Bike times, predicted and explained

watts & time is a free website for cyclists and triathletes. It answers two questions riders ask all the time and rarely get a straight answer to: how long will this course take me, and why was this ride faster or slower than that one?

Why it exists

The apps a bike computer syncs to say how fast you rode, and stop there. Take one rider on the Nice 70.3 bike course, ridden in 2019 on a time-trial bike and again in 2026 on a road bike: the second ride was 19:22 slower. Was that the bike, the position on it, fewer watts, a few more kilos, or the wind that day? Each has a different fix, and a rider deciding what to change before the next race needs to know which it was. The site is built to answer that, and to say how far each answer could be out. Read that comparison, start to finish.

What you can do here

• Predict a ride: how long a route or a race course will take, from your weight and the power you plan to hold, on a road bike, clip-on aerobars or a time-trial bike, with the range the answer could fall in.
• Find your race course: IRONMAN and IRONMAN 70.3 bike courses, each measured along the mapped roads with its climbing read off the ground, and a bike split for your own watts and weight.
• Analyse a ride: one ride file, read for what it measured: the climbs, flats and descents, the power held on each, and how aerodynamic the rider was.
• Compare two rides: two rides that share some road, and the time between them shared out between position, power, weight and the weather.
• Read the guides: the decisions riders argue about before a race, such as a TT bike, a disc wheel or clip-on bars, worked out on real courses with the numbers shown.
• Three calculators: what an aero upgrade is worth, any one of speed, power and time from the other two, and the gear ratios a climb needs.

How it works

Riding a bike is well understood physics. The power at the pedals goes three ways: pushing the air aside, rolling the tyres, and lifting rider and bike up the hills. A bike computer records the power, the speed and where the bike was. Put those together with the road and the weather, and the site can say how much of a ride's time each one took, and how much would change with a different position, more watts or a lighter bike.

The roads come from OpenStreetMap, the height of the ground from open terrain data, the weather from Open-Meteo, and the race courses from Blame the Course, where each race has a page of its own. Every page names what it used.

What it will and won't say

• Every figure says how sure it is. The range is worked out from what could actually be wrong: a power meter's tolerance, a bike nobody weighed, too little flat road to read a position from.
• "Can't tell" is an answer. Where a ride can't separate two causes, a headwind from a worse position say, the page says so instead of picking one.
• A model is not a measurement, and every chart that shows one says so.
• It explains your riding; it doesn't coach it. The figures are estimates for understanding your own rides, not training, medical or equipment advice.

Your rides stay yours

Ride files are read in your browser and never uploaded. Nothing about a ride is kept unless you choose to save an answer behind a link, and that answer loses your file name and the time of day first. What the site keeps, in full.

Free, with a few ads

Every tool is free and none needs an account. The site pays its way with a small number of ads, placed after the reading and never inside a result, and nothing from a ride is ever passed to them.

Get in touch

A question, a course that looks wrong, or a decision you'd like worked out: write to the person who runs the site, and the answer comes by email.