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How to Read a Timeslip: What Every Number Is Telling You

Every number on the slip, and what each one is telling you about the car.

The timeslip is the cheapest data logger in racing. It will not tell you everything, but read properly it tells you where a run was won, lost, or wasted — the launch, the middle, or the top end. The trick is reading it in order, because each number covers a different piece of track.

Dial-in and reaction time

At the top you will usually find your dial-in and your reaction time (RT). RT measures the gap between the green light and your front tire clearing the starting beam. A perfect light is .000 on most modern systems. Negative numbers mean you left early — a red light.

RT diagnoses the driver and the car's first move, not the car's power. If your lights vary wildly, look at staging consistency first: rolling in a slightly different amount changes how much tire has to travel to clear the beam, so the same physical reaction produces different numbers. Shallow staging gives a quicker RT but a slightly slower ET, because the car gets less of a rolling start. Deep staging does the reverse. Same car, same driver, different numbers — just from inches in the beams.

RT is not part of ET — the clock starts when you clear the beam. A bad light loses races but does not make the car look slower.

The 60-foot time

The first real performance number, and for many cars the most important. The 60-foot measures how hard the car leaves: traction, converter or clutch behavior, chassis reaction, and the first hit of power.

For context, a mild street car might sixty-foot in 1.9 to 2.1 seconds; a well-sorted bracket car in the 1.4s to 1.6s; a fast car quicker still. Your number only matters compared with your own car's history.

A tenth lost in the sixty-foot rarely comes back. In fact it usually grows — a car that leaves slow is behind on speed at every marker after it, and a common rule of thumb is that a tenth in the sixty costs roughly two tenths at the stripe in a quarter-mile car. When a run is off and the 60-foot matches the ET loss, stop looking at the engine. Look at tire pressure, burnout, track prep, staging RPM, and whether the tires spun or the car bogged.

Spin and bog can produce similar sixty-foots with opposite cures — spin needs less hit or more tire; bog needs more RPM or converter. The slip cannot separate them; your memory or a video has to.

The 330-foot time

The 330 covers the rest of the launch: the 1-2 shift on many cars, the chassis settling, the converter coupling. If the sixty-foot was normal but the 330 is off, the problem started after the hit — a lazy shift, the driver pedaling, or the engine laying over early.

This split, and the others below, is why you should log increments, not just final ET. Subtract each marker from the previous one. Increments tell you where time went; totals only tell you that it went.

The eighth-mile: ET and MPH

Halfway down a quarter-mile track — and the full race distance at eighth-mile tracks — the 1/8-mile ET and MPH are the working racer's favorite numbers. By the eighth, the launch is done and the car is showing its power-to-weight honestly.

Eighth-mile MPH responds strongly to power and air, and less to launch drama than ET. If it is down all day while the sixty-foot is normal, check density altitude before you touch anything. If MPH is normal but ET is off, the time went early.

Use this number for comparing combinations, estimating horsepower, or converting between eighth- and quarter-mile. MPH-based estimates beat ET-based ones because MPH is less polluted by traction.

The 1000-foot time

In quarter-mile racing the 1000-foot is your last checkpoint before the stripe. The split from the eighth to the 1000 shows how the car is pulling through high gear.

If the car matches its usual numbers to the eighth but falls off by the 1000, look top-end: valve float, fuel delivery running short, ignition breaking up under load, a converter slipping excessively, or the engine simply running out of cam and head. Aerodynamics also start charging rent here, especially in a headwind.

For bracket racers the 1000-foot is also a decision point: if you know your car's normal number there, you can judge whether you are on your dial before deciding whether to lift at the stripe.

Quarter-mile ET and MPH

The final ET is the headline, but by the time you have read the increments it should hold no surprises. It is the sum of everything above.

Final MPH deserves its own look. Trap speed is the best single indicator of actual horsepower at the tire, which is why horsepower-from-MPH formulas exist. Two useful diagnostics:

• Good MPH, poor ET: the power is there; the front half of the run is wasting it. Traction, gearing, converter.
• Poor MPH, ET about right for it: the car is efficient but down on power, or the air is bad. Check the weather before the engine.

Also compare MPH gain in the back half — quarter MPH minus eighth MPH. A car that gains little on the top end relative to its norm may be over-geared, under-geared, or laying over. A healthy car picks up in a predictable range run after run.

Car number, lane, and the other side of the slip

Log the admin at the top — car number, lane, date and time. Runs are only comparable when you know the lane and the air they happened in. The opponent's numbers tell you the margin and whether you were beaten on the tree or on the track.

Putting it together

After each run, ask three questions in order. Was the light what I intended? Was the sixty-foot in its normal window? Did the MPH match the weather? If all three answers are yes, the car is doing its job and any ET variation is mostly air. If one answer is no, you have a specific place to look — and a specific thing not to change everywhere else.

Write the answers on the slip before the next round. Memory edits itself; paper does not.