Eight-ride summary
41.14 km in total · 75 minutes of timer time
| Ride | Start | Helmet | Time | Distance km | Avg speed km/h | Avg power W | Normalised power / W |
|---|---|---|---|---|---|---|---|
| 01 | 06:29 | Giro Agilis | 9:32 | 5.152 | 32.42 | 200 | 207 |
| 02 | 06:44 | Trek Ballista | 9:26 | 5.107 | 32.49 | 200 | 206 |
| 03 | 07:02 | MET Codatronca / glasses | 9:27 | 5.121 | 32.51 | 200 | 205 |
| 04 | 07:20 | MET Codatronca / visor | 9:29 | 5.133 | 32.47 | 200 | 207 |
| 05 | 07:43 | MET Codatronca / visor | 9:17 | 5.157 | 33.33 | 200 | 207 |
| 06 | 08:00 | MET Codatronca / glasses | 9:15 | 5.155 | 33.44 | 205 | 210 |
| 07 | 08:19 | Trek Ballista | 9:17 | 5.161 | 33.36 | 202 | 210 |
| 08 | 08:36 | Giro Agilis | 9:17 | 5.158 | 33.34 | 203 | 210 |
Average power shows the overall effort. Normalised power also reflects harder bursts. The race estimates below use a target of 180 W.
Rides 1–4 started from rest. Rides 5–8 used rolling starts. Timer time excludes pauses.
90 km comparison.
The main model estimates a saving of about one to one-and-a-half minutes for the alternatives to the Giro.
It compares the helmets at the same power and uses 2 h 40 min as the Giro reference time.
All eight rides · Two rides per helmet setup · Same rider, bike, route, and tyre pressures
| Helmet setup | Main estimate Speed from GPS positions | Alternative estimate Recorded speed | What stands out |
|---|---|---|---|
| Giro Agilis | 0s · baseline | 0s · baseline | Reference helmet |
| Trek Ballista | 1m 25s faster | 1m 10s faster | The most consistent gain across the tested methods |
| MET Codatronca with glasses | 1m 35s faster | 10s faster | Close to Ballista in the main model |
| MET Codatronca with visor | 1m 10s faster | 25s slower | A smaller gain in the main model |
The main comparison uses the same 4.60 km section from every ride. It accounts for power, hills, and changes in speed.
How much does the method matter?
Five ways to calculate speed, each across four route selections. Every calculation uses all eight rides.
The bars show how the answer changes with the speed calculation and the selected route sections.
Ballista: gains across the methods
Across these 20 methods, the Ballista estimate ranges from about 45 seconds to 2 min 10 s saved.
MET: a wider mix of results
The glasses setup ranges from about 20 seconds slower to 1 min 35 s faster. The visor ranges from 1 min 05 s slower to 1 min 25 s faster.
Straights versus bends
A direct comparison of Trek Ballista and MET Codatronca with visor.
The straight-section estimate favours Ballista over the Codatronca with visor, despite the Codatronca’s dedicated TT design.
This comparison uses the MET with visor as the reference. Less power at the same speed means an advantage for Ballista.
| Part of the route | Distance | Ballista relative to MET with visor |
|---|---|---|
| Straighter sections | 1.68 km | 4.1 W less power |
| Rest of the route, including bends | 2.92 km | 2.7 W more power |
A consistent average across methods
All five speed calculations favour Ballista on the straighter sections, by about 4–9 W on average.
The straight-section lead switches between the two pairs of rides. The table combines both rides for each helmet.
Why the result stands out
A dedicated TT design does not automatically give every rider the lowest drag. Helmet shape and rider position work together to affect airflow.
The rest-of-route group also contains short straights, hills, and acceleration. Its result combines those features with the bends.
90 km calculator
The calculator estimates the time difference over 90 km at equal power. It always uses all eight test rides.
Main method · All eight rides · 4.60 km per ride
| Helmet setup | Estimated change | Estimated time | Power saved at the Giro reference speed | With a ±5 W difference |
|---|
At the default settings, the main gains equal about 3.5–4.5 W. The slider shows how a small power difference changes the result.
