR.
Cargo Space Planner
Calculate the total cubic feet of a box or furniture item and compare it to common SUV trunk sizes to see if it will fit.
Ride Height Change Visualizer
Visually see how changing your car's suspension height by lifting or lowering will affect ground clearance.
Tire Sidewall Visualizer
Calculate and visually preview the sidewall thickness of a tire to see how much rubber you have between the wheel and the road.
Window Tint Darkness Preview
Preview what different window tint percentages (VLT) look like from the outside of a car.
Trailer Tongue Weight Calculator
Calculate the ideal and safe tongue weight for your loaded trailer to prevent dangerous highway sway.
Roof Box Fit Planner
Check if a specific cargo roof box will fit on your car's crossbars without hitting the rear hatch when opened.