Power Meter Options
To get accurate power readings you need a device with real strain gauges that measure the physical force the legs are putting into the cranks. Smart bikes that estimate power from flywheel speed don’t count — see Cycling Power Benchmarks for why.
The good news is that you don’t need a Garmin Rally setup that costs more than a road bike to get scientifically accurate numbers.
The options, by price
1. Single-sided crank arm — ~USD 300
The most popular entry point. Replace the left crank arm with one that has a strain gauge bonded to its inside. It measures the left leg’s power and doubles it. Unless someone has a single-leg injury, the accuracy is more than enough.
- Brand: 4iiii Precision 3
- Cost: ~$300–330 new
- Catch: Must match the bike’s existing crankset (e.g. Shimano 105, Ultegra, etc.)
2. Smart pedals — ~USD 450
Pedals with strain gauges built in. Major advantage: they swap easily between a road bike and an indoor bike.
- Brand: Favero Assioma UNO (single-sided)
- Cost: ~$450–500
- Note: Widely considered as accurate as Garmin Rally for half the price. The DUO version doubles the price for dual-sided measurement.
3. Chinese-brand spider power meters — ~USD 300
The “spider” sits in the centre of the front chainring. Disruptive newcomer brands have made these affordable.
- Brands: Magene (PES P515), Sigeyi
- Cost: ~$300 for an entire crankset
- Catch: Installation requires more mechanical skill than swapping a pedal or crank arm.
4. Used market — USD 150–200
Cyclists upgrade constantly. eBay and Facebook Marketplace routinely list used 4iiii or Stages left crank arms for well under $200. Verify the model matches the buyer’s drivetrain before purchase.
5. The pro option: Garmin Rally — USD 1,000+
Dual-sided pedals, fully calibrated, top of the market. For most amateurs this is equivalent to buying Alphafly racing shoes just to jog. Unless dual-sided measurement is genuinely useful, the value isn’t there.
Free or cheap ways to test FTP without buying anything
Before committing to a power meter, it’s worth getting a real reading once on someone else’s gear:
- Cycling studios and performance labs. Many cities have indoor cycling studios for triathletes (not rhythm-based spin like SoulCycle). Drop-in passes are $20–30. Often equipped with Wahoo KICKRs, Tacx NEOs, or Wattbikes.
- High-end commercial gyms. Look for a Concept2 BikeErg (uses wind resistance, accurate) or a Wattbike (gold standard). Standard LifeFitness uprights are usually no more accurate than a smart spin bike.
- A cyclist friend’s setup. Most serious road cyclists or triathletes have a direct-drive smart trainer at home. Borrowing it for an hour costs nothing.
What a real FTP test looks like
The most common protocol is the 20-minute FTP test:
- 15–20 minute warmup with a few short hard efforts.
- 5 minutes very hard (“blow out the cobwebs”), then 10 minutes easy.
- 20 minutes at the hardest sustainable pace.
- 10 minutes cooldown.
Average power for the 20-minute effort × 0.95 = FTP.
A maximal one-hour test is the most accurate, but few amateurs can pace it well. The 20-minute protocol is the standard.