A few useful details
The Giro rides were 15 seconds apart
The first Giro ride took 9:32. The second took 9:17. The model adjusts for power and speed changes before it compares helmets.
Higher power at the start
Average power in the first minute rose from 217 W in rides 1–4 to 245 W in rides 5–8.
The later rides began at about 12–13 km/h. The main comparison leaves out the first 500 m.
The fastest ride also had more power
The 08:00 ride with MET glasses had the highest average speed, at 33.44 km/h. It also had the highest average power, at 205 W.
Compare the rides along the route
The charts show where speed and power changed. The green sections mark the straighter parts used in one of the comparisons.
1 · 0.94–1.62 km
2 · 2.32–2.89 km
3 · 4.07–4.50 km
North is at the top.
The chart smooths brief jumps in power to make the lines easier to read. The calculations use the original power readings.
Two ways to calculate speed
The device records speed and distance separately. Those two records give slightly different totals.
For the same 4,600 m section, the distance implied by recorded speed ranges from 4,460 m to 4,524 m.
That difference matters because air resistance rises quickly with speed. The main model calculates speed from GPS positions so every ride uses the same route.
| Ride start | Distance from the speed readings | Difference from 4,600 m |
|---|---|---|
| 06:29 | 4523 m | 1.68% |
| 06:44 | 4499 m | 2.19% |
| 07:02 | 4460 m | 3.04% |
| 07:20 | 4501 m | 2.16% |
| 07:43 | 4461 m | 3.02% |
| 08:00 | 4507 m | 2.02% |
| 08:19 | 4524 m | 1.65% |
| 08:36 | 4523 m | 1.68% |
The alternative speed calculations show how this difference affects the estimated helmet savings.
How the comparison works
The model uses recorded power and speed to estimate air resistance, then works out the time difference over 90 km.
This version assumes the same wind and turn technique for all eight rides.
- Rider + equipment
- 87 + 13 = 100 kg
- Bike
- Canyon Speedmax CFR
- Power meter
- Shimano
- Race reference
- 180 W / 33.75 km/h
- Assumed air density
- 1.20 kg/m³
- Tyre resistance / drivetrain efficiency
- Crr 0.004 / 97.5%
Water and bottles: The rider drank only between rides, and all bottles stayed mounted. The water stayed with the rider and bike, so the model needs no adjustment for water consumption.
The same section of road
The model lines up the GPS tracks and compares the same start and finish points. The main section runs from 500 m to 5,100 m.
The same effort
The model adds up recorded power over time. It accounts for the energy needed to climb hills and change speed.
One shared hill profile
The altitude readings differ slightly between rides. A shared profile from all eight rides gives each helmet the same hills.
Both rides count
Each helmet has one ride in each half of the test. The model compares each half against its Giro ride, then gives both halves equal weight.
The maths behind the estimates
CdA is a number that describes how much air resistance the rider and bike create. A lower number means less drag.
The test model estimates CdA from power and speed. Its estimate also includes losses that the files do not measure separately.
- P: power measured at the cranks.
- m: rider and bike mass, set to 100 kg.
- g: gravitational acceleration.
- Crr: the number used for tyre resistance.
- η: the share of pedal power that reaches the wheel.
- ρ: air density.
- D and Δh: distance and the change in height.
- v: speed. The entry and exit speeds account for the change in kinetic energy.
- ∫: a sum over time.
- C₀ and T₀: the Giro drag area and time used as the race reference.
- ΔC: the difference between the Giro and another helmet.
The model adds the energy terms across the selected sections before it calculates each ride’s CdA.
The race calculation uses a flat, still-air course. The Giro reference of 180 W and 160 minutes gives a CdA of about 0.281 m².
The slider converts the selected power difference into a change in CdA before it calculates the time.
Details of the speed and route calculations
Ride 1 defines the reference route, with a point every 5 m. Each GPS sample matches a nearby section of that route.
The search stays within 120 m of the sample’s recorded distance. The matched position can only move forwards along the route.
