In short, I just got a set of 2013 404's. I've got a 10 speed shimano drivetrain. The wheels come with a 1.85mm shim. Zipp CS insists you only need this shim and the cassette. They say you don't use the Shimano 1mm shim too. To me this makes no sense. I asked them what happens if you have a 9 speed cassette. They said same thing....... Just the 1.85mm Zipp spacer. Are they smoking something or is there something very special about the new Zipp cassette carrier?

The 9sp cassette is 1mm wider than the 10sp cassette. If the wheel is made to accept 9sp cassettes, then you will need that 1mm spacer with 10sp cassettes. If, as Zipp have said, you don't employ the 1mm spacer with 10sp cassettes, then the body will be 1mm too short to properly handle 9sp cassettes, assuming that 1.85mm spacer is used when using non-11sp cassettes.

I have a set of Enve/DT 11 speed wheels and I have a 1.85 spacer. I run 10 spd. Works great.

Well your RD will be 1mm out. As well, what I found was that without the 1mm spacer, when you tighten the lock ring, you don't feel the serrated teeth "bite" till almost full torque on the ring. With the 1mm installed the teeth bite early.

I have the 2013 404s with the 11sp freehub body. I use the 1.85 shim and also the paper thin shim that comes with the 10sp DA cassette together to get perfect shifting. This is with an otherwise all sram red drivetrain, I just use DA cassettes because they sound better and have more gear range options.

i use the Zipp 1.85mm + DA cassette 1mm shim for 10speed.
If i didn't i wouldn't be able to swap out to my Enve/Tune MAG150 without re-tuning my RD every time.

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2012 Scott Foil Premium

You absolutely use the Shimano 1mm spacer as well as the 1.85mm spacer. the service guy is wrong. If you called them again, you would probably get the correct answer.

I totally agree. Fact of the matter is that I had two conversations on the live chat, followed up by an email all insisting that you didn't need the 1mm. That's why I posted here. I'm hoping that Zipp sees this and updates their CS team on the right answer.