http://www.pinkbike.com/news/1×6-specialized-gearing-2010.html

Some people talking there about a 9-36 cassette – if that worked it could even make me get rid of my triple. With a hammershmidt it would also be great.

But would a 9t stand up to more than 5 mins of riding at a time? It's such a teeny weeny bit of metal.

I can see why its a good idea for DH spacing, with gravity on their side DH riders don't need the ultra close gearing they get from a road cassete, and they get better ground clearance as well.

Shimano are bring out a groupset for folding bikes that is 9-36, but it needs a dedicated rear hub

any 9tooth cog will need a special freehub wont it ?

having seen them work very unsuccessfully on bmxes – till you get to the mega high end stuff and even then ~! largely relys on bushes as not alot of room for bearings once an axel is in there …

dont see the appeal my self – just run a bigger chainring and MTFU.

oHHHHH, but for the average joe, its niche for the sake of it.

I heard something about microdrive in bmx being similar, sounds like a issue with it being so small.

Can you get MTB cassettes with a 10t cog?

Not AFAIK, but you'd get the same effect with a hope SS hub and half a cassette. And a 34t ring, the 9t is only nececitated to get more ground clearance (DH bike with 10" travel tends to need it more than a trail bike).

I run 27:9 on my bmx and, quite frankly, it feels horrible. Even with a chain designed to work well with 9t cogs (as it's such a sharp turn some singlespeed chains bind a bit) it feels rank to pedal. The difference between a 10t and a 9t is very noticeable is pedaling smoothness.

As has been mentioned, fitting bearings of any sensible size inside a 9t cog while maintaining a decent size axle is very tough, and requires some novel thinking make it work well.

That 9 tooth cog has been out for a while I have mentioned it on here before and yes you need a dedicated hub and there is I think only one cassette fot it.The hub is the Capreo cassette is 9 to 26

Is an overdrive chainring (like hammerschmidt but without the need to change gear) so heavy and inefficient that it's not an option?

Good info sebc, hadn't thought about the chain flowing over such a small gear…it wouldn't be very circular would it. I guess that's why 11t is the smallest we get.

Looks like I'll be sticking with the 44t for a while yet

no need to **** about with 9T cogs but 6 speed cassette freehubs and 6speed shifters should be common place on DH bikes by now.

I reckon 9T would be shit in mud and wear too quickly

I think these sort of shenanigans really show up the inadequacies of the deraillieur (sp?) Rather than fannying around with tiny cogs, why not use a hub gear style system, centrally mounted. Now a six speed hub gear isn't that heavy, and from what that article is saying, weight is not the primary consideration for this bodge, it is ground clearance. So, a gearbox system would be great for that.
Build it Shimano, and they will buy in massive quantities! Please!

I'm with you there. Hub gear by the BB, one cog on the rear so minimizing unsprung mass on the rear wheel, job done. No chainline worries, no exposed components, and you could change gear when stationary = happy mtbers

Build it Shimano, and they will buy in massive quantities! Please

not as massive quantitys as they do cassettes , chains , chainrings etc …. 3 sets a year at this end – has to be more margin in that for them – i dont condone it but thats why they dont develop it "that" well …

You're probably right trail_rat. It just pains me as it seems like the technology is all there, just waiting to have the dots joined up.

Shimano already build something simmilar, Capreo. Intended use is small wheeled commuter bikes

Here's a link:

Shimano Capreo

Don't see why this couldnt be used for a trail bike as 135mm spacing. Alas, not for DH as 150 x 12 would be required. Quite fancy having a go at hacking one of these cassettes and freehubs onto a hope bulb/similar for DH!

For sponsored racers I think it's ideal, and also who it's aimed at. More range without having to shift as much in DH racing. Not sure it's really aimed at non-racer types, more of a use it and throw it away?