MTB and Road Cassette Compatibility 11-speed?

[trailgumby]

Rather than taking up extra room we don't have to fit a dedicated exercise bike, I'm looking to get my wife a bike so she can use the Kickr Core trainer I have set up in the garage, as foot issues are causing her grief with getting exercise. Using an exercise bike has been recommended by her doctors and I'd like something interactive, so I'll get her on Zwift or Fulgaz.

As I'm using 11-speed on my roadies, I am looking at a Polygon Heist which comes with 11-speed SLX so I don't have to fluff about with changing cassettes when she wants to use it on the Kickr.

I'm expecting the cassette spacing should be the same, since the chains are the same, but would like to confirm. Both should have 142x12 rear axles.

[Duck!]

Yes, spacing is the same. However, as with any change of wheels (or trainers), different brands can have slight variations in lateral alignment of the cassettes, so a bit of tweaking may be required if swapping between trainer & wheel frequently.

MTB derailleurs are designed to work with much larger cassettes, so as you shift in to the lower gears on a road cassette, the gap between the top pulley and the sprockets gets bigger, allowing the chain to flex rather than grab the shift ramps, so shifting may get a little sloppy in the lower gears. It will become more noticeable as the chain wears.

[trailgumby]

Yes, spacing is the same. However, as with any change of wheels (or trainers), different brands can have slight variations in lateral alignment of the cassettes, so a bit of tweaking may be required if swapping between trainer & wheel frequently.

Thanks, Duck! Appreciate your advice. The trainer has an 11-30 105 cassette on it, so well within the SLX ratio range.

Sadly, I don't expect Vera will ever be tempted to ride outdoors on local roads - too many scary traffic stories from me - so it will be a matter of setting up the lateral alignment to suit my bike and then tuning the new bike's shifting to suit. But I will continue to hope

[Duck!]

It's more that the road cassette could be too small for the derailleur's ideal range.... Shimano MTB 11-sp. derailleurs are designed for a big sprocket range between 40 & 46T (with a bit of play room either way). If you go too far below the minimum ideal big sprocket size, the gap between sprocket & top pulley gets too wide & allows chain flex, so shifting can get a bit woolly in that end of the cassette.