Compare used-car turning circles for your access space

The short answer

No single turning radius is good for every car buyer. A good figure is one that lets the car complete your actual maneuver, such as the swing into your driveway, garage or parking bay, with room to spare. When you compare two cars measured the same way, the smaller figure means the car can turn more tightly.

Three things change what a published number means. The figure may be a radius or a diameter. It may be measured curb-to-curb or wall-to-wall. It may apply to one exact version of the car and not another. If you settle these three points before you compare, you avoid most mistakes.

Radius, diameter and turning circle

The turning circle is the smallest circle a car can drive with the steering at full lock, meaning the steering wheel is turned as far as it will go. The turning radius is half of that circle's diameter. Spec sheets, brochures and used-car listings often say "turning radius" when the number shown is actually the full circle. Check the label and any definition in the document before you compare figures from different sources. A 10 m radius and a 10 m diameter describe very different cars.

diameter = 2 × radius
radius   = diameter ÷ 2
feet     = metres × 3.2808
metres   = feet × 0.3048

Curb-to-curb vs wall-to-wall

The two common measurements draw the boundary at different parts of the car. Curb-to-curb measures the circle traced by the outside of the tire, which is the room the wheel needs to clear a curb. Wall-to-wall measures the circle traced by the outermost part of the body, usually the front bumper corner, which is the room the car needs to clear a wall. Swept-path engineering software, such as Invarion's RapidPath, defines the terms this way. The bumper overhangs the wheel, so the same car has a larger wall-to-wall circle than curb-to-curb circle.

For an access space, match the measurement to the obstruction. If the edge is a low curb that the bumper can pass over, the curb-to-curb figure is the relevant one. If the edge is a gate post, a garage side wall, a fence, a hedge or a parked car, wall-to-wall describes the limit better. If you compare one car's curb-to-curb figure against another car's wall-to-wall figure, the first car will look better than it really is.

How turning circle works

At full lock, the front wheels reach their maximum steering angle. On a car without rear-wheel steering, the car pivots around a point roughly in line with the rear axle. Two factors set the size of the circle:
• A longer wheelbase (the distance between the front and rear axles) gives a larger circle at the same steering angle.
• A greater maximum steering angle gives a smaller circle.
Anything that limits how far the front wheels can turn, such as wheel and tire size or how the drivetrain is packaged, can enlarge the circle.

Some vehicles have rear-wheel steering, which turns the rear wheels slightly at low speed to tighten the circle. Figures for a model with this feature apply only to cars that have it fitted. On a used car, check the actual vehicle's equipment and not just the model name.

A published turning circle describes a slow, full-lock circle. Speed affects the path a vehicle can follow. Swept-path tools such as RapidPath state their minimum centerline radius at a specific speed for this reason. Treat the brochure number as a best case at walking pace.

Estimating curb-to-curb radius from wheelbase and steering angle

A simple geometric approximation links wheelbase to the path of the outer front wheel at full lock. The example below uses made-up numbers to show the method.

outer front wheel radius ≈ wheelbase ÷ sin(maximum outer-wheel steering angle)

Hypothetical: wheelbase 2.7 m, outer-wheel angle 33°
sin(33°) ≈ 0.5446
radius ≈ 2.7 ÷ 0.5446 ≈ 4.96 m
diameter ≈ 9.9 m (to the wheel centre)

This estimate tracks the center of the outer front tire. A true curb-to-curb figure extends to the tire's outer edge, so it comes out slightly larger. The formula also ignores tire slip and suspension effects. Manufacturers rarely publish steering angles, so use the formula to understand why wheelbase and steering lock matter. Do not use it in place of a documented figure.

What a 90-degree turn into your driveway needs

A right-angle turn uses about a quarter of the turning circle. Whether it fits your access depends on more than that circle:
• how much road width you have to swing out into
• how wide the entrance is
• where the car starts the turn
• the swept path of the whole body
The swept path is the area covered by every corner of the car. The front outer corner swings wide, and the rear inner corner cuts inside the wheels' path.