The model estimates the time at each start and finish point from the nearest samples.
- GPS positions / 2 s: A Gaussian filter smooths brief jumps in position. Speed comes from the change in position over time.
- GPS positions / 4 s: The same method uses a wider filter.
- Recorded speed: Speed comes directly from the FIT file.
- Recorded speed / adjusted: A single multiplier makes the speed readings add up to 4,600 m through the main section.
- Recorded distance / adjusted: Speed comes from the change in recorded distance over time, with the same distance adjustment.
The 2 s and 4 s labels refer to the Gaussian filter’s standard deviation. The records are one second apart through the selected sections.
The shared altitude profile uses the middle value across all eight rides at each 10 m point, after each ride’s height offset is removed.
The straighter sections come from the route shape. A direction change above 25° across 40 m removes that area and 100 m on each side.
The search covers 600–4,900 m. Each remaining section must cover at least 150 m. Three sections remain, with a total of 1,680 m.
Five speed calculations and four route selections produce the 20 comparisons below. All use both rides for each helmet.
The straight-versus-bends comparison splits the main 4.60 km selection into the three straighter sections and the remaining 2.92 km.
The remaining section totals equal the main totals minus the straighter-section totals. The model calculates drag from those energy totals.
All 20 calculation methods
| Speed calculation | Part of the route | Ballista | MET / glasses | MET / visor |
|---|---|---|---|---|
| Recorded speed | 0.10–5.10 km | 1m 15s faster | 20s slower | 35s slower |
| Recorded speed | 0.50–5.10 km (main) | 1m 10s faster | 10s faster | 25s slower |
| Recorded speed | 1.00–5.00 km | 45s faster | 20s slower | 1m 05s slower |
| Recorded speed | Three straighter sections | 1m 55s faster | 10s faster | 1m 00s slower |
| Recorded speed, adjusted to match distance | 0.10–5.10 km | 1m 35s faster | 1m 00s faster | 55s faster |
| Recorded speed, adjusted to match distance | 0.50–5.10 km (main) | 1m 30s faster | 1m 30s faster | 1m 05s faster |
| Recorded speed, adjusted to match distance | 1.00–5.00 km | 1m 05s faster | 1m 05s faster | 25s faster |
| Recorded speed, adjusted to match distance | Three straighter sections | 2m 10s faster | 1m 20s faster | 10s faster |
| GPS positions, 2 s smoothing (main) | 0.10–5.10 km | 1m 35s faster | 1m 20s faster | 1m 15s faster |
| GPS positions, 2 s smoothing (main) | 0.50–5.10 km (main) | 1m 25s faster | 1m 35s faster | 1m 10s faster |
| GPS positions, 2 s smoothing (main) | 1.00–5.00 km | 1m 35s faster | 1m 20s faster | 1m 25s faster |
| GPS positions, 2 s smoothing (main) | Three straighter sections | 1m 00s faster | 1m 20s faster | 25s slower |
| GPS positions, 4 s smoothing | 0.10–5.10 km | 1m 35s faster | 1m 05s faster | 1m 10s faster |
| GPS positions, 4 s smoothing | 0.50–5.10 km (main) | 1m 30s faster | 1m 15s faster | 1m 00s faster |
| GPS positions, 4 s smoothing | 1.00–5.00 km | 1m 35s faster | 1m 10s faster | 1m 10s faster |
| GPS positions, 4 s smoothing | Three straighter sections | 1m 10s faster | 1m 20s faster | 10s slower |
| Recorded distance, adjusted to match route | 0.10–5.10 km | 1m 30s faster | 1m 10s faster | 1m 05s faster |
| Recorded distance, adjusted to match route | 0.50–5.10 km (main) | 1m 20s faster | 1m 15s faster | 1m 00s faster |
| Recorded distance, adjusted to match route | 1.00–5.00 km | 1m 30s faster | 1m 00s faster | 55s faster |
| Recorded distance, adjusted to match route | Three straighter sections | 1m 25s faster | 1m 05s faster | 50s slower |