watts&timeFiles stay in your browser

Compare two rides

Why was one ride slower than the other?

Compare two rides on the road they share and see how much of the difference was drag, power, weight, heat or stops — each with how sure it is. Your .fit files are read in your browser and never uploaded; the decoded numbers go to the server for the comparison and are not kept.

Choose your two rides

A .fit file on each row, zipped or not — pick it, or drop it on the row. A name and a weight are optional and stay with the file beside them: the weight sharpens every number, and the name replaces the date everywhere on the page.

Ride 1
or drop it here
kg
Ride 2
or drop it here
kg

Total weight is everything that moved: rider, bike, water and gear on the day. Left blank, the page uses the head unit's rider profile plus a typical bike, or reads a weight off the climbs, and says which. Once compared, each box shows the figure the page used, to be adjusted; it counts as yours only once you change it.

0 of 2 rides loaded.

What you'll find out

  • Like for like. The rides are matched by GPS and compared only on the road both took; a detour or an extra lap is set apart, not blamed on you.
  • How much was drag. Position, drafting and wind, measured from the ride rather than assumed.
  • Whether it was the wind. Drag by heading, and an optional look-up of the wind that day.
  • How much was fitness. Time lost or gained to power, with a warning when two power meters may disagree.
  • How much was weight and heat. Rider and bike weight, and how warm air is thinner and faster.
  • Where on the route. A map and a kilometre-by-kilometre view of where time changed hands.
  • What would help most. What a bottle, the drops or faster tyres are worth on your own road.

Questions

Which files work?

Any .fit file from a bike computer, such as Garmin, Wahoo or Hammerhead, including the zipped .fit.gz that Garmin Connect exports. The full breakdown needs a power meter on both rides.

Are my rides uploaded anywhere?

No. The files are read in your browser. The map loads its tiles from a map service, the elevation check loads terrain tiles from another, and the wind comes from a third; each is told the area of the ride and nothing more, and the wind service is also told the date, because the day the wind blew is the point of asking.

Do the two rides need to be the same route?

Mostly. The rides are matched by GPS; road only one ride took, such as a detour or an extra lap, is counted separately as a different road rather than blamed on you.

How accurate is it?

Every number says how sure it is, from the things that could really be wrong: an unknown bike weight, a power meter's tolerance, too little flat road. Descents are timed rather than explained, because braking would otherwise look like drag.

Can it tell a headwind from being less fit?

Often. Wind makes drag higher in one direction and lower in the other; a change in fitness shows in the power instead. Where the files cannot separate them, the page says so.

Does a wheel speed sensor make a difference?

Yes. Distance and speed are taken from your file, and your head unit measures them from a wheel sensor when it has one and from GPS when it does not. GPS wanders under trees, in cuttings and through switchbacks, and it cuts every corner, so a ride without a sensor reads a little short and its speeds a little rough. A wheel sensor with the right circumference set is the more accurate of the two, and every figure here that is measured per kilometre is measured better with one.