Can a modern, 9-speed Deore 48/36/26 crankset be run with only the 36t ring attached? Or, does the design require an outside ring? I would like to convert my 3 x 9 bike to a 1 x 9 and if this works it would be much cheaper than buying a new crankset.

Yes, you can do this but you will need some washers to take up the space on the two part chainring bolts that was otherwise taken up by the large chainring...or get track chainring bolts which are designed for single ring cranks.

-j

Modern double and triple cranks have shaped, pinned and otherwise "enhanced" chainrings to make shifting faster and easier. These are not what you want in a single chainring. See if you can find an older "flat" chainring in the bolt circle and tooth count you want. Otherwise it would be a good idea to add a "chainwatcher" to the inside of the single chainring or use a locked in place front derailleur as a quide.

+1. You can do it, but you're going to drop the chain regularly unless you take a bunch of precautions, which will end up costing you money and shooting holes in any "1x9 set-ups are awesomely simplistic" theories you may've heard. Doing a search on this will shed more light on it, but I gotta ask: why so itchy to spend time and money to reduce your gearing's range?

Thanks for this heads-up as this is the type of stuff I want to avoid, so my change may not be as simple as I'd hoped.

Surreal, it's primarily just experimentation to determine a final configuration for my "ultimate" bike. I know that's probably a pipe-dream but I'm trying to avoid N+1 and looking for relatively economical changes I can make to my existing one.

Some Sugino chainrings don't have pins and ramps. I don't know if you need a chainguide or not though.

Give it a shot with what you have and some washers and see how it goes. Leave the front derailleur in place and just set its shifter to the middle ring position. If it works your are golden, if not you can assess what you need to make it work and if the change will be worth it. Nothing lost but time and a couple of clams worth of washers.

-j

Flat, unenhanced chainrings are available from Surly and many by Suguino, SR, etc. are still lying around NOS in bike shops. However, most of these are going to have 5-bolt, 130 or 110 mm bolt circles. Surly does sell 94 and 104 mm BCD chainrings but only up to 36 teeth.

I'm not sure what vintage the OP's Deore crank is and what BCD it requires.

I think it's a 110 BCD (will check when I get home). I agree to try it. If chain wants to jump you could permanently set the front derailer to guard one side and use a chain watcher (for inside) or chain guard on the outside ring slot.

If it's a modern, 9speed Deore crank, it's a 104/64 4bolt. Deore cranks haven't had 110/74 5 bolts since the 1980s. The most easily sourced 104 36t with deep, flat teeth would be the Surly... but you're still likely to drop the chain at both ends of the cassette.