Tyre blowout, brake failure and the car that stops ahead: what the sources actually say

Three failures, and one method. A tyre lets go at speed. The brake pedal goes to the floor. The car in front stops harder than you expected. Each has a procedure that circulates with total confidence and no publisher attached, and this article was written by going to look for the publisher.

What follows is the result: the documents, what was in them, and — the longer part — what was not. Every absence here was looked for in a document opened and read.

What was opened

The American federal road-safety agency’s tyre pages cannot be reported on here at all: two of its addresses returned a refusal rather than a page. A source that refuses to serve was not read, so nothing here is attributed to it, including the sentences quoted from it second-hand.

The British Highway Code was read across three ranges: the general rules for all drivers, the motorway rules, and breakdowns and incidents. It has braking rules, skid rules and anti-lock brake rules. It has no rule for a burst tyre and no rule for a brake failure. The breakdowns range begins after the vehicle has stopped.

Virginia’s driver manual was downloaded and searched term by term. Its text contains no occurrence of blowout, flat tire, burst, brake failure, anti-lock or parking brake; its one mention of skidding is about snow tyres. Spain’s traffic authority describes a blowout in its magazine — an abrupt loss of pressure after which the tyre’s behaviour is seriously affected — and offers a run-flat tyre as the answer, without a word about the wheel or the pedal. Canada’s federal tyre route leads to defect reporting and recalls. And one manufacturer’s handbook, opened at the chapter headed in case of an emergency while driving, lists a stall, a stall at a crossing, and a flat tyre. There is no entry for the brakes.

Most of those were expected to have the answer. None did.

The blowout: the instruction exists, and it belongs to somebody

It is published, and the publisher is worth knowing. Pennsylvania’s driver manual — a consumer document for people learning to drive a car — is where the familiar sentences live. It gives the symptoms by axle: with a front tyre the steering wheel will vibrate and the vehicle will suddenly pull to one side; with a rear tyre one corner will drop suddenly and the rear will wobble back and forth. Then the instruction: hold the steering wheel tightly, stay off your brake, slowly take your foot off the gas pedal, and steer where you want to go, but steer smoothly, without large or jerky steering actions. Its road-safety pages attach the reason: braking after a blowout may cause you to skid and lose control.

The version with more detail is not a consumer document. The commercial driver’s licence manual — written for truck drivers — gives three signs rather than two. Sound: the loud bang of a blowout, which can take a few seconds to show in the vehicle’s behaviour, so any time you hear a tyre blow you would be safest to assume it is yours. Vibration: a heavy thump, which with a rear tyre may be the only sign you get. Feel: heavy steering, probably a front tyre. Its response is Pennsylvania’s with the physics spelled out — a failed front tyre can twist the steering wheel out of your hand, so keep a firm grip with both hands, and unless you’re about to run into something, stay off the brake until the vehicle has slowed down, then brake very gently and pull off the road.

The manufacturer handbook agrees and puts the emphasis elsewhere: take your foot off the accelerator and let the vehicle slow while driving straight ahead, and do not apply the brakes immediately or attempt to pull off the road, because that may cause a loss of control. The instruction usually condensed to do not brake is, in its own source, two instructions — do not brake, and do not steer for the verge either.

So the advice everyone repeats is real. Universal it is not: three publishers state it, one writing for trucks, and no road authority in the other markets read here states it.

What no source says about a blowout

No document read here publishes a speed at which a blowout becomes unrecoverable, a distance in which a car will slow with a tyre gone, a time budget for the manoeuvre, or a different procedure for a motorway than for a town street. None states what proportion of blowouts are controlled successfully, or how the outcome depends on which corner failed — the front-versus-rear distinction is published to help recognise the failure, never to predict it. And none says what the car’s own assistance will do while it happens.

Brake failure: an older instruction, and a newer one nobody joined up

Here the published guidance is thinner than the blowout’s, and older.

