Originally Posted by
sp00ki
3/32 or 1/8?
depends. track specific stuff tends to be 1/8, but there's a lot of stuff out there in 3/32 as well. The typical rationale is that 1/8 is more durable, but 3/32 is lighter. doesn't matter which you use in the long run as long as you remain consistent. ie, if you go 1/8 your cog should be 1/8, as should your chainring and your chain.
if you're looking for a "flat top" type bar, just go with risers or flat bars (these will be mtb, typically).
Your best bet is to look for a 25.4mm quil (threaded) stem and pair it with a pair of 25.4 risers (type 25.4 mtb riser into google and you'll see why). if you need the drops, that's easy too-- again, type 25.4 road bars into google and you'll find tons. Bullhorns are the same thing. you have lots of options here. stick with 25.4 to keep things simple.
chains/drivetrain: There's no real difference between 1/8th and 3/32 stuff, except that you can use 1/8th" chain on a 3/32 cog/chainring, but not the other way around. Weight has nothing to do with it.
Unless your riser/flat bars are oversized, they are probably 25.4mm. Most modern road drops are 26.0, as are most bullhorns (except the somas). Most track drops are 25.4mm. Unless they are oversized. Bottom line: pick your bars, then get a stem that fits.