Quarter-Mile Times Explained: ET, Trap Speed & What's Good

What do ET and trap speed mean?

ET stands for elapsed time: the stopwatch time from the moment your car leaves the start line to the moment it crosses the finish, a quarter of a mile later. At a drag strip the clock is started by the staging beam — a light sensor at the start line — and stopped by another at the finish. Your reaction time to the green light is recorded separately and is not part of your ET, which is why a lazy launch off the lights doesn't hurt the headline number.

One quirk worth knowing: the clock only starts once your front wheel has rolled clear of the staging beam — roughly a foot of free movement before timing begins. That 1-foot rollout is the drag-strip convention most manufacturers borrow when quoting 0–60 mph figures, and it's typically worth about 0.2–0.3 seconds compared with timing from a true standstill.

Trap speed is your average speed through the 'speed trap' — the final 66 feet of the quarter mile, exactly one-twentieth of the distance. Two beams time how quickly you cover that last stretch, and averaging over 66 feet smooths out instantaneous blips, giving a robust figure for how fast you were genuinely travelling at the line.

What is a good quarter-mile time?

It depends entirely on what you're driving, so it's more useful to think in broad bands. Roughly speaking, on a decent surface in dry weather:

• Family cars and crossovers: about 16–18 seconds at 80–90 mph
• Hot hatches: about 13.5–15 seconds at 95–105 mph, with the quickest all-wheel-drive hatches reaching into the high 12s
• Sports cars: about 12–13.5 seconds at 105–118 mph
• Supercars: about 10.5–11.5 seconds at 125–135 mph
• Quick EVs: many dual-motor saloons run 11–12 seconds, and the very quickest production EVs are into the 9s

What does the ⅛-mile split tell you?

The ⅛-mile split — your elapsed time at 660 feet, the halfway mark — cleanly separates the launch phase from the top end. A long-standing rule of thumb says a quarter-mile ET is roughly your ⅛-mile ET multiplied by 1.55, so any big deviation from that ratio is telling you something.

A strong eighth followed by a fading quarter points to a car that hits hard off the line but runs out of pull — short gearing, aerodynamic drag, or power tapering at speed, a shape familiar from many EVs. A weak eighth paired with a high trap speed means the power is there but the launch isn't: wheelspin, a bogged-down clutch, or boost arriving late. Sorting the launch is almost always the cheapest route to a better ET, which is why the split is worth watching as closely as the headline time.

Why is trap speed the honest measure of power?

ET is contaminated by everything that happens in the first few car lengths: surface preparation, tyre temperature, ambient conditions and driver skill. A moment of wheelspin off the line can add half a second to your ET while barely denting your trap speed. Trap speed, by contrast, tracks power-to-weight closely — it's why racers use trap-speed calculators to estimate horsepower, and why a big trap with a mediocre ET reads as 'fast car, poor launch' rather than 'slow car'.

Don't be surprised if your trap speed is lower than what the dashboard showed at the line. Car speedometers are legally required never to under-read, so almost all of them over-read by a few percent. Beam-measured trap speeds and GPS-derived speeds show your true speed; your speedo has been flattering you all along.

How can you measure a quarter mile legally?

The proper answer is a drag strip. Most strips run public test-and-tune or 'run what you brung' sessions where anyone with a roadworthy car can pay a modest entry fee and make timed passes on a prepped, grippy surface, with marshals on hand and a printed timeslip at the end. It's the only way to get a certified number, and it's enormous fun.

For informal benchmarking, GPS timing is the modern route. Dedicated 10–25 Hz GPS performance boxes are the benchmark hardware and typically cost £100–£300. A phone app is the accessible alternative: PitLaunch fuses the iPhone's GPS with its motion sensors, detects your launch automatically, and records quarter-mile ET, trap speed and the ⅛-mile split — alongside 0–60 and roll-on times — to the hundredth of a second with a ± confidence band on every run. Mounted rigidly with a clear view of the sky, it delivers comparable practical accuracy for road-and-track hobby use; it isn't a certified timing system, and it doesn't pretend to be.

Wherever you time, do it off the public road — a drag strip, track or closed course. Set everything up before you set off, or have a passenger operate it; never interact with the phone while driving, and always obey local laws.

Frequently asked questions