Turning Radius Calculator finds curb-to-curb and wall-to-wall turning circle diameter from a vehicle wheelbase, front track width, tire width, and the maximum front steering angle
Find Curb-to-Curb and Wall-to-Wall Circle Size with the Turning Radius Calculator
This tool works out how much room a vehicle needs to complete a full-lock U-turn, from six measurements: wheelbase, front track width, tire width, body width, front overhang, and maximum steering angle.
It’s built for anyone sizing a garage, driveway, parking structure, or loading dock against a specific vehicle’s real turning geometry, rather than trusting a single spec-sheet number that may not say which kind of turning circle it’s measuring.
Reading the Turning Radius Calculator’s Inputs and Outputs
Enter wheelbase and track width in inches or millimeters, pick whether the steering angle is measured at the inside or outside front wheel, and choose from a preset vehicle or enter custom dimensions. The output splits into curb-to-curb diameter (the outer front tire’s path), wall-to-wall diameter (the full body sweep including bumper overhang), the Ackermann angle difference between the two front wheels, and the swept path width the rear wheels cut through.
The Geometry Behind Curb-to-Curb and Wall-to-Wall
The base relationship is turning radius = wheelbase ÷ sin(steering angle), then add half the tire width to reach the curb-to-curb figure, since the outer tire’s own contact patch extends beyond its centerline.
$$R_{curb} = \frac{WB}{\sin(\theta)} + \frac{TW}{2}$$
Wall-to-wall diameter is larger still, because it accounts for the front overhang – the body swings wider than the tire the moment there’s any distance between the front axle and the bumper. A common input mistake here is entering track width (the distance between tire centerlines) into the body width field, which is meant for the vehicle’s full outer width used only in the wall-to-wall and swept-path figures.
Why the Inside and Outside Front Wheels Turn at Different Angles
Because the two front wheels trace circles of different radii around the same turn center, they can’t point the same direction without one of them scrubbing sideways. Ackermann steering geometry solves this by turning the inside wheel at a sharper angle than the outside wheel, and the calculator reports that difference directly as the Ackermann angle.
Entering a steering angle “measured at” the wrong wheel is a genuine, easy-to-make mistake, since the inside and outside angles for the same physical turn can differ by several degrees – the calculator treats these as two distinct input modes for exactly that reason.
Swept Path Width and Why the Rear Wheels Cut In
The rear wheels don’t follow the front wheels’ path – the inside rear tire tracks a tighter arc than the inside front tire, an effect called offtracking. That gap between the two paths is the swept path width, which matters most for anything with a fixed curb or wall on the inside of a tight turn, like a driveway pillar or a loading-dock corner.
Valid Input Range and Where the Math Breaks Down
Steering angle is limited to between 0° and 80°, since real steering knuckles don’t approach 90° of lock. Tire width must stay smaller than track width – entering it the other way around describes a physically impossible wheel.
When solving from the outside wheel’s angle, the calculator blocks any input that would force the inside wheel past 90°, since that configuration has no real geometric solution and would otherwise return a nonsensical result rather than an error.
Common Turning Radius Calculator Input Errors
Confusing a manufacturer’s published turning radius with turning diameter is common, since spec sheets rarely state which one they mean, and diameter is exactly double the radius.
Entering body width instead of front track width – the two are easy to mix up, but track width is measured centerline-to-centerline of the tires, while body width is the full outer vehicle width.
Using a curb-to-curb spec pulled from a brochure when the real question is whether the vehicle clears a specific garage or wall, which depends on the larger wall-to-wall figure instead.
Turning Radius Calculator: Frequently Asked Questions
What’s the difference between curb-to-curb and wall-to-wall turning radius?
Curb-to-curb tracks the outer front tire’s path and is the figure most manufacturers publish. Wall-to-wall adds the front bumper’s overhang, since the body swings wider than the tire during the turn, making it the number that actually matters against a garage wall or pillar.
Why does the inside front wheel turn at a different angle than the outside wheel?
The two wheels trace circles of different radii around the same turn center, so pointing them at the same angle would make one tire scrub sideways. Ackermann steering geometry angles the inside wheel more sharply than the outside wheel to keep both rolling freely.
Does tire width actually change the turning radius?
Yes – wider tires push the outer contact patch further from the wheel’s centerline, adding roughly half the tire width to the curb-to-curb radius. It’s a small effect on a typical passenger tire but becomes more noticeable on wide performance or off-road tires.
What turning radius do road engineers actually design around?
Intersection and driveway design leans on AASHTO’s standard design vehicles rather than any specific car: a 24-foot minimum turning radius for a passenger car (P), and 42 feet for a single-unit truck or bus (SU-30 or BUS). Those figures assume a slightly larger, more conservative vehicle than most cars or trucks in their class.
Why does my measured turning circle not match the manufacturer’s published number?
The most common reason is a radius-versus-diameter mix-up, since manufacturers don’t consistently label which one they’re quoting. The second most common reason is that the published figure is curb-to-curb while a physical measurement against a wall naturally captures the larger wall-to-wall distance instead.