Approach angle

Also called front approach angle

Approach angle is the steepest ramp a vehicle can drive onto without anything at the front touching first, measured between the ground and a line drawn from the front tire's contact patch up to the lowest point ahead of it.

What is approach angle?

Stand at the front wheel and draw a line from where the tire meets the ground forward and up, until it touches the lowest thing hanging off the front of the truck. The angle between that line and flat ground is the approach angle. It is the steepest slope you can drive onto nose-first before that thing hits the slope instead of the tire.

It has real definitions behind it, which is unusual for off-road vocabulary. United States federal law states one, in the fuel economy rules of all places: approach angle means the smallest angle, in a plane side view of an automobile, formed by the level surface on which the automobile is standing and a line tangent to the front tire static loaded radius arc and touching the underside of the automobile forward of the front tire.

The engineering standards say the same thing in their own words. SAE J1100, Motor Vehicle Dimensions, carries it as dimension A106. ISO 612:1978 defines it at paragraph 6.10, and European type-approval law cross-refers to exactly that paragraph when deciding whether a vehicle counts as an off-road vehicle at all. Both are paywalled; the federal text above is not.

Two rulebooks also put numbers on it. To be classified as an off-road vehicle in the European Union a car or light commercial vehicle needs at least 25 degrees. To qualify as an off-highway vehicle under United States fuel economy rules it needs at least 28, alongside a breakover angle of 14, a departure angle of 20, running clearance of 20 centimetres and axle clearances of 18, of which it must meet four out of six.

It is a static figure, and the rules are specific about how static. The European procedure has the vehicle unloaded but carrying fuel, coolant, tools and its spare wheel, with a 50th-percentile male manikin in the driver's seat, standing still, wheels straight ahead, on ground level to within half a percent. The American one measures at curb weight with the front wheels parallel to the centreline and the tires at the recommended pressure. Neither says anything about suspension travel and neither says anything about traction. It is one of three numbers, with departure angle at the back and breakover angle in the middle, that between them describe what a vehicle can drive over without hanging up.

What sets it

Usually the front bumper, or the plastic air dam hanging below it. On a factory truck the air dam is the first thing to go, and removing it costs a little highway fuel economy and buys several degrees. After that: the bumper's lower edge, a licence plate bracket, a winch, and on some vehicles the front differential.

Bigger tires help, because they lift the whole front of the vehicle relative to the contact patch. A suspension lift helps less than people expect on the front of an independent-suspension truck, because the lower control arms and the differential do not rise with the body.

The winch tradeoff

A winch has to live somewhere, and everywhere it can live costs approach angle. A plate bumper carries it high and tight but adds a lot of steel low down. A hidden mount behind the factory bumper keeps the stock look and puts the winch lower and further forward, with the factory valance still in front of it. Patrick's Tacoma is the second case: he gains the bumper he likes and pays in the angle he can climb.