11 speed MTB cassette on 11 speed road hub (once again!)

Question

Before I start: I know a similar question has been already answered here, but this time it comes with a twist. So here I go:

My setup:

• 11 speed road hub - stock on on my DTs
• 11 speed MTB cassette - CS-M7000-11

All the internet's wisdom says one thing: I need a 1.85mm spacer so that the cassette won't wobble. Not it my case:

• without spacer: cassette fits perfectly. Tightened anywhere between 30 and 40 Nm - no wobble!
• with spacer: cassette fits, but it sticks out by (what I consider being) a dangerous amount.

You'll ask, so what? Then fit it without a spacer! Problem is, I have another road wheelset, with a road cassette. I want to be able to swap between wheelsets without adjusting the derailleur. Without the spacer, the chainline is messed up.

If I take the cassette from the other wheelset (Shimano 105 CS-R7000) and try to fit it on this hub, then:

• without spacer: still sticks out, but slightly less so.
• with spacer: the smallest sprocket won't even bite into the rills on the freehub body. So the MTB cassette is indeed narrower.

The spacer that I have is the one needed to fit 9/10 speed cassete on 11 speed hubs (should be the same). I can't tell the exact thickness, but it is at most 1.9mm. The difference between the amounts the road vs the MTB + spacer cassettes stick out is obviously larger than any error in my measurements. I even cleaned every sprocket and spacer on the MTB cassette to rule out any gunk adding width. Here some photos:

first photo: MTB cassette + spacer (smallest sprocket removed)
second photo: Road cassette (smallest sprocket removed)

So my biggest fear is that I'll pull out the thread with the lockring. Around 35Nm it is only about 1.75 rotations in.

Anyone seen something similar before?

UPDATE:

Thanks to Nathan Knutson's suggestion, I snooped trough my old bike parts and found an old 9 speed SunRace cassette, with a lockring a tad thicker. Since the smallest sprocket on that cassette is also 11 teeth, I assumed the lockring would fit so I tried it on: 35Nm and it's already about 2.25 rotations in, much better - considering the Shimano lockring does only have 3 ridges (left in the picture below). Now I only wonder if the smallest sprocket is engaged properly, but given it is only 11t, I don't think there's nearly enough torque to rip off the tips of the splines.

Answer 1

The first photo looks about normal, with the splines barely protruding.

If the shoulder to tip length of the freehub body is 36.85mm long like it's supposed to be, and if it's a real CS-M7000-11, then there's not really a lot of places to go here.

Look carefully for any potential obstructions or grime in the freehub body shoulder area that might keep it all from seating.

You were on the right track with cleaning the cassette to eliminate the possibility of grime building up the stack height. It's possible you might need to go a little further with that.

Not wanting to ruin the FHB is a valid concern, but there have been many times I've seen minimal thread engagement like that and when you go to tighten it down anyway, it compresses down more than it seems like it was going to and it's fine.

If the thread engagement just feels wrong, It's also possible that what's going on here is there's already missing/damaged/malformed thread at the start of the lockring threads. Note that the thing that's not perfectly standard in all this is how far inset the beginning of the threads are. Every once in a while, subbing in a longer lockring is needed to help with problems like that. I can't say I've seen it on a DT, but it could still be worth looking at. I don't have any recommendations for what lockring to use in those situations; usually I've just seen what's in the scrap.