Answers
Questions and answers
What WattCut measures, what it needs from you, and what it does not claim. If something here is still unclear, ask us directly.
The basics
What is WattCut?
WattCut is an aerodynamic position-comparison service for cyclists and triathletes. You photograph the riding positions you want to compare, and WattCut simulates the airflow around each one and reports how they rank — as aerodynamic drag, and as watts at real riding speeds.
It answers one question: of the positions available to you, which is worth riding? Nothing is designated as a reference or baseline, so every position you submit is compared against every other one.
Is this a real wind tunnel?
No. The simulations are computational — the flow around your body and bike is solved numerically rather than measured in a physical tunnel, and no tunnel time is booked on your behalf. The phrase 'wind-tunnel simulation' describes what is being modelled, not a booking.
That is the trade WattCut makes deliberately. A tunnel session is more authoritative and costs several hundred euro plus a day of travel; a simulation is cheaper, repeatable, and can be run from photographs you take at home.
Who is it for?
Road cyclists, time triallists and triathletes who want to know whether a position change is worth riding before committing a season to it.
It is most useful if you already have a position you can hold and are considering changing something about it — dropping your torso, narrowing your arms, changing stem height, moving to clip-on aerobars.
How is this different from a bike fit?
A bike fit optimises for comfort, sustainable power and staying uninjured, using a fitter's judgement and your feedback in the room. WattCut answers only the aerodynamic question, and it answers it with numbers.
They complement each other rather than competing. A fit tells you which positions your body can actually hold; a comparison tells you what each of those positions costs you in watts. The fastest position is not automatically the best one.
What is CdA?
CdA is drag area — the drag coefficient multiplied by frontal area, measured in square metres. It is the single number that describes how hard the air is to push through, and for a cyclist on a flat road it is the dominant thing standing between your power and your speed.
The power needed to overcome aerodynamic drag rises with the cube of speed: P = ½ · ρ · CdA · v³. Doubling your speed needs eight times the power. This is also why a change in CdA is worth far more at 45 km/h than at 30.
Sending your positions in
What photographs do I need to send?
Two sets. First, two full-body photographs of yourself without the bicycle — one from the front, one from the side — plus your height. Those build the model of your body.
Then a front and a side photograph of each riding position you want compared, on the complete bicycle. Two positions is the minimum; there is no upper limit.
Do I need special equipment?
A phone camera is enough. What matters is even lighting, a plain background, and someone to take the photographs — or a tripod and a self-timer.
You do not need a turbo trainer, a power meter, or any measurement device. The comparison is made from the photographs and your height.
Why do you need my height?
A photograph has no inherent scale. The same image could be a tall rider standing far away or a short rider standing close. Your height is the reference that turns pixels into centimetres, and every measurement taken afterwards depends on it.
It is the only body measurement required. Everything else is read from the two photographs.
What has to stay the same between the photographs?
Everything except the position itself: the same bicycle, the same clothing, the same helmet and shoes, the same camera position, height and distance, the same lighting, the same background, and the same crank orientation.
The comparison is only as trustworthy as the things that stayed identical between the photographs. A change of jersey between two shots turns up in the result as though it were a change of position.
How many positions can I compare at once?
Two is the minimum and there is no upper limit. Every position you send is compared against every other one — there is no fixed baseline that the others are measured from.
Because nothing is designated as the reference, adding a position later does not invalidate the ones before it. It simply joins the ranking.
Can I compare helmets, clothing or equipment instead of positions?
The comparison reads what the photographs show, so anything that visibly changes the shape presented to the wind is a valid thing to compare — a different helmet is a position in its own right as far as the air is concerned.
The rule stays the same: change one thing at a time. If you drop your torso and change your helmet in the same photograph, the result tells you the combined difference but not which change earned it.
How should I sit for the photographs?
Sit as you would an hour into a ride, not as you can hold for the two seconds a shutter is open. A position you can only reach for a photograph will rank well and mean nothing.
The comparison is only useful if every position in it is one you could genuinely use for the duration you actually ride.
The results
What do I get back?
A report ranking every position you submitted by aerodynamic drag, with the gaps between them expressed in watts at realistic riding speeds rather than at a single speed.
It also describes what actually changed between the positions, so the number is attached to something you can act on rather than arriving as a bare figure.
How accurate is it?
WattCut reports differences between your own positions, photographed under identical conditions — not an absolute drag figure you could compare against someone else's tunnel result.
That is a deliberate choice rather than a limitation being glossed over. An isolated CdA number depends heavily on assumptions about equipment, clothing and conditions; comparing your own photographs against each other cancels most of that out, because the same assumptions apply on both sides of the comparison.
WattCut is in beta and does not claim a validated accuracy figure. Treat a result as information about the direction and rough size of a difference, not as a calibrated measurement.
How many watts can a better position actually save?
It depends entirely on the rider and on what changes, which is why WattCut reports your numbers rather than quoting a headline figure. A position change that does very little for one rider can be worth a great deal for another with different proportions.
What is predictable is how the saving scales. Because the power needed to overcome drag rises with the cube of speed, the same reduction in drag area is worth far more at 45 km/h than at 30. This is why the report gives watts across a range of speeds instead of one number.
Will a faster position make me faster overall?
Not necessarily. A more aerodynamic position can save watts and still be the wrong position for you. Comfort, breathing, visibility, bike handling and your ability to produce power all matter, and a position that costs you 15 watts of output to save 10 watts of drag is a loss.
The most useful position is the one you can hold and pedal hard in for the duration you actually ride. Treat a result as information, not as an instruction.
How long does a comparison take?
WattCut is in beta and turnaround is not yet fixed, so no delivery time is promised. Parts of an analysis may be completed manually during this phase.
Submitting images does not guarantee that an analysis will be produced immediately.
Beta, price and privacy
What does it cost?
Joining the beta list is free and costs nothing but an email address. Nothing is charged when you join.
Simulations are bought as a pack. During the beta, 2 wind-tunnel simulations cost €35 instead of the intended €69, and 5 cost €80 instead of €159. Registering now is what holds that price.
These are total prices in euro. No VAT is added, as WattCut operates under the German small-business rule (§ 19 UStG), so the figure shown is the figure paid.
Do I need to create an account?
No. There are no accounts and no passwords. The beta list takes an email address and nothing else, and that is the only entry point the site has.
What happens after I join the list?
You get a confirmation email, and nothing is charged. We contact you when beta places open, with the early-bird price held until then.
The list closes on 31 October 2026. A place on the list does not guarantee a beta invitation or an immediate analysis.
What happens to my photographs?
Your images are used to estimate your body proportions, reconstruct the riding positions and produce the comparison between them. During early access, parts of that may be done manually.
Nothing is uploaded at the point of joining the list — the list is an email address only.
Who is behind WattCut, and where is it based?
WattCut is run by Christian Eichler from Hamburg, Germany, and started as one triathlete's attempt to answer the position question for himself in a virtual wind tunnel.
It is an early-stage project rather than an established company, which is stated plainly rather than dressed up.
Get aero. Go faster. Same watts.
Free to join · 2 for €35 · 5 for €80 · Closes 31 October 2026