The trainer is unboxed, the legs are locked and the bike is ready to hang on it. Then you notice the chain has nothing to sit on.
Many direct-drive trainers need you to supply the cassette. Some ship with one, so check the spec sheet before you buy.
The short answer: slide the cassette onto the trainer’s freehub splines, thread the lockring on, and tighten it with a lockring tool. It takes about ten minutes. The catch is that the cassette has to match the freehub body. Get that right and the rest is easy.
This job applies to a direct-drive smart trainer, where you take the rear wheel off and the chain runs on the trainer. A wheel-on trainer keeps your own wheel, so it needs no cassette at all.
Match the freehub before you buy anything
The freehub body is the ratcheting cylinder the cassette slides onto. It comes in a few standards, and they don’t swap freely.
| Freehub body | Takes | Watch for |
|---|---|---|
| Shimano-style HG | Most 8- to 11-speed cassettes, plus Shimano 12-speed road | 8-, 9- and 10-speed cassettes need a thin spacer on an 11-speed body |
| SRAM XD / XDR | XD or XDR cassettes | Won’t take an HG cassette |
| Shimano Micro Spline | Micro Spline cassettes | Needs its own body |
| Campagnolo | Campagnolo cassettes | Different spline pattern |
Check which body your trainer has. Some makers sell alternate bodies for the same trainer, so a mismatch may be fixable without a new trainer.
Then match the speed count to your bike’s drivetrain. An 11-speed chain wants an 11-speed cassette.
Here’s a tip I’d follow. Buy a cassette with the same range as the one on your bike, say 11-28 or 11-30. Your shifting then feels familiar, and the chain length and derailleur setup stay as they are. A cassette with a bigger largest cog can mean a longer chain, and nobody wants to cut a chain on trainer day.
What you need
- The cassette (and any spacer your cassette speed calls for)
- A cassette lockring tool that fits your lockring
- A wrench or torque wrench to turn that tool
- A rag, and a little grease if the cassette instructions call for it
You don’t need a chain whip to install a cassette. You’ll want one later when it’s time to take the cassette off.
Fitting the cassette, step by step
- Unplug the trainer and make sure the freehub is clean and dry. Wipe off any dust or old grease.
- Look at the splines. One is wider than the rest, and the cassette has a matching wide slot. It only goes on one way.
- Slide the cassette on, largest cog first if it’s loose, or as one unit if it’s pre-assembled. Push it all the way down. Add any spacer before the cassette, as the instructions say.
- Thread the lockring in by hand. It should spin freely for several turns. If it fights you, back it out and check the alignment so you don’t cross-thread it.
- Fit the lockring tool and tighten with the wrench. Most Shimano-style lockrings call for roughly 30 to 50 N·m. Follow the number printed in your cassette’s instructions.
- Spin the cassette by hand and listen. It should turn smoothly with no wobble.
Keep your fingers clear of the sharp teeth as you work. A cassette is a row of small saws.
Grease, conversions and trainer tires
Should you grease the hub before installing a cassette?
A thin film of grease on the lockring threads is common practice, and some mechanics add a light coat on the splines to stop corrosion. Your cassette’s instructions win if they say otherwise. Don’t pack it on. A trainer lives indoors, so seizing is less of a risk than on a bike that sees rain.
How can I convert my bike to an indoor trainer?
You have two routes. A wheel-on trainer clamps your rear axle and presses a roller against the tire. It needs no cassette. A direct-drive trainer replaces the rear wheel, so you fit a cassette and mount the frame on the trainer’s axle adapters.
Direct drive is quieter and more accurate, but it costs more. If you’d rather skip the whole job, a smart bike like the Stages SB200 has the drivetrain built in.
Can you ride a trainer tire on the road?
I wouldn’t. Trainer tires are made for a steel roller, with a hard, heat-resistant compound that grips less than a road tire. Use them on the trainer and keep a normal tire for outdoor wheels. That only matters for wheel-on setups. A direct-drive trainer has no tire at all.
Check it before you clip in
Wahoo’s own troubleshooting steps include a simple test. With the bike off, grab the larger cogs and try to rock them toward you and away. If the cassette moves at all, stop and remove it, then recheck the freehub, spacer and lockring. Play at this point can turn into a loose lockring or a damaged freehub under hard efforts.
Then mount the bike. The axle should seat fully in the trainer’s adapters and the quick release or thru-axle should be tight. Shift through the whole cassette with the pedals turning. If the chain hesitates or skips, a small turn of the rear derailleur’s barrel adjuster usually settles it. removing the cassette is a separate job, and it’s a good one to learn before you ever need it.
Fitting a cassette is a ten-minute task with one real decision, so match the freehub and speed count first, then tighten the lockring properly.
Photo: Tacx Flux Smart Trainer – Mounted 1 by Glory Cycles, CC BY 2.0, via Wikimedia Commons. Cropped.
