Why are the tyre path and the body envelope different outlines?

Because they are produced by different parts of the vehicle moving in opposite directions. The rear wheels cut inside the front ones through a turn, so the tyre path pinches in; the front overhang swings out beyond everything on the ground. One of them shears an island nose and crumbles a pavement edge, the other takes a mirror off a pole, and a layout drawn to just one of them will fail on the other.

How sensitive is the answer to the steering angle?

Very. The turn radius goes as the wheelbase divided by the tangent of the angle, so the curve is steep at the shallow end: dropping from thirty-two degrees to twenty-eight adds more than a metre to a single-unit truck's radius. If a published minimum turning radius exists for the class, use it to sanity-check the angle before you trust the envelope.

Does this replace an AASHTO turning template?

No, and it is not meant to. The templates are the reference a reviewing authority will expect to see on the plan, and they carry behaviour this model does not — the transition into and out of the curve, the trailer path on a combination vehicle, and the class's own published minima. Use this to size a turn quickly and to sanity-check a plotted template, then plot the template.

What clearance margin is sensible?

Enough that an ordinary driver on an ordinary day does not need to be precise. Templates describe an ideal single-movement turn at full lock, which nobody drives, and the margin is where driver variation, kerb faces, parked cars and winter snow banks are absorbed. Widen it for blind turns and for sites where the driver changes every week.

Heavy Civil & Infrastructure

Design Vehicle Swept Path Calculator

The swept path of a turning vehicle: where the inside rear tyre tracks, where the front corner swings, and the band between that must stay clear.

Answers as you typeNo submit button
Every formula citedNamed published standards
Calculated in your browserNo account, nothing uploaded

SettingsSettings for this calculationUS

Market

Imperial · sales tax

Wheelbase

Front axle centre to rear axle centre on the design vehicle.

For a tractor-trailer this is the tractor's own wheelbase, and the trailer then off-tracks further still — a combination vehicle needs its published template rather than a single-unit approximation. Take the figure from the vehicle class you named, not from a truck someone remembers.

Maximum Steering Angle (degrees)

How far the front wheels can be turned at full lock.

This is the single most sensitive number on the page: the turn radius varies as one over its tangent, so a few degrees at full lock moves the whole envelope. Where a published minimum turning radius is available for the class, work backwards from it to check the angle you have entered reproduces it.

Front Overhang

From the front axle centre forward to the foremost point of the body.

This is the dimension that takes mirrors off light poles and catches canopy columns, because it swings outside everything on the ground. On a refuse or fire vehicle include the bumper, the bull bar and anything else fixed ahead of the cab.

Body Width

Overall width across the body, mirrors excluded.

Half of this is taken as the offset from the vehicle centreline to both the inside rear wheel and the outer body corner, which is close on a commercial vehicle where the track and the body are near enough the same. Where the track is appreciably narrower than the body, the inside tyre path will be a little tighter than reported here.

Clearance Margin

Added outside the body envelope for driver variation and kerb faces.

No driver reproduces a template. This margin is what separates the geometric envelope from the obstruction you are protecting, and it should grow where the turn is made blind, in one movement, in snow, or by someone who has not driven the site before.

Swept path width

17.2 ft

Medium confidence

A single-unit bicycle-model turn at steady full lock. It does not model a combination vehicle's trailer off-tracking, a transition into or out of the curve, or superelevation, and it is a check on a published template rather than a replacement for one.

Inside rear tyre path radius: 28.26 ft
Outer body envelope radius: 45.48 ft
Turn radius at the rear axle centre: 32.26 ft

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

AASHTO, A Policy on Geometric Design of Highways and Streets — publishes the standard design vehicle classes and their minimum turning paths, which are the dimensions this page is driven with and the templates a submitted plan should be checked against
Standard bicycle-model turning geometry: the turn centre lies on the rear axle line at a radius of wheelbase ÷ tan(steer angle); the inside rear wheel tracks half a track width inside it, and the outer front body corner sweeps the hypotenuse of that radius plus half the width and the wheelbase plus the front overhang.

