FSA Comet Crank Arm Set – 170 mm, MegaExo 24 mm, Direct Mount
The FSA Comet Crank Arm Set (CKM-7210T) is a pair of forged aluminium 170 mm crank arms with a 24 mm MegaExo spindle and a direct mount interface – the clean base for a Gates Carbon Drive belt drive or a single-ring build, without spider or chainring bolts.
Why direct mount?
No spider, no chainring bolts. The sprocket mounts straight onto the crank arm: fewer parts, less weight and nothing that can work loose. 
Free choice of ring. A Gates Carbon Drive direct mount sprocket for a belt drive, or a direct mount chainring for single-speed or 1x chain drive. 
Easy to change later. Want a different gear ratio? Swap the sprocket, keep the cranks. 
Forged aluminium arms. Black, with the Comet graphic – at home on steel, aluminium and carbon frames.
What is in the box
Right crank arm with the 24 mm spindle, left crank arm, a 3 mm spindle spacer and the left crank bolt. No chainring and no bottom bracket – you choose exactly the ring or belt sprocket your bike needs. On our own Booda Bikes we combine these arms with Gates Carbon Drive direct mount sprockets.
Is 170 mm right for me?
Crank length is measured from the centre of the spindle to the centre of the pedal thread. 170 mm is the most common length on trekking, urban and gravel bikes and suits most riders of average height. It also gives a little more ground clearance in corners than longer cranks.
How it fits together
The crank needs a MegaExo 24 mm bottom bracket – for threaded BSA frames the FSA MegaExo BB-7100. On the non-drive side a wave spring washer takes up side play. All of these parts are available separately in our shop.
1 – bottom bracket (two bearing cups threaded into the frame), 2 – wave spring washer, 3 – plastic spacer, 4 – left crank arm, 5 – crank bolt, 6 – drive-side crank arm with the 24 mm spindle, 7 – chainring or belt sprocket (direct mount).
Who is it for?
- Belt-drive riders. Replacing a worn or damaged crank, or upgrading to a Gates Carbon Drive direct mount sprocket.
- Booda Bike owners. Who need an original spare crank for their bike.
- Bike builders. Setting up a single-speed, gear-hub or 1x bike with a 24 mm spindle.
- Commuters and trekking riders. Who want a solid, low-maintenance crank that simply works every day.
Specifications
| Model | FSA Comet, CKM-7210T |
|---|---|
| Crank length | 170 mm |
| Spindle | 24 mm MegaExo |
| Ring mount | Direct mount |
| Chainline | 52 mm |
| Q-factor | 172 mm |
| Material / colour | Forged aluminium, black |
| Bottom bracket | FSA MegaExo 24 mm, e.g. BB-7100 (not included) |
| In the box | Right arm with spindle, left arm, 3 mm spacer, crank bolt |
Fitting
- Install the bottom bracket cups with the correct spacers for your frame shell width.
- Grease the spindle and slide the drive-side arm through the bottom bracket.
- Fit the wave spring washer on the non-drive side, then the left crank arm.
- Tighten the crank bolt to the torque printed on the bolt or given in FSA's instructions.
- On a belt drive, check the belt line and belt tension after fitting the sprocket.
Frequently asked questions
Is a chainring or belt sprocket included with the FSA Comet crank?
No. The set contains the crank arms, the 3 mm spacer and the crank bolt. Choose a direct mount chainring or a Gates Carbon Drive direct mount sprocket separately.
Is a bottom bracket included?
No. You need a MegaExo bottom bracket for a 24 mm spindle, for example the FSA MegaExo BB-7100 for BSA threaded frames.
Does it work with a Gates Carbon Drive belt?
Yes – with a Gates direct mount front sprocket. This is how we build our own belt-drive bikes.
Can I use it on a bike with a derailleur?
Yes, as a single-ring (1x) crank with a direct mount chainring. It is not a double or triple crankset.
We build and service belt-drive and gear-hub bikes every day in our Budapest workshop. Not sure which part you need? Send us a photo of your crank and bottom bracket and we will tell you what fits. FSA – Full Speed Ahead – has made bicycle components since 1993 and moved into cranksets and chainrings in 1995. FSA introduced the compact road crankset in 2004, and its MegaExo system with external bearings and a 24 mm spindle is one of the most widely used crank and bottom bracket platforms on mountain, gravel, trekking and urban bikes. FSA parts are fitted as original equipment by many bike brands, including our own Booda Bike belt-drive bikes.About FSA