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Vehicle Mechanics by the Numbers
Axle loads, resistances, traction, gearing, braking and stability, worked through one tow tractor and its trailer train
Calculate what a site vehicle needs to climb, pull, stop, turn and stay upright, using one battery-electric tow tractor and its trailers as a worked case.
Start readingAbout this book
Every vehicle that moves material around a factory or yard has to do five things: carry its load, climb, pull, stop and turn, without tipping over or losing grip. Each of those is a short calculation with a handful of inputs: masses, the position of the centre of gravity, a few coefficients, the gradient and the speed. Get the inputs roughly right and the calculations show quickly whether a vehicle, a trailer train or a site rule is reasonable. Leave them out and the first sign of trouble is a tow tractor spinning its wheels halfway up a wet ramp.
This book works through those calculations in the order a vehicle meets them: axle loads, driving resistances, traction, power and energy, gearing, acceleration, stopping, brakes, turning and stability. It is written for engineers, maintenance planners and operations leads who specify, modify or write rules for powered mobile plant. It assumes school physics: forces, moments, friction and the equations of uniform motion. Each chapter ends with an exercise and a worked answer.
The running case
This is an illustration. A manufacturer moves parts between its warehouse and two assembly lines with a battery-electric tow tractor pulling three parts trailers. The tractor has a mass of 1,800 kg plus a 90 kg driver, a wheelbase of 1,400 mm and its centre of gravity 800 mm behind the front axle and 500 mm above the floor. It drives through the rear axle, on wheels with a dynamic radius of 250 mm. Each trailer weighs 300 kg empty and carries up to 1,000 kg. The route includes a 6% concrete ramp between buildings.
The coefficients used are teaching assumptions, stated where they are used: a rolling resistance coefficient of 0.015 on concrete, adhesion coefficients of 0.6 on clean dry concrete and 0.3 on wet or dusty concrete, and a drivetrain efficiency of 0.85. Real values come from the vehicle and tyre makers and from measurements on the site’s own floors.
Source limits and professional responsibility
The supplied source is an English edition of a German automotive tables book from around 1980, without a title page. It was used only to confirm the scope of standard vehicle mechanics. Its data tables, figures and worked examples are not reproduced, and its engine and electrical material is outside this book.
Tow tractors, forklifts and other powered mobile plant are regulated under work health and safety law, and Safe Work Australia’s code of practice on managing the risks of plant sets out the duties involved. This book is educational. Its calculations help frame questions about a vehicle and a route; they do not establish that a vehicle, trailer or brake system is safe. Vehicle selection, modifications and braking performance must follow the manufacturer’s specifications and ratings, a site risk assessment and, where required, review by a competent engineer.
Who this book is for
Engineers, maintenance planners and operations leads who specify, modify or set rules for tow tractors, utility vehicles and other powered mobile plant in factories and yards.
What you will learn
- Calculate static and dynamic axle loads from mass, centre of gravity and drawbar pull.
- Add up rolling, gradient, air and acceleration resistance and test them against adhesion.
- Size motor power, gearing and battery energy for a duty cycle with stated assumptions.
- Estimate stopping distance and brake force for a vehicle towing unbraked or braked trailers.
- Check turning paths, trailer off-tracking and tipping limits, and turn them into site rules.
Inside this book
Chapters
- 01Mass, centre of gravity and axle loadsFind a vehicle's centre of gravity and axle loads by weighing and by moments, and see why the load on the driven axle sets almost everything that follows.
- 02Driving resistances: rolling, gradient, air and inertiaAdd up the forces a vehicle must overcome on the level, on a ramp and when accelerating, and see why a 6% gradient is not 6 degrees.
- 03Traction, adhesion and the wet rampFind the load on the driving axle on a slope with a trailer pulling back, compare the force needed with the grip available, and decide what to change when it is not enough.
- 04Power, energy and a battery for a shiftTurn tractive force into motor power at the ramp and on the level, build an energy budget for a trip, and check that a battery lasts a shift with every loss counted.
- 05Gearing, wheel torque and the motor curveChoose a reduction ratio from motor speed and top speed, convert tractive force into wheel and motor torque, check it against the motor curve, and see what a wheel change does.
- 06Acceleration, trip time and the performance envelopeFind what limits acceleration, calculate time and distance to top speed, build a realistic trip time, and map the steepest slope the train can climb.
- 07Stopping distance, deceleration and the downhill trainSplit a stop into reaction and braking distance, find the deceleration the brakes and tyres allow, and see why unbraked trailers on a wet downhill ramp set the site's speed limit.
- 08Brakes from pedal to tyre, and the balance between axlesFollow the force from the pedal through the hydraulics to the tyre, size the calipers for the axle loads under braking, and see why the rear wheels must not lock first.
- 09Turning circles, Ackermann steering and trailer off-trackingCalculate steering angles and turning circles, follow each trailer as it cuts inside the tractor's path on a corner, and size the swept path that aisle markings must allow for.
- 10Tipping stability, load height and the rules that come from the numbersFind the sideways acceleration at which a vehicle or a loaded trailer tips, see how load height and cross-slope erode it, and turn the whole book's calculations into a set of site rules.
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References and source notes
The manuscript and worked examples are original KEVOS® writing. References inform particular concepts; their authors do not endorse this book. Web references were consulted on 26 October 2026.
- Publisher and authors not identifiable from the supplied copy. Automotive Technical Reference (English edition of a German automotive tables book; title page absent from the supplied scan) (about 1978 to 1982, from internal evidence). Supplied scan reviewed for its vehicle mechanics pages: axle forces, driving resistances, clutch, gearbox, drive shaft, steering, suspension and brake relationships. Only standard physics relationships are used; no tables, data, figures or worked examples are reproduced.
- Safe Work Australia. Model Code of Practice: Managing risks of plant in the workplace (current model code). Cited for the duty to manage the risks of powered mobile plant. The book's calculations inform, and do not replace, a site risk assessment.
- Standard university mechanics texts. Engineering mechanics: Newton's laws, friction and rigid-body equilibrium (general reference). The relationships used (equilibrium of forces and moments, Coulomb friction, kinematics of uniform acceleration, power as force times speed) are standard results. Every number in the running case is computed in the text.