Tacx Assembly Kit for FLUX S & FLUX 2 Smart Trainer – 12mm Thru-Axle Compatibility

The Tacx Assembly Kit for FLUX S/2 – 12mm Axle is the genuine Tacx spare part that adapts the Tacx FLUX S and Tacx FLUX 2 direct-drive smart trainers for use with bikes fitted with a 12mm thru-axle. Direct-drive trainers require an axle-specific assembly kit to correctly interface with the bike's dropout and axle standard — this kit provides the correct end caps and hardware for 12mm thru-axle bikes, ensuring the rear wheel dropout sits correctly in the trainer's cassette body and the bike is held securely during hard efforts. Without the correct assembly kit, the bike will not mount correctly and the trainer cannot be used safely.

This is a genuine Tacx replacement and spare part, engineered to the same tolerances as the kit supplied with the trainer. It's the appropriate choice for riders who have purchased a FLUX S or FLUX 2 secondhand without the correct axle kit, or who want a spare kit to keep with a second bike. Note: this kit is specific to the FLUX S and FLUX 2 — it is not compatible with the original FLUX, FLUX Smart, or other Tacx trainer models. If you're unsure which axle standard your bike uses, check the rear dropout — 12mm thru-axles have a 12mm diameter bolt passing through the dropout, compared to the 5mm quick-release skewer used on QR bikes. Browse our full indoor cycling collection for trainers, accessories, and spare parts.

What It's Good For

• Adapting the Tacx FLUX S or FLUX 2 for use with 12mm thru-axle bikes
• Replacement kit for secondhand FLUX S/2 trainers missing the correct axle hardware
• Spare kit for riders with multiple bikes on different axle standards
• Genuine Tacx part — engineered to correct tolerances for safe, secure mounting

What It's NOT Good For

• Bikes with quick-release (5mm QR) axles — a different assembly kit is required
• Bikes with 12x142mm or other non-standard 12mm axle configurations — check compatibility before purchasing
• The original Tacx FLUX or FLUX Smart — this kit is specific to the FLUX S and FLUX 2
• Other Tacx trainer models (Neo, Bushido, Vortex, etc.)

Frequently Asked Questions

How do I know if my bike has a 12mm thru-axle?
Check the rear dropout of your bike. A thru-axle passes completely through the dropout and frame, with a 12mm diameter bolt that threads into the opposite dropout. A quick-release skewer is much thinner (5mm) and uses a lever-operated cam mechanism. Most modern road and MTB bikes from approximately 2016 onwards use thru-axles; older bikes typically use quick-release. Check your bike's specification or measure the axle diameter if unsure.

Is this compatible with the original Tacx FLUX or FLUX Smart?
No — this kit is specific to the FLUX S and FLUX 2. The original FLUX and FLUX Smart use a different assembly kit. Check your trainer model before purchasing — the model name is printed on the trainer body.

What is included in the kit?
The kit includes the end caps and hardware required to mount a 12mm thru-axle bike to the FLUX S or FLUX 2 trainer. It provides everything needed to correctly interface the bike's dropout with the trainer's cassette body for secure mounting during training.

Do I need a different kit for each bike?
You need a kit that matches each bike's axle standard. If all your bikes use 12mm thru-axles, one kit is sufficient — it can be swapped between bikes. If you have bikes on different axle standards (e.g., one QR and one 12mm thru-axle), you'll need the appropriate kit for each standard and swap between them when changing bikes on the trainer.