TensionPilot · Tennis string tension & setup tracking appFor players who want to play better.

Find the strings and tension that suit your game.

Track your setup and tension changes. Use your own history to guide your next string and tension choice.

Join the betaSee a measurement and history example

iPhone · AndroidFree during betaZero hardwareNo recording

Actual racquet detail screen — 42.9 lb estimate, 83% of the 52 lb setting, and measurement history

0.1.5 beta preview · Sample records Recapture pending — 10/08 detail shot (old basis labels)

We measure strings directly, check dimensions against physical test racquets, and review the calculations using stringing trials. See our measurement and review process →

ScenesHow people use it

Get to know your setup

Keep track of your strings, stringing settings, and changes over time. Refer to your own history before your next restring.

Follow the setup you string yourself

Compare your current estimate with your stringing setting, and track changes from your first measurement. Keep a reference for your next string job.

These are two scenes in the same app, not two products. One person can use both.

ExampleMeasurements and history on one racquet

Example measurement history for a racquet strung at a 52 lb reference setting. 0.1.5 beta preview Sample records

Actual racquet detail screen — 42.9 lb estimate, 83% of the 52 lb setting, and measurement history
  1. Compare the stringing setting and current estimate

    The current estimate of 42.9 lb is 83% of the 52 lb reference setting, 9.1 lb lower. The setting is what was entered on the machine and the estimate comes from the stringbed's frequency, so the gap is not all change from use.

  2. Track changes since the first measurement

    Follow the changes in your measurement history, from the first reading to the latest estimate. It is not the true tension at stringing time, nor a remaining lifespan.

  3. Look back before your next setup choice

    Tension history and play log sit together on one racquet. That is your reference when deciding whether to use a setup you liked again.

No history yet? Start with your own racquet's first measurement. A racquet without a reference setting shows the change since the first reading only. Absolute tension estimates are supported first for strings we have measured directly.

How it worksHow it works

Tapping the middle of the stringbed with a screwdriver handle
  1. 01Pick

    Your racquet and string from the list. Enter the tension and date, then start the history with an actual measurement.

  2. 02Tap

    Five taps in the middle, somewhere quiet. The mic reads the frequency. A screwdriver handle works best.

  3. 03Read

    The current estimate and measurement history on one screen. Look at tension changes alongside your play log.

EvidenceWe start by checking the data behind the math

Here is what we have checked, and what is still open.

We measure strings directly

The string data the calculation needs is measured in-house. Directly measured values and values converted from other conditions are kept apart.

We check test racquets against the physical frame

Racquet head width and length are measured with calipers and compared with dimensions derived from images. This is how we check the data used for face area.

We look at real stringing conditions

Readings are compared across racquets and stringing setups. When something is off, we look at the racquet, the string and the measurement conditions, and decide what to check next.

Measured stringbed area of 23 popular racquets
Is every 98 really a 98?

We lined up 23 racquets by measured face area. No. The same "98" runs from 94 to 99. So the tension math uses the measured area, not the number printed on the frame.

See how we measure area →
Field partner · Youngho Shin — Owner & Stringer, Tennis Cotro

A professional stringer in Korea, stringing since 2013 — an ERSA Master Racquet Technician with tournament stringing experience from ATP Challengers and WTA events to the 2023 Australian Open on a manufacturer's stringing team. He checks our measurements and experiments and advises on the app.

The tension figures in the app are estimates. The value set on the stringing machine and the value the app gives are not direct measurements of the same kind. No single number settles your ideal setup or when to restring.

RacquetPilotWhat we do now, and next

App

NowTensionPilot — string tension estimates and history. iPhone & Android closed beta.

NextYour racquet setup, too.

 Lab

NowString cross-sections, wear, color. Measured racquet face areas.

NextRacquet and accessory experiments.

 Data

NowBrowse the string data — brand, construction, gauge and whether tension estimates are supported.

NextKeeps growing.

 Learn

NowWhen to restring · what tension to pick · why tension drops.

NextMore questions answered.

An engineer who studied vibration in aircraft and helicopters switched to string vibration. These days I work as a data engineer who keeps physics in the loop. It started as a way to answer "when should I restring?" The physics was already there. No accounts, no ads. Tap, read the number, done.

By RacquetPilot LLC

BetaTry the beta with your own racquet

The current beta is free to join. It is invite-based; a nickname, an email and your device are all we need. iPhone users get a TestFlight invite, Android users a Firebase App Distribution invite by email.

Join the beta

FAQFrequently asked questions

What is the number the app shows?

A tension estimate calculated from the stringbed's frequency and the racquet and string data. It is not measured the same way as the value entered on a stringing machine.

It differs from my stringing setting. Is that normal?

It can. The two values are measured differently, so the gap is not all change from use. Check the reference shown on screen and follow the changes in your measurement history.

Do you record and keep the sound?

No. The taps are turned into a number on the device and are not saved as a recording. Details are in the privacy policy.

Can I use my string?

Any string in the list can be selected. Absolute tension estimates are supported first for strings we have measured directly; for the rest you follow the change since the first reading. See the string list.

Does it cost anything?

The current beta is free to join. Full-release terms will be announced with the launch information.

Can I use it for a shop or customer stringing?

Tools for shops and customer work are being developed separately. Ask about what is available now via Support.

Try the beta with your own racquetJoin the beta