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Discussion Starter · #1 ·
It's inexpensive, it works; it's light, it's fast. 2x9 Nine speed, 11x36 cassette. double chainrings in front, 30 x 42. Climb well, go faster downhill.

Inexpensive as long as these off the back parts keep falling through closeouts. If you want lots of teeth engaged with good chain line on a power climb, you'll want a big ring and not a 32 x 10. Forget about the low end, I can't afford a pancake plate 12 speed. That 51 is way heavier than this setup, god bless you if you can afford to replace titanium cogs. I ride six miles to the trail head, and tried the 1x craze but it was maddeningly stupid twiddling and grinding 32x11.

Even more off the back - the perfect BCD is 94, five arm. That's 90's micro drive!!! There are still low price Vuelta rings available. This way you get the 30, and a good gap to the 42 for the high end. 30 is not double doable in the common four arm 104 BCD, flat rings are too rare. Ritchey was ahead of his time, and I bought a bunch of his 42T authentic 2x9's on closeout for $5 each.

I just rigged up a Profile 180mm BMX crank with a micro drive adapter, the dual suspension has a 90's White Industries crank. There's a particular FSA 19mm exo bottom bracket which works with the Profile, as the Profile BB bearings fail in short order, they're too small when shoved inside the BB.

With a 104 bcd double setup, it's become frustrating finding flat, not narrow wide, chain rings. 32 is all you get with a 104, at least with a double.

So here it is, indexed by the robots, hoping it will help someone else see the light. For a minute this year, Shimano had the XT 180mm M8000 in double, but I can't find them now. And they came without rings.
 

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Discussion Starter · #2 ·
2x9 update

Fat rear tire required losing the triple. 30 small ring rolls better than smaller anyway. Need the big 42x12 to get to trail and back, easy on pins and rollers less friction, better chain line than 30x10. Bigger chain. On the low end, SunRace M990 9 Speed 11-40 cassette is a revelation. The SRAM X5 is rated to 36 teeth, with B tension cranked, it just makes 40. This gives the same ratio as a 110 triple 24x32, and on long grinds it is welcome relief.

On the front, a set of MTB cranks that won't wear out - Profile 180mm. This is a 5.75 spindle but 6 inches would be perfect. FSA BB4000 19mm bottom bracket is low cost and vast improvement over the old Profile internal bearings, but using three 2mm spacers between those bearings to the inside, the old profile bearing just makes contact with the shell. So there are four bearings in there. It's a major pain getting the spacers right, but this spins freely with awesome power transfer. Great for sessioning hard tail party lines.

Last bit of strangeness, this is 8 of 9 on 7. The 135mm spacing holds a seven speed cassette. The Sunrace cassette is an excellent design with three largest cogs on an alloy spider, spreading torque across cassette body where it's needed most in the low gears. But the higher gears are loose cogs. And by losing the 11 and 13, replacing with a 12, gear spacing is smooth. The wheel has less dish, first gear is moved outward for excellent chain line.

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