Overdrive

"Medical Officer: These medical supplies are needed on the plague planet, urgently!

Captain: Warp 4!

[later...]

Science Officer: Because of various complications, we might be Too Late.

Captain: Warp 9!"

- David Morgan-Mar (paraphrasing Star Trek), Darths and Droids

A character needs to drive somewhere quickly. Maybe they're in a car race, or maybe they're just racing against time. At one point, they realize they're not going to make it in time. So they... go faster.

Huh? Why didn't they just drive that fast to begin with?

Odd as it may seem, this unexplained increase in speed can have some basis in reality. It can be simplified as a cost vs. benefit decision. If somebody has "nothing to lose" and must be somewhere at a certain time then they have to speed up -- but -- if they push their machine too hard it will fail before they get there. If they had backed off slightly, then it could have broken down after they had arrived. In a race a driver will hold back simply because there's a notable difference between "the fastest they can drive" and "the fastest they can continuously drive without wear and tear completely destroying the engine halfway through the race". Smart drivers limit themselves to the latter, and use the engine-wrecking speeds in short bursts -- or for those desperate final laps. Fuel consumption is also a potential problem. Having to find out where to refuel in the middle of some prairie or ocean is not a way to get to destination ASAP. Running out of propellant halfway to the next planet and thus unable to decelerate is not a good idea either. The cost of fuel, oil (or Helium-3, or whatever) and repairs is also a factor. In most cases engines are supposed to work much longer than one or two rides and generally engines aren't so cheap that the cost of damaging one could be disregarded without a really good reason.

Then there are Nitro Boost systems, which are of limited duration by definition, and speed limits. On normal roads, a driver may initially be unwilling to flagrantly violate the speed limit -- and risk bringing the ire of the police down on them -- until they get really desperate.

Of course, in spite of the risks associated with such insane speed, it almost invariably results in victory for our protagonist, rather than catastrophic engine breakdown in the penultimate lap.

Your Mileage May Vary regarding how well the in-universe justification for Overdrive is explained. If it's explained at all. And of course, there are some instances -- say, short drag races -- where this trope makes absolutely no sense no matter how you slice it.

A Sub-Trope of Holding Back the Phlebotinum. A Sister Trope of Tim Taylor Technology, and the mechanical equivalent of a Dangerous Forbidden Technique. If it involves the risk of a catastrophic failure, it's Explosive Overclocking.

Close to, but not to be confused with, the Final Fantasy X move called Overdrive (which is listed under Limit Break).

Film

 * The podrace from Star Wars: Episode I is all over this trope. Sometimes Anakin passes other racers with ease, and other times he keeps pace with Sebulba over long straightaways. It also genuinely makes zero sense that he wasn't going as fast as he could to begin with, considering how he started the race in last place due to engine failure and his freedom was on the line.
 * Considering it was built from scrap parts, it wasn't exactly the most streamlined podracer around, although it was capable of reaching very high speeds (one of the fastest in the film). Once Anakin got ahead of most of the other racers, it is likely that he did not want to strain the engines more than necessary.
 * The game confirms this by making the engines burst into flames if Overdrive is not turned off after it overheat for long enough, which can result in your engines deteriorating. And unless you pay for the rather expensive repairs, you'll start the next race with a half-broken engine.
 * Podracing also requires inhuman reflexes. Though Anakin had the force going for him along with being a central character, it's understandable he'd rather not go the full 560 mph (that's more than the length of the empire state building every second) unless he really has to.
 * Cars is a rare subversion of the "more speed always works'' aspect of the trope: Lightning McQueen gains a whole lap on Chick Hicks and The King by skipping several pit stops--then both of his rear tires blow out in the final lap, and the race ends in a three-way tie.
 * In Galaxy Quest, the overdrive blows-out after being held down too long, leaving the ship nearly crippled.
 * The protagonist of My Science Project, a car mechanic by hobby, has a supercharger equipped on his car, which he uses to outrace an energy surge (just go with it) racing down power lines, to cut off the Imported Alien Phlebotinum device before it gets more power to warp time and space even further than it had already done to that point.
 * Done with a horse at the end of True Grit. Rooster Cogburn rides a horse so hard and fast that it eventually dies just short of his destination.

Live Action TV

 * Star Trek was a frequent offender. The Original Series played this completely straight. The Next Generation explained that speeds beyond Warp 5 damage the fabric of space-time. ...Then a new Warp engine was invented that didn't damage space-time, completely erasing the prior justification.
 * At least in TNG and later the energy requirement grew exponentially with the speed, thus if the matter wasn't urgent, they went slower to conserve fuel.
 * In The Wounded, the matter is very urgent, yet they decide to go Warp 4 so that the writers can have them step on the gas later when things go really bad.
 * Super Pursuit Mode in Knight Rider.
 * This is explained by a simple application of physics: aerodynamic downforce reduces the vehicle's speed, since the air resistance of the vehicle is increased (there's more surface area for the wind to hit). What Super Pursuit Mode accomplishes is increasing K.I.T.T.'s maneuverability at high speeds, thus preventing Michael from wrapping K.I.T.T. around a power pole . The game makes this point, too. Your maximum speed is decreased a bit, but it's much easier to steer.
 * Hyperthrust in Street Hawk, which required a planned route and clearance from Mission Control before use.

