Simple question I guess…

Do they do the same thing for 9 speed cassettes as they do for the 10 speed ones?

I’m going 1×9 and I want a leg up for the sharper climbs, I think this might be the product I’m looking for, but I’m not sure if it exists, and if it does exist, where do I shop for it?

You can get 9speed 12-36 deore cassettes, if you’re on the cheap.

(the only 9sp 36t cassettes out there)

/ runs off to CRC & finds 36t deore cassette /

I never knew that!

You can swap the 11t ring off a “normal” cassette to get the full 11-36 range too (though, it’s not always quite so simple; I had to machine mine down to get it to work, and it’s very hard steel) It is heavy though.

I suspect the Oneup one could be made to work 9-speed, but I don’t think it will as standard- the chainring spacing is different. Also it won’t work right with that big deore cassette as you can’t remove any rings from the middle, you’d end up with a 12-42 which is not that much wider range than 11-36 and still just as expensive. Or, perhaps start with an 11-34 and a 40T OneUp (or Hope, or whatever else)

All in all I don’t think it’s going to be very practical unless you have a lathe.

I’m planning on trying to make a ghetto 9 speed wide range cassette. I’m going to use a Hope 40T sprocket (Shimano specific) with a Shimano XT M770 11-34T cassette.

There are a couple of complications that mean it might not work:
(1) The reinforcing tabs near the top of the Hope sprocket are designed to make contact with the 36T sprocket on the cassette – two opposite tabs have an outer diameter of 131mm, but my quick measure of the 11-34T cassette has the dips between the teeth at 129mm and the teeth at 134mm. So it will depend where the Hope tabs align to the teeth as to whether they interfere or not. The XT cassette has pins out of back the cassette which luckily happen to just be wider than the required spacing, so I’m hoping the splines of the Hope Sprocket will rest on that. I’m happy to make up a narrow spacer to fit on the freewheel to account for the difference in 9sp and 10sp spacing (probably use HDPE plastic).

(2) On the XT cassette, the 17T is fixed to the carrier. The simplest would be to lose the 15T cog, but personally this is very useful. I’m planning to drill out the pins that hold the 17T cog on the carrier and then file the carrier down (there’s a nice line to make it easy). This way I can ditch the 17T. I might swap the 15T for a 16T, if the jump is too big.

This is all beginning to sound complicated, but I don’t want to throw out a very low mileage 1x 9-sp drivetrain just to get this to work.