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How chip timing works

Almost every organised race in the UK now times its runners with a small radio tag rather than a stopwatch. This guide explains what the tag is, how the mats on the road read it, and why a time occasionally goes missing.

What the chip actually is

A timing chip is a radio frequency identification (RFID) tag. It holds a unique code that is linked to your race number in the timing database. Most tags used in running are passive, which means they have no battery. They stay silent until they pass through a radio field at a timing point, which gives them just enough energy to send their code back.

There are two common forms:

  • Bib tags. One or two thin foil and foam strips stuck to the back of your race number. These work at ultra high frequency (UHF), are cheap enough to throw away, and are now the norm at road races from 5K to marathon.
  • Shoe or ankle chips. A small plastic disc or tag laced into a shoe or worn on a strap around the ankle. Older systems used low frequency chips that had to pass very close to the mat, which is why they sat at foot level.

Timing mats and antennas

At each timing point the organiser lays flat mats across the full width of the course, or mounts antennas on a gantry or at the side of the road. The antennas are connected to a reader with an accurate clock. As you cross, the reader powers your tag, receives its code several times in a fraction of a second, and stores each read with a time stamp.

A typical road race has timing points in three kinds of place:

  1. The start line. This records the moment you personally cross the line, which may be seconds or many minutes after the gun.
  2. Intermediate splits. Larger events add mats at points such as 5K, 10K or halfway. They give you split times and also confirm that every runner covered the full course.
  3. The finish line. Usually two lines of mats a few metres apart, so that a missed read on the first line is picked up by the second.

How the reads become results

Each reader collects a list of tag codes and times. Timing software matches each code to a bib number and then to the entrant's name, club and category. It filters the multiple reads from one crossing down to a single time, subtracts the gun time to give a gross time, and subtracts your own start read to give a net time. The difference between the two is covered in chip time vs gun time.

Results shown minutes after you finish are provisional. The timing team still checks for missing reads and swapped numbers before confirming them. Our guide on how to read race results explains what each column means.

Why a chip sometimes fails to read

Modern systems read the great majority of tags, but a few are missed at most events. The usual causes are simple:

  • A folded or creased number. Folding the bib to make it smaller can crack the antenna inside the tag.
  • The tag is covered. A jacket, a hydration vest, a bum bag, a phone or a hand held across the chest can block the signal. Water and the human body both absorb UHF radio.
  • The number is worn on the back or the leg. Bib tags are designed to face forwards on the chest or stomach, with the foam spacer holding the tag slightly away from the body.

Pin the number flat on your front at all four corners and keep it visible. If your time is missing, tell the organiser promptly with your bib number and rough finish time. There is more on race morning preparation in the race day checklist.

Disposable and returnable chips

Bib tags are disposable: you keep the number and nothing is handed back. Shoe and ankle chips may be disposable or returnable. Returnable chips are sturdier and are reused many times, so marshals collect them just after the finish line. If you drop out, the event instructions will say how to return yours.

Timing in triathlon

A paper number would not survive the swim, so triathletes wear a chip on a soft strap around the ankle. Mats at the swim exit, at the entrance and exit of transition, and at the finish break the race into five parts: swim, first transition (T1), bike, second transition (T2) and run. That is why triathlon results show transition splits as well as the three disciplines. See the triathlon guide for more.

Timing in cycling sportives

Sportives are timed rides, not races, but most still give each rider a time. The tag is commonly a sticker on the helmet or part of a handlebar number board. Riders set off in small waves, so times are net, from start mat to finish mat. Our cycling sportive guide covers what to expect on the day.