Swept-path tools separate the sweep envelope, which is the area a specific vehicle covers on a specific path, from a clearance envelope, which adds a safety margin outside that sweep. You can apply the same idea at home. Treat the car's sweep as the minimum, then add margin for imperfect steering, slopes and anything that moves, such as bins or another car. A turning-circle figure cannot show the full swept path. Use it to rank candidates, then confirm the fit on the ground.

SUVs, pickups and vans

Larger vehicles follow the same geometry. Long-wheelbase SUVs, pickups and vans tend to need more room, but wheelbase is only one factor, and steering angle can narrow or widen the gap. One model name often covers several variants that may have different figures, such as different cab and bed lengths, wheelbase options, two- or four-wheel drive, and wheel sizes. Greater overall length and front and rear overhang also widen the swept path and the wall-to-wall figure, even when the curb-to-curb figures look similar. Compare the exact variants, not the model names.

Step-by-step comparison for your access space

• 1. Sketch your access. Measure the road width in front of the entrance, the entrance width, the distance to walls and posts, curb heights, and any fixed obstructions. Note the turn you actually make, including its direction, its angle and whether you reverse in.
• 2. Decide which boundary limits you. Low curbs point to curb-to-curb. Walls, posts and parked cars point to wall-to-wall.
• 3. Identify each candidate car exactly: model year, market, body style, wheelbase, drivetrain, wheel and tire size, and whether rear-wheel steering is fitted.
• 4. Find the figure in a manufacturer document for that model year and version, such as the owner's manual, specification sheet or brochure. Record the document, page and date. Listing text is often copied and can be wrong.
• 5. Record the stated value, unit, whether it is a radius or diameter, which boundary it uses, and any stated test conditions.
• 6. Normalize only entries whose definitions you have confirmed. Convert them all to diameter in one unit on one boundary. Mark any entry with an unclear boundary as pending, not as comparable.
• 7. Rank the comparable entries. Smaller is tighter.
• 8. Check the maneuver in practice. If possible, and with the seller's agreement, try the car on your own access. Otherwise, mark out your measured dimensions with cones or chalk in an empty lot. Drive at walking pace, have a spotter watch the corners, and stop if anyone or anything is inside the swept area.
• 9. Completion check: for each shortlisted car, you can state one diameter on a stated boundary and unit, and you have checked the real maneuver or a marked-out copy of it.

Comparison worksheet

Field	What to record	Why it matters
Vehicle and configuration	Model year, market, body, wheelbase, drivetrain, wheel size, rear-wheel steer	Figures can differ between versions of the same model
Source	Manufacturer document, page and date	Lets you recheck the figure and spot copied listing errors
Stated value and unit	Number exactly as printed, in metres or feet	Avoids rounding and conversion slips
Radius or diameter	As labelled in the document	A mix-up doubles or halves the figure
Boundary	Curb-to-curb or wall-to-wall	Wall-to-wall is larger for the same car
Test conditions	Anything the document states	Shows whether figures are comparable
Normalized diameter	Only if the definitions above are confirmed	Gives a like-for-like ranking
On-site result	Completed, completed with shuffling, or failed	The decisive check for your access

Worked example (hypothetical)

Car A's documentation gives a curb-to-curb turning radius of 5.2 m, which is a 10.4 m diameter. Car B's documentation gives a curb-to-curb turning circle of 10.6 m diameter. On the same basis, Car A turns a circle 0.2 m smaller. This only compares the specified circles. It does not show whether either car can make a particular driveway turn, because overhangs, entrance width and your starting position also matter.

Now suppose Car B's 10.6 m figure were wall-to-wall rather than curb-to-curb. The comparison would no longer be like-for-like. Car B's curb-to-curb circle would be smaller than 10.6 m, so it might actually turn tighter at the wheels than Car A. Until you confirm the boundary, the ranking stays open.

Choosing between candidates

How much weight to give the turning circle depends on how tight your access is:
• Tight access: if your current or test car only just makes the turn, or needs a multi-point shuffle, make the turning circle a deciding factor. Pair it with overall length and front overhang, since those set the wall-to-wall clearance.
• Generous access: if any shortlisted car clears the turn with margin, small differences in turning circle matter little. Weigh condition, history and running costs instead.
• Close figures: when two cars differ by only a few tenths of a metre on the same basis, the on-site check is more reliable than the spec-sheet gap.