Inputs used

Wheelbase: 20 ft
Maximum Steering Angle (degrees): 31.8
Front Overhang: 4 ft
Body Width: 8 ft
Clearance Margin: 2 ft

Intermediate steps

Inside rear tyre path radius: 28.26 ft
Outer body envelope radius: 45.48 ft
Turn radius at the rear axle centre: 32.26 ft

Final result17.22 ft

Confidence note: A single-unit bicycle-model turn at steady full lock. It does not model a combination vehicle's trailer off-tracking, a transition into or out of the curve, or superelevation, and it is a check on a published template rather than a replacement for one.

What this calculation does not cover

Swept path has height as well as width. A container being tipped, a raised tailgate or an aerial device needs vertical clearance this page says nothing about.
Trailer off-tracking on a combination vehicle is additional and can be well beyond the tractor's own inside path.

Schematic, drawn to the proportions you entered — not to scale on screen.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-08-30 · in the site-wide review of 2026-09-06 · v1.0.0

Regulatory standards & verification citations2

AASHTO, A Policy on Geometric Design of Highways and Streets — publishes the standard design vehicle classes and their minimum turning paths, which are the dimensions this page is driven with and the templates a submitted plan should be checked against
Standard bicycle-model turning geometry: the turn centre lies on the rear axle line at a radius of wheelbase ÷ tan(steer angle); the inside rear wheel tracks half a track width inside it, and the outer front body corner sweeps the hypotenuse of that radius plus half the width and the wheelbase plus the front overhang.

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Designing a Site Entrance Trucks Can Useuses this calculator
Gate, keypad and apron sized off two questions: can the delivery swing in off the street, and where does the queue behind it stand while it waits?
Fencing a Site Perimeteruses this calculator
Panel counts taken off a walked line, gates sized by the wagon that uses them, and the moment balance that decides whether feet alone hold a run.
Getting Plant and Deliveries Onto Soft Grounduses this calculator
Ramp geometry off the deck, fabric and stone across the wet, and the stabiliser leg that goes through while a delivery is being taken.

Still deciding? Design Vehicle Turning Path vs Stall Count — the factors that actually differ, with no invented prices.

How to calculate design vehicle swept path in 6 steps

WheelbaseFront axle centre to rear axle centre on the design vehicle.
Maximum Steering Angle (degrees)How far the front wheels can be turned at full lock.
Front OverhangFrom the front axle centre forward to the foremost point of the body.
Body WidthOverall width across the body, mirrors excluded.
Clearance MarginAdded outside the body envelope for driver variation and kerb faces.
Swept path widthThe tool computes the swept path width from those figures and shows the formula, its sources, and a confidence rating alongside it.

Swept path width by wheelbase

Page defaults, not your figures above.

Wheelbase	Swept path width (ft)
10 ft	14.3
15 ft	15.7
20 ft	17.2
25 ft	18.6
30 ft	20
35 ft	21.4
40 ft	22.9

Frequently asked questions

Why are the tyre path and the body envelope different outlines?: Because they are produced by different parts of the vehicle moving in opposite directions. The rear wheels cut inside the front ones through a turn, so the tyre path pinches in; the front overhang swings out beyond everything on the ground. One of them shears an island nose and crumbles a pavement edge, the other takes a mirror off a pole, and a layout drawn to just one of them will fail on the other.
How sensitive is the answer to the steering angle?: Very. The turn radius goes as the wheelbase divided by the tangent of the angle, so the curve is steep at the shallow end: dropping from thirty-two degrees to twenty-eight adds more than a metre to a single-unit truck's radius. If a published minimum turning radius exists for the class, use it to sanity-check the angle before you trust the envelope.
Does this replace an AASHTO turning template?: No, and it is not meant to. The templates are the reference a reviewing authority will expect to see on the plan, and they carry behaviour this model does not — the transition into and out of the curve, the trailer path on a combination vehicle, and the class's own published minima. Use this to size a turn quickly and to sanity-check a plotted template, then plot the template.
What clearance margin is sensible?: Enough that an ordinary driver on an ordinary day does not need to be precise. Templates describe an ideal single-movement turn at full lock, which nobody drives, and the margin is where driver variation, kerb faces, parked cars and winter snow banks are absorbed. Widen it for blind turns and for sites where the driver changes every week.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.