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Crr (rolling resistance).

Field test · reverse-solve from steady-power ride

Plug in a steady, flat ride with known CdA, we reverse-solve for your tire’s rolling-resistance coefficient. Get the test protocol right and you’ll have a number you can act on. Skip the protocol and the answer is noise.

Read the protocol ↓ Skip to calculator

Field-test protocol

Crr is sensitive. Skip a step and your answer is off by 50%+.

01

Conditions

  • Calm wind, under 10 km/h ideal, under 5 km/h preferred
  • Flat road, gradient under 1%, or use a known out-and-back loop
  • Smooth surface, same surface for the entire test
  • Dry, mid-day, consistent surface temp, no overnight moisture
02

Equipment

  • Power meter, calibrated, zero-offset done before ride
  • Known CdA, from wind-tunnel, field aero test, or a Ghibli sensor
  • Tire pressure logged, pump to target, write it down
  • Same kit you race in, or your CdA reference is wrong
03

Execution

  • Steady power, ±5% of target, no surges
  • Steady position, never sit up, never change grip
  • 15+ min duration, longer averages out micro-variability
  • Out-and-back if windy, cancels asymmetric wind effects
  • Pre-weigh in full kit, rider + clothes + bike + bottles, on a calibrated scale

Reality check: Crr field-tests are noisy. Run the protocol twice and average. If the two answers disagree by more than 10% (e.g. 0.0035 vs 0.0042), one or both tests had a problem. Re-test, don’t average bad data.

Alternative, coast-down method

No power meter? Use coast-downs.

If you don’t have a power meter, or you want a simpler protocol, the coast-down method works well: ride a small downhill, stop pedaling, let the bike roll onto a flat or gentle uphill section, and measure how the speed changes.

  • Repeat 5–8 times from roughly the same start point, same position, no braking, no pedaling once coasting starts
  • Calm wind mandatory, even 5 km/h corrupts the result; this method is more wind-sensitive than power-based
  • Logs the FIT file, you need GPS speed and ideally elevation; the maths solves for both CdA and Crr from how the bike decelerates against drag + rolling friction
  • Single-speed estimate, at one speed point you can solve for Crr if CdA is known. Multi-speed coast-downs (Chung method) solve both simultaneously

The full Chung virtual-elevation analysis, multi-coast-down with FIT-file processing, simultaneous CdA + Crr fit, lives in our coaching platform. The single-effort version above with a known CdA covers most athletes’ needs.

Chung analysis with coaching

Plug in your test ride

All fields are required except the optional humidity / pressure override. Power should be your steady-state average for the test segment, not the whole ride.

Rider, bike & drivetrain
kg
kg
Helmet, shoes, bottles.
kg
%
Crank power × this %. Hub/trainer = 100%.
m²
From wind tunnel, field aero, or Ghibli avg.
Environment
m
°C
km/h
+ headwind, − tailwind.
%
hPa
Skip to use altitude-derived pressure.
Test ride
W
km
m
Net up; flat = 0.
: :

Result

— —
Speed—
Slope grade—
Power → aero—
Power → rolling—
Power → climbing—
Air density used—
Pressure used—

Interpreting the Crr number

Where your number sits and what it tells you.

< 0.0030

Excellent

Top-tier road tires (Continental GP5000 latex, Vittoria Corsa Speed) on smooth tarmac at proper pressure. Few setups achieve this in real-world conditions.

0.0030 – 0.0040

Very good

Quality road tires (28 mm GP5000, Pirelli P Zero, Vittoria Corsa) on chip-seal-grade tarmac. Where most well-set-up TT/road bikes land.

0.0040 – 0.0055

Average

Training tires, slightly worn rubber, or rougher tarmac. Or properly-set-up gravel tires on smooth surfaces.

0.0055 – 0.008

High

Gravel / cyclocross tires on hardpack, or road tires badly under-pressurized. 30+ watts cost vs. proper road setup at race pace.

0.008 – 0.015

Very high

MTB on hardpack, fat-bike on hard-packed snow, or road tires on cobbles. Surface choice dominates. Common for off-road race setups.

> 0.015

Extreme

Fat-bike on soft sand, plus-size MTB on loose terrain (e.g. Surly Moonlander on 4–5"+ tires off-road). Crr is the dominant force; aero is irrelevant.

Watt impact at 40 km/h, 75 kg system: dropping Crr by 0.001 saves ≈ 8 watts. Going from 0.005 to 0.003 = ~16 watts. Real money in a TT.

Coach note

Single-point Crr is noisy, the protocol is what makes it useful.

Even with everything done right, a single-effort field Crr has ±10% error. Three things that move the answer more than people expect:

  • CdA accuracy. If your reference CdA is off by 0.020 m², your Crr will be off by ~0.001. Lock CdA down first.
  • Wind. 5 km/h shift mid-test changes aero power by 10%+, which dumps directly into the Crr estimate. Out-and-back loops are mandatory above 5 km/h average wind.
  • Mass. Forgetting to include water bottles full vs empty (1.5 kg) shifts Crr by ~0.0005 on a flat. Weigh the actual race configuration.

The rigorous version (Chung coast-down method, FIT-file lap-by-lap analysis) sits inside our coaching platform, that’s how we test athletes for race prep. The single-effort version here gets you 80% of the way for 20% of the work; the lab/coaching version closes the loop on the last 20%.

Lab field-test Coaching

Related calculators

Gear × Speed × Power

Plug your measured Crr into the power equation to project speed at race power.

Open → Tire pressure guide

Optimal pressure changes Crr more than most riders realize.

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Want the Chung coast-down + lap-by-lap analysis?

Our coaching platform supports FIT-file lap analysis and the Chung coast-down method, solves CdA and Crr simultaneously, no prior CdA test needed. That’s how we set up athletes for race-day equipment decisions. Available with coaching.

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