Power to Weight Sheet
W/kg decides climbs, watts decide the flat. Both figures, and what a kilo is worth.
BFCBrilliance · bfcbrilliance.com/tools/cycling-power-to-weight-calculator
The arithmetic
- W/KG
- power ÷ mass
- For a CLIMB use
- rider + bike + bottles + tools
- RATE OF CLIMB (VAM)
- W/kg x 3600 ÷ 9.81 = W/kg x 367
- Realistic VAM
- that, minus 10-15% on a steep climb
- Time up a climb
- vertical metres ÷ VAM
- 250 W, 70 kg + 8 kg bike
- 3.21 W/kg total, about 1,035 m/h
- ⚠ W/kg rules CLIMBS
- raw watts rule the FLAT
- ⚠ Power needs a DURATION
- a 5-min peak will not ride a 40-min climb
- ⚠ Meters disagree
- compare yourself to yourself, not to others
Climbs planned
| Climb | Vertical m | Power used | Total kg | VAM | Time |
|---|---|---|---|---|---|
This rider
- Rider
- Date
- Power and duration
- Body weight
- Bike and kit
- TOTAL MASS
- W/KG BODY
- W/KG TOTAL
- Losses assumed
- VAM
- Climb
- PREDICTED TIME
- Actual time
- Difference
Getting a figure you can trust
- Power figure matched to the DURATION of the climb
- Bike weighed WITH bottles, tools and food on it
- Body weight taken at a consistent time of day
- Loss percentage adjusted for the gradient — more on shallow climbs
- Same power meter used for any comparison over time
- Predicted time checked against a real ride afterwards
- Cleared with a clinician before any maximal test, if there is reason to
- Hard efforts done somewhere you can afford to stop
The terrain picks the number
On a steep climb nearly all your power lifts mass, so W/kg decides it. On the flat gravity does nothing and air resistance takes almost everything — and that scales with frontal area, not weight. The big rider who rides away from you on the flat and loses on the mountain has not changed; the terrain changed which number counts.
A kilo, in seconds
Rather than arguing about whether a lighter bike is worth it, read the seconds-per-kilogram figure for the climb you actually ride. It is usually a handful of seconds — meaningful if you are racing, trivial if you are not. Worth remembering that a kilo off the rider does exactly the same job and costs nothing.