Two identical casettes but need to adjust rear derailleur

Dear all,

Last week I bought my Tacx Flux S and installed a new casette (9 speed, shimano CS-HG400-9) and I replaced my chain and casette on my bike with the same casette.

So, having two identical casette on both my tacx and my bike, I still need to adjust my rear derailleur when I place my bike on the Flux. The chain cant reach the big blade and it will slip off when I shift (which I can) beyond the smallest blade.

Is there a way to not adjust the rear derailleur every time I switch between my bike and the Tacx?


  • Hi,

    I'm having almost the same issue with a 11 speed cassette. Also two identical cassettes.

    There is 2,3mm deviation between using my rear wheel and the Tacx. 
    Installing a 2,3mm longer 12DS should help to solve my issue. 

    I have contacted the servicedesk and waiting for a solution.

    If anyone has a solution please let me know!


  • Thanks, im still waiting for the solution, so if you have heard something, please share!

  • That is a pretty large delta between the trainer cassette and the wheel cassette.  My recommendation would be to make sure your cassette on the flux is fully seated and properly tightened.  When I installed my cassette I found I had to push extra hard before I could get the lock ring to engage.  Once it did, my shifting has been nearly identical between the trainer and rear wheel.  I do have to make small fine tuning, but nothing major.

  • thanks, my problem is still that the casette is too much on the inside, because the chain can slip right off the smallest blade, which does not happen on my bike. so probably need more spacers or something.

    I also contacted the servicedesk now, asking for a solution.

  • Some cassettes need an additional spacer ring before you mount the cassette.

  • But there is only one additional spacer ring in the package, do i need another one?

  • for a long time I had that impression too. Make 100% sure your bike is really on the shaft when you close the quick release. The derailleur spring tends to push the bike upwards

  • Same question here :) curious how you solved the problem ... larger spacer, rear derailer adjustment, both, or something else?

    I'm also using an 11 speed cassette. Instructions say spacers are for 10 speed and less cassettes. But my experience is that the chain can move past the highest gear and can't get into the lowest. This is using the same cassette I used on my rear wheel (a new identical one is on order).

    I'd prefer not adjusting the derailer because I'd really like to take the bike off the trainer and get out on a ride outside when the weather is nice, without derailer adjustments. 

    Thanks for the help.

  • Same problem, also 11 speed cassette. My rear dropouts are fairly narrow (135mm) but can get it mounted with the 12x135 adaptor for the NDS, then have same issue you describe above. Looking at it the obvious thing to do is to move the cassette closer to the frame. For a 10 speed you could put some spacers on the freehub to push the cassette toward the frame, but this isnt really any option for the 11 speed cassette as you run out of freehub to keep the gear teeth aligned when installing the cassette. Only solution I can think of is installing a spacer on the non-drive side, and finding a smaller drive side adaptor (which garmin dont seem to make??). So basically keeping the cassette where it is and moving the frame (and derailleur) toward the NDS of the trainer and closer to the cassette. Or obviously change all the limit screws and never take the bike off the trainer again. Anyone heard of an alternative DS through-axle adaptor from Tacx/Garmin?

  • The long answer is no, as long as the cassettes and wheels are identically spaced. If they're not, you'll need to adjust your rear derailleur cable tension, which is easy to do yourself