Web Comics

 * Darths and Droids attempts to make sense of the Star Wars podrace by completely reinterpreting what happened at the end of the race. The Rant below that strip discusses this trope (and directly inspired this very article).

Western Animation

 * Used in the pilot episode of Tale Spin. Up until then, the overdrive existed, and it was clearly stated that you could only use it for so long before the engine overheated and blew up the Sea Duck. Baloo burned it out forever and ever during the episode; it's just as well, so we couldn't complain about him not using it in future episodes.

Literature

 * In James Blish's Cities in Flight novels the cities of the title can fly at faster-than-light speeds, but they're all equipped with a gadget called "Situation N" which can instantly teleport them away from trouble. Only thing is, it can only ever be used once per city. Why? Because if they used it more than once it would be too convenient for the author, I guess.
 * This is really a Fridge Logic issue. A city's "City Fathers" AI has this "Standard Situation N" last resort action that turns loose their accumulated information store to produce some unpredictable solution, which is then wiped from memory to prevent lazy city managers or mayors from using it frivolously. (Why would it be frivolous to use it all the time? Because it's automatically wiped from memory, so that would waste their one last-resort option . . . er . . . wait a minute . . .) In this particular case (near the end of Earthman's Burden) it teleported the cities involved away from an untenable situation; but the leaders didn't know in advance exactly what would happen. It's hard to think of a clearer case of deus ex machina; yet Blish presents the gimmick so convincingly that it took this troper, at least, many a reading before the circularity of the reasoning dawned on him.
 * Military warships in Honor Harrington series has a version, though with acceleration rather than top speed. The inertial compensator that allows the crew to survive the hundreds of gravities their drives are capable off is normally only run to 80% of its theoretical maximum capacity to reduce wear and reduce the risk of failure. It can be run higher in emergency situations but is not recommended because if it fails you only have seconds of warning and then the entire crew is reduced to a red smear.
 * A similar situation exists with the hyper generators that allow FTL but it is much rarer. The option to take the inertial compensator to full power is built in but to run the hyper generator requires physically disabling the safeties. The effect of trying to go into higher levels hyperspace and failing is described as "bouncing."
 * In the end the situation is like the Space Shuttle, the actual safespeed is higher than listed. Overtime Manticore finds they can push their compensators much higher than listed, and that 80% of that is hopelessly cautious. A Solly Admiral is thought to be bold by Solly Standards to seek 85% in a battle.
 * Deconstruction in the Sword of Truth, where it turns out that your horses do have a maximum output. You can push them past that... and you'll run them into the ground. Later in the series they've become genre savvy about this, and start taking extra horses so that they can switch them out and avoid the negative aspects of this trope.

Fanfic

 * In Half Life: Full Life Consequences, John Freeman's reaction to his brother being in mortal danger is to try to reach him by going "fast" on his motorcycle. And then events happen that cause him to go "faster", three times. Even though it was established that he was in a huge hurry and didn't have time to waste. So, basically, he felt his brother wasn't in that much danger at first.
 * But at the end of chapter 2, Gordon does berate him for getting there slow, as he is.
 * And in that same chapter it's established that John Freeman has another, faster motorcycle, which was unfortunately out of gas in the first chapter. How it was refilled in-between is a mystery.
 * In the Final Fantasy fan fic "Cid Wars", the characters are at one point trying to get somewhere by van, and each time someone said they needed to go faster, the driver upshifted. This happened a total of eight times, complete with one of the characters asking "Just how many gears does this van have?"

Tabletop Games

 * BattleTech's BattleMechs can be equipped with myomer acceleration signal circuitry (MASC for short), which when active provides about a 33% boost to maximum speed by making the 'Mech's artificial leg muscles contract that much faster. There is, however, always a chance that the added strain will result in internal leg damage, and this chance increases rapidly if the system is used over multiple turns in a row, wherefore it's useful primarily to provide short emergency bursts of speed. An alternative -- and incompatible -- approach involves using special extra-strong myomer fibers in the first place; unfortunately, those require the 'Mech to run hot enough for its weapons to start to incur to-hit penalties before their performance exceeds that of the normal version. (To make the most of these 'triple-strength myomers', a 'Mech's heat level should ideally stay at exactly 9 -- no lower, no higher, on a scale from 0 to 30 -- for extended periods.)

