I originally posted this question on the Classic & Vintage forum but nobody there could answer definitively, so I did a little test on my own. Sorry for the cross-post, but I want to report my experience here in case anyone ever goes looking for the answer to the same question. My results make me think it'll work, but if anyone has tried (and ridden) this setup, please let me know.
First my original post, then my test & results.
I know that using 8 cogs of a 9-speed on a 126mm cassette rear hub works, but I'm wondering if anyone has tried 9 of 10 on a 126mm hub. I have a NOS Vitus 979 frame that I'll be building up soon. (This is a bonded aluminum frame with 126mm rear dropouts so respacing, the simple solution, isn't recommended.) I'd really like more than 8 cogs on the back but I don't have any 10-speed parts for experimenting. From the shimano cassette dimensions that I found somewhere on Sheldon Brown's site it looks like 9 of 10 is just a mm or so wider than a standard 7-speed, but I'd hate to spend a lot of money on shifters and a cassette only to discover that it won't work.
So, has anyone here tried this?
Update in case anyone is ever wondering about this in the future: I found a couple of pieces of sheet metal in my workshop that, stacked, equaled ~1.0mm on my digital calipers, approx the difference between a standard 7 speed vs 9 of 10. I cut hole in them so that they'd fit on a cassette hub, then, using a 9-speed cassette, put on 7 cogs & 6 spacers. I put on the sheet metal parts, then the rest of the cassette. There were fewer turns required to tighten the lockring, certainly, but I do think it will work as there seemed to be enough thread engagement. There was no cassette/chainstay interference.
Comments? Am I missing anything? (I rode one of these frames for thousands of miles 20 years ago, so I'm familiar with the trade-offs.)
Original thread: 9 of 10 on 7 on a Vitus 979?