11 sp cassette with 12 sp Ultegra ... works?

Tech Tech Help
1

I have a road bike with ultegra 12 speed di2 on it. Just for fun I swapped on some 650b gravel wheels that have an 11 speed shimano cassette – and the shifting worked! It was perfect.

What? Why? I thought I’d have to change cassettes to a 12 speed. Has anyone else seen this just work?

Should I swap cassettes anyway? Is there any risk in running this setup?

2

You must have an indexing issue in there somewhere no? Get to pick if you want to use the 34 or the 11?

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3

Yeah I think so, but what’s amazing is that the indexing works so smoothly with the gears that are available and it doesn’t seem to shift off at either end, which is what I would have expected.

I think k the answer here is don’t worry be happy - but I’m mystified as to how this is working.

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4

Is there a shift which doesn’t do anything? Or is it limited so you only get 11 gears worth of shifts?

Maybe I’m overly cautious, but this would make me nervous. One chain slip while standing can cause you to crash. I say from experience :laughing:

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5

I haven’t had that experience, but yeah, this is the sort of thing that has me a little apprehensive. It works, and yet… ?

6

I’m surprised this setup shifts smoothly, but it makes sense that the chain doesn’t leap off of either the outside of the small cog or the inside of the large cog, as the cassette “stack height” is almost identical for 11sp and 12sp (12sp cassettes have narrower spacing and thinner chains to match).

The surprise over smooth shifting comes from the 12sp chain on the 11sp cassette and the indexing. Have you put the bike on the stand and taken careful notice with each shift?

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7

I did shift it on the stand, and that’s really what surprised me. There’s a little hesitation in the smaller middle cogs, but it kinda just worked.

I think I’ll put a 12sp cassette on there just to be safe. An interesting result though. Unexpected.

thanks!

8

I did this once (by accident) and noticed very quickly on my ride that something was wrong. :rofl:

Working on the stand is different to working on the road.

9

Aye. That’s my concern. Going to go get a 12sp cassette.