cicliste666

If anyone could help me figure out a drivetrain for a drop-bar 650b bike, that'd be great. I have no experience with 650 so I'm going to try it out. I have a 46/30 crankset that I'm going to use, but need to figure out (i) cassette, (ii) RD, and (iii) shifters. I'd like to use indexed DT shifters. It seems like most available wheels are for Shimano 8 or 9 cassettes, which is fine with me.

1. For the cassette, would an 11-29 be a decent choice?

2. For the shifters/rd, do I just score a set of Dura Ace 9-speed DT shifters, and then an old XTR medium or long cage (but, I take it, not Shadow or Rapid-Rise) RD? Is Shimano pretty much compatible with itself, or must I get a particular set of parts?

Sorry if these are silly questions; I have only dealt with race bikes with STI levers in the past.

bengreen79

1 - depending on your preferred cadence, your fitness level, and intended use, you may find that you don't need that low of gears on your cassette. I would personally have closer spacing. A smaller cassette would also allow you to use a standard road RD.

2 - That's a matter of preference. You might be able to find a set of off brand (Microshift) or slightly used 9 speed brifters if you like them better for just as cheap as new Dura ace DT shifters.

Tim_Iowa

Well, what type of riding are you planning to do? On-road, gravel, dirt, off-road? Lots of climbing? How much load? How strong of a rider are you; do you stand to climb, or gear down and spin?
Answers to these questions will inform your choices, especially regarding the cassette size.

I'm assuming that you're building an all-rounder bike, for a little bit of everything.

0) your 46/30 is a good crankset to start with. 46 x 11 is usually enough top gear for most folks.

1) decide on the lowest gear you require. 1:1 is a popular low gear for normal (non-loaded) riding, which would require an 11-30 cassette (11-29 is damn close). 11-32, 11-34, or 11-36 give you an even-lower low gear, but have bigger jumps in between the cogs.

2) Road components for 7 through 10 speeds use "SIS" index shifting, Shimano's older index standard. MTB components for 7 through 9 speeds also use SIS indexing, so these are all cross-compatible.
10 speed MTB is "Dyna-sys", which has a different index ratio.
11 speed Shimano is "?" and also uses a non-compatible shift ratio.
The shifters control the index (speeds), so you can mix and match. For example, you can index 10 speeds with 10-speed shifters and any compatible SIS RD.

So, YES, 9-speed DT shifters will index perfectly with a 7-10 speed road RD or a 7-9 speed MTB RD.

"Rapid-rise" means the RD moves backwards (it starts on the big cog), but it will still index fine with an SIS shifter (just backwards). Some folks like this because then both shift levers move the same direction.
"Shadow" means the RD is designed differently and more of the mechanism is under the dropout instead of outboard (it makes the RD less susceptible to damage). SIS Shadow RDs still index perfectly with an SIS shifter.

"Long cage" (aka SGS) MTB RDs can accept a 36 tooth cog, and have enough chain takeup for a triple crank.
"Medium cage" (aka GS) MTB RDs can accept a 36 tooth cog, and have enough chain takeup for a double crank.
"Medium cage" (aka GS) Road RDs can accept a 28-30 tooth cog (newest Sora/Tiagra/105 GS RDs can do 32t), and have enough chain takeup for a triple crank.
"Short cage" (aka SS) Road RDs can accept a 28 tooth cog and have enough chain takeup for a double crank.

Personally, I really like the 9 speed XT RDs; I use an RD-M772 (yes, it's "shadow") with 10-speed Shimano bar-end shifters, a 52/42/30 triple crank, and an 11-32 10-speed cassette on my touring bike.
On my gravel bike I use an RD-M663 (also "shadow") with 9 speed Shimano bar-end shifters, a 48/38/36 triple crank, and an 11-34 9-speed cassette.

XTR RDs are fine too, but some folks think they're more fiddly to set up.

One issue with newer Shimano MTB RDs: they often lack a cable tension adjustment screw (because MTB shifters always have one on the handlebar). So, you may need to add an inline adjuster in the RD cable run, or add a cable tension screw to the RD.

I converted my Rivendell Road into a 650b touring bike a couple years ago and I love it. So, feel free to ask me any more 650b-specific questions, or check out the 650b Google Group.
The Pacenti Pari-Moto tires are only $32 from Boulder bikes, and are the fastest tires I've ridden (of any size). They have 38 and 42 mm widths. They're super light but I've had zero flats in my current pair after more than 1000 miles.
I built up a set of 650b wheels with Pacenti PL23 rims, but my first 650b wheelset was these cheapos (which are still going strong on my daughter's bike).

Cross Creek

My Ultegra 6500 SS rear derailleur is rated for a maximum cog of 28, but has no problem at all with a 30. I would think other Shimano 9spd road derailleurs would handle 30 tooth cogs as well. Most 650B wheels I've seen are 8/9/10, btw. They can be used with a 7spd if you add a spacer behind the cassette. I recently built a 650B rear wheel with a 105 hub to match a front wheel I already had. I could only find the 11spd model (5800) in stock. Plan to put an 8spd cassette on it with the provided spacer.

fietsbob

It's only a little smaller wheel size 584 rim [falling between 559/26" & 622/700c] so a bit wider(40) tire fits 27" frames