HARDWARE

Supported gear

Slipstream talks standard Bluetooth. If your trainer speaks FTMS, it works — there is no approved-devices list to be left off.

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Trainers

Slipstream controls trainers over FTMS — the Bluetooth Fitness Machine Service, 0x1826 — which is the standard every modern smart trainer implements. There is no per-brand integration and no certification list, so support is not something a trainer has to be granted.

In practice that covers current smart trainers from Wahoo, Tacx, Elite, Saris, Zwift, JetBlack, Van Rysel and others. If the box or the spec sheet says FTMS, it will pair.

From the trainer, Slipstream reads the Indoor Bike Data characteristic (0x2AD2) for live power, speed and cadence, and writes to the Control Point (0x2AD9) to set resistance in ERG mode.

What will not work: trainers that are controllable only through a private, brand-specific protocol, ANT+-only equipment (phones have no ANT+ radio), and "classic" wheel-on trainers with no electronics, which can broadcast nothing at all. A dumb trainer plus a separate power meter still gives you live numbers — you just cannot be held at a target.

Heart rate

Any standard Bluetooth heart-rate strap or armband, using the Heart Rate Service 0x180D. Chest straps from Polar, Garmin, Wahoo and Coospo all work, as do optical armbands that broadcast over BLE.

Watches that only relay heart rate inside their own vendor's ecosystem are the usual exception.

Cadence

Most smart trainers report cadence themselves, in the same Indoor Bike Data stream as power, so a separate sensor is often unnecessary. Where the trainer does not report it, a standard Bluetooth cadence sensor works.

Cadence is worth having even when it looks redundant, because of what the app does with it — see below.

What Slipstream does with the connection

ERG mode is not a straight pass-through of the workout's target to the trainer. Two guards sit in front of it:

  • The cadence guard. ERG holds a target however slowly the cranks turn, so a rider who is fading grinds harder and harder and never reaches the 0 W that auto-pause watches for. Cadence is the tell, not power. Sustained pedalling below the floor — 50 rpm by default — releases the hold, and re-engaging needs a margin above it so a rider hovering right at the floor does not get flapped in and out. A trainer that reports no cadence at all never trips it.
  • Ramping. Interval boundaries can jump 150 W at once, which is its own way into that spiral. Climbs are eased in at 25 W/s; drops are never limited, because there is no reason to make relief arrive slowly.

Control-point writes are serialised, because commands have to arrive in order — a paused trainer ignores setpoints until it is resumed, and releasing a hold has to actually be sent rather than merely stopped being requested.

Platforms

Slipstream needs a Bluetooth radio and the permission to use it, so pairing works on iPhone and iPad.

Bluetooth is not available to the app in a browser, so the web build can show your history and your plan but cannot connect to a trainer.

Something not pairing?

Check that the trainer is awake and not already connected to another app or head unit — most trainers accept only one control connection at a time, and a Zwift or Wahoo app left running in the background is the usual culprit.

Still stuck: support@slipstream.app, and mention the trainer model.