Video Games

 * Boost in the Motorstorm series works this way. You have an unlimited supply of Boost, but using it heats up your engine. if you don't lay off the boost, or drive through water to cool your engine down, it will blow out your engine, respawning you near last place.
 * Romancing Sa Ga: Minstrel Song has Hasten Time and Overdrive, the ultimate Hydrology spells. Casting one of these babies lets the user instantly end the enemy's turn and either give themselves and all their allies a free turn to act -- or act five times in a row themselves, without any fear of interruption. However, the spell's big drawback is that it's a major drain on your MP, especially in Overdrive... is it worth having your caster attack five times uninterrupted when it will then take them several turns to recover?

Real Life

 * In NASCAR, a race is said to be going into Overdrive if there is a green-white-checkered finish due to a caution extending the race past the scheduled distance.
 * Many World War II-era fighter aircraft featured an engine setting called "War Emergency Power" which is Exactly What It Says On the Tin. It was intended for emergency use in combat and normally had a time limit imposed on its use, as it would wear out the engine in a very short time. WEP appeared in many forms; some aircraft engines simply had the capacity to run at power levels that would overstress their own components. In these cases, a piece of tape was inserted to stop the throttle at the maximum safe setting; if the tape was broken, the engine would need to be inspected after the flight. Other aircraft implemented WEP through the use of consumable additives. Nitrous oxide injection would cool the fuel/air charge (allowing more fuel and air to enter the cylinder on each cycle) as well as providing additional oxygen at high altitude. A few aircraft were designed for the stress of nitro injection, and were limited only by the onboard supply of nitrous. Water or water/methanol injection provided a lesser version of the same effect, but also cooled the engine and allowed it to operate beyond its radiator's normal capacity.
 * A handful of civilian aircraft -- often those intended for "bush aviation" -- also possess an "Emergency Power" setting. It's facetiously said to provide "just enough power to get you to the scene of the crash."
 * The Space Shuttle's main engines were designed for a certain maximum normal output, rated as 100%, but can run at up to 110% thrust in emergency abort situations. After a few flights it was determined that 104% was safe for continuous operation, and it was easier to routinely go to 104% than to rewrite all the documentation to make that the new 100%.
 * Most modern fighter aircraft are equipped with equipment variously known as afterburners (US), reheat (Brit), or forsazh (Rus). This system dumps additional fuel into the exhaust manifold in order to burn any oxygen that was not consumed in the main stage of the engine. This can greatly (~160%) boost the thrust at the cost of extreme fuel consumption; afterburners can empty the multi-ton fuel tanks of a jet fighter in less then 5 minutes. Go really fast if you have to, but do it too long and you'd better be ready to walk home.
 * Averted in some planes (like the SR-71 Blackbird) that are designed for high efficiency during afterburn; you can have your engines spittin' flame for as long as there's fuel available, and everything will be ok. The downside is that they are horribly inefficient when not afterburning. The Blackbird also burned a special fuel, which meant its operating costs followed the plane itself into the stratosphere.
 * Afterburners also come with a side effect of a massive thermal signature. This negates a stealth aircraft's stealth by making it visible to thermal sensors, and in general makes it much easier for heat seeking munitions to find their mark even with countermeasures.
 * Many other vehicles, both civilian and military, have a "red line" power setting which represents the maximum power available without immediately damaging the engine, and a lower "yellow line" setting which is the maximum safe cruise setting. For example, the manual for the Turbomeca Arrius 1A (a turbine engine used in helicopters) lists a maximum continuous power of 296 kW, an intermediate contingency rating of 357 kW (120% normal) usable for up to 30 minutes, and an emergency maximum for 2.5 minutes of 388 kW (131% normal).
 * The original VW Beetle is an exception in that it could safely operate all the way to the red line; in The Fifties, when it was normal for a small car to have a top speed in the range of 70 MPH, the company used this as a selling point.
 * Many cars have an aerodynamically-limited top speed, creating a situation where the engine looks like it ought to be able to take you faster, but it doesn't have enough torque to accelerate you.
 * The transmissions in most modern cars have a gear called overdrive, but it's fairly unexciting: it's just any gear with a ratio of less than 1:1- the gearbox output turns faster than the input.. Overdrive gears provide much slower acceleration than other gears, and are usually only used under conditions of steady speed and light load. Push harder on the gas while in overdrive and an automatic transmission will downshift to a lower gear for more acceleration. They're designed to save fuel, not make you go faster.
 * When done to computers, it is called Overclocking. This makes the computer faster, but also generates more heat and can cause software errors or even ruin the CPU if performed incorrectly.
 * It can cause hardware errors, which manifest as software crashes. (Generally speaking, all software assumes 100% error-free hardware.)