Tyre pressure & chain wear calculators

WatchMy.bike has two built-in maintenance calculators under Tools
in the main menu. Both start from your own bikes and components
instead of a blank form.

Tyre pressure

Tools → Tyre Pressure. Work out a front/rear pressure starting
point and save it to a bike.

1. Pick a bike. It prefills your system weight (your profile
   weight + the bike's weight), and sets the riding style and
   surface from the bike's type — a gravel bike starts on
   hard-pack, a mountain bike on off-road in inches.
2. Check the inputs. Adjust system weight, tyre width, riding
   style or surface. Tyre width has an mm ⇄ inch switch — road and
   gravel are usually mm (e.g. 32), MTB tyres are inches (e.g. 2.25).
3. Read the result. Front and rear pressure, with a bar ⇄ psi
   toggle. If the bike has tyres tracked as components, they're listed
   with a wear ring so you can see what the pressure is for.
4. Save to bike. The pressure shows on the bike's page and in the
   Tyre pressure block on your dashboard. Reopen the tool any time
   from there to recalculate — it loads your saved inputs.

The number is a starting point, not a rule. Run lower for grip and
comfort on rough ground, higher on smooth tarmac.

Chain wear

Tools → Chain Wear. Measure how worn a chain is and see how much
life it has left.

1. Pick a chain (optional). Selecting an installed chain lets the
   tool use the distance already tracked on it.
2. Set the drivetrain speed — 11/12-speed replaces at 0.5%
   elongation, 10-speed and older at 0.75%.
3. Measure with a ruler. A new chain is exactly 25.4 mm (1 inch)
   per link, with a rivet on each inch mark. Line a rivet up with 0,
   count whole links (12 is the usual span), and enter the measured
   length (mm or inch).
4. Read the result. The wear percentage, a replace/keep verdict,
   and — if you picked a chain — an estimate of how far it has left at
   its current wear rate.

If you own a chain checker tool, that's the quickest go/no-go method;
this calculator is the ruler-based fallback.

Turning a reading into a reminder

Calculators tell you where you are now. To stop guessing next time,
pair them with maintenance alerts
and service intervals — for
example, a distance-based "replace chain" interval so the chain check
becomes a scheduled prompt rather than something you remember to do.