Does not appear that this is confirmed to have worked, and I haven’t found a picture of the backside of the R8000 cassette to confirm that is has some material removed, or at least a dish but it sounds like a slam dunk…
Yup, because it’s not correct, see my post above …
The notes on the Ultegra 8000 10 speed compatible cassette can be confusing, but if you look around at the various sources, it will help clear up that this configuration is only used with the new 11-34 cassette. Shimano is so conservative that they are only allowing this for this cassette with the huge (for road) 34 tooth inner cog which should clear all spoked wheels behind this big cog.
I just installed one of these on my 11 speed gravel bike with the spacer.
Edit: DSW typed up this same info while I was pecking away on the iPad!
it sounded too good to be true
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it sounded too good to be true
Yup, exactly. Because 11-34T is way too huge for my race bike.
But I gotta say that I am having great luck with the modified Lasco cassettes … allows me to save my classic 10s wheels.
Greg @ dsw
Thanks all…great info.
Off to the machine shop I go!
Glad to help.
But you’re going to modify the cassette and not the freehub, correct?
yes modifying the cassette… 
it sounded too good to be true
Shoot… It really did:(
sorry guys. I guess I got too excited, too soon!
Yes, you are correct. I was mistaken, I forgot to say there were also some now somewhat rare dura ace hubs that also only accepted shimano 10 speed cassettes.
But those hubs (and the shimano prebuilt wheels, the rear hubs looked like the photo below) were the only exception to what I wrote. But thanks for clarifying this.
There’s still some Easton wheels floating around that used that strange 10 speed Shimano only hub. All of their EC90 and EA90 wheels from 2010-2013 (or maybe even 2014 too…I don’t remember when they started using the black free hub body) that were for ‘Shimano’ and not Campy were truly Shimano 10 speed only. They were the blue R4 hubs and those wheels still show up on ST classifieds once in awhile.
Not that it actually matters a ton here.
BTW - I just grabbed the 11 speed Ultegra R8000 11-34 cassette as well. It’s the ONLY Shimano Ultegra 11 speed cassette that fits on a 10 speed body. It was to use a pair of Stan’s mt bike wheels for cross. Appears to work great so far. Do Greg/DSW was correct again…as usual.
Just to confirm for everyone. I took about 1mm (will take a little more tonight but wife kept asking what I was doing out there…) off the back of my Shimano 105 (5800) 11-28 cassette last night and it worked on my Ultegra 6600 hub. Got the lock ring to tighten down at least a couple of turns. Will post pics if people need them, but just take your time and you should have no issues. There is plenty of room between the hub shell, the drive side spokes, and the 28t cog.
For those wondering you should take ~1.85mm off the cassette but I am taking it slow. I.E. measure twice.
Thanks again for everyone who posted.
it still can be useful for people riding single chainrings
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Yeah, if possible, you want to take about 1.8mm off the back of cassette. Less than that and you are potentially courting locking and/or freehub thread failure …