Pennsylvania gives a sequence: shift to low gear and look for a place to slow to a stop; pump the brake pedal quickly several times, which often builds enough pressure; if pumping does not work, slowly apply the parking brake, holding the release so you can let it off if the rear wheels lock and you begin to skid; and, if the vehicle still will not stop and you are in danger of crashing, turn the ignition off as a last resort — never to LOCK, which locks the steering too. The commercial manual names the symptom first, a pedal that feels spongy or goes to the floor, and gives the same three moves: downshift, pump, and use the parking brake with the release held so the pressure can be modulated.

Every one of those instructions assumes a hand lever with a release button. A current handbook describes the same emergency on a car that has a switch instead, and it is published in the parking-brake chapter rather than the emergency one: if there is a problem with the brake pedal while driving, emergency braking is possible by pulling up and holding the switch; braking happens only while the switch is held; and applying it while the vehicle is moving at normal speeds can cause a sudden loss of control. It adds a detail nobody repeats — that a continuous noise or a burning smell afterwards is a reason to have the car looked at.

What no source says about brake failure

Nobody read here publishes a stopping distance for a car braking on its parking brake alone, at any speed, on any surface. Nobody reconciles pump the pedal with the same authority’s emergency-braking page, which tells the driver of a car with anti-lock brakes to maintain firm continuous pressure and do not pump the brake pedal — the first instruction is for a failed system and the second for a working one, which is clear once stated and is stated nowhere. And the manufacturer’s emergency chapter, the document the Highway Code’s anti-lock rule sends you to, has no brake-failure entry. The instruction that does exist sits in another chapter, under another heading.

Fade itself this section has already treated, with the descent technique, in the hill article.

The car that stops ahead: the one failure that is not the car’s

The third case is the common one, and the only one where the sources are generous — because it is not a mechanical failure but a distance problem, which this section treats on its own terms in the article devoted to it.

What belongs here is the braking, and the reaction before it. Two authorities give the same emergency instruction for a car with anti-lock brakes, in almost the same words: apply the footbrake firmly and do not release the pressure until the vehicle has slowed to the desired speed; maintain firm and continuous pressure, and do not pump. The Highway Code’s rule opens by sending the driver to the vehicle handbook, which is a regulator declining to legislate a technique.

The reaction is where the confident numbers live, and where the most careful source read here refuses to give one. A crash-reconstruction manual defines perception-reaction time as the interval between the point where the operator sees the danger and the point where the action occurs, notes that measurements cover a broad range depending on the task, the stimulus, the driver’s age and condition and much else, and lists the quoted benchmarks — 1.5 seconds at the 85th percentile, 2.5 seconds for road design. Then it says the thing that makes it worth citing: a reconstructionist should not assign a value to a driver, but should use a range of values, and there is no basis for assuming a specific figure and proceeding with calculations from it. That is the opposite of how the number is normally used, including against drivers.

What the simulator does, and what it does not

The section’s crash simulator, opened on a highway rear-end, models exactly one of the three failures here, and it is honest to say which. It has no tyre model and no brake-temperature model: it cannot show you a blowout or a pedal that stops working. What it has is the variable that matters in the third case, editable — the reaction-time field, beside the point at which the driver sees the hazard.

Run the preset as it arrives. Then change nothing except that field, lowering it by half a second, and run again. The surface, the speeds and the deceleration are held constant, so the difference in where the following car ends up is purely what half a second of earlier reaction bought at that speed. It is the only quantity here a reader can move, and our own tool computes it from constants it cites. The caution is the reconstruction manual’s: the figure in that field is a range, not your reaction time.

What this adds up to

For the first of these failures the guidance is real, specific and consistent across three publishers; for the second it is real, old and quietly out of date on cars that no longer have a lever. For neither is there a measured expectation of what a driver can achieve — no speeds, no distances, no success rates.

Which leaves the honest conclusion in an awkward place, because it is not a technique. The only variable here with a cited source and a tool that computes it is the one that exists before anything fails: how much room there was, and how fast you were going into it. The procedures above are worth knowing, in the words of the people who published them. But they are what you are left with when the decision that mattered has already been taken.